A single climate-change-fueled cyclone killed 7% of Tapanuli orangutans ‪—‬ the world's rarest great apes ‪—‬ in just four days last year, new research reveals.

The study shows that "climate change-driven weather poses an immediate, catastrophic threat to the world's rarest great ape," the researchers wrote.

Tapanuli orangutans (Pongo tapanuliensis) live in the Batang Toru forest in northern Sumatra, Indonesia. Pushed to the brink of extinction by habitat destruction, the entire species consisted of 767 individuals in 2019, of which 581 lived in the forest's west block.

Then, Cyclone Senyar arrived.

Across four days in November 2025, the rare and damaging tropical cyclone caused extreme rainfall and catastrophic landslides across this west block forest region, killing approximately 58 Tapanuli orangutans. These individuals died from drowning, suffocation under landslides, or impacts from collapsing trees, according to the study, which was published June 10 in the journal Current Biology.

The loss equates to 11% of the west block orangutans and roughly 7% of the whole species.

"It is extremely worrying for the future of this ape," study co-author Serge Wich, a professor of primate biology at Liverpool John Moores University in the U.K., told The Guardian.

World's rarest great apes

Tapanuli orangutans were classified as a new species, distinct from their Bornean (P. pygmaeus) and Sumatran (P. abelii) orangutan cousins, in 2017, making them the most recently identified, and rarest, species of great ape.

Orangutans are especially vulnerable to environmental shocks because of their slow rate of reproduction; they have roughly six- to nine-year gaps between each baby. They are also heavily dependent on tree cover to survive.

In the new analysis, researchers combined pre- and post-cyclone satellite imagery with orangutan population density estimates to evaluate the impact of the flooding and landslides on the apes.

Before the cyclone, 99.3% of the Batang Toru forest west block was forested. Then, after the storm's arrival, 21.8 inches (556 millimeters) of rain fell over four days, leading to landslides across 20,517 acres (8,303 hectares) of Tapanuli orangutan habitat. The researchers identified over 50,000 "scars" from this landslide-induced habitat destruction in the forest landscape.

This habitat loss was catastrophic for the orangutans. "Given the high density (>50,000) of sudden, steppe-slope landslides causing canopy collapse and debris flow into drainage networks, and the limited opportunity for arboreal [via trees] escape during rapid slope failure, we consider mortalities by burial, trauma, or subsequent drowning to be likely," the authors wrote in the study.

The long-term effects of topsoil destruction on the food supply will also harm the remaining orangutans, the authors wrote. With topsoil containing dense networks of plant-feeding fungi, it will take time for the fruit and leaves the orangutans rely on to return.

World Weather Attribution, a research group that studies extreme weather events, found that Cyclone Senyar was intensified by a combination of human-induced climate change, an ocean oscillation called the negative Indian Ocean Dipole, and La Niña, the cooler phase of the El Niño-Southern Oscillation climate cycle.

Climate change is projected to increase the frequency and intensity of heavy rainfall worldwide, including in Indonesia. And now that El Niño is officially here, the climate event will likely make the Pacific hurricane season stronger. This El Niño period is forecast to "rank among the largest El Niño events in the historical record going back to 1950," NOAA officials wrote in a June 11 update.

"El Niño conditions will pour fuel on the fire of a warming world," U.N. Secretary-General António Guterres said in a June 2 video statement. "The world must treat it as the urgent climate warning it is."

Wild chimpanzees in Uganda are fighting a rare "civil war," which seems to have begun when a huge community divided, leading to sustained and deadly conflict between animals that had previously been allies and friends.

Conflicts between different groups of chimpanzees (Pan troglodytes) are relatively common as they compete for key resources, like fruit trees, water supplies and trees that provide suitable nesting material. However, conflicts within previously unified communities are much rarer.

About 50 years ago, primatologist Jane Goodall reported a suspected fission event in a chimpanzee community in Gombe, Tanzania, in which a larger group split into factions; males of one new faction killed an adult female and all six males in the other group over four years. But observations of the behavior were limited, and it was considered an anomaly.

Now, Aaron Sandel, an anthropologist at the University of Texas at Austin, and his colleagues have described another, much bigger, lethal conflict between the members of the Ngogo chimpanzee community in Kibale National Park, Uganda. The work was published Thursday (April 9) in the journal Science.

The chimpanzees there have been studied for about 30 years, providing extensive data on their interrelatedness and behavior. Although they were all part of a big group, they tended to form temporary "parties" that changed throughout the day as individuals moved about their territory.

But between 1998 and 2014, some of these groups became more regular cliques, such as three adult males that were consistently together.

Researchers revealed that from about 2015, the huge Ngogo community — which then numbered about 200 chimps — ruptured into two distinct clusters that lived and reproduced separately. The core of one of the groups was the clique of three adult males.

At this stage, there were still ties between many individuals in the two groups, and they still cooperated and bonded, but by 2018, the last social ties disintegrated and aggression grew during border patrols of their separate territories.

"After they split into two groups, chimps from one group began attacking and killing those from the other group and that turned into an escalated period of lethal violence," Sandel told Live Science.

Deadly raids

Raids resulted in multiple killings of adult males and, beginning in 2021, the researchers also regularly observed infanticide. The true death toll of what the researchers term a civil war is likely to have been higher, because many other individuals disappeared without clear cause, Sandel added.

"I'm sort of nervous about calling it civil war," he said. "Civil war means something very specific when we talk about humans, and chimps don't have nations and things like that, but there's an important conceptual point when thinking about war against strangers versus civil war. These are chimps that know each other."

James Brooks, an evolutionary anthropologist at the German Primate Center in Göttingen who wasn't involved in the study, told Live Science that he agrees this conflict isn't the same as a human civil war, but said the term helps people to understand the general idea.

It's still not clear why the division in the community led to such aggressive conflict, but Sandel suggested various factors that could have destabilized social ties. These include the unusually large group size, competition over food and reproduction, the deaths of five adult males and one adult female in 2014, a change from one alpha male to another in 2015 and a respiratory epidemic that killed 25 chimpanzees in 2017.

Brooks suggested the group's size could have been a factor. "Maybe they were no longer facing such an abundance of resources and became too large a group to maintain cohesion," he said.

Zoologist Liran Samuni, also at the German Primate Center and co-director of the Taï Chimpanzee Project, who wasn't part of this study, said that the Ngogo community is one of the more aggressive ones that researchers know. "The Kibale National Park is considered quite a rich environment, with the chimps living at high densities and for long life spans. But even before this split, this was one of the chimpanzee communities that was most violent in terms of encroaching on neighbors," she told Live Science.

Between 1998 and 2008, the Ngogo chimps killed at least 21 chimpanzees from neighboring groups, and expanded into their territory, resulting in population growth.

The civil war is still ongoing, Sandel said. The research paper covers data collected up to 2024, but he says further attacks have happened in 2025 and 2026.

He said the work shows that even without ethnicity, religion or political ideologies, social networks can divide, leading to collective violence.

Given that chimps are one of humans' closest two relatives, the finding reiterates how group divisions can present a danger to human societies, Brooks said, but he adds that it doesn't mean conflict is biologically determined. He pointed to bonobos (Pan paniscus) — our other closest relatives — which form stable and distinct groups. They are also aggressive, but unlike chimpanzees, they don't engage in such lethal group conflicts but form tolerant, cooperative associations, so such conflicts aren't evolutionarily determined.

"Our evolutionary past does not determine our future," he said.

How much do you know about primates like chimpanzees? Test your knowledge with our primates quiz!

"Hippie" bonobos are just as aggressive as "warrior" chimpanzees, according to a new study. However, the findings also reveal some key details about which sex is instigating the aggression. Bonobo females were more likely to attack males, while male chimps were more aggressive towards females. Female-on-female aggression in both species, they found, was significantly lower.

The work was in captive animals in zoos, so it may not apply to wild bonobos and chimps ‪—‬ but it adds to a growing body of recent research suggesting bonobos aren't as peace-loving as once described.

"I don't think that they're as peaceful as previously thought," study co-author Nicky Staes, a researcher at the Antwerp Zoo Centre for Research and Conservation in Belgium, told Live Science.

Bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) are our closest living relatives. The two species are geographically separated by the Congo River in Africa and evolved from a common ancestor between 1.5 million and 2 million years ago.

Although they are closely related, chimps and bonobos look and behave differently. Bonobos are smaller, with a more slender build, and the differences between the sexes are less pronounced than in chimpanzees. Bonobo communities are led by female coalitions; this is seen as a strategy for females to gain power over the larger males. Chimpanzees, on the other hand, have males at the top of their hierarchies.

Aggression is an important social behavior in apes, as it helps them protect territory, identify mates, assert dominance and secure resources. This aggression can range from vocal expressions of anger to physical attacks.

In the past, bonobos were seen as chimps' peace-loving "hippie" cousins because they were thought to be less warlike and more likely to use sex to resolve conflict. But recent studies have started to upend that idea. In one recently reported incident, five wild female bonobos viciously attacked a male in the Democratic Republic of Congo.

In the new research, published Wednesday (March 11) in the journal Science Advances, researchers show that bonobos are just as aggressive as chimps — but they target males and females differently.

Little difference in overall aggression

The team analyzed how 22 zoo-based groups of chimps and bonobos in Europe interacted. A researcher sat in front of the enclosure and noted each act of aggression, which ranged from shouting to physical violence, that occurred throughout the day. The team spent two to three months at each zoo, recording a total of 3,243 instances of aggression from all of the apes older than 7 years. Seven is the youngest age at which researchers have recorded a bonobo male reproducing, Staes said.

They found that there were 1,368 instances of directed aggression from bonobos and 1,875 from chimpanzees. About a third (1,193) of the instances were "contact" aggression, meaning there was physical violence between the individuals rather than just shouting or other less-violent forms of aggression. Once the data were controlled for sex, relationship and context, there was little difference in overall aggression between chimps and bonobos.

"You don't find that chimpanzees are more aggressive," Staes said. "Bonobos are equally aggressive." Among chimpanzees, males were mostly responsible for the conflicts. Male and female bonobos, on the other hand, were equally likely to pick a fight. "There's no difference between the sexes in bonobos, which was a bit surprising to us," Staes said.

However, there were differences in which sex got targeted. Male chimps were aggressive toward both females and other males, and they were also more likely to get physically violent. Female bonobos were more likely to be aggressive toward bonobo males. While there is male-male aggression in bonobos, there is seldom female-female aggression, Staes said.

But bonobos are better at making up, she said, adding that in an upcoming study, the team plans to describe how the different groups resolved conflicts.

There were also stark differences between the levels of aggression among the bonobo groups in different zoos — more so than in chimps. "Our findings contribute to a growing body of evidence suggesting that behavioral patterns in Pan, including aggression, may be more influenced by group identity than by species-wide traits," the authors wrote.

Zoos offer an interesting perspective on ape behavior. Some researchers argue that chimpanzees are more warlike because food was less available on their side on the Congo River and they had to compete with gorillas for resources. Conversely, bonobos had more food and fewer predators.

In zoos, these environmental factors are no longer at play. "The main benefit is that you take the two species out of their ecology and you really get the behavioral differences that are due to, for example, genetic changes that have occurred since the split from each other," Staes said.

Sonya Pashchevskaya, a behavioral ecologist at the Max Planck Institute of Animal Behavior in Germany who was not involved in the research, said she welcomed the new insights. "This study is particularly important in light of the 'hippie' bonobos notion famously originating in the captive setting," she told Live Science. "It is great to see the myth methodologically challenged in such a setting and with multiple groups involved."

"Aggression, as a means to navigate conflict, is a normal part of life," Pashchevskaya said. While chimpanzees are more prone to taking it to violent extremes, bonobos may "reserve real violence for the worst dangers."

The new insight into bonobo aggression could provide more clues about conflict among our closest relatives. "While conflict is inevitable," Pashchevskaya said, "there exist varying aggressive expressions, and from both sexes."

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.

Primates — the mammalian group that includes humans — are found pretty much everywhere on Earth, from equatorial rainforests to scientific research stations in Antarctica. This hugely diverse order appeared before the dinosaurs went extinct, with wild populations of non-human primates evolving to live in niches across three continents — Asia, Africa and Central/South America.

Primates don't just live in lots of places; there are also hundreds of species and subspecies. In fact, the order primates is the fourth most biodiverse mammal order in the animal kingdom — yet the majority (62.6%) of primates are threatened with extinction.

Scientists researching primates, called "primatologists," have learned a lot over the years about our closest evolutionary relatives. For example, did you know that chimps have opposable big toes, or that not all monkeys can swing through the trees? Or even that there are some primates that are neither monkeys nor apes?

Fancy yourself a primatologist? Put your knowledge to the test below!

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In late December 1985, a worker opened the door to a remote cabin in the Virunga Mountains of Rwanda and encountered a horrific scene: Gorilla researcher Dian Fossey, whose aggressive approach to conservation had pitted her against the local community, had been hacked to death with a machete, and her cabin had been ransacked.

Fossey had been working with an endangered gorilla population in Rwanda's Volcanoes National Park since the late 1960s. Along with Jane Goodall and Biruté Galdikas, she was one of the three "trimates" chosen by Louis Leakey to study primates in their natural habitat.

