Science word of the day: Cenozoic

Pronunciation: See-noh-ZOH'-ihk

What it means: The ascendency of mammals, the birth of the Himalayas, the diversification of birds ‪—‬ Earth's in its Cenozoic era, baby!

The Cenozoic is the geological era happening right now. It started 66 million years ago with the abrupt mass extinction known as the Cretaceous-Paleogene extinction event, when a massive asteroid hit Earth and wiped out the nonavian dinosaurs. It's been a busy few tens of millions of years, ushering in such hits as Earth's first cacti, whales and most (if not all) of the Grand Canyon.

How to use it in a sentence: The Cenozoic is called the Age of Mammals, but the University of California Museum of Paleontology in Berkeley would like you to know it could have been called the Age of Teleost Fish, if mammals weren't so dang self-centered.

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Science word of the day: Abiotic

Pronunciation: Ay-bye-AH'-tik

What it means: Abiotic means "without living organisms." Scientists typically use the term when referring to nonliving aspects of an ecosystem that affect organisms' growth or reproduction. Some abiotic factors might be light, water, fertilizer, nutrients or chemical elements, such as oxygen or sulfur. Others include the tides or rain. Sometimes, "abiotic" is used to describe the origin of a particular chemical. Abiotic methane, for example, comes from chemical reactions between rocks and water in Earth's crust, unlike biotic methane, which comes from decaying organic matter as well as microbes living in your gut.

How to use it in a sentence: A new "gold rush" of exploration is on for abiotic hydrogen, which forms when rocks react with water deep underground and could be a renewable, carbon-free fuel of the future.

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Science word of the day: Abiogenesis

Pronunciation: Ay-bye-oh-JEN'-ih-sis

What it means: Abiogenesis is the emergence of life from nonliving matter through chemical processes. Scientists still don't know exactly how abiogenesis happened on Earth. Theories range from lightning strikes that could have scrambled water, methane, ammonia and hydrogen into amino acids and sugars ‪—‬ the building blocks of life ‪—‬ to chemical reactions at deep-sea vents. Abiogenesis is not the same as spontaneous generation, which held that living organisms such as maggots formed directly from decaying matter. It was a compelling idea for anyone who had watched meat rot, but Louis Pasteur, inventor of pasteurization, disproved it in the 1860s by showing that microbes could only grow from preexisting microbes.

How to use it in a sentence: All life on Earth may owe itself to an incident of abiogenesis more than 3.7 billion years ago.

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Science word of the day: Autotroph

Pronunciation: AW'-tuh-trohf

What it means: Autotrophs are organisms that can feed themselves with inorganic substances such as light (for plants) or methane (certain microbes). Autotrophs were the first single-celled life-forms to colonize the planet, thriving on chemicals bubbling up from the subsurface at deep-sea vents or figuring out how to harness the sun for energy. Heterotrophs (like you, me and all fungi), arrived on the scene later to feast on these DIY-ers.

How to use it in a sentence: Stromatolites, microbial mats built by cyanobacteria, are autotrophs that thrived in ancient shallow seas.

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Animals come in a wide range of shapes and sizes, from spindly stick insects to blubbery whales. Round animals are harder to come by, but they're more common in the ocean than on land. So what is the roundest animal, and why are round animals uncommon?

At a glance, round animals might not seem that out of place on land. After all, small mammals like rabbits and pikas often look a bit spherical when their fur is puffed out and they're sitting. But Chris Law, an evolutionary biologist at the University of Washington in Seattle, said this shape is mostly an illusion.

"They're physically not as round as they appear to be," he told Live Science.

A sphere has the lowest surface-area-to-volume ratio of any shape, which is ideal for heat conservation. Law said the ability to curl or scrunch into a sphere can be essential to the survival of small animals, which lose heat more quickly than larger animals do.

Rolling into a circle can also offer protection. To safeguard their vital organs, animals like armadillos and hedgehogs roll into balls when threatened, leaving only their armor or spikes exposed to predators. But when you look at the skeletons of these supposedly round critters and their shape when they're not scrunched up, they aren't round at all, Law said.

In fact, there are several reasons why round creatures are rarely found on land. Being perfectly round all the time would make it difficult to fit into small spaces, which is a key survival technique for avoiding predators, he added, and with the effects of gravity, having a lot of unsupported round mass puts strain on an animal's body. Overly round mammals, like obese cats and dogs, often suffer joint issues and other health problems.

"As a round animal, you're probably going to lose mobility, and you're going to be picked off by predators pretty easily," Law told Live Science.

There are exceptions, however. For example, beetles are small enough not to be affected as much by gravity and can fit into nooks and crannies without much wiggling. Their round shape coupled with their hard carapace makes them more difficult for predators to eat. And rain frogs puff up into a round shape to keep predators from removing them from their hiding spots.

If we're counting animals that are only round sometimes, then pill bugs (also known as rolly pollies) might take first place for the roundest land animal. But if not, rain frogs, and beetles like ladybugs, are the top contenders for the roundest land animal. But even these animals aren't perfectly round; ladybugs have flat bottoms to make it easier to move around, and rain frogs are less spherical when not puffed up.

Round sea animals

Being round at sea is a little more feasible than it is on land. In fact, sometimes, it's critical to survival.

Karly E. Cohen, a biomechanist at Friday Harbor Labs in Washington, studies lumpsuckers, a type of fish she describes as "quite round." These bulbous fish have suction cups made of enamel on their stomachs, which they use to latch on to surfaces at the bottom of the ocean. Lumpsuckers have armor, also made of enamel, covering their round shape. According to Cohen, lumpsuckers' roundness plays a huge part in keeping them attached to the seafloor or other surface. The curve of their bodies, coupled with the tooth armor, modifies the drag around the animal, creating a force that pushes them down rather than shooting them into the water column.

Although gravity still works underwater, buoyancy helps push objects up, meaning the effects of gravity do not feel as strong at sea as they do on land. According to Cohen, lumpsuckers can get around just fine, if a bit more slowly than their more streamlined neighbors. And like pufferfish and porcupine fish, lumpsuckers' round shape and uninviting exterior make them tough to swallow ‪—‬ literally.

"There's no real good way to eat an apple whole; you have to take a bite," Cohen told Live Science. "And then this thing is armored, so it's very hard to take a bite."

All about symmetry

Despite their spherical shape, lumpsuckers don't quite win the award for the roundest animal. Lumpsuckers, like most animals, have bilateral symmetry, which means they are divided into two symmetrical sides across one plane of symmetry. But there are animals that have radial symmetry, which means they are symmetrically arranged in a circle around a central point with multiple planes of symmetry.

Echinoderms ‪—‬ which include sea stars, sea urchins and sand dollars ‪—‬ have pentaradial symmetry, which means they have five planes of symmetry arranged around a central point. According to Laurent Formery, a developmental biologist at the Oceanological Observatory of Banyuls-sur-Mer in France who studies echinoderms, scientists aren't entirely sure of the benefits of pentaradial symmetry or why echinoderms are the only modern animals that have it.

However, Formery thinks being divided into five sections instead of two may give echinoderms better sensory perception than bilaterally symmetrical animals. Echinoderms have decentralized nervous systems, meaning that instead of a brain, they have a series of neurons distributed evenly across their body, and photoreceptors all over their skin.

"They are kind of like a big crawling eye and brain, so they are receiving information from everywhere," he told Live Science. "They have a completely different way, that is difficult for us to imagine, of interacting with their environment."

Because of this unique organization, radially symmetrical animals can sense predators from any direction. They can also easily switch which segment of their body is in the lead, making it easier for them to change directions to capture prey.

Discounting their spikes, certain species of sea urchin are almost perfectly spherical. Like lumpsuckers, sea urchins' spherical shape, coupled with their spines, makes them difficult meals for predators, Formery said. Sponges lack any symmetry, so they can develop all sorts of body shapes. One species, called the death ball sponge, looks like a Sputnik lamp, with many hook-covered spheres attached to its spindly "arms."'

Under the sea, urchins in the genus Histocidaris, like Histocidaris purpurata and Histocidaris formosa, are the closest to perfect spheres, making them the top candidate for roundest animal.

Although roundness might be uncommon in the animal kingdom, Cohen said it's fascinating to study these animals and the reasons for their adaptations.

"As somebody that's interested in the tools and ways organisms work in their environments," she said, "they're a real treasure trove of evolution."

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Researchers have extracted DNA from a 50,000-year-old tooth belonging to an African antelope, setting a record for the oldest DNA ever retrieved from sub-Saharan Africa, a new study reports.

The finding suggests that DNA preservation in sub-Saharan Africa is possible for tens of thousands of years. In most cases, the region's hot climate breaks down the molecule and prevents researchers from understanding the evolution of numerous species, including ancient human ancestors and relatives.

While some temperate regions are known for preserving ancient human DNA — for instance, the Sima de los Huesos ("Pit of Bones") in Spain preserved DNA from a mysterious relative of modern humans that lived around 400,000 years ago — the sub-Saharan African climate is less forgiving. The oldest human DNA from sub-Saharan Africa is about 18,000 years old and was discovered in bones found in a rock shelter in Tanzania. And the oldest sub-Saharan animal DNA is just 9,300 years old, from an extinct antelope in South Africa.

In the new study, researchers tested whether DNA could be successfully extracted from ancient skeletons even older than that. By analyzing more than 300 teeth from animals that lived in the past 110,000 years, they discovered that small amounts of DNA could be identified even in remains from the Late Pleistocene, the latter part of the last ice age.

In a study published online May 27 in the journal Quaternary Science Reviews, researchers extracted DNA from dozens of Holocene bovid specimens younger than 11,700 years old and from four Late Pleistocene bovid specimens between 12,000 and 50,000 years old. Although many of the teeth didn't yield DNA, a handful did. The oldest DNA the researchers found came from a partial molar from an African antelope called a mountain reedbuck (Redunca fulvorufula) discovered in Boomplaas Cave in southern South Africa. The other old DNA samples came from three extinct long-horned buffalos (Syncerus antiquus) ‪—‬ two that died 21,000 years ago and one that died 12,000 years ago.

"The 50,000-year-old DNA is exciting," study first author Deon de Jager, a paleogenomics expert at the University of Copenhagen, told Live Science in an email. "But I am myself skeptical of it, for two reasons."

The reedbuck DNA is significantly older than the next-oldest DNA the researchers retrieved, from the long-horned buffalo, de Jager explained, and the reedbuck specimen was contaminated with some human DNA, which they were able to remove. These two issues mean the 50,000-year-old antelope DNA result is not ironclad. However, since the publication of the study, the researchers have also sequenced the genome of a 42,000-year-old wildebeest from Ethiopia, suggesting DNA lasts a lot longer in Africa's climate than experts once thought.

"There is of course a limit to DNA preservation in Africa, but what it is, is not clear," de Jager said. "There are certainly parts of Africa where DNA will be preserved even better than from the sites we have surveyed. Deep caves with stable, low temperatures will certainly be good candidates, but also high-elevation sites where temperatures have been very low for a long time."

The Late Pleistocene teeth that de Jager and colleagues analyzed produced very low amounts of DNA, which is thought to have a half-life of about 521 years, meaning half of the DNA in a specimen disappears every 521 years until none is left. But the amount the researchers found is still useful, de Jager said.

The DNA is sufficient for identifying evolutionary lineages, de Jager added. If they can gather enough data, researchers might be able to compare gene flow and interbreeding among species and populations.

Although these results suggest that DNA analysis is possible for understanding the past 40,000 to 50,000 years of animal and human evolution in South Africa, we may never be able to extract DNA from ancient human relatives like Homo naledi, which went extinct around 240,000 years ago, or Paranthropus robustus, which died out around 1 million years ago.

"I think the chances of obtaining DNA from Homo naledi are very, very low, unfortunately," de Jager said. "One would have to get very lucky with an incredibly well-preserved skull with the petrous bone still present, which is the best bone for obtaining ancient DNA. To get DNA from something in Africa nearly 1 million years old would probably be impossible, as the conditions in Africa are just too harsh."

How much do you know about Earth's frosty past? Find out with our last ice age quiz!

Life on Earth could continue for another 1.8 billion years, according to new research. This figure, which is based on complex climate models, is far longer than many previous studies indicated.

As the sun evolves, it is getting brighter. Our star is currently producing about a third more energy than it did at the dawn of the solar system 4.5 billion years ago. And it will continue to get hotter until it eventually dies in about 5 billion years.

Scientists have wondered for decades how long life on Earth will manage to cling to existence as the sun brightens. In 1982, James Lovelock and colleagues estimated that Earth's photosynthetic biosphere — which includes all plants and forms the basis for most of the planet’s biology — would end about 100 million years from now. Successive studies have pushed back the deadline for the death of all life on Earth.

In the new study, published May 28 in the journal JGR Atmospheres, researchers suggest that plant life could continue about 1.8 billion years into the future. That nears the time when Earth would lose its oceans to space, either through radiation splitting water atoms or runaway evaporation, in about 2 billion years.

"We were trying to show that life on Earth — complex vegetation — could survive longer into the future than previous studies had shown," study co-author Jacob Haqq-Misra, an astrobiologist at space exploration charity Blue Marble Space, told Live Science.

The boundaries of life

Life on Earth relies on photosynthesis, the process used by plants, algae and some bacteria to turn sunlight into energy. The mechanism chemically converts carbon dioxide and water into sugars and oxygen. It requires both CO₂ and sunlight.

But at certain temperatures, plants' photosynthetic machinery shuts down. Eventually, the sun will warm Earth to the point that plants are no longer able to photosynthesize, which would in turn cause entire food webs to collapse and all life to perish.

Another issue is that as the sun dies and it gets brighter, there will be less carbon dioxide in the atmosphere, effectively starving plants.

"The Earth has stayed pretty hospitable in terms of surface temperature for most of the last 4 billion years because it has a built-in thermostat" by storing CO₂ in rocks and releasing it during volcanic eruptions, Robert Graham, a planetary science researcher at the University of Chicago, who was not involved in the research, told Live science.

When it is hotter, the planet pulls more carbon dioxide out of the atmosphere and stores it in rocks underground, Graham said. This offsets the warming to keep the temperature stable but means that the carbon dioxide isn't accessible to plants.

Climate models and extreme plants

In the new study, Haqq-Misra and colleague Eric Wolf, a research scientist at Blue Marble Space, used 29 climate models to estimate what would happen to Earth's vegetative biosphere under different scenarios. They used the two extreme cases as limits — when Earth is too hot for life but the CO₂ was stable; and when there is not enough CO_2, but the temperature was stable. They then looked at the range of CO₂ and sunlight conditions in between those extremes. This enabled them to include situations in which Earth was very efficient at pulling carbon from the atmosphere when temperatures started rising.

They also included information about a variety of plants. Some plants can survive on a much lower ratio of atmospheric CO₂ than others. The study included plants that have a special photosynthetic process (known as crassulacean acid metabolism), such as succulents and orchids. These plants can sustain themselves on relatively tiny amounts of CO₂. The same is true of some marine plants, which can dissolve and access carbon in the ocean system.

Other experts were impressed by the findings.

"Haqq-Misra and Wolf have used a sophisticated 3D climate model to show that Earth's climate may remain hospitable to plant life significantly longer into the future than predicted" by simpler models, said Graham, who authored one of those earlier studies. "It's an advance over previous work and suggests that complex biospheres like that of Earth are more resilient to environmental change from stellar brightening than previously suggested."

Looking to the future

Andrew Rushby, an astrobiologist at Birkbeck University of London who was not involved in the research, told Live Science that the paper updated the concept of the lifetime of the biosphere. However, he cautioned that the results remained "broad estimates."

"It is not possible for us to predict or know the possible evolutionary adaptations that the photosynthetic biosphere may undergo in response to increasing solar output and lower [atmospheric CO₂], especially over billions of years," he said.

In their paper, the authors wrote that "limits posed by thermal stress or starvation may only reflect our observations of the biosphere today rather than hard limits on how the biosphere may evolve." There is also no way of knowing how life might adapt to new circumstances.

Haqq-Misra said that he found the results comforting. "Earth's system is resilient, and we are part of something that could have a much, much longer future," he said.

The results could also help scientists figure out what the thresholds could be on other planets. "Part of the challenge is starting with these Earth-based models, and then generalizing the physics as much as possible to be able to simulate a wider range of atmospheres," he said.

How much do you know about our blue planet? Test your terran knowledge with our Earth quiz!

Never-before-seen fossils of newly hatched crocodile-like creatures are shining new light on how our aquatic ancestors conquered land.

Early four-limbed vertebrates (tetrapods), which would eventually give rise to humans, took their first steps on land in the Devonian period, some 419 million to 359 million years ago, marking one of the most important periods in the evolutionary history of animals.

Now, a new study published Thursday (June 18) in the journal Science has revealed that these early tetrapods were less like amphibians and more like us. Rather than having a tadpole phase in their development, as many amphibians do today, new evidence suggests that they were direct developers — growing from smaller to bigger versions of themselves, like their ancestors, humans and many other animals.

The study is an important contribution to our understanding of early tetrapods' reproductive developmental biology, said Tim Smithson, a visiting academic at the University of Cambridge who specializes in early tetrapods but was not involved in the study.

It suggests that the "earliest tetrapods that took those first steps on to land were able to rely on the successful reproductive and developmental strategies of their forebears," Smithson told Live Science in an email. "Direct development made life easier — one less thing to worry about!"

The new research was based partly on fossils from early land-dwelling predators called embolomeres. These animals looked like a cross between a crocodile and an eel and ruled river, lake and swamp habitats 350 million to 280 million years ago, during the Carboniferous and Permian periods. While these creatures could grow to more than 10 feet (3 meters) long as adults, the study unveils rare fossils from Mazon Creek, near Chicago, that preserved embolomeres as hatchlings that were days to a couple of weeks old.

"These are intimate details of the first moments of these animals' lives, and we've never seen that before for this entire part of the evolutionary tree," study co-author Jason Pardo, a postdoctoral fellow of evolutionary biology at Vilnius University in Lithuania and a research associate at the Field Museum in Chicago, told Live Science.

These fossils didn't show evidence of external gills and other tadpole-like features that the researchers would have expected from an early land dweller. The researchers then checked other fossils from before and during the "fin-to-limb transition" but found no evidence of an amphibian-like life cycle in those, either.

"For as long as we've understood evolution, we've assumed this story of how we made that transition from water to land," Pardo said. "We in fact have a completely different story."

Science upended?

A statement released by the Field Museum claimed that the study upends scientists' understanding of how animals conquered the land. However, the experts Live Science spoke to disagreed with this assertion.

"The Mazon Creek material is wonderful, the study is interesting and the interpretation of the fossils is sound, but I don't think the results are terribly surprising," Per Ahlberg, a professor of evolutionary organismal biology at Uppsala University in Sweden, told Live Science in an email.

Ahlberg, who was not involved in the new study, specializes in the early evolution of tetrapods. He noted that scientists knew some early tetrapods had a larval stage similar to that of modern salamanders ‪—‬ namely, those belonging to the group Temnospondyli, which he described as the ancestral stock of modern amphibians. However, he contends that this didn't mean scientists assumed every early tetrapod was the same.

"Nobody has been arguing in recent years that ALL early tetrapods had such a larval stage or that this was essential for enabling the transition to land," Ahlberg said. "I mean, I have been working right at the core of this research field for 40 years and I have never given it any thought."

In response, Pardo agreed that specialists in the field recognized that the data didn't support that early tetrapods had an amphibian-like development. However, he argued that even among specialists, assumptions were still made about metamorphosis — a major developmental transition, like a tadpole transforming into a frog — and amphibian-like bodies.

"Onto something big"

Study co-author Arjan Mann, an assistant curator of early tetrapods at the Field Museum, first saw the study's first baby embolomere fossil during a 2016 trip to the Field Museum while working on his doctorate. At the time, the fossil was a mystery.

Mann and Pardo mused over the fossil's identity for years before high-resolution scans with scanning electron microscopy at the Canadian Museum of Nature confirmed that the ancient creature was an embolomere, according to the museum's statement.

"I think Jason and I both knew we were onto something big, since fossils of this kind of animal and from this phase, and developmental state in early tetrapod evolution have never been found or studied before," Mann told Live Science in an email.

Along with the embolomeres, the researchers looked at megalichthyid fish from before the land transition and limbless, snake-like creatures known as aistopods from during the land transition. All showed signs of direct development, they said.

"I think the take home message of this study is that we should always challenge conventional wisdom in science, especially when these older ideas do not have substantial backing," Mann said.

Scientists have discovered a vast whale graveyard stretching for hundreds of miles in the Indian Ocean, with some fossil bones dating back over 5 million years.

The deep-sea "megasite," which the researchers have named the Diamantina Zone necropolis, is the most extensive accumulation of whale carcasses and fossils ever found, the researchers reported in a new study published Wednesday (June 10) in the journal Nature.

"It covers over 1,200 kilometers [750 miles], which just defies belief," Nick Pyenson, a curator of fossil marine mammals at the Smithsonian National Museum of Natural History in Washington, D.C., who wasn't involved in the study, told Live Science. "'Megasite' is a totally appropriate term. I think they've uncovered something really special."

"The density is crazy"

Xiaotong Peng, a deep-sea researcher at the Chinese Academy of Sciences' Institute of Deep-sea Science and Engineering, and his colleagues used an underwater vehicle called the Fendouzhe submersible to survey the seafloor in the Diamantina Zone, an area of ridges and fractures in the southeastern Indian Ocean.

After initially spotting one fossil, the team conducted 32 dives covering a survey area of about 0.25 square miles (0.64 square kilometers). In total, they identified 476 whale fossils and five carcasses of whales that had died more recently, known as whale falls, at depths of between 13,800 and 23,000 feet (4,200 to 7,000 meters).

Extrapolating from these figures, the authors said there could be seven to eight whale carcasses and about 750 fossils per square kilometer in the area.

The largest carcass is a 16.4-foot-long (5 m) skeleton from an Antarctic minke whale (Balaenoptera bonaerensis), the researchers said, but most of the remains are from beaked whales ‪—‬ marine mammals we know little about because they live in the open ocean and spend a lot of time diving.

The five active whale falls are covered in bacteria that live without light or oxygen and break down the oils in the whales' bones, producing hydrogen sulfide. This source of chemical energy enables the carcasses to host diverse communities of jellyfish, brittle stars, bone-eating Osedax worms and bivalve mollusks, which together reach densities of up to 2,840 individuals per square meter, the authors discovered.

Many of the members of the whale-fall communities may also be newly discovered species, the authors wrote, because although most could be matched to the genus or family level using DNA data from samples, only one could be confidently assigned to a species: a clam known as Abyssogena southwardae.

"The density is crazy, as is the fact that they're probably all new to science," said Stephen Godfrey, curator of paleontology at the Calvert Marine Museum in Maryland who wasn't involved in the study. "It's like each one of these whale falls is a new little restaurant that opens up in a 1,200-kilometer-long [745 miles] strip mall," he told Live Science.

These are the deepest whale-fall communities ever found, with the one at about 22,000 feet (6,700 m) being about 8,200 feet (2,500 m) deeper than any other known one, according to the study authors.

A fossil deposit being formed

Peng and his colleagues recovered 43 fossils and dated 33 of them based on the ratios of strontium isotopes present. The fossils belonged to five beaked whale species and one species of baleen whale, a group that includes bowhead and humpback whales.

The oldest fossil found in the area belonged to an extinct beaked whale in the Pterocetus genus that dates back about 5.3 million years, to the Early Pliocene. Another fossil find represented a new species, which the authors have named Pterocetus diamantina.

All that remains of most of the specimens is the bony upper jaw, or rostrum. These fossils came mainly from two species: the Andrews' beaked whale (Mesoplodon bowdoini) and the strap-toothed whale (Mesoplodon layardii). Both of these species still inhabit the Indian Ocean, but the fossils the team discovered could be up to 1 million years old.

"The really awesome thing is that this megasite is showing beaked whale ecology over geologic time scales, so you are getting extinct species overlapping the fossil remains of extant species," Pyenson said.

The megasite is analogous to either the famous Lagerstätte fossil deposits, where there is high-quality preservation, including of soft tissue, or to the Burgess Shale in Canada, which has a huge abundance of animals, Godfrey said, "only here, you have one that's still forming."

Beaked whales are rarely seen, so it might seem strange to find the remains of so many individuals in one place. But Godfrey said these animals might preserve better because of the staying power of their rostra, which have one of the highest known bone densities and mineral contents among living vertebrates.

This means they can persist long enough at great depths without being dissolved or consumed by bone-eating worms that they then become encrusted with ferromanganese oxides, solidifying and encasing the bone in a kind of natural sarcophagus.

"This seals the specimen in, so it will last in perpetuity, or at least over 5 million years, and who knows how much longer," Godfrey said.

Why so many dead whales?

The authors saw many squid and fish in the dives in the Diamantina Zone, which suggests the area provides an ideal deep-water foraging ground for beaked whales. This might mean more whales live and die in the area, even though when a whale dies, its decomposition can make it expand with gas and float on the surface for great distances before eventually falling to the seabed.

Peng and his colleagues also suggested that there might be an increased risk of death by beaked whales being tempted to chase prey below their maximum observed diving depth of about 10,000 feet (3,000 m), which puts them at risk of lung collapse or decompression sickness.

Another possibility is that the V-shaped topography of the Diamantina Zone may funnel sinking carcasses into a smaller area, the authors suggested.

"I think what they're dealing with is an analogue to the terrestrial tar pits or caves that are natural traps where biological remains accumulate over time," Pyenson said.

That's only part of the story, though. Normally, ancient remains on the seabed would get covered by sediment from eroded rocks, so we'd never see the fossils. But the sedimentation rate close to the Diamantina Zone is incredibly low ‪—‬ just 0.02 to 0.22 inches (0.05 to 0.55 centimeters) per 1,000 years, the study authors noted. This means skeletal remains could be exposed for hundreds of thousands of years at the flat bottom parts of the zone and for millions of years on slopes or uplifted sections, the team said.

They think there might be other similar "necropolises" off South Africa, the Iberian Peninsula, and the remote Crozet and Kerguelen islands near Antarctica, where some fossils have already been discovered by trawling.

How much do you know about killer whales? Find out with our orca quiz!

A trove of fossils uncovered in northwestern Canada suggests that complex animals evolved in North America earlier than previously thought.

The site houses more than 100 fossils, including six taxa never found in North America before, with some dating back 567 million years. The findings push back the origins of animals that can move themselves in search of food by several million years, according to a study published May 20 in the journal Science Advances.

"For 3 billion years, life on Earth was dominated by microbes," study co-author Scott D. Evans, assistant curator of invertebrate paleontology at the American Museum of Natural History in New York City, said in a statement. Then, all of a sudden, "we get these strange-looking marine animals big enough to see and capable of behaviors we would find familiar today. If we want to understand this transition, when life first became large, complex and unmistakenly animal, this new site has tremendous potential."

Complex, multicellular animals first evolved during the Ediacaran period (635 million to 541 million years ago). At this time, North America was part of the ancient continent Laurentia, which predated the supercontinent Pangaea.

Some of these early animals from the Ediacaran are linked to modern animals, like mollusks and jellyfish, while others look nothing like any species living today. Most, however, had soft bodies without shells or bones, so fossils from this period are rare.

Scientists split the fossils that did form into three groups, or assemblages, based on when the animals lived. The Avalon assemblage (575 million to 559 million years ago) consisted of stationary animals that lived deep underwater. The White Sea assemblage (559 million to 550 million years ago) contained a more diverse group of animals that lived in shallower water, and the Nama assemblage (550 million to 538 million years ago) included the earliest animals that formed shells and bones.

In the new study, the researchers discovered several fossils of species known to belong to the White Sea assemblage for the first time in North America. These fossils date back 5 million to 10 million years earlier than White Sea assemblage fossils previously found in Europe, Asia and Australia.

Among the fossils were Dickinsonia, a flat, oval-shaped organism that absorbed algae through its entire bottom surface; Funisia, a tube-shaped creature that represents the oldest evidence of sexual reproduction among animals; and Kimberella, an early mollusk that may now be the oldest fossil species to exhibit bilateral symmetry.

"Not only is this new site highly diverse, but also it is from a part of the rock succession where we have previously lacked fossil remains," study co-author Justin Strauss, an Earth scientist at Dartmouth College, said in the statement. "This is really exciting. Given our understanding of the regional geology in northwestern Canada, there is great potential here to revisit our understanding of Ediacaran Earth history."

That potential may apply to the creatures' evolutionary history. Based on the sediment patterns in the surrounding rock, the fossilized organisms found in Canada lived in deeper water than researchers previously thought creatures in the White Sea assemblage lived. That could suggest that the animals first evolved in deep water and gradually expanded their range into shallower water — the opposite of typical animal evolution.

"We think of the deep ocean as a dark, inhospitable place, but it is also relatively stable, with few fluctuations in things like temperature and oxygen essential to most animal life," Evans said in the statement. "This stability may have provided key opportunities to support early animal life."

They sleep on our beds, steal our food, and generally rule the house. Between them, cats and dogs make up two-thirds of pet ownership worldwide. But which of the two companion animals are we more closely related to?

The answer depends on how you look at the question.

"From an evolutionary perspective we are equally related to dogs and cats," Mark Springer, a professor emeritus of evolution, ecology and organismal biology at the University of California, Riverside, told Live Science in an email.

Cats, dogs and humans are all mammals. In the mammalian family tree, which maps out how different mammal species are related to one another, both cats and dogs belong to the order Carnivora, while humans are primates. These two groups split from a common ancestor about 90 million to 95 million years ago, Springer said. Meanwhile, cats and dogs split from each other much later, around 55 million years ago.

In terms of common ancestry, "dogs and cats are more closely related to mammals such as pangolins, horses, cows, whales, bats, shrews and moles than they are to humans," Springer said. And "humans are more closely related to colugos [flying lemurs], tree shrews, rabbits, rats, and mice than they are to cats and dogs."

Genetic ties

Another way of deciding which species we are more closely related to is through a genetic lens.

If you measure how much the DNA code has changed over time, humans are about equally related to cats and dogs, William Murphy, a comparative genomicist at Texas A&M University, told Live Science in an email.

However, scientists also compare how DNA strands are organized within chromosomes. Here, a difference emerges.

Murphy explained that the ancestors of modern-day dogs went through extensive chromosome rearrangements over evolutionary time. (Such rearrangements are not unique to dogs; they occur across different animal and plant species, though scientists don't fully understand why some lineages rearrange faster than others.) Cats, on the other hand, retained a genome organization that's closer to ours. "In terms of how genes are arranged within chromosomes, humans and cats are twice as similar to each other as humans are to dogs," he said.

Because the way DNA is organized affects how genes are switched on and off, cats may be a better model than dogs for understanding human gene regulation, Murphy said.

That also makes them useful for studying genetic diseases. For example, polycystic kidney disease occurs in both humans and cats, and treatments developed for cats could help inform therapies for people.

Cats may also provide clues about cancer. A recent study found that cancer-related genes in cats are strikingly similar to those in humans, both in number and variety. One notable example involves a gene called FBXW7, which was mutated in more than half of the feline mammary tumors studied. In humans, mutations in the same gene are linked to worse outcomes in breast cancer

That said, dogs are also used to model and analyze human illness, including Alzheimer’s disease, idiopathic epilepsy, eye disease and heart disease.

Although cats may share more similarities with humans in gene regulation, to date more research has focused on dogs. This may be due in part to the fact that the complete feline genome became available later than the canine genome, as well as historical bias — cats have long been perceived as less cooperative in research settings.

So, which are we more closely related to? From an evolutionary standpoint, it's a tie, but genetically, at least in terms of genome structure, we are closer to cats.

How much of a cat fan are you? Find out by taking our cat quiz!

Over the past two decades, some studies have suggested that human brains are shrinking. But there is also evidence that IQ scores have risen over the past century.

But is it possible for us to get smarter as our brains shrink? Live Science contacted experts to find out.

First, it's important to note that a bigger brain size does not necessarily mean higher intelligence, said Jeremy DeSilva, an anthropology professor at Dartmouth College. Brain size "is only weakly related to measures of intelligence in humans. Albert Einstein's brain, for instance, was quite small, and he was Einstein!" he told Live Science in an email.

In Einstein's case, it appears that extraordinary folding patterns in several of his brain regions may help account for his genius. While there is some debate, studies suggest that there is little or no relationship between our intelligence and brain size in humans.

Have human brains shrunk?

Not all scientists agree on whether human brains have gotten smaller. However, many experts we spoke with said there is evidence for shrinkage over time.

"My research indicates that human brain size declined during the [entire span of the] Holocene by about 10% of its volume or about 150 ml on average," Maciej Henneberg, a professor emeritus of anthropological and comparative anatomy at Adelaide University in Australia, told Live Science in an email. The Holocene is an epoch that followed the last ice age, and spans from 11,700 years ago to the present day. In his research, Henneberg looked at the brain size by analyzing skulls from all over the world. In many cases, he analyzed the skeletons personally.

It's important to remember that Homo sapiens emerged around 300,000 years ago, so a brain shrinkage starting around 11,700 years ago would be a relatively recent development.

Other scientists have reported similar findings. "Our lab thinks that the data currently available show a clear, global trend toward a decrease in brain size in more recent times," said DeSilva, whose research looked at more than 5,000 skulls from people who lived in Europe, Asia, Africa and Australia. Many of the skulls date to the Holocene.

Jeff Stibel, who holds a doctorate in brain science and has published a number of papers on the topic of brain shrinkage, said the "Holocene warming period has coincided with more than a 10% reduction in brain size in modern humans." Stibel took part in DeSilva's research, and then gathered more data by analyzing the brain size of roughly 800 additional skulls from around the world.

However, some scientists disagree. Research by Brian Villmoare, an associate professor of anthropology at the University of Nevada, Las Vegas, and his team found no evidence that human brains are shrinking. "I see no evidence that, once we acquired our modern form, that our brains have changed in any meaningful way," Villmoare said in an email.

Some say more nuance needs to be considered. "Brain size in some human populations decreased over the last 15000 years," John Hawks, an anthropology professor at the University of Wisconsin-Madison, told Live Science in an email. "But there are some complexities."

Hawks noted that datasets of brain size tend to overrepresent men of European ancestry, making it difficult to determine whether there is a global trend among diverse populations.

"Brain size did rebound toward larger sizes during the last 150 years in industrializing countries," Hawks said. "This was likely mostly attributable to nutrition and correlated with body size, but whether body size accounts for the entire effect is not clear from the limited data."

Why are human brains getting smaller?

If our brains have shrunk, then why? Scientists have proposed a few ideas.

One has to do with the introduction of farming.

"During the Holocene, humans gradually introduced food production [such as agriculture and animal husbandry] that allowed them to live in larger communities," Henneberg said. "The brute physical strength required for hunting big game and protecting families against strong predators became less necessary while a smaller body size required less food, so it was favoured by natural selection."

In fact, it's not just our brains; our bodies have also shrunk. "At the end of the Ice Age, male body height was about 1.75 m [5.74 feet], whereas in mid-Holocene agricultural communities it was 1.65 m [5.41 feet]," Henneberg said. "Body mass has declined even more since we see thinner (less robust) human bones." Heights have rebounded recently in some parts of the world, and Hawks said that our brain sizes may be rebounding also.

The warming that occurred after the end of the last ice age also may be a factor. Stibel said two biological principles, known as Bergmann's rule and Allen's rule, state that "bodies and organs tend to become leaner in warmer climates to increase surface area and dissipate heat."

Another possible explanation is that human intelligence itself has changed as we have taken on more specialized jobs and share more information with each other, meaning we don't have to know everything, just a subset of knowledge to keep society going.

DeSilva said his team proposed that a "population increase, the subsequent specialization of people into specific roles in society and the growth of collective intelligence may have contributed to individual brain size decrease as modeled in some eusocial insects like ants and wasps." For instance, "I'm a decent enough anthropologist and anatomist, but you wouldn't want me fixing your car or investing your retirement savings on Wall Street."

Stibel agrees that this is a significant factor. "Some ant species that develop complex social systems see similar reductions in individual brain size as the colony carries more of the cognitive load," he said. "We appear to have done something remarkably similar with culture and technology.

"What our research suggests is that we've undergone a fundamental shift in how cognition works," Stibel added. "Rather than relying solely on individual brainpower, we've become extraordinarily dependent on cultural and technological networks."

Stibel noted that large brains can be a burden, consuming more energy which requires people to eat more food to survive. "Large brains are metabolically expensive, consuming roughly 20% of our resting energy and producing significant heat." During times when food is scarce, such as during an Ice Age, this can result in people with larger brains being more likely to die of starvation.

This doesn't mean humans are smarter or dumber than they were; it just shows our intelligence is different.

"We've likely traded some raw computational capacity for the ability to leverage collective intelligence," Stibel said. "Whether that's a gain or a loss depends entirely on how you define intelligence. And, of course, how stable the cultural and technological systems we now depend on turn out to be in the long run."

See how much you know about the most complex organ in the human body with our brain quiz!

When the dinosaur-killing meteor hit Earth 66 million years ago, many flowering plants transformed into "hopeful monsters" to endure the resulting environmental crisis. Now, new research suggests that this was not the only time these plants responded this way. In nine separate events over the past 150 million years, flowering plants have duplicated their whole genome to give themselves a better chance of survival in the face of catastrophe.

The work could help scientists understand what will happen to flowering plants, which include most of the crops people eat, as the climate changes and organisms endure another environmental upheaval.

"Waves of whole genome duplications correlate with important geological events or periods in evolution," Yves Van de Peer, a genome biologist at Ghent University in Belgium and a co-author of the paper, told Live Science.

For almost a century, whole-genome duplication has puzzled scientists. Organisms that have more than two sets of genomes are called polyploids. Humans, which have two sets of chromosomes, are diploids. Polyploids are sometimes called "hopeful monsters" because they are "monstrously" different from their parent organisms — but have the potential to survive conditions that their parents cannot and, therefore, offer hope to a species.

But these organisms are a paradox, Van de Peer said. "When you go outside and start collecting plants, there is a very high chance that you will collect polyploid plants," which are plants that have undergone a whole genome duplication, he explained. "Nevertheless, when we analyze plant genomes, we find very little evidence for many whole-genome duplications that have survived in the longer term."

That's because whole-genome duplication is a risky gamble for a plant. "It's not an easy thing, from a cell biology point of view, to deal with," he said. "There are costs involved," such as larger cells, reduced fertility and other consequences. For this reason, polyploids are often seen as evolutionary dead ends because these mutations are unlikely to endure.

Many of the crops we eat are polyploids that humans have subconsciously selected over time because of their bigger fruit or ability to survive environmental stresses, Van de Peer said. But polyploid individuals struggle to compete with other members of their species when conditions are stable, so they die out during good times. But during difficult periods, polyploids may be able to adapt better, he said.

"Bursts throughout the history of plants"

In the new study, published Friday (May 8) in the journal Cell, the researchers analyzed the genomes of 470 flowering plants, called angiosperms. They hunted within those genomes for the remnants of whole-genome duplication. Ultimately, they discovered 132 independent duplication events over the past 150 million years and used information from fossilized plants, among other methods, to date when these events took place.

In 2009, Van de Peer and colleagues showed that duplication in a handful flowering plant species clustered around the meteor that killed the dinosaurs. However, the latest research shows that the blossoming of polyploid angiosperms was not a one-off event; it has occurred many times in the past 150 million years. The researchers identified at least nine clusters of duplication incidents, all of which corresponded to important environmental events.

"We see clusterings of whole genome duplications in time, and every time it corresponds with a described, important geological event, whether it's a global cooling period, whether it's a global warming period, or whether there's an extinction event," Van de Peer said.

Kevin Bird, a researcher who studies the evolutionary genomics of polyploids at Kew Garden in London and was not involved in the new study, said the new research helps build on past work. "The study's findings are a very exciting hint at how life survives and evolves through the most extreme periods in our planet's history," he said. "Given that the initial findings in 2009 were about a single cluster of ancient duplication events around 60-70 million years ago, it was a shock that they discovered evidence for as many as nine of these bursts throughout the history of plants."

However, he noted that the research should be a starting point for further investigation. "Overall, the work is done very carefully with some of the best methods currently available, but there is always a lot of uncertainty when you're projecting back hundreds of millions of years in the past," Bird told Live Science.

In the future, as the climate changes, research into polyploids is likely to become increasingly important, scientists say.

"Polyploids are better able to cope with stress, and stressful conditions can also induce polyploidy," said Douglas Soltis, a biologist at the Natural History Museum of Florida who was not involved in the research but who collaborates with Van De Peer. "The Anthropocene [human era] will be — and probably already is — a time of stress that will induce polyploidy and also select for polyploids."

Bird agreed that climate change could trigger another burst of genome duplications, but he noted that it would take millions of years to see how this burst will shape plant evolution. "What we might expect to see in the present is that polyploid populations are better able to tolerate the weather volatility, intensification and habitat degradation brought on by climate change and other human disturbances to habitats," he said.

Van De Peer and his team are artificially making polyploid plants and investigating how they respond to stress. "There must be a stress advantage in the polyploids, but there is so much that we still don't know about that," he said.

See how much you know about natural selection with our evolution quiz!

Birds have spread their wings the world over, but they first took flight at least 150 million years ago, during the dinosaur age.

In his new book "The Story of Birds: A New History from Their Dinosaur Origins to the Present" (Mariner Books, 2026), Steve Brusatte, who is a paleontologist at the University of Edinburgh in Scotland, takes readers on a wild ride from the oldest known bird, Archaeopteryx from Jurassic Germany, through the eras, explaining how two-legged theropod dinosaurs evolved into the more than 10,000 species of birds alive today.

Around 66 million years ago, some of these small, winged creatures survived the asteroid that killed the nonavian dinosaurs. While many birds stayed small, others grew to huge sizes . Brusatte describes a bevy of lost giants, including colossus penguins, which were gorilla-size apex predators who prowled the oceans, elephant birds that stood as high as a basketball hoop and laid watermelon-size eggs, and terror birds that hammered their prey into submission with razor beaks.

Like Brusatte's other books, "The Rise and Fall of the Dinosaurs: A New History of a Lost World" (William Morrow, 2018) — which landed him the role as scientific advisor on the "Jurassic World" movies — and "The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us" (Mariner Books, 2022), he starts each new section with a vignette, drawing readers into past worlds. You can read an excerpt on Live Science, detailing the discovery of the first known fossilized dinosaur feathers.

Live Science sat down with Brusatte to discuss the original purpose of feathers, how bird flight was an evolutionary accident, and why the modern era may present the biggest threat to birds since the dino-killing asteroid wiped out their relatives.

Laura Geggel: Alright, this is the big question: Are birds dinosaurs?

Steve Brusatte: Birds are dinosaurs. Birds are dinosaurs in the same way that a T. rex or a Triceratops is a dinosaur. And that is because birds evolved from other dinosaurs. They are part of the family tree. They are just a peculiar group of flying dinosaurs. Just like bats are a strange group of flying mammals.

LG: It's thought that birds evolved from shrinking, two-legged theropod dinosaurs. How did this come about?

SB: Birds did not evolve by, let's say, a T. rex mutating into a chicken one day. That's not how evolution works. And what we see from the fossil record is a whole series of transitional fossils of dinosaurs that lived tens of millions, even hundreds of millions of years ago, evolving one by one. [They evolved] the keystone features of birds: feathers, wings, wishbones, hollow bones and big chest muscles for flying. But these things didn't all just evolve at once. They did not evolve for flying. Almost all of these things evolve for other reasons.

We see things like feathers first turn up in dinosaurs that were too big to fly that lived on the ground. These feathers are much simpler than the feathers of birds today. So, we can actually tell that a lot of the things that birds need to fly, the things that make birds, are things that actually evolved in dinosaurs. They are dinosaur features that were repurposed later on by evolution to make a flying bird.

LG: What do feathers do for an animal? Why do we think dinosaurs had them in the first place?

SB: There is nothing else alive today that has feathers. They are a bird hallmark, a calling card for birds. But what we see from fossils is that the ancestors of birds first evolved feathers. Lots of dinosaurs had feathers, so they're really a dinosaur feature.

And the incredible thing is that we see that a lot of dinosaurs had feathers. It isn't just one or two dinosaurs. And it's not even just the dinosaurs that are most birdlike or were the immediate ancestors of birds. It's many dinosaurs. There are meat-eating dinosaurs with feathers, there's plant-eating dinosaurs with feathers. There's little dinosaurs with feathers. Some of the raptor dinosaurs like Velociraptor [had feathers]. There are big dinosaurs with feathers. There's a tyrannosaur from China, a cousin of T. rex that was like 30 feet [9 meters] long that weighed something like a ton. Its body is covered in feathers.

So, if you map this onto the dinosaur family tree, really the only conclusion you can draw is that feathers were normal for dinosaurs. The common ancestor of dinosaurs would have had some kind of feather. But most of these feathers were very simple — they were not quill pens. They didn't make up wings. There's no way they could be used for flying. They looked a lot more like hair, just individual little strands similar to our hair.

The direct evidence from the fossil record [is] that feathers evolved in a simpler form. They must have been used for something else. We don't know exactly, but the best idea is that they evolved for the same reason that hair evolved in mammals, and that was to help regulate the temperature, to keep the body warm. We wouldn't really know that without the fossils. To me, as a paleontologist, that's the really cool part of the story. This is the evidence from many millions of years ago of how birds evolved.

LG: You've actually studied a number of fossils with feathers.

SB: I write about this in the story, the first time I saw a dinosaur wing. And I know it sounds hyperbolic, but it really was kind of a transcendent experience. And I'll explain why. So I was a college student at the time. I was in undergrad and I was on a trip with my mentor with Paul Sereno who's a very famous dinosaur hunter who's discovered dinosaurs all around the world. He brought me along as a research assistant and we were in China, and my god this was the first time I'd been to China, so far away from home. I grew up in the middle part of America. It was just sensory overload.

We were at the museum in Beijing and from across the room I saw on a limestone slab of rock, a dinosaur beautifully preserved. All the bones were there and it was surrounded by a halo of feathers and the arms were lined with quill pens that looked just like the feathers of modern birds.

Now, I had studied dinosaurs by this point. I was building a career in paleontology. I'd read all about birds and bird evolution. I knew that a lot of dinosaurs had feathers. But until it was in front of my own eyes, and until I saw just how similar those feathers were to the feathers of modern birds, how they formed a wing — but it wasn't a bird, it was a raptor dinosaur. Until that moment, it didn't really hit home.

So, I completely understand how this idea that birds evolved from dinosaurs or birds are dinosaurs, that can be a bit off-putting to people, a bit confusing. It just makes your head spin. But when you see it, you really see it. And since then, I've been very fortunate to go back to China to work with many great Chinese colleagues. To work at some of the museums where farmers from northeastern China bring in the fossils of these feathered covered dinosaurs. These were fossils that were formed about 125 million years ago. Volcanoes buried these entire ecosystems; they locked the soft tissues, the fine details into stone, and now the farmers in Liaoning province in China find these in abundance and bring them to museums.

It's been an incredible thing to play a small role alongside a lot of my good friends in China in studying some of these astounding animals that really capture evolution in action.

LG: The birds' reptile cousins, the pterosaurs, were already flying around when birds emerged. Did birds face much competition from their cousins?

SB: Yeah, it's a great question. A lot of people, rightly so, by the way, think that pterosaurs or pterodactyls, are dinosaurs. I mean, you often see them in dinosaur movies, you see them on the dinosaur posters and the dinosaur toy sets — but they're not actually dinosaurs. They're a separate group of reptiles that flew. They're close cousins to dinosaurs, but they are not dinosaurs, the same way a crocodile isn't a lizard.

Remarkably though, it was the pterodactyls that were the first animals with bones to ever evolve powered flight. And by that, I mean the type of flying where you have wings and you actively move those wings up and down to generate the lift and the thrust that you need for flying.

Plenty of animals can more passively fly and glide — flying squirrels, flying fish. But it's only been the pterodactyls, then later the birds, and then the bats among animals with bones that have evolved powered flight. And the pterodactyls did it by at least about 230 million years ago.

There are fossils of that age of fully formed pterodactyls with big wings, not wings made out of feathers. They did it differently. Their wings were made out of skin. They were attached to a single long finger like an E.T. finger. It was the fourth finger, the ring finger.

Now, Archaeopteryx is still the oldest bird [from] about 150 million years ago. That means that for about 80 million years, give or take, the pterosaurs were there alone in the air. I mean there would have been insects and other things, but among animals with bones, they were the only flyers.

So when birds came on the scene, when dinosaurs started to properly fly they were really interlopers in a pterodactyl world, and they really mounted an insurgency. They didn't just take over the world right away. For a long time, birds and pterodactyls lived together. And in fact, the pterodactyls only died when the rest of the non-bird dinosaurs died when the asteroid hit at the end of the Cretaceous 66 million years ago.

Again, you can do the math. That means that for more than 80 million years, there were birds and pterodactyls living together. Ultimately, really, it was just that asteroid that made the birds victorious. If not for that quirk of prehistory, who knows what the modern world might be like.

LG: There were multiple bird lineages, but only one survived the mass extinction. What set it apart?

SB: The day the asteroid hit, the 6-mile-wide [10 km] rock fell out of the sky and triggered earthquakes and tsunamis and wildfires and blocked out the sun for many years, plunging the Earth into a long nuclear winter. I mean, this was carnage.

And 75% of all species died. Among the species that died, [were] yes, T. rex and Triceratops and the long-neck dinosaurs and the duck bill dinosaurs, but also all of the more primitive birds — the ones that still had teeth, that still had long tails, that still had big claws on their hands, like raptor dinosaurs. A whole bunch of those birds were living on the day the asteroid hit, and they didn't make it through.

The only birds that survived are the modern-style birds, the ones that we know. But these are the birds that have beaks instead of teeth. They're the birds that have big wings and big chest muscles so they can fly really well. They're the birds that grow really fast. We don't really see baby birds very much in nature. They are there. You can hear them sometimes in the nest, squawking for their parents to bring them food, but they stay babies for maybe a few months at most. So birds grow super quickly.

These are all things that probably would have helped them stare down that asteroid because when the asteroid hit, you had to confront that with whatever features you had, with whatever the reality of your anatomy or biology was. There was no time for natural selection to slowly, gradually, change you generation by generation. You had to deal with the fires and the earthquakes and the acid rain and the nuclear winter. It all came at you.

If you were able to grow fast, that would help you. You could get through childhood more quickly. You could turn over the generations more quickly [to reproduce and evolve]. If you could fly, that could help you. If you were small — and these birds were small — you could hide away more easily [from predators and the hazardous, post-asteroid world]. And if you had a beak, you could eat seeds. And we know a lot of these birds could eat seeds. We find the fossil gut contents, the last meal fossilized sometimes.

Eating seeds is actually quite difficult to do. There's not a whole lot of animals that specialize in seeds, but it would have been very important if you could do it when the asteroid hit, because when the sun was blocked for a few years by all the soot from the fires and the dust and the grime from the collision, the Earth really would have gone into a winter that lasted several years. It was dark. It was cold. There was very little if any sunlight for plants to photosynthesize. And so ecosystems collapsed like houses of cards.

If you were a plant eater and you ate parts of a growing plant like leaves or fruits or flowers, you'd be in trouble. I mean, that stuff would soon be gone. But we know from modern disasters, forest fires and volcanic eruptions and so on, that seeds can last in the soil longer than any other part of a plant. That's how forests regenerate after a natural disaster.

If you could eat seeds, that might have been your ticket to survive a little bit longer. You had food that other animals couldn't get.

LG: If you fast forward to today, birds are facing many challenges. Do you want to talk about a few and why their numbers are dropping?

SB: I think birds today are facing their greatest challenge since they stared down the asteroid. There have been a number of birds that have gone extinct within human history. And many of those birds only lived in one place, often on one island. They're quite quirky birds, idiosyncratic birds, things like dodos, but also things like moas in New Zealand or elephant birds in Madagascar or a huge number of birds in Hawaii.

But extinction, I think, is really only part of the story. I mean, extinction is extinction. It's final. If the last member of a species dies, it's done. But you can have a species endure, but in a very wounded state.

That seems to be what's happening to a lot of birds, just since the time that my parents graduated from high school in the early 70s. There's been a loss of billions of birds in the standing population of North America. A lot of these species of birds, whether they're robins, different types of song birds, different types of owls or hawks or eagles … it's not that they've gone extinct, it's just that their populations have crashed. And it really is because of land use, it's because of fertilizer, it's because of pollution, it's because of climate change.

First of all, we just have to admit it's an issue, and then we have to find ways to try to mitigate against this. And I think that's where the fossil record comes in. If we have information from past extinctions or information from past episodes of environmental change, we can better understand which types of birds are more vulnerable when the climate changes or land use changes.

It is awesome to study T. rex, of course, but we do study fossils because we see them as relevant to understanding what's happening in the world today. They're clues from prehistory that give us insight. So that's where we're with birds. It is worrying, but I choose to be optimistic, for two reasons mainly.

First is that — bald eagles [and] California condors being two great examples — when we've realized that certain birds are in dire straits, we have done things to protect them. Bald eagles were super rare when I was growing up in the late 80s and early 90s, but by the end of the 90s, they were very common in northern Illinois, especially along the Illinois River, where I'm from.

Now they have these tourist packages, especially in the winter, where you go and you just watch the eagles. There's so many of them fishing on the river. So, that's a great success story, and that gives me optimism.

The other thing that gives me optimism is [that] birds are survivors. If they got through the asteroid, they're survivors. If they've survived the gauntlet of climate change and volcanic eruptions and drifting continents and rising and falling seas and all the other things that have befallen the Earth over the last 150 million years, then at least some birds, I think, will be able to face whatever humans throw at them.

That's not an excuse for us to be completely disrespectful to the environment, but it does mean that in many ways I'm more hopeful that birds can endure than maybe even our own species. We might think it's the age of mammals. We're a mammal, of course. But at least in that way, we're still in the age of dinosaurs.

Editor's note: This interview has been condensed and edited for clarity.

In the 1970s, paleontologist John Ostrom revived the theory that modern birds are evolved from theropod dinosaurs, a group that includes Tyrannosaurus rex. But a key piece of evidence was missing: feathered fossils. Then, a chance discovery in China upended our understanding of bird evolution.

In this excerpt from "The Story of Birds: An Evolutionary History of the Dinosaurs That Live Among Us" (Mariner Books, 2026), author and paleontologist Steve Brusatte looks at the monumental shift in dinosaur research after the first feathered dinosaur was discovered.

For well over a century, since its discovery in the Bavarian lithographic mines in 1861, the fossil bird Archaeopteryx was the oldest and most primitive creature known to have feathers. Then, in the autumn of 1996, this understanding was upended. Some revolutions start with a single shot; this one began with a chance encounter and a handful of photographs.

As the trees in Central Park dropped their leaves, paleontologists from around the world converged across the street, at the American Museum of Natural History, in mid-October for the annual meeting of the Society of Vertebrate Paleontology. A few weeks earlier, the Canadian dinosaur hunter Phil Currie had been in China, leading a group of tourists to dinosaur dig sites. While there, he spied something peculiar in the backroom of a Beijing museum, discovered by a farmer named Yumin Li two months prior. It was the skeleton of a small dinosaur, about the size of a chicken, fossilized as if frozen in time, in a muddy rock imbued with volcanic ash, a sign it was overcome by a sudden cataclysm.

Rapid burial had locked in the dainty details of the skeleton, but it was the stuff surrounding the bones that caught Currie's attention. The dinosaur's body was encircled by a halo of fluff. Thin, tufty, delicate strands ran along the dinosaur's back, from the top of its head to the tip of its tail. Some of the strands looked like they branched at their base. For all the world, the fuzz looked like the downfeathers of a bird.

But this wasn't a bird; it didn’t have wings, and obviously couldn't fly. It was a bona fide dinosaur — a small coelurosaur theropod, very similar to the German Compsognathus, which Huxley had held up in the 1860s as the type of transitional reptilian species birds might have evolved from.

Currie and his Chinese colleague Pei-ji Chen snapped photographs, which they printed out at the size of index cards and brought to the conference in New York. Once there, word spread fast; the rumors of a fluffy dinosaur billowed through the hallways and meeting rooms. Somebody tracked down John Ostrom, then in the twilight of his career, three decades after his discovery of the raptor Deinonychus had reignited the theory that birds evolved from dinosaurs. Currie and Chen handed him the photos. Ostrom looked shell-shocked. He began to cry, and almost fell to the floor. "I need to sit down," he stuttered, delirium taking hold.

Here it was, finally: a dinosaur with feathers. Just as Ostrom had predicted. Just as the doubters had demanded. The final piece of the puzzle, the strongest evidence that birds have dinosaur ancestry.