Fossey had no formal training in ethology, the science of animal behavior, when she set out for Africa. She began her field work in Kabara, Congo, living in a tiny tent and venturing out to study mountain gorillas (Gorilla beringei beringei) there. After civil war broke out in 1967, she escaped to the Rwandan portion of the mountains and set up a new research project near Mount Karisimbi in Rwanda.

Fossey was inspired by the work of George Schaller, a biologist who, in 1959, had also studied the gorillas of the Virunga Mountains.

"I knew that animals try to stay out of your way. If you go quietly near them, they come to accept your presence. That's what I did with gorillas. I just went near them day after day, which was fairly easy because they form cohesive social groups. Soon, I knew them as individuals, both their faces and their behavior, and I just sat and watched them," Schaller said in a 2006 interview.

Fossey operated on this same principle of patient, unobtrusive observation. Still, the gorillas initially fled from her, and she spent hours tracking and trailing them across the misty forest.

After a year, they stopped fleeing at her presence and started beating their chests and vocalizing. It was a bluff meant to scare her off, but it was still far from their ordinary, natural behavior, she said in a 1973 lecture. After two years, she received two young gorillas, Coco and Pucker; rehabilitated them; and learned about gorilla young by observing them.

"I came to know the gorillas' need for love and affection, and the young gorillas' need for constant play," she said.

It would take three years before the gorillas came to accept her presence and reveal more naturalistic behavior, she said in the lecture.

During her decades in Virunga, Fossey described and learned to mimic the vocalizations of gorillas, including the "belch vocalization" that signifies contentment. She also elucidated their tight-knit family structures, courtship and mating rituals, as well as documented the occasional murder of infant gorillas by rival males.

Although she would eventually earn her doctorate in zoology from the University of Cambridge, Fossey spent her first years studying the gorillas with no formal training. Perhaps because of her initial lack of training, she formed close bonds with individual animals and tended to ascribe more humanlike motivations and descriptions to their actions than is typically accepted in formal zoology. She often described gorillas as more altruistic than humans.

"You take these fine, regal animals,'' she told an interviewer, as reported by The New York Times. ''How many fathers have the same sense of paternity? How many human mothers are more caring? The family structure is unbelievably strong.''

She formed a particularly close bond with a gorilla she nicknamed Digit — so named for his damaged finger — who did not have playmates his age. Digit was killed by poachers in 1977.

The last years of Fossey's life were increasingly focused on conserving the gorillas' dwindling habitat and combating poachers. She used confrontational methods, such as burning snares, wearing masks to scare poachers, and spray-painting cattle to prevent herders from bringing them into the national park, according to the Dian Fossey Gorilla Fund.

She also shot over the heads of tourists to scare them away and told her graduate students to carry guns, according to The Washington Post.

Given that many of the people living on the fringes of the park lived in poverty and resorted to expansion and herding to survive, this did not earn her good will with many of the locals.

Fossey's murder was never solved. Many think poachers were responsible for the killing, but other theories have been floated as well.

Killing neighbours and taking over their lands led to a baby boom for a chimpanzee community in Uganda — potentially showing why it can be advantageous for chimps to start wars.

Chimpanzees (Pan troglodytes) have long been known for violent conflict or "warfare." It was first documented by English primate researcher Jane Goodall, who in 1974 observed the chimpanzee community in Gombe National Park in Tanzania splinter into two warring groups, leading to a four-year battle that resulted in the deaths of all the males in one group. But why the animals persisted with the violence for so long wasn't clear.

To shed light on this, the lead author of a new study Brian Wood, an anthropologist at the University of California, Los Angeles, and his colleagues examined data collected on chimpanzees in Kibale National Park in southwestern Uganda over more than three decades.

Between 1998 and 2008, the Ngogo chimpanzees of Kibale engaged in violent clashes with their neighbors. During this decade of conflict, at least 21 chimpanzees from neighboring groups were killed, and in 2009, the Ngogo chimpanzees expanded into an area previously inhabited by their rivals, boosting their territory by 2.5 square miles (6.4 square kilometres) or 22%.

The records revealed that in the three years before the territorial expansion, the female Ngogo chimps gave birth to 15 offspring. But in the three years after it, they gave birth to 37 youngsters, more than doubling their fertility rate.

What's more, the infants born after the expansion were more likely to survive: they went from having a 41% chance of dying before the age of 3 to just an 8% chance of it. The study was published Nov. 17 in the journal PNAS.

"At the time, it was very obvious to the field workers that the chimpanzees were experiencing a baby boom. We expected to see that in the data, but not the boost to survivorship," Wood told Live Science.

The work provides the best evidence yet that, for chimpanzees, expanding territory after killing off rivals can directly boost reproductive success, he said. The chimpanzees’ territorial expansion gave them access to more food, and the subsequent improvement in nutrition and health probably led to higher female fertility and better survival rates among the young, Wood added.

The boost to survival rates could come down to two factors. The first, Wood said, is an improvement in the health and energy of the mothers, and the other the removal of rival males.

"The survival being higher makes sense because a major source of mortality for chimpanzee babies is getting killed by their neighbours," Michael Wilson, who studies the behavior and biology of chimpanzees at the University of Minnesota and wasn't involved in the study, told Live Science. "What this study supports is the idea that under certain conditions, it is adaptive to defend group resources and kill members of neighbouring groups. The chimpanzees are looking out for their own group, essentially."

Yet, if there is a benefit for the winners, there will be a cost to the losers, Wood said. He thinks it is likely to be a zero-sum game and there would probably be no overall gain in chimpanzee numbers because while the victors benefit, others lose.

The scientists behind the study claim that the findings could help shed light on the evolution of violence in humans. Because there is lethal violence in our closest living relatives — chimpanzees and bonobos (Pan paniscus) — some scientists have previously suggested this trait may have been present in our shared common ancestor, which probably lived six or seven million years ago, Wood said.

Competition over access to land and resources is still an ever-present part of the human condition, he said, but it is generally transformed by the human ability to mediate and avoid conflict.

"Ongoing conflict in the world over resources has echoes of what chimps are up to, but I don't think that's a favourable comparison if you happen to be involved," Wood said.

In general, there's a striking difference between humans and chimpanzees when it comes to intergroup relations, Wilson said. "If a chimpanzee sees a male from a neighbouring group, the only way he can benefit is by imposing some cost on that male, taking his territory or taking his life."

When people see a stranger from another group, there is a chance that they can benefit from interacting with them, he said.

It is this that has allowed humans to create multi-level societies with ties of trade, kinship and ritual forming larger units of social organization.

"In the modern world, the benefits from intergroup interactions have grown so enormous and the costs of war have also multiplied so enormously that it's generally a pretty dumb idea to start a war," Wilson said.

Five wild female bonobos in the Democratic Republic of the Congo brutally attacked one of their male group mates, disfiguring his face almost beyond recognition, ripping off one of his ears, and biting his testicles in an unprecedented act of violence for the species, scientists report.

Researchers arrived a few minutes late to the scene, so they aren't entirely sure what sparked the ferocious act, which lasted around 30 minutes. However, they suspect the male bonobo may have tried to harm one of their infants, the authors reported Oct. 6 in the journal Current Biology.

"We didn't see the onset of the attack, but it's hard to explain in other ways, like what's the function of this remarkably extreme violence," study lead author Sonya Pashchevskaya, a doctoral researcher at the Max Planck Institute of Animal Behavior in Germany, told Live Science.

There has been only one other documented case of such an attack, in a different bonobo population around 186 miles (300 kilometers) away, and that appeared to be punishment for attempted infanticide, she explained.

This recent assault, which happened Feb. 18 in the LuiKotale bonobo community in Salonga National Park, is the most extreme case of violence in a wild bonobo population to date and challenges the stereotype of bonobos being the nonviolent "hippies" of the primate world.

Bonobos (Pan paniscus), along with chimpanzees (Pan troglodytes), are our closest living relatives. But unlike chimpanzees, bonobos have a reputation for "making love, not war," with individuals frequently using sex to relieve tensions.

However, male-male aggression is still common, and female bonobos are known to team up to fight males who threaten them or their young. This female "coalitionary" behavior seems to underpin the female dominance hierarchy in the species and could explain the "lack of lethal aggression or infanticide" in bonobo societies, the authors noted in the study.

There was nothing untoward on the morning of the attack. "It was a usual data collection day," Pashchevskaya noted. The team, which included local field assistants and research assistants, were following small subgroups of bonobos from the roughly 60-strong LuiKotale community through the forest.

Suddenly, bonobo screams erupted from roughly 0.3 miles (0.5 km) away. Pashchevskaya assumed the high-pitched screeches were excitement from catching small antelope prey.

"The bonobos who I was with at that time, they all just drop from the trees and start sprinting down there," she said. She followed in hot pursuit and arrived at the scene just a few minutes after it all started.

"First thing that immediately happens is, I smell blood," Pashchevskaya recalled. When the team spotted a group of five females stomping on, beating and biting a male lying head down on the ground, she realized this was not about an antelope hunt.

The male victim, a 19-year-old called Hugo, lost most of his hair in the assault, as well multiple toes, part of his ear, and the flesh on his knuckles. The assailants then licked his blood off their fingers.

No group member tried to intervene, despite the entire community being present. "Everybody is very silent. It's like a forest with bonobos has never been so quiet," Pashchevskaya said. "This is nothing I've ever seen before."

Two days before, Pashchevskaya noticed Hugo trying to grab one of the attacker's infants, which the team speculated may have sparked the attack as an act of retaliation.

"Of course, this is just one observation two days before, but if this kept happening, it could have potentially triggered an attack," she said. "Other females would join this potentially, because this is then someone they can also recruit [in the future]."

Hugo eventually managed to walk away, but has since been missing, leading the team to suspect he died from his injuries. "There's no way he survived," Pashchevskaya said.

Nahoko Tokuyama, a primatologist who researches bonobos at Chuo University in Japan but was not involved in the recent work documenting the attack, said that although she wasn't surprised by the group assault, she did not expect such grave injuries.

"I had previously believed that wild female bonobos, while sometimes becoming violent, would not injure an opponent to such a severe extent," Tokuyama told Live Science in an email.

However, she cautioned that Hugo may still be alive. "Bonobos have a fission-fusion society, and it is possible for a male to spend long periods alone," she said. "In our long-term studies, we have had cases where males who had not been seen for several months returned to the group, so the question of whether Hugo died needs to be considered more carefully."

The act of kissing may have started long before modern humans existed, a new modeling study suggests.

Kissing stretches back roughly 21 million years, to the shared ancestor of humans and other large apes, according to the study, published Wednesday (Nov. 19) in the journal Evolution and Human Behavior. Meanwhile, Homo sapiens likely emerged around 300,000 years ago.

The researchers also concluded that kissing most likely occurred in Neanderthals, the closest extinct relatives of modern humans, and that Neanderthals and modern humans may have kissed each other.

"This is the first time anyone has taken a broad evolutionary lens to examine kissing," study lead author Matilda Brindle, an evolutionary biologist at the University of Oxford, said in a statement. "Our findings add to a growing body of work highlighting the remarkable diversity of sexual behaviours exhibited by our primate cousins."

Model kissing

Before dating the world's oldest kisses, an international team of researchers defined what it means to kiss. This was important, because other mouth-to-mouth actions in nature look similar to kissing. For example, mother orangutans and chimpanzees transfer chewed food to their infants mouth to mouth, and fish engage in "kiss fighting" to assert dominance or compete for territory. Ultimately, the researchers defined kissing as "non-aggressive, mouth-to-mouth contact that did not involve food transfer," they wrote in the statement.

Based on this definition, various modern-day primates — including bonobos, gorillas, chimpanzees, orangutans, macaques and baboons — have been observed kissing.

The researchers then used a statistical method called Bayesian modeling to reconstruct the evolutionary history of kissing. They treated kissing as a biological trait and tested many possible ways this behavior could have evolved to see how likely it was that different ancestors also kissed. They ran the model 10 million times to make sure the results were strong and reliable.

They concluded that kissing evolved once in the common ancestor of large apes (Hominidae) sometime between about 21.5 million and 16.9 million years ago.

However, kissing was absent in ancestral Macacina and Papionina (groups that include macaques and baboons), suggesting that kissing evolved separately in the modern-day species belonging to these groups. The team determined this by extrapolating back in time from the behavior of modern-day species to that of their common ancestors.

Although more evidence is needed, the researchers said kissing might have evolved from the practice of pre-chewing and transferring food from a mother to an infant. This practical food-sharing behavior may have been repurposed into what we now recognize as kissing.

How this fits in with earlier kissing research

The finding that Neanderthals kissed not only each other but also modern humans isn't exactly news to anthropologists.

"I am not sure that the current study adds anything substantially new to our knowledge of this behavior in Neandertals," April Nowell, a Paleolithic archaeologist and professor of anthropology at the University of Victoria in British Columbia who was not involved with the study, told Live Science in an email.

But the new study does align with previous findings. Nowell noted that "intriguing evidence" came in 2017, when a different research group compared microbes preserved in the dental plaque of a Neanderthal who lived 48,000 years ago with those found in modern human mouths. The team concluded that Neanderthals and H. sapiens may have kissed each other, although the microbial overlap could also reflect shared food or water, said Nowell, who was not a part of that study.