A crafty journalist from The New York Times caught wind of the excitement, and the next day, the front page of the Saturday edition blared with the headline "Feathery Fossil Hints Dinosaur-Bird Link," along-side articles about Bill Clinton's reelection campaign and a Yankees World Series preview. Above the bold print was a drawing of a small meat-eating dinosaur, running on its hind legs, small arms curled up, its tail a long seesaw for balance, its neck, back, and chest covered with bushy fuzz.

The artwork was needed, because the Chinese authorities barred publication of the photos. Before the year was out, Chinese scientists published a formal description of the fossil and gave it a name: Sinosauropteryx, the "Chinese reptilian wing," in honor of its transitional status between dinosaurs and birds.

Sinosauropteryx was the firing gun for a fossil rush, as farmers across Liaoning Province — a bucolic region of fields and rolling hills along the Chinese border with North Korea — fanned out in search of more feathered dinosaurs.

They knew the land better than anyone, and they knew museums would pay top money for such precious fossils. Soon, they were finding feather-covered dinosaurs in droves. The whole area, it turned out, had been bombarded by volcanic eruptions in the Jurassic and Cretaceous Periods, which quickly entombed entire ecosystems.

This was the key to the fine preservation: Normally soft bits like skin and feathers decay before a skeleton can harden into a fossil, but in this one remarkable place, feathers could easily fossilize. It was a dinosaurian Pompeii. As the new millennium dawned, the mounting Chinese discoveries transformed our image of dinosaurs.

One feathered dinosaur became ten, then hundreds, then thousands of skeletons, belonging to several dozen distinct species. Some, like the ostrich-size Beipiaosaurus, were adorned with simple filaments that looked like oversize versions of the bristle feathers of modern birds. Others, like the original Sinosauropteryx, had more complex feathers that resembled little paintbrushes, with many individual bristles branching from a root in an untidy tuft.

Much more extravagant were the feathers of the turkey-size Caudipteryx and dromaeosaurid "raptors" like Sinornithosaurus, which had true quill pens with a central shaft and many barbs extending off the sides to form vanes. Sometimes, these pennaceous feathers lined up along the hand and arm, making what could only be described as a wing, like in the crow-size Microraptor.

The roster of feathered dinosaurs got richer and richer. Even tyrannosaurs were in on the makeover: two early cousins of T. rex called Dilong and Yutyrannus were found coated in bristle and tufty feathers. Most of these plumose dinosaurs were theropods, members of the great group of meat-eaters on the family tree, but a few plant-eaters like Psittacosaurus, a primitive cousin of Triceratops with tiny horns on its head, had mohawks of bristles along their tails.

And most of these feathery fossils were from China, but soon they started to turn up elsewhere, like in Siberia, where a herd of hundreds of dog-size, duck-billed dinosaur cousins called Kulindadromeus were overwhelmed by their own volcano. This herbivore was resplendent with bristles on its head and body, branching downy tassels on its arms and legs, and curi-ous ribbonlike streamers on its knees — while meanwhile there were also scales on the lower legs and tail. Although Kulindadromeus was a vegetarian distantly related to theropods, its branching tufts — each formed by six or seven short filaments arising from a common anchor — look like they could be plucked from Sinosauropteryx or another meat-eater.

Initially, there was some skepticism that these wispy fossilized structures on the backs, tails, and arms of dinosaurs were true feathers. It was a legitimate question when Sinosauropteryx was first unveiled: Could its little strands and bristles have been something else, like degraded skin, or a freak by-product of decay and fossilization?

The discovery of full-on pennaceous quills — with shafts, barbs, and vanes — in species like Caudipteryx and Microraptor proved that many of these were genuine feathers. But what of those simpler filaments in other dinosaurs? We can be confident they are real. They not only look like the bristles and down feathers of birds today, but they share the same structure: They are hollow, chemical analysis shows they are formed of those rare CBP proteins, and when you look at them under powerful microscopes, you see they are full of melanosomes, the minuscule bubbles that hold pigments and give modern feathers their colors.

Still doubt it? Then gander at one of the most improbable fossils ever discovered, from Myanmar, announced in 2016. It's a tail of a juvenile theropod embedded in amber, shrouded in feathers, their details preserved in stunning 3D. Suspended in yellow resin, like a bug frozen into an ice cube, the feathers seem almost alive.

They may as well be bundles of down that slipped out of a pillow and stuck onto your sofa. They have a small central shaft, which branches into barbs, which further branch into barbules. And they are clearly observed growing from follicles in the skin. They are absolutely feathers, and fulfill every definition we use to characterize feathers in modern birds — but they are plastered to a dinosaur.

This bounty of feathered dinosaurs, fundamentally, was that final piece of evidence to verify what has now become paleontological consensus: Today's birds evolved from dinosaurs.

Excerpted from the book THE STORY OF BIRDS: A New History from Their Dinosaur Origins to the Present by Steve Brusatte. Copyright © 2026 by Stephen (Steve) Brusatte. From Mariner Books, an imprint of HarperCollins Publishers. Reprinted by permission.

Some fungi can produce proteins that freeze water, which may allow them to reach into the atmosphere and trigger rain. Now, scientists have discovered the secret to this process: a gene from ancient bacteria.

Researchers have long known that some bacteria have proteins in their cell membranes that allow them to freeze water at relatively high temperatures, about 23 degrees Fahrenheit (minus 5 degrees Celsius) ‪—‬ a process known as ice nucleation. Certain species of fungi can do this as well, but much less was known about how it worked in that kingdom of life.

"We just wanted to figure out how this works," said Boris Vinatzer, a microbiologist at Virginia Tech and co-author of the new study, which was published March 11 in the journal Science Advances.

Vinatzer and his colleagues studied the genomes of two strains of fungi in the Mortierellaceae family to find their ice-nucleating protein. They had a couple of leads: They knew the protein was secreted into the environment rather than stuck to the fungal cells, and they knew roughly how big it was. So they looked for genes that had those characteristics and were similar to known bacterial ice-nucleating proteins.

They were surprised to find a candidate that was almost identical to a bacterial gene called InaZ. And when they transferred that fungal gene into a yeast cell, the yeast gained the ability to create ice as well.

"We confirmed that that particular DNA fragment actually makes ice nucleation proteins," he told Live Science.

This suggests that, at some point in the past, perhaps millions of years ago, an ancestral fungus acquired the gene from its bacterial neighbors ‪—‬ a process known as horizontal gene transfer ‪—‬ and then made it its own.

Less clear, however, are how the fungi are using this ice-making ability and what evolutionary advantage it gives them. "We really have no idea so far," Vinatzer said.

Bacteria that have ice-nucleating proteins are often ones that attack plants, such as Pseudomonas syringae, which infects corn. Scientists think these bacteria use the ice-forming proteins to damage the plant, allowing nutrients to seep out or the bacteria to invade.

One of the fungi in the new study was from lichen, a hybrid colony of fungus and algae that grows on rocks and trees. Vinatzer speculated that the ice-nucleating proteins may allow the fungus to pull water from the air, thus providing a necessary-but-scarce resource for the lichen.

"On mornings when there is high humidity and low temperatures, the fungal proteins can trigger a frost on the lichen that then melts and provides water later in the day," he said.

But perhaps the most intriguing aspect of these ice-making bacteria and fungi is that they may be able to influence the weather, seeding the clouds to call down rain.

Ice-forming bacteria like P. syringae are known to be part of the water cycle and play a significant role in precipitation. They get swept up into the clouds by wind or evaporation, where their ice-nucleating ability generates tiny crystals that eventually get large enough to fall as rain or snow. It seems likely that the ice-nucleating proteins secreted by fungi undergo a similar process, Vinatzer said.

Because a single fungus can secrete many proteins, with each acting as an individual ice nucleus, there may be many more of them in the clouds than there are rain-making bacteria. "That suggests fungi may actually be more important than bacteria in influencing the weather," he said, which could benefit not only the fungi on the ground but the entire ecosystem.

These newly discovered fungal proteins could be useful for humans as well, Vinatzer suggested. Cloud-seeding operations currently use a toxic chemical called silver iodide to generate ice crystals, but maybe it could be replaced with a benign organic protein.

"These proteins could be an alternative to toxic silver iodide," Vinatzer said. "If we can figure out how to produce them, why not use them instead?"

During the Triassic around 205 million years ago, a newly-identified relative of modern crocodiles stalked its prey, but not in the water, a new study finds.

Like other ancient crocodile cousins, this newly identified species hadn't yet ventured into the water. Instead, it hunted its prey on land, much like a modern fox or jackal, the researchers said.

It would have been a fearsome predator, with its fossil suggesting "specialization for a powerful bite," the researchers wrote in the study.

The specimen was originally discovered decades ago, in 1948 at Ghost Ranch, New Mexico, in a well known dinosaur death bed. At the time, it was tentatively cataloged as a specimen of Hesperosuchus agilis, a small, early relative of crocodiles and alligators. But now, the new study shows that the creature's unusually short snout and thick, reinforced skull set it apart as an entirely new genus and species, though the creature lived — and died — at the same time and place as H. agilis.

"This is the first really strong evidence we have of coexistence between two functionally different-looking crocodylomorphs," study co-author Miranda Margulis-Ohnuma, a paleontologist at Yale University, told Live Science. Crocodylomorphs include modern crocodiles, alligators, caimans and their extinct relatives.

The fossil of the short-snouted creature, newly dubbed Eosphorosuchus lacrimosa, was uncovered in a Late Triassic (237 million to 201 million years ago) formation. The animal's skull, the bones of one of its back legs, one vertebra, and three scales were preserved. The creature would have been about the size of a large dog.

"It was in the basement of the Peabody Museum [at Yale] for, literally, 75 years," Margulis-Ohnuma said. "People would sometimes come visit and look at it, but it had never been identified."

In the new study, published Wednesday (April 15) in the journal Proceedings of the Royal Society B: Biological Sciences, Margulis-Ohnuma and her colleagues categorized the fossil in detail and compared it with a fossil of H. agilis found about 15 feet (5 meters) away. The animals in this section of Ghost Ranch lived at the same time, and they died and were buried in a single event, possibly a flood.

E. lacromisa has a much shorter snout than H. agilis, the team found. It also has a larger, triangular postorbital — a bone in the skull — and matching features on its lower jaw that may have accommodated strong muscles for chomping. Together, those traits suggest the creature had a very powerful bite.

Because E. lacrimosa and H. agilis lived alongside each other, the team suspects they occupied different ecological niches. For example, crocodilians with shorter snouts may have fed on larger, less-agile prey than species with longer snouts did.

"It's really cool that it's not a lineage that's just struggling to take off — at this point, there's already diversity," Margulis-Ohnuma said. "We're really getting a snapshot of the very beginning of functional diversity across crocs."

Scientists don't know much about the early stages of crocodylomorph evolution. There aren't many of these animals preserved in the fossil record, Margulis-Ohnuma said, and many crocodylomorph species from the Triassic are represented by a single fossil specimen.

"For early crocs, we're very data deficient, so every new fossil that comes out is changing the story," Margulis-Ohnuma told Live Science. "If we can continue to describe this material that we have, and ideally find new fossils, it will change the story every single time."

A newly discovered trove of fossils in southwestern China is shifting the timeline of when complex animals evolved.

The diversity and complexity of animal life is thought to have increased rapidly beginning around 539 million years ago, in an evolutionary burst known as the Cambrian explosion. But the new fossil site suggests that some of that complexity was already present several million years before the Cambrian explosion, during the end of the Ediacaran period (roughly 635 million to 539 million years ago).

Among the fossil finds were bilateral worm-like animals that may have anchored themselves to the seafloor, early comb jellies, and relatives of starfish and sea cucumbers that likely used tentacles on their heads to catch food. Other fossils bore little resemblance to modern animals or to known Ediacaran or Cambrian species.

"One specimen looks a lot like the sand worm from Dune," study co-author Frankie Dunn, a researcher who studies Ediacaran organisms at the Oxford University Museum of Natural History, said in a statement.

Some simple multicellular creatures, such as sponges, first appeared during the Ediacaran period. But most modern animal phyla showed up during the subsequent 13 million- to 25 million-year-long Cambrian explosion, including chordates, the phylum that includes humans and other vertebrates.

The new fossil discovery suggests that some of that complexity had already arisen by the late Ediacaran. Uncovered as part of the Jiangchuan Biota collection of fossils in southwestern China, the collection contains more than 700 specimens of fossilized animals and algae dating to between 554 million and 539 million years ago. Researchers reported the findings Thursday (April 2) in the journal Science.

"When we first saw these specimens, it was clear that this was something totally unique and unexpected," study co-author Luke Parry, a paleobiologist at the University of Oxford, said in the statement.

The fossils from this site are mostly flat imprints of the organism on the surrounding rock, known as carbonaceous films. Unlike the three-dimensional imprints left by durable body parts, such as bones and shells, carbonaceous films capture some details of the organism's soft tissues, such as its gut and mouthparts.

This less-common method of preservation might help to explain why scientists haven't found evidence of these more complex animals in the Cambrian until now.

"Our results indicate that the apparent absence of these complex animal groups from other Ediacaran sites may reflect differences in preservation rather than true biological absence," study co-author Ross Anderson, a researcher who studies the evolution of complex life at the Oxford University Museum of Natural History, said in the statement. "Carbonaceous compressions like those at Jiangchuan are rare in rocks of this age, meaning that similar communities may simply not have been preserved elsewhere."

For 60 years, the earliest known human species has also been one of the most mysterious. Homo habilis was added to our family tree in 1964. But it's long been unclear exactly what the ancient species, which lived between about 2.4 million and 1.65 million years ago, looked like.

That's because, until recently, only three very incomplete fossilized skeletons had been unearthed.

Then in January, researchers described a fourth, more complete skeleton — and it revealed that H. habilis had an anatomy very unlike our own. The discovery has some researchers asking a big question: Is the earliest known human ancestor not human after all?

"As we have discovered more fossils, we've stretched the definition of the Homo genus," Bernard Wood, a paleoanthropologist at the George Washington University in Washington, D.C., told Live Science. "Maybe this time we just stretched it too far."

Obviously our species, Homo sapiens, belongs in the Homo genus. We also know that our closest living relatives, the chimpanzees and bonobos, don't. This means that the human genus evolved at some point after our evolutionary lineage, which includes humans and our closest extinct relatives, split away from the chimpanzee line, an event that occurred more than 5 million years ago. So, when exactly did the human genus evolve?

One approach would be to argue that it dates to the split with the chimpanzee lineage. But the first creatures that appeared after the split don't look much like we do. They include species, like Australopithecus afarensis, that had long, ape-like arms and relatively small brains.. This species existed in Africa between about 3.9 million and 2.9 million years ago, and includes the famous Lucy skeleton. Very few researchers consider Lucy to be human.

Most anthropologists, however, have historically considered H. habilis a member of the Homo genus.

Few skeletons

The first, very incomplete Homo habilis skeleton was discovered in Tanzania in the 1960s. The 1.75 million-year-old specimen included fragments of the skull, from which it was possible to estimate that they came from an individual whose brain had been roughly 45% the size of the average living person's. This may sound small, but that was substantially bigger than the average australopithecine's brain, which was about 35% the size of ours. Because of this evidence, the skeleton was placed in our Homo genus, and given the name Homo habilis, meaning handy or skillful human, it was a decision that most researchers have accepted.

But the H. habilis skeleton described in 2026 complicates things. This skeleton is 2 million years old, and was found in Kenya, about 500 miles (800 kilometers) north of where the first H. habilis remains were unearthed. Just like the first skeleton, the Kenyan skeleton is far from complete. But the bones that survived give us our best ever look at H. habilis's arms, said study co-author Carrie Mongle, a paleoanthropologist at Stony Brook University in New York. The problem is that those arms aren't like ours. Instead, they are long and ape-like, similar to the arms of our australopithecine relatives like Lucy.

"They are very much australopith-like," Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York City, told Live Science. In an article published earlier this year, Tattersall argued that these ape-like arms are a clear indication that H. habilis wasn't a member of the human genus.

He isn't the first to make this suggestion. Wood and his colleague, Mark Collard, an archaeologist at Simon Fraser University in Canada, argued in 1999 that H. habilis wasn't a member of the human genus. By then, the second and third H. habilis skeletons had been discovered, and although extremely incomplete, they hinted that the species had limb proportions unlike ours — something that the fourth skeleton confirms.

Wood and Collard suggested transferring the species to the same genus as Lucy, which would mean renaming Homo habilis to Australopithecus habilis. Tattersall doesn't think that's a good solution, because the species had human-like brain size and teeth. He thinks habilis should be put in its own genus, although he hasn't yet come up with a name.

A different approach

Other researchers, meanwhile, suspect that Wood and Tattersall are both wrong.

They think there is no need to rename H. habilis despite its arms. "Those ape-like limb proportions don't necessarily tell us all that much," Carol Ward, an anthropologist at the University of Missouri, told Live Science. This is because of the way most evolutionary scientists operate when they are defining species and genera.

We know that our very earliest ancestors, living just after the split with the chimpanzee line, spent plenty of time climbing trees, where long, ape-like arms would have been useful. Gradually, they adapted to spend more time walking on the ground before ultimately evolving into humans.

These bipedal ancestors probably no longer needed long, ape-like arms. But crucially, Ward said, long arms were almost certainly not a hindrance to survival either. Under those circumstances, even the first species in the Homo genus might have retained the long arms of their ancestors, because there was no strong evolutionary pressure to shorten them. Why arms eventually shrank is still not entirely clear, although some researchers think shorter arms may have brought some subtle advantages while running and using tools. This suggests there was weak evolutionary pressure for shorter arms, meaning they shrank, but at a relatively slow rate.

There's a broader point here. "We want to think there was this big change with Homo, that we're different from everything else that came before," Ward said. "But this H. habilis skeleton supports the idea that maybe there was a more gradual transition from australopiths to Homo."

This idea highlights an awkward problem that scientists are still grappling with.

Evolution is so complicated that it's surprisingly difficult to divide living things into clear groups, such as species, which is one reason why there are now dozens of different ways to define species, and a heated debate on which one is the best. It turns out that genera are just as difficult to define, which means there isn't actually any agreement on what a genus is, Wood said.

In other words, researchers will probably continue to debate whether or not H. habilis is in the human genus, for the simple reason that they still can't fully agree what a genus actually is.

Human origins quiz: How well do you know the story of humanity?

Before Neanderthals went extinct, they experienced a major upheaval that resulted in just one of their genetic lineages surviving in Europe and then expanding across the continent, a new study shows.

The findings, published March 23 in the journal PNAS, may shed light on what ultimately doomed the Neanderthals.

Neanderthals were among the closest relatives of modern humans (Homo sapiens), with their lineages diverging around 500,000 years ago. Although Neanderthals once ranged across Eurasia, they are generally thought to have gone extinct about 40,000 years ago.

DNA recovered from Neanderthal fossils can shed light not just on their extinction but on their history in general. In the new study, researchers examined DNA from mitochondria in cells, which help generate energy for the body, and get passed down from mothers to offspring.

The scientists gathered 10 mitochondrial DNA sequences from Neanderthals excavated from six archaeological sites in Belgium, France, Germany and Serbia. They analyzed them alongside 49 Neanderthal mitochondrial DNA sequences released in previous research.

The team found that in Europe, where Neanderthals ultimately died out, several mitochondrial DNA lineages existed until about 65,000 years ago. After this point, these groups were replaced by a single Neanderthal mitochondrial genetic lineage originating from southwestern France. These "Late Neanderthals" proceeded to disperse across Europe.

"This tells us there was this major disruption in Neanderthal history," study senior author Cosimo Posth, a paleogeneticist at the University of Tübingen in Germany, told Live Science. "There was really a genetic transformation."

Posth noted that about 75,000 years ago, glaciers came to dominate Europe.

"We don't think our findings suggest that Neanderthals were migrating to the Mediterranean," he said. "We think Neanderthal groups in northern Europe perished, while a Neanderthal group that was already in southwestern France survived this climate change and then went on to expand across a broader region. Neanderthals had experienced multiple glaciations before, but the last one proved harsh on their survival."

The study also found that "there was a kind of genetic impoverishment among the Late Neanderthals," Posth said. "Since they appeared to emerge from this single group, their genetic diversity overall was reduced drastically compared to what came before — they were all extremely similar on a genetic level across Europe, from Spain to the Caucasus to northern Europe."

This low genetic diversity ‪—‬ which grew most pronounced about 42,000 years ago, shortly before Neanderthals generally died out ‪—‬ "might have played a role in their extinction," Posth noted. "We don't think there was a single reason the Neanderthals went extinct, but this lack of genetic diversity would have made them more predisposed to not really survive climatic changes and other disruptions."

Likewise, Neanderthal groups in the Altai Mountains of Siberia were more closely related to each other than to European Neanderthals, and these Siberian Neanderthals also had low genetic diversity and lived in small, isolated groups, another March 23 study published in the journal PNAS found.

Despite this low genetic diversity, the Late Neanderthals in Europe appeared quite diverse across sites in terms of their artifacts and art. "So after the Neanderthals re-expanded across Europe, we think that Late Neanderthal groups were not highly connected with each other," Posth said. "This would have led to more inbred groups, explaining the low genetic diversity, but also more cultural and archaeological diversity, since these groups were isolated and so would have developed more specialized cultures."

"We've seen evidence that Neanderthal populations replaced each other, and this paper really creates a ground story as to why that might be — because Neanderthals went extinct in places all the time, and then other Neanderthal groups went in and recolonized the same places," Fernando Villanea, a population geneticist at the University of Colorado Boulder who was not involved in the study, told Live Science.

Future research could seek to test these findings by analyzing DNA from Neanderthal cell nuclei instead of their mitochondria, Posth said. However, this will be a major challenge, as DNA from nuclei is several hundred times less abundant than DNA from mitochondria in cells.

Neanderthal quiz: How much do you know about our closest relatives?

Two Neanderthals present at the same cave site 10 millennia apart were distant relatives, a tiny 110,000-year-old bone fragment from the Altai Mountains in Siberia reveals. The fragment has also produced the fourth full genome of a Neanderthal to date, shedding light on how small and isolated Neanderthals were long before they disappeared around 40,000 years ago.

Researchers found the bone fragment in Denisova Cave, which both Neanderthals and Denisovans lived in off and on for nearly 300,000 years. In a study published Monday (March 23) in the journal PNAS, the researchers compared the genome of the 110,000-year-old Neanderthal male (called D17) with three other complete Neanderthal genomes to better understand Neanderthals' population structure.

The researchers compared the genome of D17 with the genome of a female Neanderthal (called D5) dated to 120,000 years ago from the same cave. They found that, while D5 was not a direct ancestor of D17, the two Neanderthals belonged to closely related lineages connected by a common ancestor. This distant biological relationship suggests Neanderthals had a long-term presence in the Altai region, the researchers said.

"But it is likely that Denisova Cave was part of a broader landscape used repeatedly by these Neanderthal populations over time, rather than a site occupied by a single, continuous group," study first author Diyendo Massilani, a genetics professor at the Yale School of Medicine, told Live Science in an email.

The study results also revealed that Neanderthals in the Altai region lived in very small and highly isolated populations of 50 or fewer people, as shown by stronger genetic markers of inbreeding. Specifically, researchers found that the individuals they analyzed had large sections of identical DNA, an indication that their parents were very closely related — as close as first cousins, for example.

The new research complements previous studies that showed Neanderthals lived in smaller and more isolated groups than our own species did. A 2022 study indicated that one Altai Neanderthal community numbered around 20 individuals, while another study provided evidence of a group being isolated for roughly 50,000 years. Many researchers have pointed to inbreeding and isolation as causes for Neanderthals' disappearance around 40,000 years ago. But the latest results suggest that Neanderthals also survived for long periods under extreme conditions of isolation and small population size.

Massiliani and colleagues also discovered that Altai Neanderthals were very different from later European Neanderthals. In their genetic analysis, the researchers found that Altai Neanderthal D17 was more closely related to D5 than either of them was to Neanderthals in Europe or to later populations in the Altai region. This suggests that Neanderthal populations from eastern and western Eurasia became genetically different from one another in a relatively short time frame and within a fairly small geographic area.

"Even though the individuals from which we have genomes were separated for only about 50,000 years on average, they reached levels of difference similar to what we see today between some of the most distinct human populations, like people from Central Africa and Papua New Guinea that separated about 300,000 years ago," Massilani said.

Likely because they were small and isolated, Neanderthal populations became genetically distinct from one another much more quickly, Massilani said. This may have been because in small, isolated groups, a process called genetic drift can cause random genetic changes to become more common over time.

"We already knew that Neanderthals were not a single, homogeneous population spread across Eurasia, but a patchwork of groups shaped by complex demographic processes, including divergence, migration, local extinctions and replacements," he said. "What is striking in our results is just how differentiated these populations could become."

The high amount of genetic separation and differences between groups may have limited Neanderthals' ability to adapt to environmental changes, Massilani said.

The study provides new details about how Neanderthal populations were structured, one expert said.

"To have two sequenced Neanderthals in such a close geographic place does bring new and more fine-grained insight" into their population, Léo Planche, a population geneticist at Paris-Saclay University's Interdisciplinary Laboratory for Digital Sciences who was not involved in the study, told Live Science in an email. "We start to have enough Neanderthal genomes to actually have some claim about their population structure. Populations are groups of individuals, so the more data the better."

Editor's note: This article was updated on March 27, 2026 to note that the vast majority of Neanderthals went extinct 40,000 years ago, not 34,000 years ago as was previously stated.

Neanderthal quiz: How much do you know about our closest relatives?

The discovery of an enigmatic ape's 18 million year-old fossils in Egypt hints that the ancestors of all living apes, a group that includes humans, may have originated in northeast Africa or Arabia, a new study finds.

Scientists have long assumed that modern apes originated in East Africa, but the newfound fossils, which belong to a new genus and species, suggest they emerged farther north.

"Discovering a fossil ape in this region is both significant and somewhat surprising," study first author Shorouq Al-Ashqar, a paleontologist at Mansoura University in Egypt, told Live Science in an email. "But it also highlights how incomplete our picture has been."

Previous research has established that apes first appeared at least 25 million years ago. They soon flourished, diversifying into dozens of species and spreading across Africa, Europe and Asia.

But relatively few of these ancient apes were on the evolutionary line leading to modern apes ‪—‬ a group that includes humans and other great apes, along with gibbons and siamangs. Moreover, the apes that were on our ancestral line seem to have been confined largely to East Africa. As such, this region has long appeared to be a good place to search for the origins of modern apes.

However, after finding the fossilized remains of an ape that lived in what is now northern Egypt between 17 million and 18 million years ago, Al-Ashqar and her colleagues challenge this idea in a study published March 26 in the journal Science.

The remains, discovered in 2023 and 2024, are very incomplete ‪—‬ just a few fragments of lower jawbone and some worn teeth. But Al-Ashqar and her colleagues established that the remains didn't belong to any known ape species. The researchers have assigned the fossils to a new genus and species named Masripithecus moghraensis; the genus name translates to "Egypt monkey or trickster" in Arabic and Greek, while the species name refers to "Wadi Moghra," where it was found.

The find is important, said Sergio Almécija, a biological anthropologist at the Miquel Crusafont Catalan Institute of Paleontology in Spain who was not involved in the study. "Any new fossil ape discovery is precious because of their scarcity, especially when it comes from a region where their presence has previously gone unnoticed," he told Live Science in an email.

To determine where M. moghraensis fits in the ape evolutionary tree, Al-Ashqar and her colleagues looked at the age and anatomy of a range of ape fossils, as well as evolutionary information in the DNA of living apes.

The analysis placed M. moghraensis on the ancestral line of living apes, just before the split between the great-ape group and the gibbon-siamang, or "lesser ape," group. This implies that M. moghraensis was very closely related to the last common ancestor of all living apes. That, in turn, suggests this common ancestor must have lived in roughly the same place as M. moghraensis.

"The highest odds are [that it lived] in the northern part of the Afro-Arabian landmass," study co-author Erik Seiffert, an evolutionary biologist at the University of Southern California in Los Angeles, told Live Science in an email.

However, not everyone agrees with this interpretation. Almécija describes it as "a bit far-fetched." He would like to see far more complete fossils of M. moghraensis before any attempt to update mainstream scientific ideas about the last common ancestor of living apes.

But Al-Ashqar said the jaw and teeth are among the most useful skeletal parts for working out the evolutionary history of apes. "In mammalian palaeontology, dental anatomy is a cornerstone for interpreting diet and evolutionary history," she said.

Moreover, the idea that modern apes originated in North Africa and Arabia about 17 million years ago fits to some extent with known evidence, according to David Alba, a paleontologist at the Miquel Crusafont Catalan Institute of Paleontology who wasn't involved in the analysis.

For instance, today's nonhuman great apes are found in Africa and Southeast Asia, and fossils show great apes once lived in West Asia, too. Given this information, and the fact that today's lesser apes are found in South and Southeast Asia, "modern hominoids [apes] must have gone through northeastern Afro-Arabia," Alba told Live Science in an email, although this doesn't necessarily mean they originated there.

The exact evolutionary significance of M. moghraensis remains unclear, but its discovery hints that there are more ape fossils yet to be found in and around Egypt. "Further work there could significantly refine our understanding of early ape evolution," Al-Ashqar said.

Human origins quiz: How well do you know the story of humanity?

Humans have evolved the ability to live anywhere on Earth, thanks to gradual changes to our biology and our knack for developing new technologies, like clothes and shelter. This adaptability is often touted as being unique to our species, Homo sapiens.

In his new book, "Adaptable: How Your Unique Body Really Works and Why Our Biology Unites Us" (Penguin Random House, 2025), Herman Pontzer, a professor of evolutionary anthropology and global health at Duke University, explores how local environments work in tandem with genetics to produce the full spectrum of diversity we see in people today.

The book journeys through the human body and focuses just as much on what connects us as it does on the conditions required for differences to arise. Pontzer weaves in his work with contemporary hunter-gatherer populations, like the Hadza in Tanzania, to explore the lifestyles of pre-farming cultures and how the stark departure from these ways of life for many people today is making us sick.

"Adaptable" is a finalist for the PEN/E.O. Wilson Literary Science Writing Award, which celebrates excellence in nonfiction in the physical or biological sciences. The winner will be announced March 31 at the Literary Awards Ceremony and will receive a $10,000 cash prize.

Live Science spoke with Pontzer about his book and why understanding why and how diversity occurs is essential for questioning and challenging scientific misinformation.

Sophie Berdugo: Why did you decide to write the book now?

Herman Pontzer: In having conversations about "Burn" [Pontzer's book on the science of the metabolism (Penguin, 2022)], it became very clear to me that when you move outside of the ivory tower and start having these conversations more broadly, that there's just a lot of misunderstanding and misinformation about just how the body works in general. It's not just our metabolism. The metabolism is one of those blackbox things that we love to blame everything on and people don't really understand what it means or how it works.

SB: What is your favorite fact about the human body that you feel is completely underappreciated?

HP: I mean, where to start? Your kidneys. Kidneys are the forgotten essential workers of the body. And I could start anywhere, but let's start there ‪—‬ because if I say brains or hearts, people go, "Yeah, those are important; we know that."

Your kidneys, man: 180 liters [47.5 gallons] of water a day [are] filtered through your kidneys. All of the detox stuff that you think you're doing with the supplements you're taking, they're [your kidneys are] doing it for free and better. Somehow our bodies have learned to regulate water in a way that's different from the other apes, because we evolved in a dry environment. So, it's the interplay of water balance across our whole systems.

Spleens ‪—‬ let's do another unappreciated organ. Most people don't even know what their spleen does, I think. But among others, it's an immune function organ. Your spleen is this reservoir for red blood cells. And so, whether you're at altitude and you need a little bit more oxygen, your spleen gets bigger to be this bigger red blood cell reservoir for that.

There's this fascinating population called the Sama in the Philippines. They spend their lives on boats and in the ocean, and they forage underwater. And so there's been local adaptations, local evolution to give them bigger spleens [to have more blood oxygen when holding their breath for long periods under water when diving for food]. The alleles, the gene variants, that give them bigger spleens have become more common, and now people there have bigger spleens, on average, than everybody else.

Literally everywhere you look in the body, there's a story that I bet you haven't heard of.

SB: That case of the spleen being enlarged in this population in the Philippines is a great example of a local adaptation. Could you explain how these local adaptations occur?

HP: To talk about those local adaptations becomes a little bit tricky because they do happen, right? Certain populations do have a trait that gets more common there, or bigger or smaller, whatever it is. Natural selection can shape a trait in a population, but it's actually pretty rare because the conditions have to be just right.

So how do we do it? Local adaptation is just like any other kind of evolutionary adaptation. The reason a certain trait becomes common in a place is because it helps individuals there survive and reproduce. And that could be anything from being the right body shape and size to having a bigger spleen that helps you forage underwater. Anything that helps you survive and reproduce could end up as a local adaptation.

But the important thing here for why we see these localized events happening — and what makes them different from things that affect our whole species — is that it really has to be localized to a specific environment. It can't be that if the same trait is good everywhere, then that trait's going to spread because there's so much interbreeding, gene flow as we call it, that eventually if it's a good trait everywhere, it'll get everywhere.

So it has to be just good there. There has to be something about that trait that makes it really helpful right there but not other places. And that has to persist for generations and generations so that there's enough time for selection, because natural selection acts very slowly over generations. So it has to be good for survival and reproduction, has to be very localized and persistent for generations and generations.

Very few selection pressures meet all those criteria. Skin color is a good example of one that does ‪—‬ the best skin color to have in terms of ultraviolet light production. The darker your skin, the more protected you are against ultraviolet light damage versus having lighter skin if you need to be able to make more vitamin D, because that's the trade-off.

Those conditions have been around since the sun and the Earth have been where they are. There's always been more ultraviolet light at the equator and less towards the poles, and so that gradient has been really consistent. And then we see, surprisingly, a really consistent gradient in local populations' skin tone, how much melanin they make and, therefore, how dark their skin is.

[Then there are] things like high-altitude adaptations. The Himalayas have been thousands of meters tall since forever basically, for our purposes. And so humans living there have always had that selection pressure to be able to handle high altitude. And so you see altitude adaptations there. That's the kind of stories we see with local adaptation.

Where we get into trouble is when people talk about local adaptations with things like heart disease. There's been the argument in the '90s that Black Americans might be more likely to have heart disease because there's some localized set of alleles that affects their heart function that makes them more likely to develop hypertension and heart disease. Well, that doesn't make a lot of sense, because the selection pressures on the heart have been kind of the same for our whole species forever.

Same with all these ridiculous and really dangerous things about IQ evolution in different populations. Having a smart brain has been selected for — it's been a good idea — for our whole species since forever. And so any traits that make us have smarter brains are going to be selected for equally everywhere. Gene flow is going to push them all around.

SB: So hypothetically, if I was born with the same genetics but in the Philippines, like your earlier example, instead of the U.K., would the environment override the genetic hand I've been dealt?

HP: The way I try to talk about genetics in my classes and in the book is, your genetics — the hand you're dealt — kind of gives you a universe of possibilities where you could end up. Now, it's not unlimited. There's nothing that you could ever do to me that would have made me 8 feet [2.4 meters] tall, right? My parents could have given me all the best nutrition. I was never going to be 8 feet tall, or even 7 feet [2.1 m] tall, for that matter. So there are limits.

So I don't think of it as overriding. I think whether nature or nurture is what you see emerging more, it's almost always nurture. The environment usually has a much, much larger effect. But they really work together.

SB: What role does epigenetics play in shaping how you develop over developmental time, rather than evolutionary time?

HP: It's a wonderful example of nature and nurture working together because epigenetics is the environmental effects on your body that actually sort of change the way that your genes act for the rest of your life. An environmental experience, a stress, can affect the body in a way that it actually affects the genome, which affects your DNA so that a particular gene might be turned off or actually amplified. It can have different effects for the rest of your life.

But what's really interesting about epigenetics is this possibility that those changes might persist across generations. And so we know this is true in mice, that the epigenetic effects on the genome that we see within a lifetime are somehow transmitted to the offspring and they will have those same epigenetic effects. So the environment experienced by mom as she's growing up could actually affect her offspring when they're born and for their lives.

We have some interesting hints that it's also happening in humans. It's a really exciting space to watch in biology. I don't think we have the full answer yet for humans; it's just so hard to do the work because you're talking about studies that take decades, basically. But it's an exciting new frontier in the sort of nature-nurture interface.

SB: Would you mind explaining what evolutionary mismatches are, and why they're important?

HP: Our species evolved as hunter-gatherers. And so that environment's been the norm for humans for millions of years actually, even before we were Homo sapiens. Being a hunter-gatherer looks different depending on where you are in the world and what time frame we're talking about, but it always involves a lot of physical activity. It always involves foods that you're getting from the wild environment around you. It generally involves a fair amount of pathogens and stuff — the world's dirty out there in the wild. And so they're the kind of environments that our bodies are evolved to be best at because that's what shaped us.

Our environments today are so different from that, and that's the mismatch. The environment that I'm living in right now —‬ my house is climate controlled; I've got thousands of calories of food in the refrigerator; if I don't want to walk around too much today, I don't have to. I've got all sorts of antibacterial soaps and antibiotics if I need them.

Our environments have shifted so much that we're well outside the kind of micro-adjustments our bodies are used to making over a lifetime. And so our physiologies respond in ways that can be bad ‪—‬ so, heart disease, allergies, all sorts of modern ailments that we know didn't used to be common but are common now because of that mismatch.

SB: You mentioned how you see the human body as an anthropologist. You talk throughout the book about the Hadza and other contemporary hunter-gatherer populations. What can we learn about local adaptations from these populations?

HP: We are an incredibly diverse species. Our ability to adapt to our different environments and the cultural adaptations we see, the biological — that's our superpower. That's why there's 9 billion of us and not 9 billion of some other primate. We are as successful as we are because of this adaptability, this flexibility. And what that means is that if we only look to our own population, if I only did this book pulling what we could understand from my fellow Americans, it would be an impoverished book. There would be less to say, and we'd learn less about our bodies and ourselves because we wouldn't have the full extent of human diversity to pull from and learn from.

SB: Your book covers a lot of ground. What do you hope readers take away from it?

HP: More than anything, I hope it gives them the tool set to engage because they're going to put that book down, and the next day they're going to read the paper or be online, and they're going to see some new study about the brain or about diet or they're going to hear some headline about vaccines. And I want people to have a tool set to digest that, make sense of it, and ask the right questions about how we interpret all of this and move forward.

SB: What are those key questions that you hope readers will start to ask?

HP: First of all, to understand that diversity is multilayered. And so, just because I know the color of your skin, it doesn't mean I know anything else about you. I can understand something about that and why people's skin might be darker or lighter and understand that that's a separate question completely from hearts and heart health, or intelligence or anything, really. All these systems develop independently. So, when we think about diversity, we need to move away from the categories that we're taught and [away from] putting everybody in a bucket, and understand this is multilayered. It's true for yourself; it's true for everybody else.

Science has done a lot of work in the past couple hundred years, at least, on the human body to develop some really important consensus ideas around health. We know what kinds of diets keep us healthy. We know that vaccines keep us healthy. We can understand these things and move forward, comfortable in that knowledge. So the debates, for example, around vaccination, I think, are hurtful because we actually have been debating vaccines for 300 years at least, and the evidence is really clear that they're one of the biggest public health victories ever.

So both the kind of concrete details like that, but also the kind of mental tool kit to how we understand diversity. I think those are two different things to walk away with.

Editor's note: This interview has been condensed and edited for clarity.

Humans are the only species with a chin — a feature absent from even our closest relatives. Indeed, it's such a unique anatomical quirk that it's one of the main traits anthropologists use to identify Homo sapiens remains in the fossil record.

Yet, for such a defining feature, we know surprisingly little about its evolutionary purpose. So why are we the only species with a chin?

This question is hard to answer because experts haven't agreed on a single definition of a chin. While some researchers have argued that animals like elephants and manatees have chin-like protrusions, they’re not the same T-shaped structures that protrude beyond our own bottom teeth. As a result, some scientists have moved away from thinking of the chin as a single trait, instead referring to it as the collective result of interactions between many different parts of our head and jaw.

"So much about the chin is complicated," said Scott A. Williams, an evolutionary morphologist at New York University. "It cannot be quantified by a single metric but is rather composed of a constellation of morphological features."

A better understanding of the chin's function, in turn, could help scientists craft a definition. Experts have proposed several possible purposes for the chin.

Some have suggested that as we evolved smaller teeth, the chin appeared to reinforce our lower jaw and keep our teeth from breaking as we chewed. Others believe the chin may be linked to yet another unique human trait — our capacity for speech — with the chin providing an anchor point for our tongue muscles. And still others say the variation in how pronounced our chins are offers a hint that it could be linked to sexual selection.

Noreen von Cramon-Taubadel, an evolutionary morphologist at the University at Buffalo in New York, set out to winnow that list by determining whether the chin could have evolved by random chance or if evolution has been acting upon it directly.

To do so, von Cramon-Taubadel and her team studied dozens of traits linked to head and mandible size, including nine traits associated with the chin. Then, using an evolutionary tree of 15 hominoids — a group that includes humans, their fossil ancestors, gorillas, chimpanzees, orangutans and gibbons — they looked at whether those traits have changed more or less over time compared to random chance. Either result would suggest a role for natural selection in the evolution of the lower jaw.

Compared with other species, "the human cranium is more different from our ancestors' than we would expect given how much time has passed," she said. However, only three of the nine chin-specific traits appeared to be under direct selection.

Together, the team's results, published in the journal PLOS One, suggest the chin may be what's known as a spandrel — a term borrowed from architecture to describe a feature that is a side effect of something else. Coined by evolutionary biologists Stephen Jay Gould and Richard Lewontin in 1979, the concept of a spandrel was introduced to argue against the view that every feature must serve a specific, evolved purpose.

"Instead, it appears that structurally, we have to have a chin, but not because the chin evolved to have a particular function," von Cramon-Taubadel told Live Science. "More and more studies are showing that things that we used to think were terribly important in terms of differences between humans and other apes actually could evolve just by random drift and gene flow."

Von Cramon-Taubadel said the group's findings appear to be more strongly influenced by known major landmarks in human evolution, including when we started walking upright and growing larger brains.

Despite these takeaways, von Cramon-Taubadel and Williams agree that the question is far from settled. It's unknown, for example, when traits like speech first appeared, so it's difficult to link them to chin evolution. While Williams accepts that the chin may not have evolved for a specific purpose, that doesn't make it arbitrary.

"It is still one of the defining features of our lineage that is present in some form in every human living on the planet today," he said.

Human skeleton quiz: What do you know about the bones in your body?

Long before dinosaurs roamed the land, Earth looked very different from the planet we know today. Around 500 million years ago, most of Earth's surface was bare rock and dry soil. There were no trees, no grass and no flowers. Life existed almost entirely in the oceans.

Then something amazing happened: Plants began to grow on land.

This moment was one of the most important events in Earth's history because it changed the planet forever. As a geoscientist, I am interested in changes in the diversity of flora and fauna — that's plants and animals — over time.

Predecessors of plants lived in water

The story of plants begins in the water. The earliest plantlike organisms were simple, tiny green life-forms such as algae. You can still see algae today as seaweed along beaches or as green slime on rocks in ponds.

Algae have lived in Earth's oceans and lakes for over 1 billion years. They can make their own food, using sunlight, water and carbon dioxide to create sugars. This process is called photosynthesis; it releases oxygen — the gas we need to breathe — as a byproduct.

At first, Earth's atmosphere had very little oxygen. Over millions of years, photosynthesizing organisms like algae and some bacteria slowly released oxygen into the air. This change, sometimes called the Great Oxygenation Event, made it possible for larger and more complex life to evolve. Without oxygen-producing organisms, animals, including humans, could never have existed.

Scientists believe the first true plants evolved from green algae around 470 million years ago. These early plants lived in shallow water near shorelines, where conditions changed often. Sometimes they were underwater, and sometimes they were exposed to air. This habitat helped them slowly adapt to life on land.

Getting a foothold on dry land

Moving onto land was not easy. Water plants are supported by water and can absorb nutrients easily, but land plants faced new challenges. How would they avoid drying out? How could they stand upright without floating? How would they get water and nutrients from dry ground?

To survive, early plants evolved important new features. One key adaptation was a waxy coating, called a cuticle, which helped keep water inside the plant. Plants also developed stronger cell walls that allowed them to stand upright against gravity. Simple rootlike structures, called rhizoids, helped anchor plants to the ground and absorb water and minerals from the soil.

The earliest land plants were very small and simple. They looked similar to modern mosses, liverworts and hornworts, which still grow today in damp places like forest floors and stream edges. These plants did not have true roots or stems, and they stayed close to the ground. Fossils of early land plants, such as Cooksonia, date back to about 430 million years ago and show small branching stems only an inch or two tall.

Even though these plants were tiny, they had a huge impact on Earth. As plants spread across land, their roots helped break down rocks into soil, a process called weathering. This created richer soil that could support more life.

Plants also released more oxygen into the atmosphere, improving air quality and helping animals breathe. Plants created new habitats and food sources, allowing insects and other animals to move from water onto land.

Increasing complexity across millions of years

Once plants became established on land, evolution continued. Around 420 million years ago, plants evolved vascular tissue: tiny tubes that transport water and nutrients throughout the plant. This adaptation allowed plants to grow taller and stronger because water could be moved upward from the roots to the leaves. These vascular plants included early relatives of ferns and club mosses.

With vascular tissue, plant life really started to flourish. By about 360 million years ago, vast forests covered much of Earth. Giant ferns and treelike plants, some over 100 feet (30 meters) tall, dominated the landscape. Over time, dead plant material from these forests was buried and compressed, eventually forming coal, which people still use as an energy source today.

Another major step in plant evolution was the development of seeds, around 380 million years ago, found in seed ferns. Other seed plants, such as early conifers — a group that includes modern pine trees — could reproduce without needing water for fertilization. Seeds protected plant embryos and allowed plants to survive harsh conditions like drought or cold.

The most recent major plant evolution happened around 140 million years ago, when flowering plants, what scientists call angiosperms, appeared. Flowers helped plants attract animals like insects and birds, which spread pollen and seeds. Fruits developed to protect seeds and help them travel. Today, flowering plants make up most of the plants we see, including trees, grasses, fruits and vegetables.

The first plants didn't just survive; they transformed Earth. They changed the atmosphere, built soil, and created ecosystems that allowed animals to thrive on land. Thanks to plant evolution, Earth became a green, living planet full of diverse life.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

Fruits and vegetables quiz: Do you know where pumpkins, blueberries and broccoli come from?

Nature is full of relationships: predator and prey, parasite and host, competitor versus competitor. But there is another, often-forgotten relationship that involves species working together for each other's mutual benefit.

These relationships, called mutualisms, can be found across the natural world. For example, leaf-cutter ants collaborate with colonies of fungi they actively cultivate. Because leaf-cutter ants can't digest plants themselves, they grow fungi in their nests and feed them leaf clippings. The fungi benefit from being actively fed, and the ants eat some fungi to access the plant nutrients. Neither species would survive without the other.

In his new book, "The Call of the Honeyguide: What Science Tells Us About How to Live Well With the Rest of Life" (Hachette Book Group, 2025), Rob Dunn, a professor of applied ecology at North Carolina State University, explores these complex interdependencies found across the natural world, including the numerous mutualisms humans engage in, such as our relationships with dogs and with the microbes in our guts.

"The Call of the Honeyguide" has been nominated for the PEN/E.O. Wilson Literary Science Writing Award, an annual award for excellence in nonfiction in the physical or biological sciences. The award comes with a $10,000 cash prize, and the results will be announced March 31 at the Literary Awards Ceremony.

Live Science spoke with Dunn about his book and how mutualism is at the very root of what it means to be human.

Sophie Berdugo: Could you explain what mutualisms are and how you got interested in them?

Rob Dunn: Mutualisms — as ecologists and evolutionary biologists think about them — are relationships between two species when both benefit. So it's cooperation among species. Ecologists and evolutionary biologists would measure that cooperation in terms of what we call fitness: Are the individuals more likely to survive and have offspring if they're partnering with each other?

But if we think about modern human mutualisms, it becomes a little trickier to think about how we should measure them. And this is a question I think about throughout the book. What does it mean to have a mutually beneficial relationship with a dog or a cat or a cow or a pig or wheat? But fundamentally, at its base, it's two species that together benefit more than they would going it on their own.

I got interested in them very early in my career. I spent a lot of time in the tropics, where lots of mutualisms are very conspicuous, and just became fascinated with all the different ways that species in the wild are partnering in a landscape in which we often think more about predation and parasitism and competition. This sort of kinder, gentler part of nature — that is nonetheless complicated — has long fascinated me.

SB: What made you decide to write this book now?

RD: In the last few years, I've been working more and more on human mutualisms and all kinds of strange mutualisms: humans and the microbes that live in our belly buttons, humans and the microbes in sourdough bread, humans and cats.

The more and more virtual we've become, the less and less aware we are of these interdependencies that we have all over the place. They don't go away, but we don't tend to them. We seem to be in terms of history today at maximum virtualness, maximum focus on our screens and on indoors, and there's just not much precedent for paying so little attention to these other species that we're engaged with. It felt like a time to tell this story.

I have also spent more and more time with archaeologists and anthropologists who have really made it clear to me how much more diverse these relationships have been through time and across cultures than we appreciate.

SB: I mean, even now we're having a virtual interaction! I'm really intrigued by what you were saying there about your work with archaeologists and anthropologists. Could you share some of the insights you've learned through those collaborations, and how these mutualisms really teach us about who we are as a species?

RD: One kind of vignette would be thinking about our closest living relatives, chimps and bonobos, and the mutualisms they engage in. One of the things that's very clear with chimps is they depend on every one of their actions on the plants that they eat. They depend on the figs for food, and the figs depend on them to disperse their seeds and carry them from one place to another.

That's a very ancestral relationship for us. We all once lived in trees; we all once benefited from those trees; we all once benefited from those fruits. And so that's one kind of thing we see in looking to a more ancient past. We still benefit from trees, but the nature of the relationship has changed. I think, often, when we look at other cultural or ancient contexts, there are lessons there, but the lessons are modulated by the way we live now.

Every time you take one of these examples and pick it apart, it gets more complex. The figs depend on the chimps, but the figs also depend on very specific wasps that pollinate them. Each fig species has a different fig-specific wasp. So embedded in the chimp-fig mutualism is this other mutualism, which is so often the case.

To take a very different kind of example, a number of researchers have started to focus on what you might call co-predation, where humans and other species team up to predate a third species. It's now clear that, in several different human cultures and populations, people have formed partnerships with dolphins — the dolphins help herd fish into a bay, and then humans net the fish. And by netting them, the dolphins get a few more.

This is a relationship people in parts of Brazil still have and it probably emerged culturally many times.

The dolphins seem to be in charge. It's the dolphins that tell the humans when to gather. It's one cultural group of dolphins partnering with one cultural group of humans. It's really an elaborate relationship that depends on particular people, particular dolphins. It's embedded in culture.

Then there's the trickiness of nature; this relationship really sucks if you're the fish.

None of this is ever simple. One way to think about it is if you're in a mutualism, you're better than if you're not. They always involve trade-offs, but nonetheless, [they] are this element in nature that has a different way of working than what we tend to think about.

SB: I'm really intrigued about who may be initiating these mutualisms. Could you explain how mutualisms are formed?

RD: If you think about that human-dolphin mutualism, you have two intelligent sets of beings that are negotiating a relationship in which each is constantly making choices about whether or not to participate.

In this case, it looks like the initiation comes from the dolphins, and then the humans respond.

Other kinds of mutualisms start in simpler ways. Humans partner with yeast and lactic acid bacteria and fruit. In that context, what does that look like to start with? Well, some of our ancestors were choosing fruit that was alcoholic, or lactic, over fruit that wasn't. They weren't consciously choosing to engage in a mutualism. They were implicitly choosing one set of species — the ones in those fruits — versus the set of species in a different fruit. They didn't need to be conscious of it; they just needed to be making a choice.

Over evolutionary time, if you're not talking about fully conscious choices, mutualism is favored by each partner trying to figure out how to more consistently get the other partner to participate. As the yeast produced more alcohol; our ancestors evolved new ways of processing the alcohol. You get these reciprocal evolutionary changes that favor the persistence of the relationship.

When our ancestors lived in tropical forests and we were trying to get as many calories as possible, those yeast were producing alcohol from the sugars and fruit, which was really rich in calories, which benefited their ancestors.

But it looks very different in [for example] modern Ohio. What's the relationship between the yeasts that produce alcohol and humans? The yeast are still benefiting. It's often the case that humans are not. It's the same relationship, but in a new context. You might argue that sometimes the yeasts are now parasites of humans.

And then what do you measure? Do we want life expectancy? So should we measure a good partnership as one where we live the longest? Do we want well-being? Do we want a richly lived, fun life? Depending on how you answer those questions, which of these relationships are mutually beneficial in a way that we might think of as some kind of mutualism?

One of the fun things about writing this book is not having to answer a question like that but being able to play with it, thinking about, how do we make sure we're having the conversations to ask these questions?

SB: Could you explain the mutualism some populations have with honeyguides and why you decided to pick that relationship as the titular mutualism for your book?

RD: Honeyguides are these sort of lovely — but not visually exciting — brownish birds that live across sub-Saharan Africa. They have a fundamental existential problem: They primarily eat wax, but they can't get into beehives on their own. So they evolved a behavior wherein they go into human settlements, and they do a specific flight and a specific call that says, "I found a honey beehive. If you just follow me and crack it open, you can have all the honey you want. I don't even like honey; just leave me the wax."

Many different cultures respond to the honeyguide. I think it's very unclear whether they independently responded to the honeyguide or it's just such an ancient relationship that it's part of the ancestral human story for much of Africa.

But for me, in thinking about that story, it's also kind of a parable. It's nature calling to humans, and humans deciding whether or not to reply. And I think nature still calls to us in all these ways, but we're now really bad at paying enough attention to reply.

If a bird flew to you in your backyard and offered to change your life in a beneficial way, would you even be paying enough attention to notice?

SB: In terms of your own relationship with the mutualisms that you're aware of in your own life, are there any that you are particularly intrigued by, and are there any that you really try to nurture?

RD: I spend a lot of time thinking about the relationship between humans and the microbes we use to ferment foods. The traditional cultural understanding of those relationships is so rich and so understudied that I just find it fascinating and often so rewarding. Embedded amidst the loud culture of the virtual global world are these hidden stories of deep local knowledge, of how to work with these microbes to produce delicious food that also benefits them.

In my daily life, there's a beaver that benefits me because it dams a little creek not far from my office, and fills it with more biodiversity and more birds, and those bring me joy. I'm not cultivating the beaver, but I'm cultivating my attention towards it.

SB: A key message in your book is the need to nurture these mutualisms. You call it "a call to action for a more mutualistic, less-lonely future." Could you unpack exactly what you're hoping readers will take away from the book?

RD: I think the simplest call to action is to please pay attention to the rest of the living world. It is all around you. It is on your body. It is in your gut. It is covering your loved ones. It is your dog, your cat, the plants in your backyard. It is the microbes that are helping to form clouds and falling on you every time it rains.

I think the first and most important thing is to pay attention, to realize it's there, to begin to be able to name it, to know the trees around you, to know the ants are around you. To be aware that when you smell your beer, you're smelling the consequence of a living organism dividing in that beer and breathing into your mouth.

I think, in a time when so many feel lonely, remembering part of the remedy to that loneliness is connecting to other humans. But another part, I think — and I'll say this as often as somebody's listening — is connecting to other species.

We spent the vast majority of our evolutionary history in trees, in forests, in grasslands, surrounded by the rest of life. And we're in this super-weird moment right now where that is — for so many of us — far away. And it is hard to overstate how evolutionarily unprecedented that is.

What does it look like to think about what mutualisms we want in the next hundred years? Can we be a generation that's so creative that we begin to embark on new mutualisms?

Editor's note: This interview has been edited and condensed for clarity.

Lizards, birds and fish often sport vivid colors, from neon pink to deep violet, but most mammals are fairly drab. So why don't mammals match the vibrant hues of other animals?

A number of factors culminate in the browns, blacks and whites that make up most mammalian coats. The first has to do with color expression. Matthew Shawkey, an evolutionary biologist at Ghent University in Belgium, explained that animals generally express color in two main ways: through pigments and through structures. Pigments exist within the skin and coat of the animal itself and reflect and absorb light to create certain colors. Structural coloration, on the other hand, involves nanoscale shapes and patterns on top of skin, feathers or scales that can distort light to produce bright, iridescent colors.

Animals can use one method, or sometimes both, to express color. According to Shawkey, however, mammals don't really use either. Of the many color-producing pigments — such as carotenoids, porphyrins and pterins — mammals have just one type: melanin. The presence of that one pigment generates all of the colors seen in mammals, Shawkey said, and its absence creates the white regions seen in animals like zebras and pandas.