Additionally, we already know that H. sapiens and Neanderthals mated during a roughly 7,000-year-long pulse, so it's possible that some kissing occurred when that happened assuming that some ancient mating behaviors were similar to those of today.

That said, it's unclear how widespread kissing was among our human relatives. Because kissing isn't a universal behavior among modern humans — only about half of cultures engage in it — Nowell said the same variability may have existed in the past. If Neanderthals kissed, she said, "then it might have been a behavior that some Neandertal communities engaged in while others did not."

Scientists still aren't sure why kissing persists across so many species, especially given the potential downsides, such as the spread of disease. One idea is that kissing helps individuals boost reproductive success. For example, kissing a potential partner may help people gauge a mate's quality through subtle chemical cues which can offer clues about a person's overall health, genetic compatibility, immune system, and the makeup of their oral microbiome, the researchers wrote in the new study. Researchers have also proposed that kissing strengthens social bonds and may even benefit immunity by allowing the exchange of microbes.

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

Chimpanzees use a variant of the "scientific method" — discarding prior beliefs if convincing new evidence comes along to change their minds, new research suggests.

When tasked with finding a tasty treat hidden in one of two boxes, chimps (Pan troglodytes) evaluated several strands of evidence. And they switched their choices if new, contradictory evidence emerged, the study found.

The findings are evidence that chimps use metacognition, or thinking about thinking, to weigh evidence and plan accordingly.

"When they revise their beliefs, they actually explicitly represent the evidence they have, and they weigh different types of evidences," study co-author Jan Engelmann, a comparative psychologist at the University of California, Berkeley, told Live Science.

Humans routinely use metacognition to weigh different strands of evidence and create plans based on the information available. We also update our strategies when our plans don't go as we hoped.

Scientists have long known that primate species can assess evidence. Chimpanzees look for food by tracking crumb trails and will seek out more information if existing evidence isn't clear. But we didn't know if chimps could perform a key metacognitive task: changing beliefs in response to new evidence. Engelmann's team used several behavioral tests to answer this question, all of which involved food rewards placed in one of two boxes. In the first two tests, the chimps were trained to choose one of the boxes to receive the food inside and presented with two pieces of conflicting evidence as to which box contained the food. The chimps were presented with one piece of evidence, chose a box, and then given the other piece of evidence and allowed to choose again.

The evidence varied in strength. In one "strong" evidence condition, the team cut a window into the side of one of the boxes, which enabled the chimp to see the food inside. To give "weak" evidence, the researchers shook the other box to indicate something was inside it. The apes were far more likely to change their minds when the researchers presented strong evidence after their initial choice than when they presented weak evidence.

But these results didn't tell the researchers why the chimps changed their minds.

"You can revise your beliefs without really thinking about the evidence," Engelmann said.

The researchers arranged a third test in which they showed the chimps three boxes. One box had strong evidence that it contained food, the second had weak evidence, and the third had none. Before they could pick, the "strong evidence box" was removed. Left with a binary choice, the apes consistently picked the weak evidence over no evidence at all. This showed that the chimps considered both the strong and weak evidence in their decision-making, rather than just considering the strong evidence without reflecting on the other options available, Engelmann said.

In the final experiments, the researchers tested two further metacognitive abilities in the apes. This time, after the researchers presented the weak and strong evidence for the two boxes, they offered another piece of weak evidence. This was either the same weak evidence as before — the researchers rattling the box to show something was inside it — or a new piece of evidence: the sound of a researcher dropping a second piece of food into the box.

The apes were more likely to change their mind and choose that box when they heard two different pieces of evidence, rather than the same piece of evidence twice, showing that they considered how various pieces of evidence combined to strengthen an argument.

In the final test, the researchers again added extra evidence for the apes to consider after they had made their first choice. This time, the new evidence undermined the first piece of evidence; for example, by showing the chimps a pebble inside one of the boxes that could have made the rattling sound they had previously heard. The apes consistently responded to this contradictory evidence by changing their mind.

To Cathal O'Madagain, a cognitive scientist at the University of Mohammad VI Polytechnic in Morocco who was not involved with the study, this final experiment was key to proving the apes' metacognitive ability. "Study five is showing a kind of rationality that studies one and two are not showing," he told Live Science. Test five showed that the original and contradictory evidence were linked, and the apes' changed minds reflected that they were "keeping track" of the original information, he added.

O'Madagain said that the paper, in concert with other, earlier studies of chimpanzee rationality, shows that chimps passed what he called the "high bar" of rationality, making choices based on evidence and keeping that evidence in mind as their world changed. The new findings suggest that discoveries about other animals' minds aren't limited by their shortcomings, but by our own, O'Madagain said "The biggest constraint on our understanding of other animals' intelligence is our ability to come up with appropriate ways to check it."

Engelmann and his team now plan to extend their experiments to other non-human primates to see if they can pass this rationality test, too.

Lab monkeys initially thought to be carrying a range of diseases have escaped from a truck in Mississippi following a crash — prompting law enforcement officers to kill a number of the animals. However, it's still unclear just how dangerous they are.

The truck, which was carrying rhesus macaques (Macaca mulatta) from Tulane University, overturned in Jasper County on Tuesday (Oct. 28), with several monkeys breaking loose — although the exact numbers have yet to be reported.

At the time of writing, three monkeys are still on the loose, according to an update from the Jasper County Sheriff's Department. The authorities believed that the monkeys were aggressive to humans and carried herpes, COVID-19 and hepatitis C. But Tulane University has subsequently said that the monkeys weren't infectious.

"The primates in question belong to another entity & aren't infectious," Tulane University wrote in a post on X on Tuesday. "We're actively collaborating with local authorities & will send a team of animal care experts to assist as needed."

Following Tulane University's statement, the sheriff's department clarified that the driver of the truck had told law enforcement that the monkeys were dangerous.

"The driver of the truck told local law enforcement that the monkeys were dangerous and posed a threat to humans," Jasper County Sheriff's Department wrote in a post on Facebook. "We took the the appropriate actions after being given that information from the person transporting the monkeys. He [the driver] also stated that you had [to] wear PPE equipment to handle the monkeys."

Sheriff Randy Johnson has since said that the monkeys still needed to be "neutralized" because of their aggressive nature, the Associated Press reported on Wednesday (Oct. 29).

Are rhesus macaques dangerous?

Rhesus macaques are medium-sized monkeys, and they could pose a threat to humans if they decided to attack. However, it's unclear whether the escapees were likely to do that.

The sheriff's department wrote on Facebook that the escaped monkeys each weighed approximately 40 pounds (18 kilograms). This would be exceptionally large for a rhesus macaque and is likely an overestimate, unless the individuals were overweight. Male rhesus macaques, which are larger than females, typically weigh about 17 pounds (7.7 kg), according to the University of Wisconsin–Madison's Wisconsin National Primate Research Center, while the New England Primate Conservancy states that this species can weigh up to 22 pounds (10 kg).

Aggression is a natural part of macaque behavior, and while they don't normally direct it at humans, they regularly scrap among themselves. The New England Primate Conservancy states that fights between monkeys can be frenzied and violent, with rhesus macaques aiming for the eyes, face, limbs and genitals in order to maim or kill their opponents.

In other words, rhesus macaques can be dangerous if they want to be. Although they also have a range of peaceful behaviors, such as grooming.

Rhesus macaques have the widest geographic distribution of any non-human primate and can frequently be found living in close proximity to humans across their native range of Asia. They are often considered pests because of their penchant for stealing our food. Macaque species do occasionally bite or attack people, but this is a consequence of them becoming too habituated to humans in our expanding urban environments and losing their natural fear of people.

Macaques in labs, like the ones that escaped in Mississippi, have historically had a reputation for being aggressive, but experts have also argued that this aggression can be brought on by poor husbandry and handling practices. Lab monkeys are sometimes hand-reared by humans, which can lead to a range of abnormal behaviors not typically seen in the wild or in captive monkeys raised by other monkeys, such as self-biting and more aggression toward humans. Each individual monkey also has its own personality. And captive monkeys can have relatively calm and gentle demeanors.

There aren't any reports of the escaped monkeys attacking humans before they were killed. Tulane University has also said that the monkeys had "not been exposed to any infectious agent," the Guardian reported.

There are still a lot of unknowns surrounding the monkeys, including who owned them, who was transporting them, where they were heading, and for what purpose they were being used, according to the Associated Press.

Lab monkeys

Rhesus macaques are the most common monkeys used for testing in labs. Experimenting on these monkeys can be extremely valuable to scientific research and has led to a plethora of breakthroughs, including the development of various vaccines, including mRNA vaccines against COVID-19.

The use of monkeys in labs is also controversial. For example, in 2023, hundreds of scientists called for an end to "cruel" monkey experiments at Harvard Medical School and elsewhere. These included visual recognition studies in which juvenile monkeys had their eyes sewn shut for their first year.

Macaques on the run

This isn't the first time lab monkeys have escaped. For example, in 2020, a group of macaques reportedly escaped from a lab in India and took several COVID-19 blood test samples after attacking a lab assistant, Sky News reported. More recently, 43 monkeys escaped from a lab in South Carolina and went on the run, the Associated Press reported.

The descendants of escaped rhesus macaques are also living in the Silver Springs State Park in Florida. In the 1930s, a commercial river boat captain put six macaques on an island as a tourism ploy, not realizing that rhesus macaques can swim. The monkeys soon left the island and spread along the river.

Two weeks on from Jane Goodall's death, many have been reflecting on her life, including her scientific legacy and how she changed humanity's connection to the natural world.

As a pioneering primatologist, Goodall was the first to spy many behaviors and characteristics in the chimpanzees (Pan troglodytes) of Tanzania's Gombe National Park that had been assumed to be unique to humans, including tool use, warfare and personalities.

Goodall’s observations revolutionized our understanding of chimps; and her unconventional approach, stemming from a lack of formal scientific training, enabled her to make several contributions that changed the face of animal research. Yet this would prove to be a double-edged sword, leading her to use methods that primatologists no longer consider helpful today.

So what were Goodall's contributions to primatology? And did any fall short? Live Science spoke to chimpanzee experts to unpack her enduring impact on chimp research, including how some of her initial observations biased our understanding of how chimps think and behave, and the ways scientists have learned from the unintended consequences of her early decisions.

One of the most notable examples of Goodall’s unwitting defiance of strict scientific conventions can be found in her giving individual names to the Gombe chimpanzees and remaining open-minded to their capabilities.

"She didn't know that she wasn't supposed to give them names. She didn't know that you weren't supposed to talk about feelings and emotions and personal histories," Elizabeth Lonsdorf, a professor of anthropology at Emory University who studies the Gombe chimps, told Live Science. "Her real gift to us was firmly planting that as a basic understanding of chimpanzees so that we can design better science with that in mind."

Recognizing the need to consider the personal histories of chimps was pivotal, and by establishing the first long-term study of chimps, Goodall ignited an entire research field. The Gombe chimps are now followed daily by a dedicated team of expert Tanzanian trackers, and, since 1960, scientists have collected over 165,000 hours of data on their behavior.

Researchers can now track chimpanzees' development from birth to old age using these data, watching how each generation transfers skills and knowledge onto the next. "Chimps live 60 years so you can't actually ask those questions without five, six decades of research," Lonsdorf said.

The Gombe community now contains the fifth generation of chimpanzees descended from the original chimps Goodall studied, with family lineages grouped according to the first letter of their mothers' names.

'Friendship' as the 'F'-word in primatology

Naming chimps goes beyond tracking, and has opened the door to new research avenues. Laura Simone Lewis, a primatologist at the University of California, Santa Barbara, told Live Science that while captive chimps clearly respond to their own names, she is currently investigating whether they also recognize those given to their groupmates.

Finding evidence that chimps keep track of each other's names would suggest that the underlying capacity to understand social labels could have emerged before the evolution of human language, Lewis said. "That comes directly from Jane's work of naming chimpanzees."

This research also carries on Goodall's work of investigating social bonds in chimps. Lewis noted that many of Goodall’s early observations about the social and emotional lives of chimps were anecdotal, and so were discounted.

In fact, "friendship" was considered the "f" word in primatology for over 40 years after Goodall's first observations. Lewis is still careful when using the term, yet its growing acceptance among primatologists is based on years of empirical research, and points to the validity of Goodall's first insights. "We often call them close social relationships, but what they really are are friendships. And they are long-lasting, very closely bonded relationships between animals that can last for decades."

This sentiment is echoed elsewhere. Liran Samuni, a primatologist at the German Primate Center who studies cooperation and intergroup relationships in chimps, said that despite chimps' bad reputation for aggression, she "cannot think of a primate species [aside from humans] that is also as cooperative and as dedicated to each other as chimpanzees are."

The distinction is that chimps are very friendly to their ingroup and "systematically hostile to the outgroup," Sylvain Lemoine, a primatologist at the University of Cambridge, told Live Science.

Chimpanzees' "social landscape is made of their own community and of the neighboring communities," Lemoine said. And at any time, they run the risk of being ambushed by hostile neighbors, he added.