Moreover, the composition of the hairs that make up mammal fur limits the structural colors mammals can display. Hair is not a complex structure like feathers, scales and skin are, so it's not surprising that it cannot produce the nanoscale patterns necessary for structural color, Shawkey noted.

For example, mandrills (Mandrillus sphinx), which break the drab-mammal rule with their bright red and blue, have those colors only on spots without fur. Sloths, which sometimes have green patches, get this coloration from algae that grows on their fur, not from pigments or structures on the hairs themselves.

Evolution of color

So why don't most mammals have the tools to create vibrant hues? One hypothesis is that when mammals first evolved, dinosaurs were the apex predators and mammals were prey. To avoid being eaten, mammals spent more than 100 million years as primarily nocturnal animals (and most remain so today).

Those millions of years had a big impact on mammals' appearance. In a 2025 study co-authored by Shawkey and published in the journal Science, a research team compared pigment-storing structures called melanosomes in modern mammals to preserved melanosomes found in six Jurassic and Cretaceous-age mammal fossils. They found that all of the mammal fossils were some shade of brown or gray.

Because these prehistoric animals were living primarily in the dark, darker colors would have helped mammals avoid predators. "Any bright color would have been selected against," Shawkey told Live Science.

In the 66 million years since the nonavian dinosaurs went extinct, mammal diversity has exploded to over 6,000 species. Now, there are mammal species, both nocturnal and diurnal, that have no natural predators. However, mammals have remained mostly brown, gray and black.

This could be due to most mammals' continued lack of color vision, said Ted Stankowich, a behavioral evolutionary ecologist at California State University, Long Beach. Researchers speculate that mammals sacrificed some color vision in order to gain better night vision during the age of the dinosaurs. Most mammals still have dichromatic vision, meaning they only have two of the three types of cones that help the eye perceive color. Dichromats can't see colors such as red, orange, turquoise and purple, and generally can't see colors with as much saturation as trichromats, which have all three types of cones.

The purposes animals primarily use color for — attracting mates and other communications within their species, blending in with camouflage, and signaling to predators that they are poisonous or otherwise dangerous — don't work when their partner or predator can't see the colors they're using. Some mammals have actually used this lack of color vision to their advantage. For example, although tigers look orange to our trichromatic eyes, they look green to their mammalian prey, making them perfectly camouflaged amongst the grass when on the hunt.

Instead of using vibrant colors, Stankowich said, many mammals use patterns and contrasting colors, such as black and white or brown and yellow, to signal to each other. Skunks and polecats, for example, use black and white spots and stripes to let predators know they have a stinky trick up their sleeve. The African wild dog, known for its unique patterning, has a distinctly white tail that researchers think is used for signaling while on the hunt. The Indian giant squirrel, known for its high-contrast black, reddish brown and orange-yellow patterning, may use this as camouflage against various kinds of predators.

Because mammals have adopted new ways of color signaling, there might not be much of a reason for them to regain color vision. (The few mammals with trichromatic vision — primates, including humans and some monkeys — evolved color vision for very specific reasons.) Stankowich noted that the few mammals that display bright blues and reds, such as baboons, golden snub-nosed monkeys and mandrills, are also among the mammals with the best color vision.

Fluorescence and iridescence

Recent studies have highlighted some other exceptions. For example, many mammals fluoresce under ultraviolet light, which the human eye cannot detect but some other mammals can. Moreover, Jessica Dobson, an evolutionary biologist at Ghent University, and colleagues have discovered iridescence in a handful of mammal species not previously known to have this shimmery feature.

"It was a light-bulb moment," Dobson said of this iridescence discovery, which happened when she opened a museum drawer and sunlight hit the preserved pelts of several tropical rat species at just the right angle. Dobson isn't sure whether these iridescent colors serve any evolutionary purpose, but she said it is nonetheless exciting to know that there are still mammalian color mysteries to unlock.

"When you start looking, mammals are more colorful than we give them credit for," Dobson said.

Animal quiz: Test yourself on these fun animal trivia questions

The mysterious disappearance of our Neanderthal cousins may have been related to preeclampsia, a life-threatening complication of pregnancy and/or the postpartum period, doctors propose in a new study. But experts in paleoanthropology are not convinced.

In a paper published Jan. 30 in the Journal of Reproductive Immunology, an international team of neonatologists and OB-GYNs argued that preeclampsia and eclampsia — a related disorder that involves one or more seizures during pregnancy or the postpartum period — have "never been seriously considered in hypotheses concerning Neanderthal reproductive biology and their eventual extinction."

These conditions are not fully understood by medical experts, but they appear to be related to an evolutionary quirk of the human placenta — which, given the number of genes we share with our extinct relatives, also may have affected the Neanderthal placenta. (However, the researchers did not investigate any such genes in the new study.)

Preeclampsia in human species

Preeclampsia involves dangerously elevated blood pressure and can put strain on the pregnant person's heart and other organs, including the kidneys and liver. The condition affects up to 8% of pregnancies today, and it can also occur during the postpartum period. It can also progress to eclampsia, which involves seizures and, sometimes, brain damage. If not treated, both conditions can be life-threatening for the pregnant person and the fetus.

Research into preeclampsia has shown that abnormal, shallow implantation of the placenta in the uterus may be one possible cause of the condition. The exceptional metabolic demands of babies of large-brained human species were likely responsible for the deep implantation of the placenta to ensure sufficient maternal-fetal nutrient transfer, the researchers wrote.

An inadequately placed placenta's efforts to acquire adequate nutrients for the fetus can lead to a rise in maternal blood pressure, particularly in the third trimester, when the fetus's brain is rapidly developing, according to this hypothesis. This can lead to preeclampsia, eclampsia and fetal growth restriction, all of which complicate pregnancy and threaten the survival of mothers and babies.

Given this insight into preeclampsia, the study authors wrote that the condition "may have constituted an additional, underappreciated selective pressure on Neanderthals, contributing to their extinction." They hypothesized that Neanderthals "may have lacked a key protective mechanism" against preeclampsia that some of the study authors previously suggested modern humans have. This idea, however, is still speculative and such a mechanism has yet to be found.

If Neanderthals lacked a "maternal safety mechanism" to avoid preeclampsia, this may have led to reproductive loss and maternal mortality, thus hastening their extinction as a group, the team proposed.

Anthropologists respond

But experts in Neanderthal archaeology and genetics are not convinced, particularly since the new study does not provide any evidence that Neanderthals dealt with preeclampsia.

"The 'preeclampsia doomed Neanderthals' framing goes well beyond the available evidence," Patrick Eppenberger, co-head of the Evolutionary Pathophysiology and Mummy Studies Group at the Institute of Evolutionary Medicine in Zurich who was not involved in the study, told Live Science in an email.

While Eppenberger agreed that preeclampsia is uniquely human and linked to the evolution of the human placenta, he said that "what is much harder to support is the claim that it was more frequent or more lethal in Neanderthals than in early Homo sapiens or that it played a primary role in their disappearance, especially given Neanderthals' long persistence" over more than 300,000 years.

In his own research, Eppenberger discovered that a red blood cell gene variant between Neanderthals and modern humans may have caused some hybrid babies to fail to survive, which could have hastened their extinction.

"Why Neanderthals went extinct is a question that has captured the imagination of the public and researchers," April Nowell, a Paleolithic archaeologist at the University of Victoria in Canada who was not involved in the study, told Live Science in an email, and "everyone is looking for a smoking gun."

But the reasons for Neanderthals' disappearance are complicated. "I have long argued that differential survivorship of the littlest Neanderthals is key to understanding the Neanderthal story, but I am not particularly persuaded by this study," Nowell said.

If the researchers are correct that H. sapiens evolved a mechanism to mitigate preeclampsia, Nowell said, the condition could have contributed to Neanderthals' extinction. But given the widespread evidence of gene sharing among groups of humans, "to my mind, it is equally possible that Neanderthals, Denisovans and Homo sapiens shared this mitigating mechanism," Nowell said.

"I think the paper is an interesting evolutionary-medicine thought experiment," Eppenberger said. Although there is no direct evidence currently that Neanderthals had higher rates of preeclampsia or eclampsia than modern humans do, Eppenberger said, there may be ways to test the researchers' theory, including investigating genes involved in maternal-fetal immune interactions and in the regulation of placental and fetal growth. But we might not get a clear answer.

"Genetics can provide clues about plausibility and population differences, but it likely won't 'confirm' preeclampsia in Neanderthals the way clinical data would," Eppenberger said.

The study authors did not respond to a request for comment by the time of publication.

Neanderthal quiz: How much do you know about our closest relatives?

Cannibalism might seem like a rare and unnatural occurrence, but the behavior has arisen in several snake lineages throughout evolutionary history, often triggered by environmental stressors, scientists theorize.

When researchers reviewed 500 reports of cannibalistic behavior across snake species, they found that cannibalism has evolved independently at least 11 times, according to a study published Nov. 2, 2025, in the journal Biological Reviews.

These cannibalistic behaviors occur in diverse contexts, but overall, cannibalism is common and seems to emerge repeatedly because it's beneficial to snakes in situations where they need to make opportunistic dietary choices, the researchers suggest.

"For us humans, we don't think of cannibalism as something common –– it's something weird and disgusting," Bruna Falcão, lead author of the study and a graduate student in biology at the University of São Paulo, told Live Science. "But for snakes, it's good for them; it's good for their ecological fitness. … It's strategic."

Evolutionary advantages of cannibalism

Some of the best-known examples of cannibalism in nature are seen in spiders and praying mantises during mating, as it may be beneficial for females to eat their mates. "Cannibalism is widespread throughout the animal kingdom," Xavier Glaudas, a biologist and National Geographic Explorer who was not involved with the study, told Live Science.

Although scientists previously considered the behavior maladaptive –– meaning it's not beneficial for a species overall –– more and more studies reporting cannibalism in animals hypothesize reasons for the evolution of the behavior. For example, it could help parents control brood size, or it might arise as a response to limited resource availability, a form of population control, or an opportunistic predation choice.

Cannibalistic behavior in snakes has typically been recounted in brief and isolated reports, Glaudas said. For example, his research team described male Montpellier snakes (Malpolon monspessulanus) feeding on female snakes in France — a behavior thought to be driven by limited food resources, especially during times of scarcity outside the mating season. (It would be considered unusual for males to eat females during the mating season, as this would reduce mating opportunities.)

In addition to being widespread in snakes, cannibalism has evolved independently across different snake lineages and regions, according to the study, which combined numerous reports to explain the behavior.

The research team gathered 503 cases of reported cannibalism across 207 snake species. The reports spanned a wide range of snake groups, as well as all continents where snakes live, including reports of snakes both in the wild and in captivity.

"None of us expected that … snakes could be so cannibalistic, and no one was talking about it," Falcão said. "The more we were searching, the more cases we found."

Cannibalism was most common in the Colubridae, Viperidae and Elapidae families, the team found. Colubridae is the biggest family of snakes and made up 29% of all reports. Because this family is not typically known to prey on snakes, however, the authors proposed that most cases of cannibalism in this group may be connected to stressors such as a lack of other food sources. Members of the Viperidae family, which includes vipers, made up 21% of all cannibalism reports. But these were mostly cases in captivity, the researchers noted, so captivity-related stressors, like confinement to small spaces with limited food, may have resulted in cannibalism.

Elapidae, the snake family that includes cobras, accounted for about 19% of the cannibalism reports. This wasn't very surprising, the researchers said, because cobras are known to prey on other snakes in the wild.

Almost half of the cannibal snake species have generalist diets, according to the study, and the researchers linked this dietary flexibility to cannibalistic behavior when necessary. However, Glaudas suggested this connection may not be clear, since the researchers defined only 47.7% of the cannibal snake species as generalist; evidence for the relationship would be stronger if the percentage were higher, he said.

"In regard to the idea that cannibalism could be more common in generalist species, I am a bit more skeptical about the data presented," Glaudas said.

Cannibalistic behavior does seem to be correlated with jaw structure, so whether a snake has jaws that can open wide enough to consume another snake is a key factor; there were no reports of cannibalism in snake species without this ability.

When the researchers analyzed cannibalistic behavior across snakes' evolutionary history, they concluded that the behavior evolved independently at least 11 times throughout the snake evolutionary tree.

Because most reports of cannibalism in snakes are anecdotal, Glaudas said, the study provides a useful overview. This is a "welcome study that allows us to get a better understanding of the correlates of cannibalism in snakes," Glaudas said.

Snakes form a highly successful branch of the evolutionary tree. They are found on all continents except Antarctica and have adapted to most ecological niches, the study authors noted. Because cannibalistic behavior appears in many different types of snakes throughout the world, Falcão said, it might reflect their ability to adapt opportunistically to their circumstances. "It's really surprising for [cannibalism] to evolve independently 11 times in snake lineages," she noted.

The review could not encapsulate all reports of cannibalism in snakes — many are in less-accessible, older books and archives — so there's likely much more to discover on the topic, Falcão said.

"Ghost lineages" may sound paranormal, but the term is rooted in real science that genetic studies have revealed only relatively recently.

So what is a ghost lineage?

A ghost lineage is an extinct population that has left no fossils but whose traces can still be detected in the genomes of many living things, including humans and other primates. University of Wisconsin-Madison palaeoanthropologist John Hawks defines them as "ancient groups that became extinct, but not before contributing some of their own genes to other populations that survived."

In animals generally, not just in humans, finding ghost lineages has "mostly been by accident," Love Dalén, an evolutionary geneticist at Stockholm University who studies extinct animals, told Live Science. "Our goals have been to study the evolution of mammoths, bovids and lemmings, and finding these ghost lineages was quite unexpected."

In their analyses of ancient DNA recovered from the frozen fossils of key ice age animals that are now extinct — including mammoths, Pleistocene yaks and certain types of lemmings — Dalén and colleagues have detected several ancient populations that were revealed only by genetics.

These ghost lineages indicate that genetic diversity — the range of inherited traits within a population — was greater during the last ice age than it is now. "This is definitely a pattern we see in Arctic species that are alive today," Dalén said. "Nearly all of them had much higher genetic diversity in the past, and to me this illustrates how important past climate change has been in shaping present-day biodiversity."

But ghost lineages are too important to leave to chance findings. "It becomes more and more clear that we need to use an ancient DNA approach to fully quantify past changes in biodiversity," Dalén said.

Human "ghosts"

Genetic ghosts in human evolution are especially interesting to scientists because they reveal a much more complex story of human evolution than many experts supposed.

The ghost lineages detected in the genomes of modern humans and our extinct relatives have revolutionized the study of millions of years of human evolution.

Most scientists once thought human evolution had progressed at a steady pace through known stages, culminating in the emergence of Homo sapiens in Africa about 300,000 years ago and its eventual replacement of all other forms of humans, with some limited interbreeding.

But genetic analyses over the past two decades have revealed traces of several human ghost lineages in the ancestry of people today and in the ancient DNA recovered from fossils. These human ghost lineages are echoes of archaic groups that existed for hundreds of thousands or even millions of years but that left no known fossils.

"Our discipline has gone from a simplified, straightforward linear model of evolution to a 'bushier' model in describing the last 7 million years," Michael Petraglia, a paleoanthropologist at Griffith University in Australia, told Live Science in an email.

The human evolutionary "tree" grew ever larger and less well defined — turning into a "braided stream" of ancient groups — as more ghost lineages were identified, he said, and it is still growing.

When newfound fossils match "ghost genetics," lineages become "de-ghosted," and de-ghosting human ghost lineages is an important area of research. "With the application of DNA, it has become clear that gaps in our evolution existed, suggesting the presence of ghost populations for which the fossil record was not clearly present," Petraglia said.

"Superarchaic" ancestors

Scientists have seen traces of human ghost lineages in the genomes of some modern-day human populations in parts of West Africa, Asia and Oceania, and Petraglia said paleoanthropological research has focused on a group of "superarchaic" hominins known only from their genes.

This ancient human ghost lineage separated from our own family tree of modern humans, Neanderthals and Denisovans between about 2 million and 1.8 million years ago — roughly when Homo erectus was the dominant species in Africa.

There are no fossils from the superarchaic ghost lineage, so scientists have only inferred its existence from the presence of ghost genes in their analyses of Neanderthal, Denisovan and H. sapiens genomes.

But the picture is complicated because of the confusion created by interbreeding. "Genetic work suggests that the ancestors of Denisovans, Neanderthals and Homo sapiens met and interbred a number of times," Petraglia said. "This has set off debate as to finding the last common ancestor and understanding the line of descendants."

There is genetic evidence that the Denisovans interbred with the superarchaic lineage in at least two distinct interbreeding events, resulting in a relatively high number of "ghost" genes from the superarchaic human lineage in the genomes of Denisovans and those of modern humans with Denisovan ancestry.

"These are exciting times in human evolutionary studies, and there is growing support that hominin evolution was much more complex than imagined before, including multiple interbreeding events that make us what we are today," Petraglia said.

Human evolution quiz: What do you know about Homo sapiens?

Beneath Earth's surface lies a kingdom of undiscovered microscopic life. These "intraterrestrials" survive in some of the harshest conditions on the planet — and scientists are hunting for these microbes.

In this excerpt from "Intraterrestrials: Discovering the Strangest Life on Earth" (Princeton University Press, 2025), author Karen G. Lloyd, a microbial biogeochemist at the University of Southern California Dornsife, examines the idea of evolution among life that can survive for hundreds of thousands — if not millions — of years in a dormant state and what it might be waiting for to "wake up."

"Intraterrestrials" is short-listed for the Pen/E.O. Wilson Literary Science Writing Award.

How does one evolve to stop growing for thousands of years? Recent work suggests that microbes buried deep in oceanic seafloor sediments may be doing just that. Such organisms can be referred to as intraterrestrials, small microorganisms living inside Earth's crust all around the globe. To answer this tough evolutionary question, first we have to think about what these organisms would experience in their lifetimes. These slow organisms wouldn't be concerned about the length of a day. They're buried so deep that they can't detect the sun anyway. They probably wouldn't even notice a change in season.

However, they might care about other, longer geological rhythms: the opening and closing of oceanic basins through plate tectonics, the formation and subsidence of new island chains, or new fluid flows brought on by slow formation of cracks in Earth's crust. The biology I was taught in school considered these events to be evolutionary drivers for a species, not an individual.

For instance, Darwin's finches evolved new beak shapes because they had been isolated on an island with a particular shape of seed to eat. This evolution happened over the geological timescale of island formation, but it occurred in a species lineage, not in an individual bird. We know, however, that individuals are also capable of changing along with the rhythms of their environment. An individual Arctic fox's (Vulpes lagopus) fur changes from white to brown when the snow melts every spring. Many people (though sadly, not me) wake up at the same time each morning without the aid of an alarm. Daily and yearly rhythms seem like reasonable things for a person or an animal to keep track of.

Ice ages, less so. Anticipating changes over longer timescales seems ridiculous. It would be silly to suggest that an individual finch would have evolved the ability to swim because it had an innate anticipation that its island would subside into the sea in 100,000 years. Or that a beetle in the Gobi Desert could only reproduce when it ate an Amazon rainforest seed because it was born millions of years ago when South America and Africa were nestled into each other, and its DNA instructed it to reproduce when the tectonic gap closed again.

These scenarios make no sense for animals, but they may be reasonable for the intraterrestrials. An individual that lives for a million years might be evolutionarily predisposed to count on something as slow as island subsidence in the same way that we are evolutionarily predisposed to wait for the sun to rise tomorrow. To fully understand intraterrestrials, we may have to rethink what qualifies as an evolutionary cue.

Living for millions of years

The fact that living cells likely exist in a nongrowth state for very long timescales raises two important questions. Can a microbe be adapted to avoid cell division for thousands of years or longer, rather than having it just happen by accident? And, if so, how does evolution work for an organism that seemingly never produces offspring?

Let's tackle that first question by stating it this way, in order to help us place this finding in the context of Darwinian evolution. Are these microbes evolutionarily adapted to hang out in this undead, dormant state for thousands or millions of years, or do they just persist because cells don't need any special adaptations to stay alive for so long?

To me, living for hundreds of thousands of years seems unlikely to happen without adaptation. Too many physiological changes are required to support this lifestyle for it to be a side effect of a "normal" fast-paced life. Furthermore, if this lifestyle is accidental, then their main growth-supporting lives must occur in some other environment. But we rarely see the types of microbes we find in the subseafloor elsewhere. It's not as if they were normal seawater microbes happily swimming around, dividing and growing when they fell to the seafloor and forgot to die.

On the contrary, most of this highly diverse group of microbes seem to exist only in marine sediments. Given this, they may be just as selected for in marine sediments as parrots are in a rainforest. Indeed, we find that at increasing depths in marine sediments, microbes make enzymes with a higher specificity for the type of substrates that are available in the subsurface, suggesting that they are specially adapted for this environment.

Subsurface microbes also have adaptations that enable ultraslow metabolisms and cell divisions. This suggests that they are somehow evolutionarily poised to be in a long-term nongrowing state. But here we have a problem. According to Darwin's theory of natural selection, these cells must grow and make new progeny to evolve. Natural selection works because, during reproduction, organisms experience mutations. And when an organism has a mutation that is beneficial, the mutation increases the organism's fitness, so the organism's progeny outcompete those of the nonmutated organisms, resulting in more progeny that have the mutation. These further generations continue to do better than the nonmutated lineages, and eventually the mutation spreads throughout the population.

Voilà, adaptation has occurred through natural selection. But how can we even think about Darwinian evolution in populations that don't reproduce? How can you become adapted to not have babies? I don't think Darwin had nongrowth in mind when he described survival of the fittest.

Luckily, we have a good model in short-term seasonal dormancy. Here dormancy during winter has an evolutionary advantage because the dormant organisms have larger populations remaining once conditions are ripe for growth again in the spring. These organisms thus have a head start on other organisms and can pass their dormancy genes along to a larger population of progeny in the spring and summer.

This is textbook Darwinian natural selection. Let's extend that model to dormancy that lasts for thousands of years in marine sediment. We have to think of an event that intraterrestrials could possibly be waiting for that would pull them out of dormancy when they're buried hundreds of meters deep in Earth's crust. If we encounter a dormant microbe in soil in winter, we can presume that it's waiting to start growing again in summer. What is the equivalent situation for a deeply buried marine sediment organism that is dormant for thousands to millions of years?

Let's do a thought experiment to jailbreak our brains from our implicit assumptions about lifespan. Imagine human lives only lasted about 24 hours. You'd be born at midnight, rebel against your parents at breakfast, settle down and have babies just before lunch, and pick up fishing as a retirement hobby around dinnertime. By midnight, your loved ones, who themselves were only born a few hours ago, would huddle close and hold your hand as you'd pass away peacefully at the ripe old age of a day. If everyone did that, hundreds of human generations would come and go within a single winter. Throughout that time span, which would represent a significant chunk of human history, the deciduous trees would remain brown and lifeless.

The permanent deadness of trees would be taken as an undisputed fact, and scientists like me would probably write grants to understand whether or not trees are alive, given that they don't seem to grow or make progeny. Of course, if you stretched back far enough, humans would have been present for the fall or even summer, but that might have been so many generations back that a stable form of writing had yet to be invented.

We 100-year-lifespan humans know that trees are just waiting to take advantage of the summer sun. But the day-lifespan humans would be stumped. When we think about life in the subsurface, are we like day-lifespan humans contemplating a tree? Are long-lived intraterrestrials waiting for wake-up cues we don't recognize because our lives are too short to see them? What is even the point of living for hundreds of thousands of years anyway?

There must be some reason these intraterrestrials stick around so long. There is evidence that long-term dormancy has a selective advantage. When you let the laboratory workhorse Escherichia coli sit around with no food for months or even years, many of the cells enter a state of long-term dormancy where they are alive and metabolizing, but they're not growing nearly as quickly as they do when you feed them. If you mix these next-to-dead E. coli with a fresh batch of fast-growing E. coli and starve them both, the old geezers beat the living daylights out of the sweet little young 'uns.

This growth advantage in stationary phase (GASP) may be the secret to why intraterrestrials live so long. Maybe they're waiting for something that only happens thousands of years later so they can be the ones to take advantage of the new situation. They might act as monks, accustomed to deprivation while the gluttons die around them.

Life on geological timescales

So what are these microbe-monks waiting to wake up for? Seasonal cycles are way too fast. The only things slow enough are geological processes. For instance, island subsidence, floods, drought or storms often occur on hundred- to thousand-year cycles. Submarine landslides, earthquakes, tsunamis and volcanic eruptions might shift materials around on even longer timescales, exposing intraterrestrials to new food sources that coax them out of dormancy after hundreds of thousands of years.

It seems odd to say that a microbe is adapted to wait for something as infrequent as a volcanic eruption, but Earth's history shows that you can rely on volcanic eruptions, as long as you've got time to wait for them.

If we really let our imagination run wild, individual microbes might be adapted to events with even longer periods like glacial cycles, which shift every 30,000 years or so. Or the slow movement of tectonic plates. As new seafloor pops up in mid-ocean ridges, the existing seafloor is constantly being pushed away from the middle of the ocean, like a person standing on a moving walkway at an airport. The seafloor eventually jams into a continent in the slowest-motion train wreck ever. Some of the sediments and the intraterrestrials that live in them will get dragged on the subducting plate down to eventually be crushed at temperatures and pressures that kill all life as we know it.

Even for extremophiles, being dragged all the way down to the mantle would definitely be an evolutionary dead end. However, some of the sediments that are in the early stages of being subducted under continental plates might be returned through cracks and fissures that open in the overriding plate. During this collision, some of the seafloor sediments are shoved upward in accretionary prisms and the attendant faults created by earthquakes or other plate deformations.

Could all this piling up, faulting and burbling up to the surface be what the intraterrestrials are waiting for? Let's think through the implications. This would mean that the individual microbial cells that we pull up in our drilling ships that appear to be dormant are just waiting patiently for the ultraslow movement of the plates to squish them into a continent, where they have a chance of resurfacing and recommencing growth.

The evolutionary payoff for waiting for millions of years in deep marine sediments would be to return to the upper seafloor again where the food is more nutritious, at which point the microbe would pass its genes along to future generations. Like any standard Darwinian natural selection, the individuals that have the best adaptations to being dormant for millions of years would have a growth advantage once they arrive back to the surface, ensuring that those adaptations become stable in the communities. Is getting tossed back up into surface sediments an intraterrestrial's version of summer?

Adapted from INTRATERRESTRIALS: DISCOVERING THE STRANGEST LIFE ON EARTH. Copyright © 2025 by Karen Lloyd. Reprinted by permission of Princeton University Press.

The spotted lanternfly has spread across the United States with unrelenting speed — and now we have a clue as to why: living in cities seems to have helped these invasive insects evolve to be more resistant to stresses.

"Cities may act as evolutionary incubators that help an invasive species to better deal with pressures like heat and pesticides, which then helps them to better adapt to new environments," lead author Fallon (Fang) Meng, a biologist at New York University, told Live Science.

The spotted lanternfly (Lycorma delicatula) is a planthopper that uses its long mouthparts to suck sap from plants. The insect is native to China, but has spread through South Korea, Japan and to the U.S., where it was first detected in Pennsylvania in 2014, but is now seen in 19 states in the eastern U.S.

Its preferred host plant is the tree of heaven (Ailanthus altissima), which is also an invasive species — but it is able to sup on a wide range of plants, including economically valuable ones like grapevines, hops, maples, fruit trees and hardwood trees.

Spotted lanternflies can weaken plants, and as they feed, they also excrete a sticky, sugary fluid that promotes the growth of sooty mold. What's more, when bees decide to forage on this sugary waste rather than visiting flowers it gives the honey they produce a smoky aroma and a lingering aftertaste, although this honey is still safe to eat.

All this adds up to a potentially huge financial impact. For example, a 2019 study estimated that in Pennsylvania alone, if uncontrolled, the insect's effects could cost $324 million annually.

Lanternfly genetics

To get a better handle on how the lanternflies have adapted so well to life in the United States, researchers sequenced the genomes of lanternflies from urban and rural areas in Shanghai, China, and from New York City, Connecticut and New Jersey. The study was published Wednesday (Feb. 4) in the journal Proceedings of the Royal Society B: Biological Sciences.

In the lanternfly populations in China, they found clear genetic differences between those in the urban and rural areas. "Even though they're just 30 kilometers [19 miles] away, they have very strong population differentiation," Meng said.

This is probably because although lanternflies can fly, they need to feed continuously, so they stick close to the host trees on which they depend. This means it is easy for populations to stay separate, Meng added.