Goodall’s observations on chimp aggression were also foundational. She was the first to observe lethal aggression between chimpanzee groups, and documented what has become known as the Gombe Chimpanzee War, which was a four-year-long conflict caused by the splintering of the Kasakela community.

At first, Lemoine said, researchers dismissed this as an artificial behavior that resulted from Goodall feeding the chimps bananas — called "provisioning." By plying the chimps with food, Goodall could entice the whole group to one central spot to observe their interactions more easily. However, this high concentration of sought after resources dangerously heightened the competition between the chimps.

It is now known that intergroup violence is common across chimp populations, and "whether this community in Gombe split because of the provisioning is another question," Lemoine said.

This exemplifies an important point, however. While Goodall's open-mindedness meant she ignored unproven presumptions made by experts during her time, such as warfare being unique to humans, she also made decisions that ultimately had unexpected negative repercussions.

Not all chimps are Gombe chimps

The fact that Goodall’s early work was centred on one community at one site, Gombe National Park, also created another unintended consequence: The long-lasting assumption that the behavior and social structure of the Gombe chimps was the same across all chimp communities. "This is something that people who study chimpanzees are still grappling with," Samuni said.

We now know that chimps across Africa can vary considerably from one another. For example, the intensity of intergroup competition among chimps varies depending on the animals’ social structures, Samuni told Live Science, with a 2014 large-scale study published in the journal Nature finding that East African chimps were more lethal than those in West Africa. They also found that groups with more adult males witnessed a greater number of killings.

Also, Goodall observed that female chimps were antisocial, generally sticking to themselves while males gathered to interact. This is true on its face: Females in East African chimp communities, like those in Gombe, do tend to be more peripheral members of the group, Samuni explained.

But this is far from true everywhere. Females in West African chimp communities are "extremely central to the social network," Samuni said. Nonetheless, the first impression made by Goodall’s observations left a long-lasting presumption that all female chimps were antisocial, a bias that took years to overturn.

However, Lonsdorf said that she never viewed Goodall's work as putting blinders on researchers. Goodall's observations simply lay the groundwork for studying variation by developing a "baseline framework of how a chimpanzee behaves," she said.

Times have changed

A lot has changed since Goodall's initial observations. These days, the Gombe chimps are given Swahili names rather than English ones, and naming individuals in the local language is common across sites. In addition, chimpanzees are no longer provisioned at any site.

Also, researchers can now collect data beyond observations. "Nowadays, our science is largely interdisciplinary or multidisciplinary," Alejandra Pascual-Garrido, a primatologist at the University of Oxford who works with the Gombe chimps, told Live Science. There is now a genetics lab in Gombe, making it possible for researchers to study paternity and the health of the gene pool.

The days of closely interacting with chimpanzees as Goodall did are likewise long gone. Researchers now wear masks to avoid getting animals sick and keep their distance to stay safe, and primatologists work to ensure photographs of people very close to primates aren't shared as they can undermine conservation efforts and encourage the pet trade. Pascual-Garrido noted that the old images of Goodall hugging chimpanzees would be considered "completely unacceptable" by primatologists nowadays.

It's important to remember that Goodall was doing what seemed to work at the time, and had no other site to learn from. Samuni said "the fact that she did not come with those predefined ideas and concepts actually allowed her to see things that other people may have missed or may have thought, 'okay, it cannot exist.'" Pascual-Garrido agreed. "She saw the world differently and she made the world see the world differently," she said.

When Jane Goodall stepped off her boat into what is now Gombe National Park in Tanzania on July 14, 1960, she began a journey that would change science forever.

Armed with her notepad and binoculars, Goodall perched far away from the chimpanzees (Pan troglodytes) she had been sent to observe and worked to gradually build their trust. This patience gave the chimps time to "habituate" — the process whereby wild animals acclimatize to human presence to the point that they start to behave normally around them.

This simple act was Goodall's first revolutionary step, enabling her to follow the chimps and meticulously observe their behaviors and individual quirks. Habituation is now the routine first step for animal behavioral research.

Goodall's legacy in conservation and environmentalism is immeasurable. People across the world praised her accomplishments and grieved her death on Wednesday (Oct. 1) Here are the five biggest ways she changed our understanding of our closest living relatives.

Chimp the Toolmaker

Goodall's first revolutionary discovery was that humans were not unique in making and using tools. In October 1960, she spied David Greybeard — a high-ranking adult male who was the first to relax in her presence — poking a stick into a termite mound to fish out its occupants.

Until this point, scientists assumed that only humans had the brains for such behavior. "It is in making tools that man is unique," Kenneth Oakley, a 20th-century physical anthropologist and palaeontologist, wrote for a conference held at the Natural History Museum in London in 1947. "The shaping of sticks and stones to particular uses was the first recognisably human activity," he said.

The field of chimpanzee, and wider animal, tool use is now a burgeoning research field, with chimpanzees across Africa known to fish for termites, while West African chimps are experts at using stones to crack open hard-shelled nuts. Primatologists now routinely observe chimps using tools to infer how hominins may have solved similar problems, including termite-fishing.

Each to their own

Goodall defied convention by giving each member of the Kasakela chimpanzee community a name, such as Flo, Fifi and Goliath, as opposed to a number. Off the back of this, she noticed that each individual had its own personality, with David Greybeard, for example, being very gentle, while Frodo was a known bully.

Because of Goodall, finding individual differences in how chimpanzees act and think is now unsurprising, but this discovery paved the way for a flurry of research into how personality maps onto behavior. This is important because differences in behavior can have large evolutionary consequences, especially if this impacts the ability to survive and reproduce — the key principle behind evolution by natural selection.

Mother-infant relationships

The birth of a new infant, Flint, in the early 1960s gave Goodall the opportunity to observe mothers caring for their newborns. Every interaction she saw was a new scientific discovery.

For example, Goodall noticed how, as infants mature, mothers began to actively wean their young by denying nursing opportunities and rejecting attempts to hitch a ride on their backs, while simultaneously exposing their infants to more and more social interactions.

Scientists now know that mothers play an essential role in the learning periods for complex behaviours such as tool use. A 2019 study published in the journal PNAS found that chimp mothers in the Republic of Congo could even be actively teaching their infants how to termite-fish by giving them their own stick rods as hand-me-downs.

I'll be there for you

Beyond mother-infant bonds, Goodall also observed that chimpanzees form strong, long-term connections with their family and other members of the group. Research has since found that individual chimpanzees create close bonds with those outside of their own sex and rank, and will share food with their buddies.

Moreover, primatologists now know that chimps have an exceptional social memory that complements these bonds, with 2023 research in the journal PNAS finding that chimps recognize their former group mates almost three decades after they last laid eyes on one another.

As such, Goodall's discovery was key for unlocking the previously unknown social lives of our closest living relatives, and revealed what these relationships can teach us about human social and cultural evolution.

For example, these close relationships, and the corresponding social tolerance this creates, are the foundation for learning in chimps — with chimps acquiring a vast array of behavior from others. In fact, being tolerant toward one's groupmates is argued to be fundamental for primates, including hominins, in evolving to make and use tools.

A taste for blood

Goodall's time in Gombe also revealed that chimpanzees are not the vegetarians they were once believed to be. Instead, they're omnivores who actively hunt for meat. Red colobus monkeys (genus Piliocolobus) are the main prey for the Kasakela community, but it is now known that chimps across Africa hunt a wide range of species.

For example, chimps in Uganda hunt duiker, a type of antelope, while the Fongoli chimps in Senegal craft spears to kill bushbabies.

Goodall also discovered violence between members of different groups, with this discovery paving the way for what is now extensive research into chimpanzee border patrols, group level cooperation and reconciliation behavior.

We now know that oxytocin — the bonding hormone — is involved in post-conflict reconciliation, showing its importance not only in building relationships, but repairing them.

Chimpanzees could be consuming the equivalent of a beer and half a day from eating alcoholic fruits, according to the first estimates of wild chimp alcohol intake.

By virtue of their fruit-filled diets alongside natural fermentation, chimps (Pan troglodytes) in Uganda and the Ivory Coast probably eat around 0.5 ounces (14 grams) of ethanol a day.

That doesn't mean the chimps are getting drunk. But it could mean that our predilection for alcohol comes from exposure to ethanol from fermented fruit in ancestral diets, according to research published Sept. 17 in the journal Science Advances.

"They're definitely not getting drunk," study co-author Aleksey Maro, a primatologist at University of California Berkeley (UC Berkeley), told Live Science. "If you had two drinks split through the whole day, you wouldn't feel much either."

The idea that humans have a taste for alcohol because it first appeared naturally in our diets is called the "drunken monkey hypothesis," and was proposed by study co-author Robert Dudley, a professor of integrative biology at UC Berkeley. Dudley's hypothesis postulates that there was a period of primate evolution during which our early ancestors couldn’t metabolize fermented fruits, and so were missing out on high calorie meals.

To tap into this nutritious resource, primates evolved to be able to hold their liquor by being able to break down ethanol.

However, until now scientists have only directly observed chimps eating fruit known to contain ethanol once, reporting chimps in Guinea-Bissau eating and sharing naturally-occurring fermented African breadfruit in 2022.

"I'm as skeptical as everyone else about the drunken monkey hypothesis," Maro said, "so I've taken care to do my own sleuthing."

To figure out how regularly chimpanzees could be consuming ethanol rich fruits, Maro and his team followed two groups of chimps: The Ngogo chimpanzees in Uganda and the Taï chimpanzees in Côte d'Ivoire. They observed the chimps for three periods lasting several months between 2017 and 2021.

The researchers took samples of freshly fallen fruit whenever they encountered them eating. From this, they retrieved 254 ripe fruit samples from 15 fruit species in Ngogo and 245 samples from six species in Taï.

To estimate the alcohol content in the samples, the team either analyzed the alcohol vapor found inside the fruit or used a chemical reagent that turned yellow on contact with ethanol.

They found that the Ngogo chimps ate fruit with an average ethanol concentration of 0.32%, meaning that there was 1.1 ounces (32 grams) of ethanol in every 3.5 ounces (100 grams) of the total weight. The fruit eaten by the Taï chimps had a remarkably similar average ethanol concentration at 0.31%.

Maro and his team then used pre-existing data on chimp diets and body weights to estimate the chimpanzees' daily ethanol intake across the two populations. They found that both male and female chimps consume approximately 0.5 ounces ethanol per day, which is around 2.5 standard drinks when adjusted for their smaller body size.

Matthew Carrigan, a molecular biologist at the College of Central Florida who was not involved in the research, said that while the results aren't necessarily surprising, they are exciting because it's moving forward an "important question about human ethanol addiction and evolution."

However, Carrigan pointed out that "there's a very wide range" in the error bars, meaning that the chimps could be eating as little as 0.14 ounces (4 grams) of ethanol per day, or as much as 0.85 ounces (24 grams) — the difference between less than one drink or four.

Maro also acknowledged that the research samples could have been fruits the chimps refused to eat. The next step is to investigate if the chimps are opting to avoid or seek out individual fruits based on their degree of fermentation, Carrigan said.

Ultimately, humans and chimpanzees "evolved to get calories without getting drunk," Carrigan said. "Otherwise, if we evolved to get drunk, then we would not evolve to metabolize the ethanol faster."

Jane Goodall, the world's foremost expert on chimpanzees, has died at the age of 91, the Jane Goodall Institute (JGI) confirmed in a statement on Wednesday (Oct. 1). Goodall died of natural causes in Los Angeles, California, while on a speaking tour.

Goodall "was a remarkable example of courage and conviction, working tirelessly throughout her life to raise awareness about threats to wildlife, promote conservation, and inspire a more harmonious, sustainable relationship between people, animals and the natural world," the JGI statement reads.

Dame Valerie Jane Morris-Goodall was born April 3, 1934, in London. As a child, Goodall was fond of animals, including the 1920 book "The Story of Dr. Dolittle," and intrigued by the ecosystems of Africa. On a trip to Kenya in 1957, she met paleoanthropologist Louis Leakey, who convinced Goodall that studying the behavior of chimpanzees (Pan troglodytes) might provide insights into the behavior of early human ancestors.

Goodall began her research into chimpanzees in 1960 after arriving at Gombe Stream National Park in Tanzania. With no formal academic training in a research area dominated by men at the time, Goodall spent months quietly observing the apes, giving them names such as Fifi, Passion and David Greybeard.

"It isn't only human beings who have personality, who are capable of rational thought, emotions like joy and sorrow," Goodall said in a 1996 PBS documentary.

In 1966, Goodall took a break from working at Gombe and completed a doctorate at the University of Cambridge. Her doctoral thesis detailed her years' worth of study at Gombe. One key observation that Goodall made at the national park was that chimpanzees were capable of making and using tools — she famously saw one of the apes strip a stick to "fish" for termites in a mound.

The discovery of chimpanzee tool-making counteracted the prevailing assumption at the time that only humans were intelligent enough to make tools. The revelation inspired Leakey to declare, "We must now redefine tool, redefine man, or accept chimpanzees as human!"

Goodall was the first person to document that chimps hunt and eat meat, revealing they are omnivores rather than the vegetarians scientists thought they were. She also saw chimps embrace one another in mourning after the death of a troop member and develop a kind of primitive language system.