This separation means the urban lanternflies in Shanghai evolved genetic tolerance to stresses that the rural ones didn't, adapting them to the hotter conditions of cities, and boosting their ability to detoxify and metabolize toxins and pesticides.

In the U.S., however, the lanternflies were genetically similar across all locations, even though some were sourced from locations 124 miles (200 kilometers) apart. The same genes that evolved for city living were further adapted in U.S. populations, according to the study.

Using demographic modeling on the genomic data to reconstruct the recent history of the lanternflies, researchers revealed three genetic bottlenecks, when populations were established from a limited pool of insects. One was more than 170 years ago, when Shanghai underwent rapid urbanization. The second aligned with when lanternflies moved from China to South Korea in 2004, and the third was in 2014 when the insects arrived in Pennsylvania — probably hitchhiking on goods shipped from overseas.

Adapting to China's cities may have primed the lanternfly to tolerate other hot, polluted environments, Meng said. "We should study invasive species and urbanization as interconnected parts of a whole. Those two major aspects are too often studied in isolation, but their effects actually can compound in synergistic and surprising ways."

The ability to handle a wider range of toxins might be helping spotted lanternflies spread in the U.S., said Zach Ladin, an ecologist at the University of Delaware, who wasn't involved in the study.

The relatively high densities of tree of heaven give spotted lanternflies a foothold in many cities, he told Live Science, "but some of those genes that they found that are related to overcoming toxic chemical exposure could really help them switch hosts and take advantage of other plants."

Ladin added that the new genetic information could help people slow or contain the spread of spotted lanternflies. "From a chemical control perspective, now we have some genes to target which could be important in making sure we're not just driving resistance to certain chemicals," he said.

New species may have evolved surprisingly quickly after the asteroid impact that wiped out the nonavian dinosaurs, researchers have found.

New plankton species may have appeared less than 2,000 years after the Chicxulub impact, which occurred about 66 million years ago, adding to an ongoing debate over how quickly new species arose in the wake of the collision. This suggests life rebounded much faster than scientists previously thought, researchers report in a study published Jan. 21 in the journal Geology.

"It's ridiculously fast," study co-author Chris Lowery, a paleoceanographer at the University of Texas Institute for Geophysics, said in a statement. "This research helps us understand just how quickly new species can evolve after extreme events and also how quickly the environment began to recover after the Chicxulub impact."

After the roughly 7.5-mile-wide (12 kilometers) asteroid struck off the coast of the Yucatán Peninsula in the Gulf of Mexico, dust and soot from the impact temporarily blocked out the sun. Cold, dark conditions lasted about 10 years, and roughly 75% of plant and animal species went extinct.

Based on estimates of how quickly sediment accumulated in the ocean and when fossils of new plankton species, such as Parvularugoglobigerina eugubina, started to appear, many experts think it took about 30,000 years for the first new species to show up.

But that estimate assumes that ocean sediments built up at a constant rate over that time period. Although that's often the case in ocean environments, it wasn't necessarily true after the Chicxulub impact.

In the new study, the researchers turned to a different marker: helium-3. This isotope falls to Earth with interplanetary dust at a constant rate. By measuring the helium-3 throughout a sediment layer, scientists can tell how long it took that layer to build up. For the study, the researchers used previously collected helium-3 measurements from six sites to calculate when new fossil species arrived.

Based on this analysis, P. eugubina appeared an average of 6,400 years after the impact across those six sites, the team found. At some sites, the new calibration suggests that other species likely emerged even sooner, less than 2,000 years after the asteroid struck. Between 10 and 20 species of plankton appeared within about 11,000 years, though there's still some debate over which fossils count as separate species, according to the study.

"The speed of the recovery demonstrates just how resilient life is," study co-author Timothy Bralower, a geoscientist at Penn State, said in the statement. "To have complex life reestablished within a geologic heartbeat is truly astounding."

New species typically take millions of years to develop, but that process can speed up during times of stress, such as after the asteroid impact.

That recovery may help give scientists a sense of how quickly new species could arise in response to human influence. "It's also possibly reassuring for the resiliency of modern species given the threat of anthropogenic habitat destruction," Bralower added.

Evolution quiz: Can you naturally select the correct answers?

Same-sex sexual behavior among primates could be shaped partly by specific environmental and social conditions, according to a new study comparing 59 species.

Same-sex sexual behavior (SSB) in animals is increasingly recognized in the scientific community as widespread, as it's documented across the animal kingdom in about 1,500 species. Untangling how and why it emerged across so many diverse species is challenging, however. The new study, published Jan. 12 in the journal Nature Ecology & Evolution, found SSB may be beneficial — at least for primates — when ecological conditions are harsh and social conditions are complex.

While the study authors emphasized that this research on SSB in nonhuman primates does not address modern human sexual orientation or identity, they hope the findings will foster open discussion about the benefit of sexual diversity in nature and society.

"[The findings] do suggest that the orientation toward individuals of the same sex has a very strong evolutionary history, and it's nothing bizarre or derived or unnatural," said Durham University primatologist Zanna Clay, who was not involved with the new study. "In fact, it's likely part of the evolutionary fabric of our societies."

Primate same-sex bonding to navigate harsh conditions

Research suggests SSB facilitates bonding in socially complex animals. In bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), it is associated with reduced tension, conflict resolution and the strengthening of alliances. For golden snub-nosed monkeys (Rhinopithecus roxellana), SSB and grooming strengthen social bonds in harsh, cold climates with scarce resources.

Genes also seem to play a role. In a 2023 study of rhesus macaques (Macaca mulatta), Vincent Savolainen, a biologist at Imperial College London, found SSB to be about 6.4% heritable, meaning the tendency toward this behavior can be passed down genetically from parents to offspring. But such a small percentage leaves a lot of uncertainty around what else might cause it to arise.

To explore the ecological and social context, Savolainen and colleagues conducted a meta-analysis of SSB studies across primates. Of the 491 species, they found the behavior documented and prevalent in 59 species. SSB is more likely to occur when species face a drier environment, scarcer resources, and a lot of predators, according to the study. It is also more common in species with complex social systems, greater size differences between males and females, and longer lifespans.

These trends suggest SSB might serve as a social strategy to reinforce bonds, manage conflict or build alliances, driven by the ecological and social pressures a group faces. "Species that have particularly challenging environmental and social pressures have evolved, independently of common ancestry, same-sex sexual behavior as a way to manage the pressure and navigate the social dynamic," Savolainen said, "forming coalitions, bonding, helping them deal with the challenges they face."

If predators are especially abundant, for example, having a socially close group that can trust each other's alarm calls is beneficial, Savolainen said; SSB offers one way to form or maintain relationships.

Chimpanzees and bonobos are known to engage in SSB when navigating ecological challenges, said Clay. "In a resource-poor situation, you need to cooperate and learn to tolerate each other," Clay said. "If there's food scarcity, having techniques to maintain and keep social bonds going is important."

However, while the trends are notable, it's not so simple to draw parallels across species that display SSB. "It points to some common explanations that might cut across deep taxonomic divisions, but there is a risk you're obscuring some of the nuance in individual lineages," said Nathan Bailey, an evolutionary biologist at the University of St Andrews who was not involved with the new study. "Does this behavior emerge for different functional reasons, under different selective pressures, in different lineages? They're starting to scratch the surface of that."

Savolainen said SSB has been traditionally underreported, so the new findings highlight its significance in a broader understanding of primate behavior. "Same-sex behavior is as important as feeding, fighting, or looking after young," he said.

The research could help paint a more complete picture of social and sexual behavior in primates. "People tend to separate reproductive sex and social sex, whereas actually I think the social element of both is very important and should be integrated," Clay said.

But can these findings shed any light on human behavior? Our early hominin ancestors likely experienced various ecological and social pressures, including those linked to SSB for the primates in this study, the study authors pointed out –– but it's unclear whether these pressures would have contributed to the evolution of same-sex sexual orientation in hominin species in a similar way.

Generalizing the results to humans is tricky, according to the researchers and experts, without behavioral data from our hominin ancestors, and considering modern human culture and identity is so complex.

"I don't think this tells us much about what's going on in humans," Bailey said. "There seems to be a huge diversity of explanations [of SSB] across animals, even in closely related lineages, so it doesn't stand to reason to me that any one particular explanation in animals would map onto human beings."

The study also points to a key reason primates, including humans, have succeeded so well across the globe: adaptability. "We're not fixed to one mating system, one behavioral system," Clay said. "To me, the fact that sexual behaviors can expand [under different conditions] reflects that behavioral flexibility which is really important for primate success."

One of my favorite activities is going to the zoo where I live in Knoxville when it first opens and the animals are most active. On one recent weekend, I headed to the chimpanzees first.

Their breakfast was still scattered around their enclosure for them to find. Ripley, one of the male chimpanzees, quickly gathered up some fruits and vegetables, sometimes using his feet almost like hands. After he ate, he used his feet to grab the fire hoses hanging around the enclosure and even held pieces of straw and other toys in his toes.

I found myself feeling a bit envious. Why can't people use our feet like this, quickly and easily grasping things with our toes just as easily as we do with our fingers?

I'm a biological anthropologist who studies the biomechanics of the modern human foot and ankle, using mechanical principles of movement to understand how forces affect the shape of our bodies and how humans have changed over time. Your muscles, brain and how human feet evolved all play a part in why you can't wiggle individual toes one by one.

Comparing humans to a close relative

Humans are primates, which means we belong to the same group of animals that includes apes like Riley the chimp. In fact, chimpanzees are our closest genetic relatives, sharing almost 98.8% of our DNA.

Evolution is part of the answer to why chimpanzees have such dexterous toes while ours seem much more clumsy.

Our very ancient ancestors probably moved around the way chimpanzees do, using both their arms and legs. But over time our lineage started walking on two legs. Human feet needed to change to help us stay balanced and to support our bodies as we walk upright. It became less important for our toes to move individually than to keep us from toppling over as we moved through the world in this new way.

Human hands became more important for things such as using tools, one of the hallmark skills of human beings. Over time, our fingers became better at moving on their own. People use their hands to do lots of things, such as drawing, texting or playing a musical instrument. Even typing this article is possible only because my fingers can make small, careful and controlled movements.

People's feet and hands evolved for different purposes.

Muscles that move your fingers or toes

Evolution brought these differences about by physically adapting our muscles, bones and tendons to better support walking and balance. Hands and feet have similar anatomy; both have five fingers or toes that are moved by muscles and tendons. The human foot contains 29 muscles that all work to help you walk and stay balanced when you stand. In comparison, a hand has 34 muscles.

Most of the muscles of your foot let you point your toes down, like when you stand on tiptoes, or lift them up, like when you walk on your heels. These muscles also help feet roll slightly inward or outward, which lets you keep your balance on uneven ground. All these movements work together to help you walk and run safely.

The big toe on each foot is special because it helps push your body forward when you walk and has extra muscles just for its movement. The other four toes don't have their own separate muscles. A few main muscles in the bottom of your foot and in your calf move all four toes at once. Because they share muscles, those toes can wiggle, but not very independently like your fingers can. The calf muscles also have long tendons that reach into the foot; they're better at keeping you steady and helping you walk than at making tiny, precise movements.

In contrast, six main muscle groups help move each finger. The fingers share these muscles, which sit mostly in the forearm and connect to the fingers by tendons. The thumb and pinky have extra muscles that let you grip and hold objects more easily. All of these muscles are specialized to allow careful, controlled movements, such as writing.

So, yes, I have more muscles dedicated to moving my fingers, but that is not the only reason I can't wiggle my toes one by one.

Divvying up brain power

You also need to look inside your brain to understand why toes and fingers work differently. Part of your brain called the motor cortex tells your body how to move. It's made of cells called neurons that act like tiny messengers, sending signals to the rest of your body.

Your motor cortex devotes many more neurons to controlling your fingers than your toes, so it can send much more detailed instructions to your fingers. Because of the way your motor cortex is organized, it takes more "brain power," meaning more signals and more activity, to move your fingers than your toes.

Even though you can't grab things with your feet like Ripley the chimp can, you can understand why.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

Scientists have reconstructed the head of an ancient human relative from 1.5 million year-old fossilized bones and teeth. But the face staring back is complicating scientists' understanding of early human evolution and dispersal, according to a new study.

The rebuilt fossil skull, called DAN5, shares traits with Homo erectus, the first early human relatives to have modern body proportions and to disperse from Africa. But the skull also has some features associated with the earlier species Homo habilis. The findings suggest a complex evolutionary path from early human ancestors to H. erectus, researchers reported Dec. 16 in the journal Nature Communications.

DAN5 was discovered in the Gona study region of northern Ethiopia and was first reported in a 2020 study published in the journal Science Advances. The fossils are between 1.5 million and 1.6 million years old and were thought to belong to a small H. erectus female based on the shape and size of the skull.

"We already knew that the DAN5 fossil had a small brain, but this new reconstruction shows that the face is also more primitive than classic African Homo erectus of the same antiquity," study co-author Karen Baab, a paleontologist at Midwestern University in Arizona, said in a statement. This could mean that the population from the Gona region might have "retained the anatomy of the population that originally migrated out of Africa approximately 300,000 years earlier," she said.

To reconstruct DAN5's face, the researchers used micro-computerized tomographic (CT) scans of 10 fossils — five fragments of facial bones and five teeth — to build a 3D model. The process was like "a very complicated 3D puzzle, and one where you do not know the exact outcome in advance," Baab said. "Fortunately, we do know how faces fit together in general, so we were not starting from scratch."

The shape of DAN5's braincase was similar to that of H. erectus. But some of the facial features such as large molars and a flat and narrow nose were more similar to features in the older human ancestor H. habilis.

A similar mix of old and new traits was previously observed in 1.8 million-year-old H. erectus fossils from Dmanisi in the Republic of Georgia, which led some scientists to believe that the species evolved in Eurasia from an earlier Homo population. Older H. erectus fossils dating back 1.8 million years have also been found in Africa. But DAN5 is the first African fossil to have the same mixture of attributes as the Dmanisi hominins, which could support the hypothesis that H. erectus evolved primarily in Africa like other hominins before it. Further complicating the picture, though, is the fact that the DAN5 fossils are younger than those from Dmanisi, suggesting the mixture of old and new traits persisted in Africa for at least 300,000 years.

In future work, the team plans to compare the DAN5 fossils to 1 million-year-old human fossils from Europe, including some that have been identified as H. erectus and as Homo antecessor — a later human relative that lived 1.2 million to 0.8 million years ago — to better understand variability in face shape in the early Homo genus. The team also plans to investigate whether DAN5 might be a product of interbreeding between multiple Homo species.

"We're going to need several more fossils dated between one to two million years ago to sort this out," study co-author Michael Rogers, an anthropologist at Southern Connecticut State University, said in the statement.

Human evolution quiz: What do you know about Homo sapiens?

From a distance, it might have looked like a small child was wending her way through the waving grass along a vast lake. But a closer look would have revealed a strange, in-between creature — a big-eyed imp with a small head and an apelike face who walked upright like a human.

She may have looked warily over her shoulder as she walked, on alert for saber-toothed cats or hyenas. She may have used her strong arms to climb the shrubby trees nearby, searching for fruit, eggs, or insects to eat. Or perhaps she simply rested on the shores of the croc-infested waters, gulping down water on a hot day.

She likely had no idea it was her last day on Earth.

Roughly 3.2 million years later, her skeleton was unearthed by paleoanthropologist Donald Johanson and his team on the International Afar Research Expedition.

The stunningly complete fossil was nicknamed "Lucy." And her remarkable species, Australopithecus afarensis, may have been our direct ancestor. Our discoveries about Lucy have transformed our understanding of humanity's tangled family tree.

Fifty years later, we know so much more about her species. In fact, anthropologists have learned so much about Lucy and her kind that we can now paint a picture of how she lived and died.

Her last day may have been filled with companionship, but it also entailed a relentless search for food. And it was likely dominated by the ever-present fear of predators.

"I suspect that the last day in her life was filled with danger," Johanson told Live Science.

Finding Lucy

The modern story of Lucy began on Nov. 24, 1974, in Hadar, Ethiopia. Johanson and then-graduate student Tom Gray stumbled upon a bone poking out of a gully. Following two weeks of careful excavation, their team recovered dozens of fossilized bones. Together, these bones made up 40% of the skeleton of a human ancestor, making it the most complete skeleton of an archaic human species that had ever been found.

Pamela Alderman, another member of the expedition, suggested the team nickname the skeleton Lucy, after the Beatles song "Lucy in the Sky with Diamonds."

"And it just became iconic," Johanson said, "a moniker that everybody knew."

Lucy’s discovery transformed the study of ancient human relatives.

"I was in high school when she was found," John Kappelman, a paleoanthropologist at the University of Texas at Austin, told Live Science. "It really did reset the way paleoanthropology worked."

Lucy's skeleton, along with subsequent discoveries of other fossils of her species, have given anthropologists a wealth of information about what is essentially the halfway point in human evolution. At 3.2 million years old, Lucy and her kind lived equidistant in time from our ape ancestors and contemporary humans.

"She's our touchstone," Jeremy DeSilva, a paleoanthropologist at Dartmouth College, told Live Science. "Everything sort of comes back to her as the reference point, and she deserves it."

"A lot like us"

One thing is fairly certain: Though there were some obvious differences, Lucy looked and acted a lot like us.

"If we saw her coming out of a grocery store today, we would recognize her as upright walking and some kind of human," Johanson said.

Although her strong arms and the shape of her finger bones suggest Lucy could climb trees, her pelvis and knees were clearly adapted to walking on two feet.

The size of Lucy's thigh bone also revealed that she was only about 42 inches (1.1 meters) tall and 60 to 65 pounds (27 to 30 kilograms) — about the size of a 6- or 7-year-old child today. And the eruption of her wisdom teeth showed that, although she was in her early teens when she died, she was a fully mature young adult.

"Australopithecus in general was maturing fast," DeSilva said, "and it makes sense if you're on a landscape full of predators." In species that are frequently prey, individuals that mature faster are more likely to pass on their genes. But australopithecines were unique—while their teeth and bodies matured quickly, their brains grew more slowly, telling us that they relied quite a bit on learning for survival, DeSilva said.

Her discovery also settled a debate that was raging in the early 1970s: Did our big brains evolve before we learned to walk upright? Lucy's head, which was not much bigger than a chimp's, showed the answer was no. Our ancestors became bipedal long before they evolved large brains.

Lucy's clan

Because her skeleton was found on its own, Lucy's "social life" is a little murkier than other parts of her daily life. But many researchers think she lived in a mixed-sex group of about 15 to 20 males and females, not unlike modern-day chimpanzees do.

And although there's no direct evidence, Lucy's skeletal maturity suggests she could have had a baby. Bringing that relatively large-headed newborn through her relatively narrow pelvis would have been challenging, which means she may have had the help of a primitive "midwife."

If Lucy had a baby, she also likely had a partner. Other A. afarensis fossils, such as those of Kadanuumuu, show male australopithecines were only slightly larger than females, which, in primates, usually corresponds to more monogamous pairings.

Lucy and her kind would have spent a significant amount of their time avoiding becoming another animal's lunch. "These small creatures would have been nice hors d'oeuvres for a sabertooth or a large cat or hyena," Johanson said.

Perhaps because of that omnipresent danger, the group likely relied on each other.

"I think they had each other's backs and helped each other out," DeSilva said, "especially when they were in dangerous situations."

A healed bone fracture seen in Kadanuumuu provides evidence that these primates cared for one another. Around 3.6 million years ago, this male australopithecine broke his lower leg. By the time he died, though, the break was fully healed.

"On that landscape with that many predators, no doctors, no hospitals, no casts, no crutches, how in the world do you survive if not for social assistance?" DeSilva said. "It's really strong evidence that they didn't leave each other for dead."

Lucy's last day

Lucy probably started her last day much like any other, waking up from the treetop nest made of branches and leaves where she slept, along with her group, before setting off to find food.

It's not clear whether she would have been alone or in a group when she left to forage; if she did have a baby, she may have carried it.

But there's no doubt that she would have spent a significant part of her day looking for food. She most likely ate a few staples, such as grasses, roots and insects, chemical elements in her tooth enamel showed. She may have happened upon the eggs of birds or turtles and promptly gobbled them up as tasty, protein-rich treats. And if she was lucky enough to come across a carcass of a large mammal, such as an antelope, that hadn't been picked clean, she and her troop mates may have pulled the flesh from the bone, using large rocks.

"They can't afford to be picky eaters as these slow bipeds in a dangerous environment," DeSilva said. "They're eating everything they can get their hands on."

However, there's no evidence that Lucy’s species used fire to cook any of their food.

Death at the water's edge

In the past 50 years, we've created a picture of Lucy's last moments. It's not clear exactly why she was by the lake; maybe she was thirsty, or perhaps it was a great spot to look for food.

But there are two main theories for how she died.

"Perhaps she was down there at the water and — bam! — a crocodile comes out," Johanson said. "Crocodiles are incredibly fast, and it's a dangerous place if you're a little creature" like Lucy.

Johanson found one carnivore tooth mark on Lucy's pelvis, and it had not healed, meaning it occurred around the time of her death. Although the animal that made the mark has not been conclusively identified, "we know that australopithecines were preyed upon because there are a number of examples," Johanson said.

In 2016, Kappelman and his colleagues put forward an alternate ending for Lucy: a catastrophic fall from a tree.

Based on high-resolution CT scans and 3D reconstructions of Lucy's skeleton, Kappelman identified fractures in her right shoulder, ribs and knees that were unlike the typical fracturing that occurs in fossils crushed under the weight of dirt and rocks for millions of years.

"Something traumatic happened here during life," Kappelman said.

The kinds of fractures Lucy suffered are consistent with a fall from a considerable height, perhaps from a tall tree in which she was foraging for food.

"She hit on her feet and then her hands, which meant she was conscious when she hit the ground," Kappelman said. "I don't think she survived very long."

It's not clear whether she was alone when she died. But even if she was with others of her kind, they likely wouldn't have done much with her body.

There's no evidence that A. afarensis "bodies were treated any differently than any other animal," DeSilva said. "Maybe there was some curiosity around it, and then they carried on."

Primate researchers have documented other species' curiosity about inanimate bodies. For example, chimpanzees often care for the body for a few hours or days after death, sometimes guarding the body.

Lucy's group may have done the same for her until her body was naturally buried, which would have happened quite rapidly, perhaps by a flood or mudslide.

In the end, though, "we know very little about how any of these creatures died," Johanson said.

Lucy lives on

Thanks to Johanson's 1974 discovery of Lucy — as well as other important findings, like the "First Family" and the footprints at Laetoli in Tanzania — we now know quite a lot about A. afarensis.

"It was a highly successful species that was comfortable in lots of different habitats," Johanson said; A. afarensis fossils have been found in Kenya in addition to Ethiopia and Tanzania. "From an evolutionary perspective, her species was highly adaptable," he said.

Lucy has had a broad impact on the field of anthropology.

"The discovery of Lucy really hit the start button for looking in older and older sediments in Africa," Kappelman said. As a result, we have found numerous ancient hominin species and now have 50 years' worth of fossil evidence that human evolution was messy and complex.

Lucy was the only human ancestor discovered at Hadar. But a couple dozen miles away at Woranso-Mille, a paleontological site in Ethiopia, Yohannes Haile-Selassie, director of the Institute of Human Origins at Arizona State University, and his colleagues have found evidence of a strange land inhabited by multiple humanlike species between 3.8 million and 3.3 million years ago. For instance, Lucy's kind coexisted alongside another ancient relative, A. anamensis.

Would they have been friends, enemies, competitors or something in between? Right now, anthropologists still have little idea what this landscape teeming with ancient hominins would have looked like.

But perhaps 50 years from now, we'll have a better picture of how Lucy's kind interacted with these other ancient hominins. Even then, Lucy will likely remain one of the most famous fossils of all time.

"I like to think all fossils are pretty special," DeSilva said, "but there's nothing like Lucy."

Editor's note: This article was originally published in November, 2024 as part of a special package written for the 50th anniversary of the discovery of a 3.2 million-year-old A. afarensis fossil (AL 288-1), nicknamed "Lucy."

It's a long-held idea that turtles can tuck their heads into their shells when threatened. But is it true? And is this protective trick why turtles the world over have shells today?

The answer is that some types of turtles can, and others can't, experts told Live Science. And even though shells can be protective for some of these reptiles, fossil evidence suggests that shells evolved for entirely different reasons.

Tortoises are one type of turtle that can tuck their heads into their shells. This terrestrial subgroup of turtles emerged 50 million years ago, Tyler Lyson, senior curator of vertebrate paleontology at the Denver Museum of Nature and Science, told Live Science. They typically move slowly, so they rely on their shells to protect them from predators. Most tortoises can draw their heads into their shells, which typically also have a domed shape with more space inside to make that possible.

Several terrestrial turtle species, which split their time between land and water, can do the same.

"Turtles have two ways of tucking the head in," Jason Head, a professor of vertebrate evolution and ecology at the University of Cambridge, told Live Science. "We have what are called the side-neck turtles. They have long necks, and they literally fold the head and neck to the side over one of their arms. And then there are the snake-neck or S-neck turtles, which put a loop into the neck, and can actually pull the neck into the shoulder girdle."

One example is the eastern box turtle (Terrapene carolina carolina), whose bottom shell, known as a plastron, is fitted with a hinge that even allows it to completely close up the shell.

But sea turtles are one group of turtles that cannot pull their heads into their shells. Sea turtles have much sleeker, lighter shells that contain no space for them to tuck their heads inside. "This is to lighten the load," Head said, and it allows sea turtles to swim faster to escape predators.

How turtle shells evolved

So, how did some turtles develop this lifesaving trick? To find out, we need to explore how turtle shells evolved, which takes us back almost 300 million years in the fossil record.

"The turtle shell is a complicated structure. It's made up of over 50 bones," Lyson said. "Bone" is the key word, because fossils reveal that turtle shells are part of their skeletons. And while the modern turtle's shell looks like a solid unit, it's actually made up of two skeletal features that evolved separately.

"The first thing we see in the evolution of the turtle shell is the broadening of the ribs, and we see that in Eunotosaurus africanus," a creature that lived in southern Africa 260 million years ago, before dinosaurs roamed Earth, Lyson told Live Science. Lyson first described Eunotosaurus' contribution to turtle evolution in a 2013 study. Researchers think that these creatures spent time burrowing underground to escape the heat and that the development of wider ribs supported more muscle mass that enabled them to do that.

Then, in Germany, the 2015 discovery of a 240 million-year-old fossil called Pappochelys showed a shell-less animal with wider upper ribs paired with thicker belly ribs — known as "gastralia" — on its underside. By 220 million years ago, an aquatic animal called Odontochelys found in China had developed a fully unified belly plate — the plastron — partly from the expanding gastralia.

"Myself and others think that the evolution of the plastron was a ballast for basically going deeper into the water column," Lyson explained. It's also possible the plastron developed to protect turtles from predators swimming below, he noted.

The first evidence of a fully formed turtle shell comes from 210 million years ago, in the shape of a fossilized creature called Proganochelys, whose thick upper ribs had fused together with dermal bone, forming a closed carapace, attached to a lower plastron. The opening for the turtle's head was formed from shoulder bones that connected the top and bottom of its shell, Lyson explained.

Most evidence suggests that these reptilian creatures, called Pantestudines, ultimately led to modern-day turtles. However, Head noted that similar features — like widened, overlapping ribs — also developed in other animals millions of years ago, including some thought to be more closely related to mammals.

"It's an active area of research, with new discoveries coming all the time," Head said.

The shells of these turtle ancestors developed as a response to varied evolutionary pressures, but today, the turtle's shell is used primarily for self-defense, Lyson noted. "The modern-day function isn't necessarily related to how that feature arose," he said. "It wasn't until you got the full advent of the shell that it was for protection."

The turtle's resilient shell has seen these creatures through almost 300 million years of history, and Lyson thinks it's one reason they've managed to survive three of Earth's five mass extinctions.

"We see the fossil record, and we can see the line in the sand where dinosaurs and lots of other things go extinct," Lyson said. "And we see turtles marching right across that line."

Evolution quiz: Can you naturally select the correct answers?

Graying hair could be a sign that the body is effectively protecting itself from cancer, a new study suggests.

Cancer-causing triggers, such as ultraviolet (UV) light or certain chemicals, activate a natural defensive pathway that leads to premature graying but also reduces the incidence of cancer, the research found.

The researchers behind the study tracked the fate of the stem cells responsible for producing the pigment that gives hair its color. In mouse experiments, they found that these cells responded to DNA damage either by ceasing to grow and divide — leading to gray hair — or by replicating uncontrollably to ultimately form a tumor.

The findings, reported in October in the journal Nature Cell Biology, underline the importance of these sorts of protective mechanisms that emerge with age as a defense against DNA damage and disease, the study authors say.

Graying hair as cancer defense

Healthy hair growth is dependent on a population of stem cells that constantly renews itself within the hair follicle. A tiny pocket within the follicle contains reserves of melanocyte stem cells — precursors to the cells that produce the melanin pigment that gives hair its color.

"Every hair cycle, these melanocyte stem cells will divide and produce some mature, differentiated cells," said Dot Bennett, a cell biologist at City St George's, University of London who was not involved in the study. "These migrate down to the bottom of the hair follicle and start making pigment to feed into the hair."

Graying occurs when these cells can no longer produce sufficient pigment to thoroughly color each strand.

"It's a sort of exhaustion called cell senescence," Bennett explained. "It's a limit to the total number of divisions that a cell can go through, and it seems to be an anti-cancer mechanism to prevent random genetic errors acquired over time propagating uncontrollably."

When the melanocyte stem cells reach this "stemness checkpoint," they cease to divide, meaning the follicle no longer has a source of pigment to color the hair. Ordinarily, this occurs with old age as the stem cells naturally reach this limit. However, Emi Nishimura, a professor of stem cell age-related medicine, and colleagues at the University of Tokyo were interested in how this same mechanism operates in response to DNA damage — a key trigger for cancer development.

In mouse studies, the team used a combination of techniques to track the progress of individual melanocyte stem cells through the hair cycle after exposing them to different harmful environmental conditions, including ionizing radiation and carcinogenic compounds. Intriguingly, they found that the type of damage influenced how the cell reacted.

Ionizing radiation caused the stem cells to differentiate and mature, and ultimately activated the biochemical pathway responsible for cell senescence. As a result, the melanocyte stem cell reserves were rapidly depleted over the hair cycle, thus halting the production of further mature pigment cells and leading to gray hair.

Meanwhile, by essentially switching off cell division, this senescence pathway prevented the mutated DNA from passing into a new generation of cells, thus lowering the likelihood of those cells forming cancerous tumors.

Exposure to chemical carcinogens — such as 7,12-dimethylbenz[a]anthracene (DMBA), a tumour initiator widely used in cancer research — appeared to bypass this protective mechanism. Instead of switching on senescence, it toggled on a competing cellular pathway.

This alternative chemical sequence blocked cell senescence in the team's mouse studies, enabling the hair follicles to retain their stem cell reserves and the ability to produce pigment, even after DNA damage. That meant that the hair retained its color, but in the long term, the unchecked replication of damaged DNA led to tumor formation and cancer, the team said in a statement.

These findings reveal that the same stem cell population can meet opposite fates depending on the type of stress they're exposed to, lead study author Nishimura said in the statement. "It reframes hair graying and melanoma [skin cancer] not as unrelated events, but as divergent outcomes of stem cell stress responses," Nishimura added.

The next step will be to translate this understanding into human hair follicles, to see whether these observations in mice carry over to people, Bennett said.

This article is for informational purposes only and is not meant to offer medical advice.

In his book "One Hand Clapping: Unraveling the Mystery of the Human Mind" (Prometheus/Swift Press, 2025), New York University neuroscientist Nikolay Kukushkin traces the evolution of human consciousness. He starts the story with the emergence of the first DNA on Earth and then highlights key evolutionary landmarks that paved the way to us — namely, modern-day humans. In the following excerpt, Kukushkin describes the "social brain hypothesis," which posits that human intelligence arose, in part, to help us keep track of our increasingly complex social groups.

What made us human

In the past, many explanations of human uniqueness focused on what gave us the ability to become as intelligent as we are, rather than why we would want to be so intelligent. We often take it for granted that intelligence is what every animal obviously wants, and we just figured out a better evolutionary path toward it. One classic explanation for this involves, for example, walking on two legs, caused by a transition from trees to grasslands, which freed the hands from climbing and allowed us to do more complicated things. Another explanation focuses on our increasingly meat-based diet, which allowed for larger brain sizes. These factors certainly played critical roles in allowing us to become who we are. But they alone don't necessarily explain what is so good about being intelligent in the first place. We just assume that to be self-evident.

I think it's a bit of a self-serving assumption, like jellyfish wondering why no one else has managed to evolve stinging cells. We like to believe that we somehow won evolution — a notion we discussed in chapter 3 when talking about complexity and perfection. We have this image of an ape standing up, picking up a stick, and being rewarded for this achievement with a massive brain.

But the truth is, intelligence comes at a price, and for many species, the benefits just aren't worth it. A brain such as our own takes prodigious amounts of energy away from a body already burning through its fuel: a gram of brain tissue uses ten times the amount of nutrients as an average gram of the human body. Besides, a bigger brain is heavier and easier to damage. So there are considerable evolutionary costs to an enlarged brain. For any given species, these costs eventually outweigh the diminishing returns of brain enlargement. All brains have an evolutionary stage at which they are large enough. If a double-sized brain provided rhinos with a survival advantage, over millions of years their brain would have certainly doubled in size — you have to have very little awareness of evolutionary history to believe that we alone cracked some code that eluded everybody for eons. For rhinos, there wasn't any extra advantage in larger brains, so their brains turned out just as they did. The question is not why humans succeeded where others failed — as we tend to think — but why we needed supercomputers when others were fine with calculators.

There's an interesting pattern that may explain it. If you measure the size of the cerebral cortex — the brain's "machine of understanding"— in different primate species relative to the rest of their brain and plot it against the number of group members typical for each of those species, the two numbers fall on a straight line: the more members, the bigger the cortex. Humans are number one on both accounts — our cortex is the largest relative to the rest of the brain, as is our typical group size, estimated around 150 — that's the number of people in a typical hunter-gatherer society and a typical cap on the number of active social acquaintances that we moderns can maintain. For example, corporate organizations often naturally fragment into units of about 150 people.

Why would that be? This is far from a resolved question, but the proponents of the so-called social brain hypothesis say that reason is that social behavior is a uniquely demanding task, putting unprecedented strain on our brain's capacities. All mammals, to some extent, use their brain as a mirror, understanding others' behavior by modeling it inside their own mind. But primates, whose defensive groups swell into the tens and even hundreds, had to contend with tens and hundreds of these complex, interconnected models of other group members — their personalities, their emotions, their mutual relationships — which one of them did what to whom at what point and so on, a tremendous trove of complex data that we, humans, take to be as natural as eating dinner but that would befuddle even the smartest non-primate. In short, the social brain hypothesis states that social life is what pushed us to become intelligent.

The way this explanation differs from others is by offering an incentive rather than simply means to achieve it: yes, free hands, meat diet, and many other factors made our brain possible, but the reason we needed it in the first place was to remember all our friends who helped us fight monsters.

As cheesy as it sounds, I think about it all the time. There have been many different fables told about the birth of the human species: that it was work that made us human (this was the communist narrative — an ape picking up a tool) or maybe that it was violence (this is the narrative from "2001: A Space Odyssey" — an ape picking up a weapon). Those were not just scientific theories — they were origin stories, as important for a modern mind to make sense of itself as myths were to an ancient mind. An origin story is told to explain what you are really about, and in doing so, it doesn't simply describe the past but provides a template for the present. If you are about work, then work is the pillar on which your life should naturally stand. If you are about violence, then there is no sense trying to avoid it. But the more we learn about ourselves, the clearer it becomes that we are really about others. Our entire essence is to carry tens and even hundreds of peers inside our brains, to navigate the vicissitudes of their emotions and relationships, to derive both meaning and joy from living life together. It has long been recognized, for example, that happiness depends far less on individual well-being than on the richness of social contacts. Social life has a profound effect on us, and not just mentally but physically: for example, the Harvard Study of Adult Development, which began in 1938 and tracked hundreds of people for several decades, famously showed that close relationships are better predictors of long and happy lives than social class, IQ, or even genes. Too often, modern lives let us forget a firmly established fact: friends are worth living for. The social brain hypothesis puts an origin story behind this simple truth.

It also puts the birth of our species in a broader context. Our brains started swelling in size long before the first Homo sapiens. All primates share the relationship between group size and the cerebral cortex, which means that it always took a large brain to handle many peers.

And that, in turn, means that sooner or later, something like a human was inevitable.

When eukaryotes first started extracting energy from other organisms, this set the trajectory toward the human species — eventually there was bound to be someone who could control fire and even nuclear fission. There's something similar that the social brain hypothesis points to, at the deepest level. Once primates were swept in a drive to enlarge their groups and brains, eventually there was bound to be someone with groups large enough and with brains advanced enough to start talking to each other, inventing symbols and abstract categories — and from that, finally, there was bound to arise some form of culture, art, and civilization.

It is this final essence — an abstract, symbolic language passed from person to person by cultural transmission — that completes the design of a human being that we had seen gradually crystallize over billions of years. But to understand why language was so important for our species, we must now take a detour. Most books about human evolution begin right about here and proceed through the past few million years to the present, during which apes gradually evolved into several species of Homo, of which today only one survives — the "wise" one, or sapiens. But our quest instead takes us inward, into the human brain, into the sea of electrical signals pulsing through this astounding machine that runs our conscious minds.

Curious Kids is a series for children of all ages. If you have a question you'd like an expert to answer, send it to CuriousKidsUS@theconversation.com.

If evolution is real, then why is it not happening now? — Dee, Memphis, Tennessee

Many people believe that we humans have conquered nature through the wonders of civilization and technology. Some also believe that because we are different from other creatures, we have complete control over our destiny and have no need to evolve. Even though lots of people believe this, it's not true.

Like other living creatures, humans have been shaped by evolution. Over time, we have developed — and continue to develop — the traits that help us survive and flourish in the environments where we live.

I'm an anthropologist. I study how humans adapt to different environments. Adaptation is an important part of evolution. Adaptations are traits that give someone an advantage in their environment. People with those traits are more likely to survive and pass those traits on to their children. Over many generations, those traits become widespread in the population.

The role of culture

We humans have two hands that help us skillfully use tools and other objects. We are able to walk and run on two legs, which frees our hands for these skilled tasks. And we have large brains that let us reason, create ideas and live successfully with other people in social groups.

All of these traits have helped humans develop culture. Culture includes all of our ideas and beliefs and our abilities to plan and think about the present and the future. It also includes our ability to change our environment, for example by making tools and growing food.

Although we humans have changed our environment in many ways during the past few thousand years, we are still changed by evolution. We have not stopped evolving, but we are evolving right now in different ways than our ancient ancestors. Our environments are often changed by our culture.

We usually think of an environment as the weather, plants and animals in a place. But environments include the foods we eat and the infectious diseases we are exposed to.

A very important part of the environment is the climate and what kinds of conditions we can live in. Our culture helps us change our exposure to the climate. For example, we build houses and put furnaces and air conditioners in them. But culture doesn't fully protect us from extremes of heat, cold and the sun's rays.

Here are some examples of how humans have evolved over the past 10,000 years and how we are continuing to evolve today.

The power of the sun's rays

While the sun's rays are important for life on our planet, ultraviolet rays can damage human skin. Those of us with pale skin are in danger of serious sunburn and equally dangerous kinds of skin cancer. In contrast, those of us with a lot of skin pigment, called melanin, have some protection against damaging ultraviolet rays from sunshine.

People in the tropics with dark skin are more likely to thrive under frequent bright sunlight. Yet, when ancient humans moved to cloudy, cooler places, the dark skin was not needed. Dark skin in cloudy places blocked the production of vitamin D in the skin, which is necessary for normal bone growth in children and adults.

The amount of melanin pigment in our skin is controlled by our genes. So in this way, human evolution is driven by the environment — sunny or cloudy — in different parts of the world.

The food that we eat

Ten thousand years ago, our human ancestors began to tame or domesticate animals such as cattle and goats to eat their meat. Then about 2,000 years later, they learned how to milk cows and goats for this rich food. Unfortunately, like most other mammals at that time, human adults back then could not digest milk without feeling ill. Yet a few people were able to digest milk because they had genes that let them do so.

Milk was such an important source of food in these societies that the people who could digest milk were better able to survive and have many children. So the genes that allowed them to digest milk increased in the population until nearly everyone could drink milk as adults.

This process, which occurred and spread thousands of years ago, is an example of what is called cultural and biological co-evolution. It was the cultural practice of milking animals that led to these genetic or biological changes.

Other people, such as the Inuit in Greenland, have genes that enable them to digest fats without suffering from heart diseases. The Turkana people herd livestock in Kenya in a very dry part of Africa. They have a gene that allows them to go for long periods without drinking much water. This practice would cause kidney damage in other people because the kidney regulates water in your body.

These examples show how the remarkable diversity of foods that people eat around the world can affect evolution.

Diseases that threaten us

Like all living creatures, humans have been exposed to many infectious diseases. During the 14th century a deadly disease called the bubonic plague struck and spread rapidly throughout Europe and Asia. It killed about one-third of the population in Europe. Many of those who survived had a specific gene that gave them resistance against the disease. Those people and their descendants were better able to survive epidemics that followed for several centuries.

Some diseases have struck quite recently. COVID-19, for instance, swept the globe in 2020. Vaccinations saved many lives. Some people have a natural resistance to the virus based on their genes. It may be that evolution increases this resistance in the population and helps humans fight future virus epidemics.

As human beings, we are exposed to a variety of changing environments. And so evolution in many human populations continues across generations, including right now.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

"Consciousness," although challenging to define, can be thought of as a first-person awareness of one's surroundings and oneself. You sense the world through your eyes, nose, ears and hands, and track your internal bodily states via interactions between your cells. These data streams collide to give rise to your personal perception of the world, your place within it, and your motivations for moving through it.

An enduring question about consciousness is how this state of awareness comes about. Is consciousness simply the result of a bunch of chemical reactions? Or is there some extra "secret ingredient"?

In the book "One Hand Clapping: Unraveling the Mystery of the Human Mind" (Prometheus/Swift Press, 2025), New York University neuroscientist Nikolay Kukushkin explores these questions. To do so, he traces the evolutionary history of human consciousness from the formation of Earth's first DNA molecules to present-day Homo sapiens. Kukushkin studies memory in non-brain biological systems, such as human kidney cells, as well as in simple organisms such as sea slugs. He also considers himself a "molecular philosopher."

"I like to think about mental processes, philosophical questions of life and existence from the ground up," Kukushkin told Live Science. Originally published in Russian, a new edition of "One Hand Clapping" has now been released in English. Live Science spoke with Kukushkin about the book and his views on the nature of human consciousness.

Nicoletta Lanese: In this book, what is your working definition of "consciousness"?

Nikolay Kukushkin: It can be defined from the top down, from our personal experience, or you can attempt, as I do, to define it from the ground up.

The top-down description would be consciousness is the first-personness of it all — the fact that to me, experience feels different than looking at someone else's experience, that internally, there is something else than just "facts of life" [meaning biological systems].

I was having this debate with a philosopher colleague [who questioned], "How can the directionality of consciousness arise from the physical facts of the brain being there?" But to me, it's not a problem. Physics is directional — a rock "wants" to fall down. This potential energy is the gravitation of a system towards an energy minimum, and I think everything is that. It's just a level of complexity. A rock gravitates towards an energy minimum; for a rock, it just means falling down. A cell gravitates towards an energy minimum; for the cell, it might mean predicting the environment in some way. You get to a brain, you form these predictive expectations — millions of neurons talking to one another.

I think what puzzles them [proponents of the top-down definition] is the very directionality of a system towards some state, because they think the default is no directionality. I don't think there is such a default. I think physics, the entire universe, is directionality. Time is this unit of one thing leading to another, this unit of causality. So, if everything consists of these grains of causality, then I don't think it's that puzzling that we are driven towards anything, that there is some sort of drive of the system towards a state.

My ground-up definition of consciousness would be this particular form of causality as it plays out in our brain. And the reason why we think of it as "different" is because it's circular. We have this circulation of causality through the networks of our brain. We form predictions that affect how we perceive new data. That affects our predictions; that affects how we perceive new data.

There's this circular motion of causality that makes us constantly reevaluate our beliefs, including our beliefs about what we are and who we are, and what does it all mean and where we're currently present. And that rolling motion is consciousness, in my definition. I guess I challenge the top-down people to say, what else is missing?

NL: You note that this feedback loop helps set humans apart from computers — how so?

NK: The difference is that they [computers] form their perception — we could call it "the model" — before they start inferring. Basically, first they form their "beliefs," and then they start generating predictions based on those beliefs. What we do is we constantly circulate those things. Every prediction, every belief, everything we perceive, affects the model — and then the model feeds back on what we perceive, and it's a constant motion.

I think it's [consciousness is] possible to achieve in an artificial computer, but it requires a different microchip, because we currently have memory and processing separated. That's just the constraint of a silicon chip. If we had a more biologically similar chip that simultaneously memorizes and infers, and that would be constantly generating its own new beliefs — well, that I think is how AI starts really thinking for itself. Because then it can not just act upon what it was trained on, but it can train itself on its own inferences.

NL: In the book, you discuss stages in our primate ancestors' evolution that laid the groundwork for the human brain. What, then, introduced that next level of intelligence, what we think of as "humanness"?

NK: There's a couple of answers to this. First, what we often perceive as this unique humanness that's categorically different is not necessarily such a categorical difference. It's much more of a smooth transition.

There's a general trend that the size of the primate cortex — the "thinking part" of your brain — correlates with the size of the social group. And we humans are number one on both counts. The more friends you have, the bigger your brain has to be, because it's a really uniquely complicated operation to perceive the intentions and the motivations and the emotions of this large group of people. It becomes exponentially more complex as you add more people, because you have to take into account not just what each individual person thinks but then what each individual person thinks about each other.

What I'm describing is basically the "social brain hypothesis," though I would call it a theory. It's an explanation for why we're so smart, and it says that we are so smart because we are social. Traditionally, it was believed to be the other way: We are social because we have such a great brain. But this hypothesis is the other way around. We were forced to become social because of all this collective protection, and that is so complicated to handle for the brain that we had to become smarter, and we have to grow these larger and larger and larger brains. Eventually, you hit the point when you're a human.

NL: Are there other theories?

NK: So far, I've talked about this gradual progression, but there is a second answer. I think there is also something categorically different about humans, and that is language. It's not to say that Homo sapiens is necessarily the only species that has ever spoken any language — there's some debate about that. But I do think there's something categorical about language in this transition between animal communication and human communication.

That's the fact that our language is infinitely generative. There is no equivalent, as far as we know, in the animal kingdom of an infinitely generative system of communication. It's passed from human to human, like this cognitive virus, and there must have been a moment when this passage has become stable — when it took off, essentially. We have this natural tendency to create a language and pass it on.

NL: Do you see that as an extension of humans' theory of mind — being able to acknowledge and understand others' viewpoints?

NK: Absolutely, yes, I would agree with that. I think that the reason why we developed this language is fundamentally social. We wouldn't have developed it if we were solitary creatures.

There's this idea that language and the brain co-evolved together. You have to think of them as flowers and pollinators. It's not that flowers were caused by pollinators or pollinators were caused by the flowers; they both evolved together, mutually reinforcing each other, and I think the same is true for language in the human brain.

NL: You also raise this idea in the book that it was basically inevitable that humans — or some similar organism — would evolve on Earth. Why is that?

NK: When eukaryotes appear [in the history of life on Earth], I think that is this key moment in our history that sets in motion a trajectory that will eventually, like you said, almost predictably lead to the human species.

Why do I believe that? In this moment, what was created is this new type of organism, this "supercell" consisting of both bacteria and archaea that fused together. What this new cell is able to do that nobody else could do before is eat other organisms whole and steal energy away from them. It has a special membrane that it can bend and form vesicles inside, these bubbles in which it can contain its prey. And it has this powerhouse of the cell — mitochondria, the bacteria that entered this archaeal host.

That gives eukaryotes access to unprecedented quantities of energy and sets in motion this evolutionary arms race. They get greedy on this energy; they build up these massive, impressive, energetically expensive cells. But now these cells depend on a constant supply of prey, of somebody to eat. It will perish unless you keep adding more energy, and everybody else around you has the same problem. They need to eat and not be eaten. That sets in motion this evolution of even more complicated cells, of even more convoluted defense or offense, and then teeth and claws and shells.

As you get more complex, you become more vulnerable, too. Bacteria barely care about these mass extinctions; for them, an environmental cataclysm is easy to recover from. But as your organisms become more complex, they become really vulnerable. We started investing into more ways for these organisms to avoid danger, to be self-guided. Maybe to prevent their accidental death, give them a brain to make sure that it can tell where danger is, and so it can avoid that death.

Once you have a brain, well, you can't possibly include everything about that brain into the genetic instructions that you pass from generation to generation. The whole point of a brain is that it needs to learn for itself. Once you create that, this organism starts thinking for itself. It starts acquiring its own motivations that are not prescribed in genes. It starts developing its own thoughts, and that's how you eventually get to us.

We are a culmination of this trajectory. There wasn't anything special about our lineage, our line of evolution, compared to everything else. Eukaryotes compared to bacteria and archaea are special in precisely the same way as humans are special amongst all the creatures around us.

Editor's note: This interview has been lightly edited for length and clarity.

In 1943, a physicist and a biologist published a paper that confirmed one of the central pillars of Darwin's theory of evolution.

The paper, by Max Delbrück of Vanderbilt University and Salvador Luria of Indiana University, described a simple experiment, called the "fluctuation test," that showed that mutations arose spontaneously in bacteria, rather than emerging in response to "selection pressures."

The question had been debated since Darwin published his classic "On the Origin of Species" in 1859. Darwin proposed that natural variation occurs randomly in all creatures and environmental pressures then make some of those variations better or worse for certain organisms in their "struggle for existence." Over time, those traits become more common as the fittest organisms survive and multiply. In contrast, French naturalist Jean-Baptiste Lamarck proposed in the early 1800s that variation could be induced by environmental pressures.

When Delbrück and Luria did their experiments, Darwin's theory was thought to be correct for plants and animals, but some scientists believed that interactions between bacteriophages — viruses that attack bacteria — and their bacterial hosts could somehow induce bacterial resistance to the phages.

Delbrück came into the field by accident. The disaffected physicist had emigrated to the U.S. from Germany due to the hostility of the Nazi regime and became interested in the idea of modeling genetics using ideas derived from quantum mechanics and atomic theory.

While researchering in California, he met a researcher who was studying a newly characterized bacterium called Escherichia coli, which had been cultured from Los Angeles sewage. The researcher had identified a phage that preyed on the E. coli. Delbrück was blown away by how easy it was to identify and count individual phage particles under a microscope.

"You could put them on a plate with a lawn of bacteria, and the next morning every virus particle would have eaten a macroscopic 1 mm [0.04 inch] hole in the lawn," Delbrück recounted in an oral history taken in the 1970s. "This seemed to me just beyond my wildest dreams of doing simple experiments on something like atoms in biology."

In December 1940, at Cold Spring Harbor Laboratory in New York, Delbrück met Luria, an Italian-Jewish doctor. Like Delbrück, Luria had fled the Nazis, and like Delbrück, he had been bored with his chosen specialty.

Luria had seen some early work on phages and had also become enamored with the idea of using phages to investigate genes as if they were a collection of atoms. At the time, people understood the idea of genes but had little understanding of what they were made of.

About nine months after they met, the duo decided to test whether phages could induce resistance in E. coli. They were stuck on how to proceed, until Luria chatted with a colleague who was playing the slots. He realized statistics could be used to distinguish between random mutations and ones induced by the phages — in other words, to determine the direction of the cause and effect.

They filled a bunch of tubes with E. coli and then exposed the bacteria to phages and serially cultured them on plates. If mutations were acquired, they reasoned, all of the plates would develop E. coli with resistance mutations at roughly the same proportions, and only after the phage was introduced to the plates. By contrast, if mutations arose randomly, there would be more variation in the number of resistant bacteria between cultures; some would be "jackpot plates" with many more resistant E. coli because they happened to evolve resistance genes early in culture growth, as opposed to later on.

This became known as the "fluctuation test," and the duo published their findings confirming that mutations arise randomly in bacteria in 1943.

That same year, they began collaborating with Alfred Hershey, a microbial chemist then at Washington University in St. Louis. The trio would go on to show that phages contained more than one gene and that the viruses could swap genetic information with each other within the same bacteria, known as genetic recombination. Later, Hershey and collaborator Martha Chase showed that DNA was the carrier of that genetic information. Hershey, Luria and Delbrück would earn the 1969 Nobel Prize in physiology or medicine for their contributions to genetics.

Interestingly, while their work cemented the Darwinian hypothesis that natural selection acts upon random variation, some newer research suggests that not all mutations are completely random. Mutation rates in "essential genes" occur at lower rates than in more incidental ones, at least in certain plants. And recent research suggests that if the team had chosen a different bacterium and phage system to study — such as one that used the bacterial immune system CRISPR to fight off phages — the statistical results would not have been so clear-cut.

When a caterpillar hatches from its egg, it spends the first few weeks of its life eating as much as it physically can. Then, it hangs itself upside down from a leaf or stem and sheds its outer skin to reveal its chrysalis. Inside, the caterpillar's body breaks down, and specialized cells called imaginal discs begin to form the framework of the butterfly that will emerge. Within weeks, it will be ready to mate and start the process all over again.

The process of metamorphosis is so strange, it almost seems like science fiction. So how did such a peculiar life cycle evolve in the first place?

The answer traces back about 480 million years ago, to the very first insects on Earth. These bugs didn't undergo major metamorphic changes throughout their lives, fossil evidence suggests; they simply emerged from their eggs as smaller versions of their adult selves. As they aged, they molted their skin to grow larger and larger. Today, there are still some insects that don't undergo metamorphosis, such as silverfish (Lepisma saccharinum) and jumping bristletails (in the order Archaeognatha).

But according to James Truman, a biologist and professor emeritus at the University of Washington, something changed about 400 million years ago. Small genetic mutations caused the adult and juvenile phases of insects to look different — a phenomenon called incomplete metamorphosis. Rather than hatching as tiny versions of their adult selves, insects that undergo incomplete metamorphosis — called hemimetabolous insects — start their lives in what's called the nymph phase.

Nymphs still roughly resemble their adult relatives, but they also have little pads where wings will grow. Each time the nymph molts, the wing pads develop further, until their final molt reveals functional adult wings. Those wings are what made incomplete metamorphosis such a big evolutionary step forward for insects — wings are so delicate that it would be difficult to hatch with fully functional wings, so it was easier for wings to develop with the insects throughout their lives.

After roughly another 50 million years, Truman said, more genetic mutations changed the early life stages of insects even further. These genetic shifts created holometabolous insects, which are insects that undergo complete metamorphosis. Rather than hatching out of their eggs as nymphs, these insects started to emerge as larvae — worm-like creatures that look nothing like their parents.

"The identity of the parents is [in] no way reflected in the identity of the young. There's just no resemblance at all," Truman told Live Science. "The [Latin] term for 'larva' means 'mask,' and indeed, the larval stage masks the adult stage."

Evolutionary benefits

Today, there are about 5.5 million insect species on Earth, and more than 80% of them undergo complete metamorphosis. Metamorphosis has likely been such a success because it provides insects with many evolutionary advantages, the first of which was flight. Hemimetabolous insects were the first animals to develop functional wings, and they took to the skies far before any vertebrates did.

"For 100 million years, the insects had the air as their playground," Truman said. "It's this ability that really allowed insects to take over."

Complete metamorphosis has even more advantages. Because the larval and adult life stages are so different, juveniles and adults can specialize in different things; generally, larvae spend most of their time eating, whereas adult insects are more concerned with reproducing. In some cases, the adults of some species, such as luna moths (Actias luna), don't even have functional mouths; after metamorphosis, they spend the rest of their short lives finding a mate and never eat again.

Metamorphosis also brings benefits related to resource competition, Truman said, because adults and larvae can eat entirely different diets. In many species, larvae often feed on short-lasting resources, such as carcasses and worms, whereas adults feed on longer-lasting resources, such as nectar. This means the larvae and young aren't competing for the same food, so greater numbers of each age group can survive.

Metamorphosis mysteries

While the evolutionary advantages of complete metamorphosis are clear, the details of how this complex process first evolved remain murky.

"There are two main schools," Xavier Bellés Ros, an ad honorem researcher at the Spanish National Research Council, told Live Science in an email.

One idea, supported by Bellés Ros, proposes that complete metamorphosis evolved as the nymph stage split into the larval and pupal phases. The opposing camp, supported by researchers including Truman, argues that the larval stage originated from an embryonic phase known as the pronymph, the brief phase when an insect first begins to emerge from its egg.