But Goodall also documented disturbing behaviors never seen before, such as dominant females killing the young of other females.

"We found that chimpanzees can be brutal — that they, like us, had a darker side to their nature," Goodall wrote in her book "Reason for Hope: A Spiritual Journey" (Grand Central Publishing, 2000).

In the 1970s, Goodall became increasingly concerned about conservation efforts at Gombe and throughout Africa, and in 1977, she founded the non-profit Jane Goodall Institute. JGI maintains a presence at the Gombe Stream Research Centre — now the longest ongoing chimpanzee study in the world — and also helps teach young people around the world about environmental conservation.

Until her death, Goodall traveled the world nearly 300 days a year, speaking about wildlife conservation and environmental crises, according to the JGI statement. Her public lectures often began with "Dr. Jane" pant-hooting a chimpanzee greeting to her audience, and she would emphasize the collective power of individual actions for the benefit of the environment. In a 2002 essay published in Time Magazine, Goodall wrote that "the greatest danger to our future is apathy."

In a statement, Audrey Azoulay, director-general of UNESCO, said that "Dr. Jane Goodall was able to convey the lessons of her research to everyone, especially young people. She changed the way we see Great Apes. Her chimpanzee greetings at UNESCO last year — she who so strongly supported our work for the biosphere — will echo for years to come."

Goodall is survived by her sister, Judy Waters, her son, Hugo Eric Louis van Lawick, who was nicknamed "Grub" as a child, and three grandchildren. Grub spent his early years at Gombe, and Goodall's observations of chimpanzees helped her understand how to raise her son, she told People Magazine in 1977.

"The chimpanzees have an extremely close bond between mother and child," she said, "and I raised Grub this way."

During her 60 years of working with primates and spreading a message of environmental conservation, Goodall inspired other women to become scientists and received numerous awards, including Commander of the Order of the British Empire (1995), United Nations Messenger of Peace (2002), French Legion of Honour (2006), and the Presidential Medal of Freedom, which she was awarded in January 2025 by U.S. President Joe Biden.

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.

In the primate world, alpha males rarely dominate females, scientists have discovered — and there are about as many examples of males dominating females as there are of females dominating males.

The researchers investigated intersexual dominance across more than 100 primate species and discovered that, in most primates, neither sex is clearly dominant over the other, challenging historical assumptions that males are usually more domineering.

The researchers' findings, published July 7 in the journal PNAS, paint a nuanced picture of intersexual relationships, with both sexes often capable of winning aggressive contests against one another.

And in the minority of species where there is clear-cut dominance, males and females typically employ different strategies to rule over others.

"Critically, while primate males gain power via physical force and coercion, female empowerment relies on alternative pathways, such as reproductive strategies to gain control over matings," study first author Élise Huchard, a senior researcher who studies mammal behavior at the University of Montpellier in France, said in a statement.

Related: Chimps develop fashion trend by shoving grass in their ears — and in their butts

Historically, scientists often assumed that males were the dominant sex across mammals. However, male mammals don't always have a size advantage over females, and in recent decades, researchers have documented plenty of cases where females reign supreme, from matriarchal orcas (Orcinus orca) leading their pods to aggressive female meerkats (Suricata suricatta) outranking their male counterparts. The same is true in primates, with female dominance recorded in species like bonobos (Pan paniscus) and ring-tailed lemurs (Lemur catta).

To investigate intersexual relationships in primates across multiple species, the researchers analyzed data from 253 primate studies. The team found that aggressive encounters between males and females were common in primates, making up around half of all contests, but they were rarely one-sided.

The researchers measured the winner of intersexual contests in 151 populations across 84 species, and found that males always won in 25 populations involving 16 species, while females always won in 20 populations involving 16 species. The outcome was more complex in the remaining 106 populations of 69 species, where there were moderate sex biases, according to the study.

Dominance varied not only across different primate species but within a single species. For example, different female bonobo populations won between 48% and 79% of their contests, while female patas monkeys (Erythrocebus patas) won between 0% and 61% of their contests. The researchers noted that Angolan talapoins (Miopithecus talapoin) could exhibit strict male dominance, strict female dominance, or no clear bias between the two, depending on the group observed.

The researchers investigated the mechanisms behind this varied dominance in primates and found that physical characteristics played a role, but so did where and how the animals lived. Female dominance mostly occurred in populations where females had reproductive control, meaning they decided whether to mate. For example, this was typically the case for monogamous species living in trees where females could escape males, and where conflict posed less of a threat to offspring a female was already carrying. In contrast, male dominance was more common in ground-dwelling species where males were bigger and controlled mating with multiple females.

"Recent research started to challenge the traditional views of male dominance being the default status, and our study now provides a more comprehensive exploration of variation in intersexual dominance relationships," study co-author Peter Kappeler, head of behavioral ecology and sociobiology at the German Primate Center research institute, said in the statement.

Captive chimpanzees have started dangling grass out of their ears and butts in an unusual fad-like "trend," a new study finds.

The chimps (Pan troglodytes) insert a blade of grass or stick into their ear or rectum and then just let it hang there for a while, researchers reported. The behavior doesn't appear to have any physical or medical purpose, but spreads socially from chimp to chimp.

Researchers first reported the grass-in-ear behavior in 2014. At the time, only one group of chimps living at the Chimfunshi Wildlife Orphanage in Zambia exhibited the behavior. Now, another of the sanctuary's groups has independently adopted the behavior and introduced a daring new style — wearing the grass in their rectums. The researchers described the new behavior in a study published July 4 in the journal Behaviour.

The two groups don't have any contact with each other, but they do share the same human keepers. Researchers suspect that the ear part of the behavior originally came from chimps copying their human caretakers, before spreading through the groups and changing slightly.

"These caretakers reported that they sometimes put a blade of grass or a matchstick in their own ears to clean them," study lead author Edwin van Leeuwen, an assistant professor of animal behavior and cognition at Utrecht University in the Netherlands, said in a statement. "Caretakers in the other groups said they did not do this. The chimps in the one group then figured out to stick the blade of grass in another place as well."

Related: Watch boozing chimps share alcoholic fruit. Is this how social drinking started?

Social animals often copy behaviors from one another. These behaviors are typically centered around finding food or some other critical survival skill. However, researchers have also occasionally documented temporary fads spreading through populations without an obvious benefit. Some orcas (Orcinus orca) in the Northwest Pacific are famous for this, having developed a bizarre habit of swimming around with dead salmon on their heads.

The authors of the new study first noticed the grass-in-ear behavior in a female chimp named Julie in 2010. Julie repeatedly put blades of grass in her ear and let them hang there. Researchers later recorded seven other members of her group picking up the trend. Julie died in 2013, but some of the group continued with the behavior, suggesting it had become a cultural tradition, according to the study. The second group then began performing the behavior in 2023.

To re-study this trend, researchers observed all of the sanctuary's chimps over 12 months between 2023 and 2024. Only two chimps from Julie's group were still wearing grass in their ears — one of which was Julie's son. Meanwhile, in the other group, a male named Juma was identified as the possible innovator of the daring new grass-in-butt variation, which spread to most of his group mates within a week, according to the study.

The researchers suspect that captivity played a role in the trends. Wild chimps, which haven't been observed engaging in such seemingly frivolous behaviors, fill their days finding food and have to deal with many more challenges than captive chimps, which typically have their meals delivered.

"In captivity, they have more free time than in the wild." Van Leeuwen said. They don't have to stay as alert or spend as much time searching for food."

The jury is still out on what the chimps are getting out of their grassy orifice accessories. However, the researchers speculated that this kind of social learning may help bolster social identity and social cohesion.

"It could also serve a social purpose," Van Leeuwen said. "By copying someone else's behaviour, you show that you notice and maybe even like that individual. So, it might help strengthen social bonds and create a sense of belonging within the group, just like it does in humans."

Wild capuchin monkeys have been kidnapping infant howler monkeys, putting them on their backs and taking them for a ride. The trend, which began with one male, spread to other members of the group, and has resulted in deaths of at least four infants since 2022.

"The sort of rate at which we see the infants appearing suggests they are not just finding these infants, they are getting them," study co-author Zoë Goldsborough, a behavioral ecologist also at Max Planck Institute of Animal Behavior in Konstanz, Germany, told Live Science. The unprecedented behaviour was spotted by camera traps set up on Jicarón Island off the coast of Panama.

Panamanian white-faced capuchins (Cebus imitator) are social monkeys, living in groups in the forests of Central America. The monkeys are smart and learn fast, and were being monitored by motion-triggered cameras to study tool use.

The team from the Max Planck Institute started putting the camera traps on the ground on Jicarón Island in 2017.

"These monkeys don't have terrestrial predators, so these capuchins spend the overwhelming majority of their time on the ground," co-author Brendan Barrett, an evolutionary behavioral ecologist at the Max Planck Institute of Animal Behavior, told Live Science.

The cameras revealed the capuchins using stones like hammers to crack open snails, fruit called sea almonds and hermit crabs. But Goldsborough, Barrett and their colleagues also saw something even more surprising.

Related: Which animals have entered the 'Stone Age'?

The first glimpse of the odd behavior was in January 2022, when one juvenile male capuchin — whom the researchers named Joker after the "Batman" character because of a scar near his mouth — was seen carrying an infant howler monkey on his back. In the months that followed, Joker was spotted carrying four different howler infants for periods of as long as nine days.

And the behavior soon caught on. From September of the same year, four other young male capuchins were caught by the cameras carrying infant howler monkeys for days at a time. A total of 11 infant howler riders were spotted in all, the researchers report in a study published Monday (May 19) in the journal Current Biology.

How the capuchins got hold of the infants is unknown, because it happened away from the cameras, but the researchers think the capuchins are abducting them from adult howler monkeys (Alouatta palliata coibensis). "It very likely happens in the trees," Goldsborough said.

"I think the term abduction is realistic and adequate for this," Katherine MacKinnon, a biological anthropologist at Saint Louis University in Missouri, who wasn’t involved in the research, told Live Science.

MacKinnon said the howler monkeys are much bigger than capuchins, but they're slower. "I've watched them grapple with capuchins and it's like watching the howlers in slow motion and the capuchins on 45 record speeds. Howlers can put up a fight, but capuchins are in another class."

The abducted howler infants seemed healthy at first, but were very young, so needed milk from their mothers to survive. Their health worsened in the days following their abductions and at least four of them died, probably from malnourishment.

"We have confirmed deaths of four and for the others it's unknown. Some of them, the youngest ones, are one or two days old, so it's unlikely that a lot of them survived," Barrett told Live Science. Three infants were carried for at least a day after dying.

In two sightings, the carrying male capuchins embraced their infant riders, but generally, they just carried them neutrally. However, the capuchins did seem to get annoyed if the young howlers did something they didn't like, such as attempting to suckle, and would bite or push them away.

"We did sometimes see them being affectionate or affiliative towards the howler monkey infants," said Barrett. "It's almost like a kid having a jar of lightning bugs. They think it's cool. But from the lightning bugs perspective, it's not the best situation."

So why have the capuchins been kidnapping baby howlers? There are anecdotal reports of female capuchins adopting the young from other species, and male capuchins do sometimes carry the young of other capuchins and play with them, but the researchers don't think they are doing it out of a desire to be caring.

Given that carrying around the howlers doesn't seem to bring any kind of social benefit, Barrett suggests the male capuchins are doing it because they are bored and have nothing better to do — the highly intelligent monkeys have no predators and few competitors on Jicarón Island, giving them ample time for destructive social innovation.

"It is a very capuchin thing to do. They're very curious. They like to poke and bother all other creatures," Susan Perry, an evolutionary anthropologist at the University of California, Los Angeles, who wasn’t involved in the research, told Live Science. "I would guess that they don't mean any harm to these babies, but they don't get that the howlers need milk."

"It only takes one member of these social groups to come up with a strange behavior," said MacKinnon, and then it can spread. She gives the example of Japanese macaques (Macaca fuscata) that learned to wash sweet potatoes in the sea, after one female started the trend.

Perry suspects it is linked to other male capuchin behavior. Males leave the group they were born into to find a new group to take over — but they need to stick together to make a success of it. "If they don't have male allies, they're basically sunk," she said. So, males do a lot of bonding when young. As part of this, they sometimes grab and carry around unrelated male infants, Perry said. "So, they are already primed to sort of kidnap infants."

"Usually, [the capuchin] mum gets the infant back because they're traveling as a cohesive group," said Perry. "In this case, probably the capuchins grabbed the howlers and then ran for it. And they didn't see the howler group again and the mum didn't get her baby back."

The behavior could be bad news for the howlers on Jicarón, which are an endangered subspecies.

Barrett thinks there are about four or five groups of howlers in the area. "The number of infants we saw could be all the babies from those groups," he said.

All the researchers Live Science spoke with said that the traditions of capuchins are often short-lived, and all hoped that this one would also peter out soon, perhaps when the males doing it leave the group.

"They're gonna run out of howlers at some point, but I hope it will end before that happens," said Perry.

On its face, a comparison of monkeys and apes seems straightforward: Modern primates have defining physical features and behaviors that clearly sort them in different categories.

Beginning with living animals, those differences are easy to pick out. Most monkeys have tails; some have prehensile tails, which means they can grasp and hold things. They're quadrupeds, meaning they use all four limbs to get around. They have four limbs that are about the same length, as well as a flexible spine.

Monkeys can be subdivided into Old World and New World classifications based on where they live. Old World monkeys live in Africa and Asia, while New World monkeys live in Central and South America, according to the Pan African Sanctuary Alliance. Old World monkeys are also known as African-Eurasian and New World monkeys as Neotropical.

Apes, on the other hand, don't have tails. Their "orthograde" body plan makes them capable of standing upright and gives them disproportionate limbs, with long arms and shorter legs. Inversely, humans — which are also apes — have long legs and shorter arms. Apes also have a larger brain relative to their body size than monkeys do, which has critical implications for intelligence.

"There is a significant difference in intelligence between monkeys and apes," Becky Malinsky, curator of primates at the Smithsonian's National Zoo and Conservation Biology Institute, told Live Science in an email. "While monkeys are capable of complex thinking, they generally have a lower cognitive capacity than apes."

Related: What did the last common ancestor between humans and apes look like?

Apes can be subdivided into the great and lesser apes based on their size. Great apes include chimpanzees (Pan troglodytes), eastern gorillas (Gorilla beringei), western gorillas (Gorilla gorilla) and bonobos (Pan paniscus) — all of which live in Africa — and orangutans (Pongo), which live in Southeast Asia. Lesser apes comprise gibbons and siamangs, which live in Southeast Asia. Although humans are also great apes, this article focuses on non-human primates.

Monkey versus ape genetics

But when you consider their evolutionary history, the difference between apes and monkeys is murkier.

"From the surface, it seems like a very easy thing to discuss," Sergio Almécija, a senior research scientist of biological anthropology at the American Museum of Natural History in New York City, told Live Science. "But that superficial impression, I think, [is] based on living animals only."

According to a review published in the journal Science in 2021, of which Almécija is the lead author, humans diverged from apes — specifically chimpanzees — between 9.3 million and 6.5 million years ago.

But apes and monkeys diverged from their last common ancestor even longer ago: between 23 million and 34 million years ago, according to a 2013 paper published in the journal Nature. The authors analyzed the oldest known fossils from Old World (African-Eurasian) monkeys and apes, found in the Rukwa Rift Basin in southwestern Tanzania: a partial jawbone with three teeth from an ape, and a single molar from a monkey. The team classified these novel fossil primates, calling the ape Rukwapithecus fleaglei and the monkey Nsungwepithecus gunnelli. Geological dating of the rock layer in which these fossils were found indicate they’re about 25.2 million years old.

Still, there's much more to learn about how primates evolved over millions of years. "The fossil record can lead to varying interpretations and debate," Malinsky wrote.

"It's really much more complex than we think," Almécija said. "We don't have as much information as we think we do to answer some of these questions."

Injuries may heal much more slowly in humans than they do in other mammals, including our closest primate cousins, scientists say.

In a study published Tuesday (April 29) in the journal Proceedings of the Royal Society B: Biological Sciences, researchers found that human wounds healed around three times more slowly than the same injuries in nonhuman primates, including chimpanzees (Pan troglodytes), which, along with bonobos (Pan paniscus), are our nearest living relatives.

This difference in healing rates between humans and chimps was not present between other species of primates, nor between nonhuman primates and other mammals, like rodents. The discovery suggests humans evolved slower healing at some point in our ancestry.

"This finding indicates that the slow wound healing observed in humans is not a common characteristic among primate order and highlights the possibility of evolutionary adaptations in humans," the researchers wrote in the paper.

Human wounds heal in several stages, starting with clotting to prevent bleeding, followed by immune cells, like neutrophils and macrophages, rushing to the area to kill bacteria and remove dead tissue and debris. Next, the body repairs the damaged tissue: Fibroblast cells make collagen, a protein that provides structure and strength; new blood vessels form to supply nutrients; and skin cells migrate across the wound to cover it.

Other mammals heal in much the same way we do, with minor differences. Some species — like rats, mice, horses and cats — heal via a method called wound contraction, in which the edges of the wound are pulled together like stitches in sewing.

In the new study, the researchers tested how healing rates differed between humans, nonhuman primates and other mammals.

The researchers tested wound healing in olive baboons (Papio anubis), Sykes' monkeys (Cercopithecus albogularis) and vervet monkeys (Chlorocebus pygerythrus) that had been captured in the wild and subsequently housed at the Kenya Institute of Primate Research. The primates were anesthetized and given a 1.6-inch (40 millimeters) wound, and the surface area, length and width of the wound was measured every day afterward.

To measure wound healing in chimpanzees, meanwhile, the researchers analyzed photographs of naturally occurring wounds on five chimps at the Kumamoto Sanctuary of Kyoto University in Japan.

These wounds were located across the upper limb, lower limb, back, buttocks, abdomen, face and back of the hand, and were photographed at two- to seven-day intervals. The healing rate in humans and rodents was also measured. Twenty-four human volunteers who had operations to remove skin tumors had their wounds photographed daily at the University of the Ryukyus Hospital in Japan. The rat and mouse wounds were created and monitored in the lab.

The researchers found that there was no statistically significant difference between the wound-healing rates among the four nonhuman primate species, and no difference between the healing rates of primates and those of rats and mice. They also found that the wound-healing rate in humans was about three times lower than that seen in the nonhuman primate species.

"The results obtained indicated a common healing rate among cercopithecines [a group of Old World monkeys], which constitute a significant portion of the primate order, and chimpanzees, which are genetically and phylogenetically the closest relatives of humans. This observation suggests that non-human primates share a common healing rate," the researchers wrote.

This finding indicates that humans may have evolved slower healing relatively recently, after diverging from our last common ancestor with chimpanzees 6 million years ago, the researchers said.

Developing a slower healing rate seems counterintuitive, as slower healing may reduce our ability to avoid predators and access food, and it uses up more energy needed for growth and reproduction.

The researchers suggested that humans' slower healing may have arisen due to differences in body hair, skin thickness or sweat-gland density. Increased concentration of sweat glands would have led to a decrease in body hair density, possibly leaving the skin more vulnerable to injury. This may have sparked the evolution of a thicker layer of skin to increase protection, which in turn may have resulted in slower healing rates, the researchers suggest. Human social groups, as well as our first forays into medicinal plants, may have helped to mitigate the disadvantages of slower wound healing, the team proposed.

However, more research is needed to truly understand the reasons for the slow healing, the researchers said.

"A more comprehensive understanding of the underlying causes of delayed wound healing in humans requires a comprehensive approach that integrates genetic, cellular, morphological, fossil human skeletal and extant non-human primate data," the researchers wrote.

Chimps have been spotted sharing alcoholic food for the first time, hinting that ancient ape behaviors gave rise to social drinking in humans.

Researchers filmed the boozing chimpanzees (Pan troglodytes) gorging on fermented fruit in West Africa as part of a new study exploring alcohol consumption in one of our closest living relatives. The footage is the first evidence that nonhuman great apes consume alcohol together, supporting the idea that social aspects of consuming alcohol are deeply rooted in the ape family tree.

Humans have a history of gathering together to eat, drink and be merry. This feasting behavior has a number of social benefits and can help boost social bonds — though drinking alcohol also carries health risks. Now, the footage of chimps sharing fermented fruits has left researchers wondering whether chimps get similar social benefits from consuming alcohol in a group.

"Chimps don’t share food all the time, so this behaviour with fermented fruit might be important," study co-author Kimberley Hockings, an associate professor in conservation science at the University of Exeter in the U.K., said in a statement. "We need to find out more about whether they deliberately seek out ethanolic [alcoholic] fruits and how they metabolise it, but this behaviour could be the early evolutionary stages of 'feasting'."

The researchers published their findings Monday (April 21) in the journal Current Biology.

Related: 'Contagious' peeing may have deep evolutionary roots, chimp study suggests

Alcohol consumption is likely common in the natural world. Lots of wild foods, including fruit, sap and nectar, contain the kind of alcohol humans put in drinks (ethanol) and thus will be ingested by many animals, including primates.

Humans have been producing and drinking alcoholic beverages for around 9,000 years. However, our ancestors — and the ancestors of chimps — developed an enhanced ability to metabolize alcohol around 10 million years ago. This adaptation suggests that alcohol consumption is an ancient ape behavior.

To learn more about how chimpanzees consume alcohol, the researchers observed chimps eating naturally fermenting fruit from African breadfruit trees (Treculia africana) in the Cantanhez National Park in Guinea-Bissau. The team used camera traps to film the chimps eating and analyzed the alcohol content in the fruit.

The researchers observed the chimps sharing African breadfruit on 10 separate occasions and found that 90% of this shared fruit contained alcohol. The alcohol content wasn't high by human standards, with a maximum of 0.61% alcohol by volume (ABV) — a beer is usually around 5% ABV. However, the impact of alcohol on a chimp's metabolism is unknown, and they might not need as much as we do to feel a buzz.

A chimp's diet can be up to 85% fruit, so if plenty of that is fermented, then they may be consuming significant amounts of alcohol. That said, the researchers noted that the chimps probably aren't getting drunk, as that would be detrimental to their survival chances, according to the statement.

The study also highlighted that chimps gain benefits from consuming fermented fruit that have nothing to do with alcohol consumption. For example, the exterior of fermented fruit is softer than less ripened fruit, so chimps find it easier to open and eat.

While the researchers said their study supports the idea that alcohol consumption is rooted in ape evolutionary history, they noted that more work is needed to fully understand the social side of alcohol consumption.

Primates are a group of mammals that includes humans and our close relatives, such as apes, monkeys and lemurs. Monkeys, such as capuchins and macaques; prosimians, like lemurs and tarsiers; lesser apes, such as gibbons; and great apes, like gorillas, chimpanzees and orangutans, are all primates. Our close extinct relatives, such as the Neanderthals, were also primates. Most primates live in tropical climates close to the equator, though some live in colder or snowy environments, like the mountains of Japan.

Primates have larger brains than most other mammals of their size. This gives them advanced learning and problem-solving abilities. Many primates also live in complex social groups and communicate through vocal sounds, body language and facial expressions. Humans' closest living relatives are chimpanzees and bonobos — and a few of these animals have even been taught to understand some human language.

5 fast facts about primates

• Humans are primates, and chimpanzees and bonobos are our closest surviving relatives.
• Chimpanzees and capuchin monkeys use tools to get food.
• Primates often groom each other by picking off dirt and ticks, not just to stay clean, but also to build friendships and settle fights.
• Unlike many other mammals, which can see only two colors (blue and green), most primates can see three colors (blue, green and red).
• Kanzi, a bonobo born in captivity who was given language lessons, could play Minecraft and Pac-Man, and understand when his keepers spoke to him in English.

Everything you need to know about primates

Primate pictures

Discover more about primates

—Monkeys: Facts about the largest group of primates

—Chimpanzees: Intelligent, social and violent

—Why haven't all primates evolved into humans?

Editor's note: This article was updated at 4.20 a.m. ET on May 2, 2025 to correct the locations where primates are found.

Modern humans have uniquely small and flat faces, especially compared with our Neanderthal cousins' notoriously robust faces and large noses, but the reason for this difference has eluded paleoanthropologists. Now, researchers have determined that human faces grow slowly and stop growing during early adolescence, whereas Neanderthals' faces kept growing into early adulthood.

"These two human species followed different developmental trajectories for their facial bones," Alexandra Schuh, a postdoctoral researcher at the Max Planck Institute for Evolutionary Anthropology in Germany, told Live Science.

In a study published Monday (March 24) in the Journal of Human Evolution, Schuh and colleagues analyzed the midface region of 174 skulls of Homo sapiens, Neanderthals and chimpanzees. By including skulls from individuals throughout childhood and into adulthood, the researchers were able to investigate facial ontogeny — how the facial bones of the skull develop and grow.

The researchers used two techniques to closely examine the skulls. First, they created virtual 3D models of the skulls and digitized over 200 landmarks on the upper jawbone to look at patterns of growth and development. Then, they undertook microscopic analysis to look for bone formation and bone resorption, a normal process in bone remodeling that helps the tissue retain its structure and strength.

Related: 28,000-year-old Neanderthal-and-human 'Lapedo child' lived tens of thousands of years after our closest relatives went extinct

"We found that bone formation is predominant in Neanderthals — from birth on — who develop larger and more projecting faces," Schuh said. "In contrast, present-day humans exhibit significantly higher levels of bone resorption."

The new research showed that both chimpanzees and Neanderthals had larger, faster-growing faces, while modern humans have smaller faces that stop growing sometime during adolescence.

"Earlier growth cessation is a distinctive feature of our species," Schuh said. "We have identified a unique developmental pattern seen exclusively in Homo sapiens."

Experts have put forth numerous explanations for why Neanderthals had such large faces and noses, including adaptation to a cold climate, higher energy needs, the chewing of tough foods, and the use of their teeth as tools. Explanations for humans' small faces, on the other hand, include the invention of cooking and increases in brain size.

But the reason humans evolved these uniquely small faces is a particularly complex question in paleoanthropology that has not yet been solved. "However, our study addresses aspects of the 'how,'" Schuh said, "providing an important first step toward understanding these processes."