Scientists do know some of the key genes that control the larval, pupal and adult stages of insects with complete metamorphosis. "Each stage seems to be controlled by a master regulatory gene," Truman said. What remains unclear is how those same genes function in simpler insects that develop without such drastic transformations.

Still, researchers say the enduring mysteries of metamorphosis are part of its appeal.

"After 30 years of working with it (and I'm still working), I've only unraveled a few mysteries," Bellés Ros said. "There's still a lot of work to be done, work that should prove fascinating for future generations of entomologists."

Evolution quiz: Can you naturally select the correct answers?

A fatal genetic incompatibility between Neanderthals and modern humans may have hastened the extinction of our ancient cousins, new research suggests.

Researchers found that different versions of a gene tied to red blood cell function may have caused Neanderthal-human hybrid women to miscarry their fetuses.

When Neanderthals and early modern humans met in Eurasia around 45,000 years ago, "they exchanged genes — and may also have passed on hidden reproductive risks that shaped the fate of both lineages," Patrick Eppenberger, co-head of the Evolutionary Pathophysiology and Mummy Studies Group at the Institute of Evolutionary Medicine in Zurich, and colleagues wrote in a study posted to the preprint database bioRxiv Sept. 29. (It has not been peer-reviewed yet.)

The researchers focused on the PIEZO1 gene, which affects red blood cells and is found in both modern humans (Homo sapiens) and Neanderthals. They discovered that the PIEZO1 gene differed between Neanderthals and modern humans.

The Neanderthal variant, which is similar to the variant found in other great apes, allowed the hemoglobin in red blood cells to cling more tightly to oxygen molecules, while the novel H. sapiens variant allowed oxygen to be passed more efficiently into surrounding tissue. Neanderthals may have maintained the original variant because it was beneficial for surviving extreme cold and periods of starvation, the researchers suggested.

But when maternal blood has abnormally high amounts of oxygen bound to hemoglobin, that means low levels of oxygen are passed on to a fetus through the placenta. This can cause hypoxia (oxygen deficiency) or restricted growth of the fetus or miscarriage.

But because of the way the PIEZO1 gene variants are inherited, the incompatibility would arise only when a hybrid Neanderthal-human mother mated with a modern-human father or with a hybrid Neanderthal-human father.

"Many of their offspring would fail to survive," the researchers wrote. This, in turn, would mean Neanderthal women would pass on less of their mitochondrial DNA, which is carried in the egg and passes from mother to child, the authors wrote in the study. Over the course of several generations of mating between Neanderthals and humans, this may have significantly compromised hybrid Neanderthals' ability to have kids, the researchers noted.

"The PIEZO1 incompatibility may have accelerated the demise of the Neanderthals by gradually eroding their reproductive capacity whenever the two groups interacted," they wrote.

April Nowell, a Paleolithic archaeologist at the University of Victoria who was not involved in the study, told Live Science in an email that the study adds a much-needed piece of the puzzle to the question of Neanderthal extinction — namely, maternal-fetal incompatibility in oxygen transfer during pregnancy.

"It's super interesting that an allele [gene variant] that may have saved Neanderthals in the past was their ultimate undoing when they began to interbreed with modern humans," Nowell said.

John Hawks, a biological anthropologist at the University of Wisconsin who was not involved in the study, told Live Science in an email that the maternal-fetal incompatibility of PIEZO1 was intriguing and analogous to other genetic blood conditions, such as Rh factor incompatibility in modern humans.

"This is one of many potential cases where the gene variant coming from an archaic population had some bad effects, causing it to decline in frequency over time in modern people," Hawks said.

But PIEZO1 is not the final answer to the question of Neanderthal extinction.

"There are no single-gene explanations for what was a long and complicated interaction across many archaic human groups, as modern humans entered the places where they lived and interacted with them," Hawks said.

Eppenberger and colleagues emphasized in their study that the effect of interbreeding between Neanderthals and modern humans was likely drawn out and subtle — "more akin to rust weakening a structure than a single catastrophic blow" — and that more research along these lines is needed.

"It is worth pondering how many other loci in the genome might have similarly given rise to hybrid incompatibilities," they wrote.

Humans and our ancestors have been exposed to lead for up to 2 million years, researchers have discovered — overturning the belief that lead poisoning is a relatively modern phenomenon.

What's more, widespread exposure to the toxic metal may have affected the evolution of our species' communication abilities. This would have given Homo sapiens a key advantage over our cousins, the Neanderthals, who were more susceptible to lead's toxic effects, the study suggests.

"Evolution often advances through adversity. Stressors like drought, food/water scarcity, or toxins don’t just threaten survival; they can also drive the selection of traits that make species more adaptable," said study co-author Renaud Joannes-Boyau, professor and head of the Geoarchaeology and Archaeometry Research Group (GARG) at Southern Cross University in Australia. "Lead exposure may be one such hidden force in our evolutionary history," he told Live Science in an email.

However, experts noted the study has limitations, as it estimates lead exposure by measuring lead levels in the teeth of many human and related species.

"It is not obvious whether the amounts of lead detected in the ancient teeth actually were enough to have an impact on health," said John Hawks, an anthropologist at the University of Wisconsin–Madison who was not involved in the study. "Measurements of chemicals in tooth enamel have become incredibly sensitive. It may be that they are detecting such small levels that made no difference," he told Live Science in an email.

Lead is toxic, and high levels of the metal in the body can cause multiple health issues, particularly in children, according to the Cleveland Clinic. It can damage the nervous system, particularly the brain, and other organs and cause severe learning and behavioral problems.

Nowadays, most lead poisoning is the result of human activities and products, such as paint, mining and smelting, according to the Environmental Protection Agency.

But lead also occurs naturally and can be "found throughout Earth's crust, practically in all rocks, soils, sediments, and waterways at various concentrations," the researchers wrote in the study, published Oct. 15 in the journal Science Advances.

"Animals, including humans, can be exposed to substantial levels of lead by drinking contaminated water, ingesting contaminated food, or inhaling polluted air (e.g., smoke from fire and dust storms)," the team added.

Contaminated teeth

In the new study, researchers looked at 51 fossilized teeth dating to between 1.8 million and 100,000 years ago from a variety of species, including Homo sapiens and our closest relatives, Neanderthals, as well as relatives such as Australopithecus africanus and Paranthropus robustus, and the extinct ape Gigantopithecus blacki.

"Teeth form incrementally during childhood, so they preserve a detailed record of early-life exposure, the period when the brain is most vulnerable," Joannes-Boyau said.

The analysis revealed that 73% of the samples showed "clear signals of episodic lead exposure," according to the study. This shows that lead exposure is not a modern phenomenon but has instead impacted human ancestors and relatives for millions of years.

Exposure levels varied, with some lower than modern industrial levels and some higher, but were generally enough to cause impacts in a young, developing brain, Joannes-Boyau noted.

Growing minibrains

To investigate how lead exposure may have shaped the development of Homo sapiens, the researchers created two different versions of brain "organoids" — miniature, simplified models of full-size human brains.

Each organoid version featured different variants of the gene NOVA1. Modern humans have a unique version of this gene that's important for brain development and has also been linked to language skills. Neanderthals and other human relatives have a slightly different version of this gene.

When exposed to lead, the organoid with the modern NOVA1 gene showed greater resistance to the toxic metal than the organoid with the archaic variant. In particular, the Homo sapiens NOVA1 version seemed to help maintain the activity of a gene called FOXP2, which plays a crucial role in the development of human speech and language.

"When the brain is exposed to stressors like lead, the modern NOVA1 variant helps maintain stable FOXP2 function, protecting pathways linked to speech, communication, and cognition," Joannes-Boyau said.

In contrast, in the brain organoid with the archaic variant of NOVA1, FOXP2 expression was altered when exposed to lead.

Study co-author Alysson Muotri, director of the University of California San Diego Sanford Stem Cell Education and Integrated Space Stem Cell Orbital Research Center, noted that this could have given humans an evolutionary advantage.

"Most likely, the modern variant NOVA1 emerged after lead exposure, but was rapidly selected as it gave us an advantage over other hominids," such as Neanderthals, he told Live Science in an email. "This is another example of evolution in action."

But the data on the NOVA1 gene is open to interpretation, Debbie Guatelli-Steinberg, professor in the Department of Anthropology at The Ohio State University, told Live Science in an email.

"The authors argue that the human NOVA1 variant gave humans a competitive advantage over other hominins, including Neanderthals," Guatelli-Steinberg said. "This idea is speculative."

Hawks said the study raises questions about how these ancient human ancestors and relatives were exposed to lead. "Did they take in lead when they used sparkly minerals as pigments?" Hawks said." Did they absorb it in pollutants from burning? Or from the plant foods they ate? These are open questions. I'd love to know the answers."

Neanderthal quiz: How much do you know about our closest relatives?

If you love figs, you may have heard some unsettling lore about them: that every fig hides a wasp, because these insects need to crawl inside and die in order for the fruit to grow. But are there really wasps in the figs we eat, or is this just a myth?

The answer is somewhere in between. Wasps do play an essential role in the life cycle of many types of fig trees, but most figs from the supermarket are likely bug-free.

Fig wasps are a group of hundreds of species of small insects that spend much of their life inside figs. They're about the size of a fruit fly, and they're not the same type of wasps that sting humans. Figs and fig wasps have evolved alongside each other for millions of years, leading to a special relationship called mutualism, or a link between two species that benefits both of them.

"Fig trees and fig wasps are a great example of a mutualism," Charlotte Jandér, a plant ecology and evolution researcher at Uppsala University in Sweden, told Live Science in an email. "Other examples of mutualisms include trees and the mycorrhizal fungi that help the trees take up nutrients, animals and their gut microbes, and flowering plants and pollinators in general."

In the case of figs and fig wasps, the fruit gets pollinated and the wasp is able to reproduce, leading to a mutualism. But this relationship is rather complex.

What we think of as the fig "fruit" is actually a hollow structure called a syconium filled with tiny flowers. Generally, when a female fig wasp crawls inside a synconium from a female fig tree, she spreads pollen, which the plant needs in order to produce seeds and ripen. The hole that the wasp crawls in is very small, and she may lose her wings and antenna in the process and can even die inside the fig.

So, it's possible that some types of figs may have dead fig wasps inside them.

But that doesn't necessarily mean the figs we eat have wasps inside. Not all types of figs require pollination in order to ripen. Humans eat the fig species Ficus carica, which has several cultivars that are parthenocarpic, meaning they can produce ripe fruit without pollination — and therefore, without fig wasps.

"Most figs we eat in the US have no wasps inside them," Carlos Machado, a biology professor at the University of Maryland, told Live Science in an email.

Mission figs and Brown Turkey figs are two commonly-sold fig cultivars that don't require wasp pollination to ripen and produce seeds, Jandér said. This doesn't apply to all figs that humans eat, though; Smyrna figs, Calimyrna figs, and wild figs around the Mediterranean all rely on wasps for pollination.

"Most wild figs do require pollination to produce ripe fruit," Machado explained. That means these types of figs could have a tiny wasp inside them — but it's still not a guarantee.

Related: How do plants with seedless fruit reproduce?

Just because a wasp was once in the fig, doesn't mean it's still in there by the time the fig is eaten. The synconia of Ficus carcia have a large enough opening that the fig wasp is sometimes able to leave the structure after entering. If the wasp does die inside, her body generally gets squished and decomposes from the process of the fig maturing, Jandér said.

"Even if there were remnants of the original pollinator there you probably would not see them," Jandér explained. Any crunchy texture is more likely from the plant's seeds, not wasp remains.

The fig wasp life cycle

Although wasps sometimes die inside figs, these fruits are actually an essential part of their reproduction cycle. Just as most types of figs need wasp pollination to make new fruit, fig wasps couldn't reproduce without the help of fig trees.

When a female wasp crawls into a fig syconium from a female tree — the type of figs we eat — she only pollinates it, because the flowers inside are too long for her to lay her eggs on. But if she ventures into a synconium from a male tree — which are called caprifigs and generally not eaten by humans — she'll start to lay her eggs.

There, the eggs hatch and develop from larvae into young wasps, which mate while still inside the fruit. Generally, the male wasps die inside the caprifig after mating, though they do help chew a tunnel that allows the female wasps to escape, sometimes even offering themselves as bait for the predatory ants that may be waiting outside. Eventually, the fertilized female wasps burst out in search of a new fig to lay their eggs in, carrying pollen from the old caprifig with them.

There are over 850 species of fig trees, and each one can only be pollinated by a specific species of fig wasp, Jandér said. The relationship between these plants and animals evolved millions of years ago, and both Machado and Jandér pointed to its importance. As a keystone species — an organism that many other plants or animals in the ecosystem rely on to survive — fig trees and their relationship with wasps continue to be of great interest to researchers.

"There are other plant-pollinator mutualisms in nature, but the fig-fig wasp mutualism is possibly the most diverse and most consequential of all," Machado said.

The first hint of a brain developed on Earth around 600 million years ago, and now, some version of the organ can be found in nearly every animal in the world.

Humans have the largest brain size relative to body size of any species, as well as an impressive ability to accumulate knowledge over time. And yet, the human brain is remarkably similar to the brains of other animals; they have the same electrical and chemical signaling system.

The vast evolutionary history of the brain, from the very first nerve cells to the modern human cerebrum, is covered in a sweeping two-part BBC series presented by Jim Al-Khalili, a renowned science communicator and theoretical physicist at the University of Surrey in the U.K.

In "Horizon: Secrets of the Brain," Al-Khalili surveys the animals and fossils shaping our understanding of how the brain evolved over millions of years, and the scientists unraveling each piece of the puzzle. Live Science picked Al-Khalili's brain about the show, how the human brain evolved and what the past 600 million years of evolution means for us today.

"Secrets of the Brain" will be available in the U.K. from Sept. 29 on BBC Two. For British residents abroad with with a valid TV license will need to use a VPN — or Virtual Private Network — to tune into iPlayer as usual. Our colleagues at TechRadar recommend NordVPN.

Sophie Berdugo: We normally think of you as being in the realm of theoretical physics — what led you to this show about the brain?

Jim Al-Khalili: In part because I do "The Life Scientific" on BBC Radio 4, I'm quite comfortable saying, "This is an area I don't work in; it's not my specialist area, but I want to talk to someone who does know what they're talking about." So I thought this was a good opportunity to learn about something.

After all, the human brain is the most complex system in the entire universe, and so we don't understand how it works entirely. We're starting to learn about human consciousness and so on, but one of the things that's missing is that I didn't understand how it fitted into evolutionary history.

We know humans are smart and smarter than any other animal, and usually it's [the explanation is] "Oh, that's because we developed language, or because we've got opposable thumbs." But I knew it had to be more than that. And what I found fascinating was digging into this long story of how the brain — not necessarily the human brain — but how the brain evolved and grew over hundreds of millions of years, rather than just 1 or 2 millions of years.

SB: Were there any questions that you had going into the docuseries that you ultimately discovered science doesn't actually know the answer to yet?

JAK: Well, certainly the ideas of what separates humans from our primate cousins. The usual argument is that we developed language or that we have metacognition and theory of mind. [Metacognition refers to an awareness and understanding of one's own thought processes, and theory of mind refers to an ability to understand that other individuals have their own perspectives and mental states.]

But, of course, other primates do have that as well, to a lesser extent. This idea of metacognition, [and] being able to imagine yourself in another person's shoes, other primates have that as well.

Then there's the development of language. But one of the surprising things I learnt on the program was that, while other primates like gorillas don't have language, they develop syntax. The idea that syntax doesn't necessarily relate to language and words and grammar, but more broadly, it means putting things in some logical order. How gorillas reach for and grab some nettles and how they fold them up and roll them in a ball and eat them and so on, that also is a form of syntax. So the idea that syntax evolved before language and that that was the important step left me thinking, "So what is it that separates us?"

Then the final part of the program says it's because we are social animals; the "social brain hypothesis" explains that we have such large brains because we have complex social systems and interactions with each other. But then other primates have that as well — bonobos and chimpanzees and so on.

So I was left with this question that all the things that we thought should separate us from other primates — language, metacognition, social brains — all exist in the other primates. We have accelerated away from them in a way that is, you know, it's not just a little bit — we are way, way more complex in terms of our thinking and thoughts than other primates. So that's something that I still feel, personally, I haven't got a clear answer to.

SB: I was also left thinking that at the end of the second episode — that we have so many similarities with our closest living relatives and also species that are distantly related to us, like marine mammals. But how is it that the evolution of our brain ultimately resulted in us being able to have this conversation now and think about how other animals think?

JAK: My view is that there's some sort of bootstrap mechanism going on so that the more complex the world around us is, and the complexity of our actions and interactions become; the more there's a need for the brain to process the data, to analyze, to calculate and so on. So there's nothing specifically different about the human brain from other higher mammals', in terms of intelligence. It's just a matter of degree.

We live in complex societies now, but I wouldn't say that we are more intelligent than a human five, six, seven thousand years ago. Evolution doesn't work that fast. And they didn't have books and electronics and so on, and they were just as intelligent as us.

So whatever separates humans from other higher mammals, whether it's primates or dolphins or whatever, it's not because we created a complex world. It's something else. I'm sure it's not something banally simple like opposable thumbs. Yeah, I'm sure that helps, but that can't be the answer.

SB: And in the show, you explore hand adaptations and changes in social environments as separate events, when they're ultimately all evolutionarily linked.

JAK: Oh absolutely, yeah, and I think that's one of the shortcomings of having to tell a story like this. You have to break it down into steps.

It's all very well talking about early organisms in the sea before the Cambrian explosion and the eye developing before the brain. Great, that's quite neat. So there are certain sequential stories that one can tell, and then with the various extinction events that accelerated evolution, just for survival purposes.

But you're right; certainly once you get to the last, say, 10 million years and primates are evolving, lots of different factors are competing with each other and bootstrapping and interconnected. But to tell the story, you have to break it down into steps, and sometimes that makes it sound like, "Well, first we had to develop this and then once we got that sorted, then we developed something else," and so on.

SB: Was there a period within the 600 million years covered in the program that you would love to spend a day in, to see exactly how the organisms alive at the time were behaving and surviving, and how that relates to brain evolution?

JAK: What I found very fascinating was the Permian mass extinction, sometimes called the "Great Dying," where almost all life disappeared. Volcanic eruptions, climate change, ocean acidification and all that stuff. But that 5% [of marine animals] did survive. [90% of life on Earth was killed.]

I did a piece to camera in the program where I said, "They could slither under the mud, find nooks and crannies." But it would be fascinating to see, what sort of environment was that 250 million years ago that wiped out 95% of all life, but 5% survived? Did they just get lucky? Did they just keep their heads down? Or did they have something different about them that the other 95% didn't have that they managed to survive?

They weren't just smarter, you know. They had to become smarter in order to survive, because the brain needed to evolve to cope with the new challenges. But I hadn't quite appreciated that the Permian mass extinction almost stopped life from continuing on Earth. So that's fascinating. Thankfully, some did survive.

SB: I think we can all be thankful that there were some who survived!

We worry about climate change now, but the climate change that happened after the Permian mass extinction was so much more extreme. How could any life possibly still carry on existing? I just find that fascinating.

SB: Absolutely, and that was something I wanted to ask you: How does learning about the evolution of the brain help us understand ourselves and the world today, especially in light of challenges like the climate crisis and the advent of artificial intelligence (AI), which you touched in the show?

JAK: Being able to appreciate the uniqueness of the human brain, or something about our brain that makes us uniquely human, I think is an important lesson.

Our relationships with each other, that we have these complex structures and societies — we have shared cultures and beliefs and memories and history and so on, which is something that is uniquely human. Something that if we develop AI … and I expect this will happen, it will one day be conscious. It will be sentient, self-aware, but it won't be human. Because it hasn't been along that journey that we've been through. You can't simulate or replicate that.

Nor would we feel we should. Why would you want to create artificial intelligence that's exactly like a human? Well, you've got humans to do whatever you want the AI to do. And if it becomes conscious and self-aware, then it should have just as many rights as a human; it's living and sentient, then it's not just a machine.

For people to appreciate just how special the brain is and how special humans are, [it] might give people pause for thoughts, given that we don't seem to have learned lessons about utilizing those aspects of what we say makes us human. We sometimes forget empathy, compassion and kindness. Those sorts of things make us human.

And you'd think with the current issues and challenges we face in the 21st century, it's a reminder of how long a journey, not humans, but our brain, the central mechanism, has had in reaching where it's at now. To somehow waste that would be quite tragic.

SB: I was really struck by the similarities the show highlighted between humans and other life on Earth — for instance, at the very start of the first episode, you talk about the zooplankton and how they have the same rod and cone cells in their eyes that we have today.

JAK: The axon and the neuron are things that evolved to serve a particular task. Light-sensitive receptors needed to send signals to motion cells to tell an early organism to move towards or away from the light. But those axons and neurons are what we have in our brains now, so clearly they evolved to create a certain job and clearly then became useful. And once they became more interconnected, their complexity served more and more different purposes.

So there is that, that the brain has in common. And of course we are using neural networks [computer systems inspired by the network structures of the brain] to develop artificial intelligence. So that trick is so useful that that's become the standard way of developing machine learning in AI, even though the AIs that we have today are still dumb. They may fool us into thinking that they're being smart and we're having a conversation with them, but I always say, "However clever you think ChatGPT is, it's not conscious, but your dog is conscious."

ChatGPT, if in the middle of a conversation, you then leave your laptop and go off on holiday for a week, ChatGPT isn't sitting there thinking, "Oh, I wonder where Jim's gone. I was having a great chat. I miss him." But your dog would miss you. So your dog may not be able to talk to you and appear as though it's as clever as you, but it has that special thing called consciousness which AI doesn't yet have.

Editor's note: This interview has been condensed and edited for clarity.

Chimpanzees, along with bonobos, are humans' closest living relatives. In fact, you may have heard that humans and chimps share 98.8% of their DNA.

But is this actually true? And what does "similar DNA" actually mean?

The truth is that the frequently cited 98.8% similarity between chimp (Pan troglodytes) and human (Homo sapiens) DNA overlooks key differences in the species' genomes, experts told Live Science.

Human and chimp DNA is made of four basic building blocks, or nucleotides: adenine (A), guanine (G), cytosine (C) and thymine (T). The genomes of both species can be thought of as a "string of the letters A, C, G and T … about 3 billion letters long," David Haussler, scientific director at the UC Santa Cruz Genomics Institute, told Live Science in an email.

When scientists compare human and chimp DNA, they identify the letter (nucleotide) sequence in both genomes and look for stretches of DNA where there is a lot of overlap between the two genomes. Then, they count the number of matching letters in these regions.

"It is like comparing one version of a very long novel to another, very slightly edited version," Haussler said.

Related: Are you genetically more similar to your mom or your dad?

Early research suggested that human and chimp genomes are more than 98% identical. "What it means is that for each part of the human genome where the chimp has a corresponding DNA sequence, on average 1 out of 100 nucleotides (single A, C, T or G bases) is different," explained Katie Pollard, director of the Gladstone Institute of Data Science and Biotechnology at the University of California, San Francisco.

For context, humans share about 99.9% of their DNA with each other, Haussler said.

But the 99% figure is misleading because it focuses on stretches of DNA where the human and chimp genomes can be directly aligned and ignores sections of the genomes that are difficult to compare, Tomas Marques-Bonet, head of the Comparative Genomics group at the Institute of Evolutionary Biology (CSIC/UPF) in Barcelona, Spain, told Live Science in an email.

Sections of human DNA without a clear counterpart in chimp DNA make up approximately 15% to 20% of the genome, Marques-Bonet said. For example, some bits of DNA are present in one species but missing in the other; these are known as "insertions and deletions." In the course of evolution from a common ancestor, some pieces of DNA in one species broke off and reattached elsewhere along the chromosome.

So, while earlier studies suggested a 98% to 99% similarity, comparisons that include harder-to-align regions push that difference closer to 5% to 10%, Marques-Bonet said. "And if we account for the regions still too complex to align properly with current technology, the true overall difference is likely to exceed 10%," he said.

In fact, a 2025 study found that human and chimpanzee genomes are approximately 15% different when compared directly and completely. But if this direct method is used, then there is even a lot of variability within species themselves — up to 9% among chimpanzees, the 2025 study found.

"Against this backdrop, the close genetic relationship between humans and chimpanzees has not changed," Martin Neukamm, a chemist at the Technical University of Munich who was not involved in the 2025 study, wrote in a translated article.

The differences between human and chimp genomes lie mostly in noncoding DNA, the segments that do not code for a specific protein and that make up about 98% of the genome, according to Pollard.

Differences in noncoding DNA have a big impact. While coding DNA contains the instructions for protein building, "regulatory regions" found in noncoding DNA control how, when and where these proteins are made, Marques-Bonet explained. They act like switches, controlling whether a gene is turned on or off.

That's why a small tweak in the genome, especially in these regulatory regions, can ripple out into large differences in traits. "A small change in the DNA can have big consequences for how that DNA is expressed," Haussler said, "and, in turn, changes in expression can lead to even bigger changes in phenotype — the scientific term for traits like hairy or not, large or small, etc."

So, while chimps and humans share the same genetic tool kit, how those tools are used makes a big difference. "Humans and chimps are made up of essentially the same building blocks (proteins), but these are used in somewhat different ways to make a human versus a chimp," Pollard said.

Most people imagine our early primate ancestors swinging through lush tropical forests. But new research shows that they were braving the cold.

As an ecologist who has studied chimpanzees and lemurs in the field in Uganda and Madagascar, I am fascinated by the environments that shaped our primate ancestors. These new findings overturn decades of assumptions about how — and where — our lineage began.

The question of our own evolution is of fundamental importance to understanding who we are. The same forces that shaped our ancestors also shape us, and will shape our future.

The climate has always been a major factor driving ecological and evolutionary change: which species survive, which adapt and which disappear. And as the planet warms, lessons from the past are more relevant than ever.

The cold truth

The new scientific study, by Jorge Avaria-Llautureo of the University of Reading and other researchers, maps the geographic origins of our primate ancestors and the historical climate at those locations. The results are surprising: rather than evolving in warm tropical environments as scientists previously thought, it seems early primates lived in cold and dry regions.

These environmental challenges are likely to have been crucial in pushing our ancestors to adapt, evolve and spread to other regions. It took millions of years before primates colonised the tropics, the study shows. Warmer global temperatures don't seem to have sped up the spread or evolution of primates into new species. However, rapid changes between dry and wet climates did drive evolutionary change.

Related: Our ancient primate ancestors mostly had twins — humans don't, for a good evolutionary reason

One of the earliest known primates was Teilhardina, a tiny tree dweller weighing just 28 grams — similar to the smallest primate alive today, Madame Berthae's mouse lemur. Being so small, Teilhardina had to have a high-calorie diet of fruit, gum and insects.

Fossils suggest Teilhardina differed from other mammals of the time as it had fingernails rather than claws, which helped it grasp branches and handle food — a key characteristic of primates to this day. Teilhardina appeared around 56 million years ago (about 10 million years after the extinction of the dinosaurs) and species dispersed rapidly from their origin in North America across Europe and China.

It is easy to see why scientists had assumed primates evolved in warm and wet climates. Most primates today live in the tropics, and most primate fossils have been unearthed there too.

But when the scientists behind the new study used fossil spore and pollen data from early primate fossil environs to predict the climate, they discovered that the locations were not tropical at the time. Primates actually originated in North America (again, going against what scientists had once believed, partly as there are no primates in North America today).

Some primates even colonised Arctic regions. These early primates may have survived seasonally cold temperatures and a consequent lack of food by living much like species of mouse lemur and dwarf lemur do today: by slowing down their metabolism and even hibernating.

Challenging and changeable conditions are likely to have favoured primates that moved around a lot in search of food and better habitat. The primate species that are with us today are descended from these highly mobile ancestors. Those less able to move didn't leave any descendants alive today.

From past to future

The study demonstrates the value of studying extinct animals and the environment they lived in. If we are to conserve primate species today, we need to know how they are threatened and how they will react to those threats. Understanding the evolutionary response to climate change is crucial to conserving the world's primates, and other species beyond.

When their habitats are lost, often through deforestation, primates are prevented from moving freely. With smaller populations, restricted to smaller and less diverse areas, today's primates lack the genetic diversity to adapt to changing environments.

But we need more than knowledge and understanding to save the world's primate species, we need political action and individual behaviour change, to tackle bushmeat consumption — the main reason primates are hunted by humans — and reverse habitat loss and climate change. Otherwise, all primates are at risk of extinction, ourselves included.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.