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

Kanzi, a male bonobo with advanced language aptitude, has died at the age of 44 according to a statement by the Ape Initiative, the conservation and research center in Des Moines, Iowa, where he had lived since 2004.

As an infant, Kanzi, who was born at the Emory National Primate Research Center in Atlanta, Georgia, accompanied his adoptive mother Matata to language lessons. But while Matata was not interested in learning from her human caretakers, Kanzi surprised them by quickly learning the lexigrams, or symbols that map to words, that the researchers were trying to teach his mother, in much the same way human children learn language by listening to their parents talking.

Primatologists have used lexigrams since the 1970s to understand how chimpanzees and bonobos think and communicate. Using a special lexigram keyboard, the great apes are encouraged to communicate with their caretakers by pressing different buttons or pointing to pictures.

Researchers taught Kanzi more than 300 lexigrams, and Kanzi combined them to create new meanings, an important aspect of symbolic thinking — something which experts previously assumed only humans were capable of.

But Kanzi was also able to understand and respond to requests in spoken English. In a study undertaken when Kanzi was 8 years old, he and a 2-year-old human child were given 660 spoken instructions. Kanzi outperformed the child, suggesting his linguistic ability was at least as good as a human toddler's.

Related: Chimps learned tool use long ago without human help

In another study, Kanzi learned some American Sign Language (ASL) simply by watching videos of Koko the gorilla, who had previously been taught to use ASL. And when separated by a wall from his sister, Panbanisha, Kanzi vocalized a sound for 'yogurt' that Panbanisha understood.

Although Kanzi showed one-of-a-kind linguistic abilities for an ape, he didn't speak in the same way humans do. Researchers think this is related to the anatomical differences between chimpanzee and human vocal tracts. However, a 2024 study published in Scientific Reports suggests that chimpanzee vocalization abilities may have been underestimated, as these apes can produce novel sounds and have the brain capacity necessary for speech.

Beyond his language skills, Kanzi showed off his ability to make and use stone tools, earning him the epithet "bonobo genius." He was then taught to build a fire and cook food, demonstrating his ability to learn behaviors key to human evolution.

Later in life, Kanzi was even taught to play video games. He seemed to understand how to beat the arcade game Pac-Man and defeated the final boss of Minecraft.

On March 18, staff at the Ape Initiative found Kanzi unresponsive. He was being treated for heart disease, according to the statement, but necropsy results clarifying his cause of death are pending.

Evolution quiz: Can you naturally select the correct answers?

Chimpanzees tend to pee when others in their group do, in a phenomenon scientists have dubbed "contagious urination."

Because groups of people often go to the bathroom together too, and chimpanzees are our' closest living relatives, this social behavior could be traced back to our common ancestor, researchers said.

"In humans, we know that our decision to urinate is influenced by social contexts that lead us to urinate simultaneously with others, and that this simultaneous urination could also promote further social bonding," study co-author Shinya Yamamoto, a wildlife researcher at Kyoto University, told Live Science in an email. "Our study with chimpanzees clearly shows that they share some similarities in this phenomenon, suggesting the deep evolutionary origin of contagious urination."

The team decided to study the behavior after noticing that a group of chimpanzees at a zoo tended to urinate at about the same time, and wondered whether it could be similar to contagious yawning, which has been observed in other primates and wolves.

Related: Humans' big brains may not be the reason for difficult childbirth, chimp study suggests

For the study, published Monday (Jan. 20) in the journal Current Biology, researchers observed 20 chimpanzees in captivity at the Kumamoto Sanctuary in Japan for more than 600 hours.

They found that when one chimpanzee in the group peed, others were more likely to follow. The researchers recorded the number of urinations that occurred within 60 seconds of one another, and then compared these data with randomized computer simulations. The study found that this contagious urination behavior increased with physical proximity, so chimpanzees seeing another chimpanzee close to them peeing were more likely to follow suit.

Social rank also influenced this behavior: Chimpanzees with lower dominance ranks were more likely to pee when others were peeing. Social closeness, measured by time in close proximity and grooming with another chimpanzee, had no effect on the peeing phenomenon — unlike with social yawning, which increases in socially closer pairs.

Contagious urination could be important to social group cohesion, coordination or reinforcing social bonds, the researchers said.

The behavior could exist to encourage "state-matching," where chimpanzees improve group cohesion by all being in a similar state, study co-author Ena Onishi, a wildlife researcher at Kyoto University, told Live Science in an email. The behavior could also reinforce social connections.

Another possibility is that multiple chimpanzees urinating in a single location can deter or confuse predators, by reducing the risk of being tracked through scattered urine odors.

While no similar studies have yet been conducted on chimpanzees in the wild, some researchers have noted similar behaviors in wild populations, Onishi said. The researchers are also curious about whether other species show this contagious urination behavior.

"We are greatly influenced by the presence of others, even in mundane activities," Onishi said. "For example, in both chimpanzees and humans, behaviors like yawning, walking, rhythmic tapping, and even pupil size are known to be contagious."

Studying contagious urination could help scientists understand the behavior of humans' common ancestors with chimpanzees, and the origin of the social custom in humans, Onishi said."

There's been a lot going on in animal news this year.

Perhaps the best animal story of 2024 came right at the end of the year, when orcas (Orcinus orca) started wearing salmon hats again after a 37-year hiatus from the fabulous fad. And while scientists don't really know why orcas are balancing dead fish on their heads, the best guess is there is so much of their favorite food — chum salmon (Oncorhynchus keta) — available, it's a way to save it for later.

But there was plenty of other news from the animal kingdom this year. We found out that female gibbons do the robot and "vogue" — but only if they're sure someone else is watching. Researchers aren't sure why the apes do it (the dancing was seen in wild and captive gibbons), but it seems to relate to sex, food and their social lives.

Speaking of food, we had two never-before-seen cases of predators eating each other. In the sea, a pregnant portbeagle shark (Lamna nasus) got gobbled up by another shark — likely a great white shark (Carcharodon carcharias) or a shortfin mako (Isurus oxyrinchus). And on land, a Burmese python (Python bivittatus) was seen feasting on an even bigger reticulated python (Malayopython reticulatus) from the tail up, while it was still alive. A Burmese python in Florida also swallowed a deer whole by stretching its mouth to almost the limit of what is physically possible for the species.

In the insect world, scientists discovered that ants carry out life-saving operations by performing amputations on injured nestmates — becoming the only known animal in the world other than humans to do so.

Cassius, the world's largest captive crocodile, died in November, having potentially reached the ripe old age of 120. He was captured in the Finniss River, near Darwin, Australia, in 1984 after he started eating livestock, attacking boat engines and fighting other crocodiles. Scientists are now studying his bones to find out exactly how old he was when he died.

And it wasn't just living animals making headlines. In August, Siberian gold miners accidentally stumbled upon the mummified remains of a woolly rhino (Coelodonta antiquitatis) with its horn and soft tissues still intact. A winemaker in Austria found hundreds of mammoth bones while renovating his cellar, and scientists performed an autopsy on a 44,000-year-old mummified wolf pulled from the permafrost.

Related: 35,000-year-old saber-toothed kitten with preserved whiskers pulled from permafrost in Siberia

Researchers in the U.K., meanwhile, discovered what could have been the biggest marine reptile ever found. This ichthyosaur, which lived 200 million years ago, is estimated to have been a whopping 82 feet (25 meters) long. Also from the age of the dinosaurs, palaeontologists in Morocco discovered a never-before-seen species of marine lizard with "dagger-like" teeth; and in Brazil, heavy rains exposed one of the oldest dinosaur skeletons ever discovered.

And where the living and long-dead collide, scientists now say the de-extinction of species like the woolly mammoth (Mammuthus primigenius) and Tasmanian tiger (Thylacinus cynocephalus) is "closer than people think." Researchers working on the effort claim bringing back ice age megafauna could help restore ancient ecosystems, boost carbon storage and mitigate climate change — but it remains to be seen whether it will cause catastrophic, unintended consequences.

"We have this hubris as humans that we can control our technology," Oswald Schmitz, a professor of population and community ecology at Yale University, told Live Science. "I'm not so convinced."

Animal news quiz 2024

Given an infinite amount of time, an infinite number of monkeys randomly prodding keys on a typewriter could, in theory, eventually replicate the works of William Shakespeare. At least, that's what a thought experiment called the infinite monkey theorem states.

The infinite monkey theorem was first proposed by mathematician Émile Borel in 1913, and it's been a popular way to understand randomness and probability for decades. But could a monkey really type out Shakespeare?

Although it's an interesting theoretical exercise, this task is probably impossible within the lifetime of our universe, experts told Live Science. That's because the "infinite" component is a key part of the infinite monkey theorem. The chance of a monkey randomly typing anything coherent is very unlikely. However, in the context of infinity, even the most unlikely things could eventually occur.

But our universe isn't infinite, Stephen Woodcock, an associate professor of math and physical sciences at the University of Technology Sydney and co-author of a study about the infinite monkey theorem, told Live Science. "It'll last for a very long time, but it won't last forever," Woodcock said. "There will be a lot of monkeys born, but there will not be an infinite number of monkeys born."

Related: Can you count past infinity?

Not enough monkeys, not enough time

To see whether the infinite monkey theorem was actually applicable in the real world, Woodcock and a colleague did some calculations with theoretical chimpanzees. (Chimpanzees are apes, not monkeys, but the researchers chose them because they, along with bonobos, are our closest relatives.) Assuming that a chimpanzee spent most of its life tapping away on a typewriter, they calculated the probability of the primate typing a word, a sentence, a book and the complete works of William Shakespeare.

They found that the chance a chimp would type the word "banana" in its entire lifetime of about 30 years was only about 5%. A sentence was even less likely. In fact, the likelihood of any of the chimpanzees currently living in the world typing, "I chimp, therefore I am," in their lifetimes was 2 x 10^-20.

"In practical terms, it's basically certain that no chimp alive now would ever type that if you left it for its entire lifetime," Woodcock said. However, the researchers found that in the unlikely event chimps kept breeding and typing for the rest of the universe's lifetime (about 10¹⁰⁰ years), there was a near-certain chance that one chimp would eventually write the sentence.

But when it came to replicating a whole book in the next few trillion years, things started to look very unlikely. Woodcock found there was a "vanishingly small chance" any future chimp would ever mimic "Curious George," let alone Shakespeare, before the heat death of the universe.

The results are a reminder that even in the context of massive numbers, infinity is still incomprehensibly larger. It's also evidence that while thought experiments can help convey interesting concepts, they don't necessarily apply to the real world.

"Just because something is certain in the infinite limit doesn't mean that that has any bearing in our finite universe," Woodcock said.

Real-life infinite monkeys

In their research, Woodcock's team went a little bananas, using calculations that relied on some very generous assumptions. They supposed the chimps typed one character every second of the day for 30 years straight, used a slightly simplified keyboard and pressed each successive key at random.

We know these assumptions probably aren't realistic, because the infinite monkey theorem was once simulated in real life. As part of a 2002 art exhibit, a group at the University of Plymouth in the U.K. gathered six Celebes crested macaques (Macaca nigra) at Paignton Zoo in England and gave them a keyboard for four weeks.

"As the computer was warm, it was quite popular, and there was some writing produced," Geoff Cox, an organizer of the experiment who's now a professor of art and computational culture at London South Bank University, told Live Science in an email.

Unfortunately for Shakespeare enthusiasts, that "writing" was just five pages of gibberish consisting mostly of the letter "S." "It was a hopeless failure in terms of science but that's not really the point," Cox told The Guardian in 2003. "It was more like a little performance."

To him, the "performance" told a story about the nature of animals. "Animals are not machine-like or rule-based systems and instead exhibit unpredictable behaviours," he told Live Science.

Some of those unpredictable behaviors? Bashing the computer with a rock and pooping on the keyboard.

Difficult births are not unique to humans, a new analysis of chimpanzee pelvic bones has revealed.

The findings suggest that complicated births may not have arisen in humans as a trade-off between our need for big brains and pelvises suitable for upright walking — a notion termed "the obstetrical dilemma."

Instead, it's likely "the obstetrical dilemma started much earlier than the old hypothesis predicted and was present in the last common ancestor shared by chimps and humans," Caroline VanSickle, a biological anthropologist at Des Moines University, who was not involved in the study, told Live Science in an email.

What's more, "our ancestors the australopithecines likely were already susceptible to the birth complications that we encounter today," study lead author Nicole Webb, a paleoanthropologist at the University of Zurich, told Live Science in an email, "and they may have even required some sort of birth assistance like us."

Related: Which animal can have the most babies at one time?

Those birthing challenges include problems such as shoulder dystocia, where the baby's shoulder gets stuck, and obstructed labor, which today can be solved by procedures such as cesarean section.

In a study published Oct. 23 in the journal Nature Ecology & Evolution, Webb and her team digitally scanned pelvic bones from 29 chimpanzees and generated 3D models. The team looked for subtle differences between male and female pelvises.

By analyzing the shapes of the chimp pelvic bones, Webb and colleagues found that females had larger, rounder pelvic canals and that the tops of females' hip bones were oriented differently than males'.

The fact that the team found differences in childbirth-related regions of the pelvis suggests there is significant evolutionary pressure to keep that region suitable for carrying and delivering babies, Webb said.

In their 3D simulations of chimpanzee birth, the researchers also found a "tight cephalopelvic fit" — meaning the space between the fetal skull and the maternal pelvis is very small in chimpanzees, just as it is in humans.

This human-like pelvic characteristic is surprising, the researchers noted in their study, particularly because, in humans, the tight fit of our infants is usually explained by a trade-off between needing to walk upright — which requires a shorter and wider pelvis with a birth canal that is narrow front-to-back — and giving birth to big-brained babies.

Humans can give birth to infants with large heads thanks in part to a complicated rotational birth, where the fetus twists and turns in the birth canal, usually emerging face down.

But great apes don't have giant brains, nor do they move around on two feet, so the human-like pelvic traits seen in the chimpanzees led the researchers to wonder why there is a tight fit in chimps. It also raised questions about the origins of the obstetrical dilemma. "It is not primarily an adaptation to giving birth to large-brained infants because we show in this study that these changes happen prior to significant brain expansion," Webb said.

To explain these differences, there were probably gradual obstetrical compromises over millions of years of primate evolution, Webb and colleagues suggest in the study.

Long before humans began to give birth to large-brained infants, and even before our ancestors began to walk on two feet, evolutionary trade-offs arose between the need for a large birth canal and the need for primates with upright torsos to move and climb.

In the researchers’ new theory, human infants are born helpless, with brains that continue to grow after birth; otherwise, they would not make it out of the birth canal. "Chimps may be subtly trending towards this pattern too," Webb said.

"If true, anthropologists may have found an explanation for why some of our bipedal ancestors seemed to have a challenging time giving birth despite having small brains — they may have faced the same birthing challenges as that common ancestor shared with chimpanzees!" VanSickle said.

A fuller reconstruction of chimpanzee birth is needed to better understand the evolution of both humans and our ape relatives, but direct observation of great-ape birth is rare.

"Ideally, future work will figure out how to model the non-skeletal components of chimpanzee birth, which may someday lead us to modeling birth in human ancestors," VanSickle suggested.

Female gibbons perform rhythmic robotic dances for attention or because they're frustrated, researchers say — even glancing over their shoulder while they move to make sure someone is watching.

The scientists observed four species of gibbons in captivity and surveyed studies of gibbons both in captivity and in the wild to analyze dance-like behaviors. They found that the apes performed in a variety of contexts. They published their findings Aug. 29 on the preprint server BioRxiv.

Dance-like behaviors exist throughout the animal kingdom: in birds, bees and many more. But "for non-human primates, the evidence of dance is still scarce, which is what makes the gibbons findings so exciting," study co-author Pritty Patel-Grosz, a linguistics professor at the University of Oslo, told Live Science in an email. "It is also rare that in gibbons, it's the females that dance, and not the males. This is not what we typically find in the animal kingdom."

Great apes — our closest non-human relatives, who include bonobos, chimpanzees, gorillas and orangutans — have not shown any convincing evidence of dance-like behaviors, according to the research team. But crested gibbons, which are lesser apes, have shown evidence of something that looks like dance in previous research.

Related: Strange love: 13 animals with truly weird courtship rituals

"Gibbons dancing was often described as a 'robot dance', but to us it rather looks like some kind of vogueing," Patel-Grosz said.

The researchers examined three aspects of the behavior to define it as dance: whether the movements are intentional, rhythmic and performed in a way that shows non-random structure. The gibbons in the study showed intentional movements, checking for an audience by looking over their shoulder while dancing. The dance was rhythmic, as the length of time between movements in a sequence was uniform — like the gibbons were following a beat. And the structure of the dance was non-random, with movements grouped together.

"When we observe a human dance performance, we will often see that some dance movements are similar to each other in a way that makes us think that they 'belong' together," Patel-Grosz said. "If I'm dancing six steps in one direction, and then six steps in another direction, then we can establish that these are two groups, each consisting of six steps."

The researchers are unsure exactly why the gibbons dance. These lesser apes danced both in the wild and in captivity, and in both cases only sexually mature female gibbons engaged in the behavior. Dancing in the wild was primarily connected to copulation with males, while in captivity it was connected to other contexts as well, such as social interactions, to solicit grooming or, when directed at humans, in anticipation of feeding or social interaction. "The dances occasionally appear to be driven by frustration in connection with excitement," Patel-Grosz said.

The structured, rhythmic and intentional nature of the gibbons' dance means it shares characteristics with human dance. However, the researchers noted that because our last common ancestor with gibbons lived over 20 million years ago — and because our closer great ape relatives fail to exhibit similar dance behavior — it's unclear whether the way humans dance is connected to the way gibbons dance.

The research team is interested in understanding why dance might evolve in a particular primate species not in another — for example, in our great ape relatives.

The menstrual cycle plays an essential role in human reproduction. However, most other animals don't experience menstruation.

So, which other species have periods, and what's the evolutionary point of bleeding periodically?

According to Deena Emera, an evolutionary biologist at the Buck Institute for Research on Aging, scientists know of around 85 mammal species, or less than 2% of mammals, that have a menstrual cycle. Most of these are primates, including our closest living relatives chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). Scientists have also discovered menstrual cycles in a few species of bats, elephant shrews and most recently spiny mice (Acomys cahirinus).

Because these animals aren't all closely related, the trait likely evolved convergently, meaning there must be some evolutionary benefit to it, Emera told Live Science.

Related: Are you genetically more similar to your mom or your dad?

Beyond these creatures, there are other animals that periodically bleed through their reproductive organs. Owners of unspayed dogs may know the unfortunate experience of finding blood on their favorite couch and realizing their pet has gone into heat, also called estrus. However, the bleeding that dogs experience comes from a different source than in menstruating animals.

In animals that bleed while in estrus, an increase in the hormone estrogen while the animal is fertile causes the blood vessels inside the vagina to dilate. This results in small amounts of blood leaking out of the vessels and getting expelled.

In menstruating animals, periods happen because of estrogen and a second hormone called progesterone. Additional hormones are also involved in maturing and releasing an egg in the lead-up to menstruation.

Progesterone is a hormone needed to maintain a pregnancy, and in menstruating animals, it starts to increase before the animal is pregnant. And before that increase happens, a rise in estrogen causes the uterine lining to thicken and new blood vessels to develop. Then, once an egg is released, progesterone starts to rise as estrogen falls.

If pregnancy doesn't then occur, the female's progesterone levels drop, and the newly formed blood vessels and other new tissues slough off in the form of period blood and bits of tissue. In non-menstruating mammals, the uterus does not transform in response to progesterone levels until after the female becomes pregnant, Emera said.

To Emera, this difference is intriguing from an evolutionary perspective. "The question isn't really, 'Why do we menstruate?'" Emera said. "The question is, 'Why do we prepare our uterus for pregnancy before we're even pregnant?'"

Nobody is quite sure what the answer is. But according to Emera, it could have to do with the fact that menstruating animals all give birth to small litters. Humans, primates, bats and elephant shrews usually have just one offspring at a time, while spiny mice have just one to four pups — far fewer than most mouse species.

Related: 10 of the strangest pregnancies in the world

Menstruating animals also have longer pregnancies, or "gestation periods" than their non-menstruating counterparts. Spiny mice, for example, have a gestation period of nearly double that of other mice. Because these animals devote so much time and energy to so few offspring, it's important that their offspring survive.

Researchers have found that, when the uterine lining is transformed for pregnancy, it can detect chemical cues released by the embryo that raise or lower its chances of successfully implanting. These chemical signals reflect aspects of an embryo's viability. This quality-assurance step happens in all mammals, but in menstruating animals that pre-build their lining, it happens much earlier.

"When you have a situation where a female is investing a lot, you totally expect systems to evolve to screen as early as possible against those offspring that aren't going to make it," Emera explained.

Robert Martin, a retired evolutionary biologist and academic guest at the University of Zurich, thinks menstruation may also play a role in sperm storage. Bats, for example, can store sperm in their reproductive tract for up to 200 days before fertilization, and humans have been documented to store sperm for up to nine days in the female reproductive tract.

When sperm stick around for too long, however, they start to degrade, which could cause chromosomal issues should they fertilize an egg, Martin told Live Science. He hypothesizes that the shedding of the uterine lining enables animals to shed this old sperm and make space for newer, more-robust sperm.

There are other theories as to why menstruation happens, but there is no concrete proof for one theory over the others. Martin said that more research needs to be done on menstruation, both in humans and other animals.

"There's been very little research, but there are so many practical applications," he said.

Editor's note: This article was updated at 2:15 p.m. EDT on Aug. 13 to note that around 85 mammals species are known to menstruate and to clarify what happens in pregnancy in non-menstruating animals. 

While we are the only species to scrutinize our reflections in a mirror every day, we are not the only ones to recognize ourselves in reflective surfaces. 

Scientists have tested for mirror recognition in a wide array of species, starting with research on chimpanzees (Pan troglodytes) published in 1970. Animals ranging from ants to manta rays to African gray parrots (Psittacus erithacus) have been scrutinized for signs of self-awareness when presented with a mirror. A small handful realize that they are looking at themselves. Many don't. And a number have displayed inconclusive behaviors. 

These mixed results have led researchers to debate the usefulness of the test and how it helps scientists understand animal cognition. 

Related: Which group of animals has the most species?

"Many animals don't pass," Frans de Waal, a primatologist at Emory University, told Live Science. De Waal has conducted self-awareness tests on capuchin monkeys — which failed. "They need to self-inspect a visual mark in front of a mirror without any training or rewards. It needs to be spontaneous. Most of the claims in the literature don't fit this description."

So which animals have passed the test?

In the 1970 chimp experiments, four chimpanzees were anesthetized and marked with red dye on their faces. When they awoke, they examined the areas that had been marked in the mirror, indicating an understanding that they were viewing themselves.

The mark test is now considered the most conclusive proof of mirror self-awareness. 

Other great apes have also passed the test. Orangutans recognized themselves — and even identified marks on their bodies — in a 1973 study.

Bonobos were observed inspecting areas of their bodies they would not otherwise be able to see using a mirror in a 1994 study. The results for gorillas have been more inconclusive. 

Monkeys typically view their reflections as another animal — though a series of controversial studies showed that some species can identify themselves following extensive training regimens. 

This has been true of other animals as well, casting doubt on the implications of those studies. "Does that training process negate the outcomes of the mirror test for the species that require it?" wonders Ellen O'Donoghue, a cognitive psychologist at Cardiff University in the U.K., who has studied learning in pigeons. Critics of tests that use training exercises suggest that such learned behavior is not reliable evidence of self-awareness.

Until recently, the only other terrestrial mammal that has convincingly passed the test was an Asian elephant (Elephas maximus) at the Bronx Zoo.  However, a January, 2024 study in the journal Neuron suggested that mice, too, seem to recognize modifications to their own body in a mirror. 

Studies on dolphins suggest that they too can discern their own reflections. A 1995 study using video rather than mirrors and a 2001 study that used mirrors both indicated that dolphins use their images to examine marks made on their bodies. 

In 2008, researchers studying Eurasian magpies (Pica pica) found the first evidence that non-mammals were capable of mirror self-recognition. Pigeons have also passed the test — but only after a rigorous period of conditioning. And in 2022, wild Adélie penguins (Pygoscelis adeliae) showed signs of mirror self-awareness as well, though they did not react to colored bibs placed around their necks in lieu of marking their bodies.

Tests on lower-order animals have proven particularly controversial. A 2015 study suggested that ants might possess some self-awareness because they attempted to remove blue paint from their heads when looking at their reflections. Two studies have suggested that fish may recognize themselves. One, from 2016, found that manta rays seemed to examine themselves and blow bubbles when shown a mirror. No mark test was conducted though. And a 2019 experiment on cleaner wrasses  (Labroides dimidiatus) found that they attempted to remove dye marks made on their undersides after spotting them in a mirror. And in the 2024 mouse study, researchers found mice removed marks from their body; those that could see the smudges removed them, while mice that couldn't see the smudges because they blended in with their fur color did not. The researchers also went a step further, scanning the brains of the mice as they removed the smudges. They found a subset of brain cells, called ventral hippocampal CA1 neurons, lit up during the mirror test. Whether a similar circuit plays a role in human self-recognition remains to be seen.

The fact that these supposedly more-primitive organisms pass the mirror test, while some of the most intelligent non-human animals, including African gray parrots, have failed it, has called its utility into question. It is unclear whether these investigations demonstrate a true sense of the self in the human sense or whether they simply indicate a sophisticated bodily awareness.

"The mirror test can index one aspect of self awareness," O'Donoghue told Live Science. "There's a tendency to look at self awareness as all or nothing. That's probably not true. It's probably more of a gradation."

Editor's Note: This story was updated on Friday, June 28 at 2:20 p.m. E.D.T. to note that mice pass the mirror test.

War and violence can often seem like uniquely human acts that have been present for most of our recent history. But do other animals wage "war"? In this excerpt from "The Beast Within: Human as Animals" (2024, Johns Hopkins University Press), scientific researcher Jessica Serra looks at the dark side of chimpanzees' (Pan troglodytes) behavior to show that our closest living relatives also have a taste for warfare.

Among nonhuman mammals, hostility between rival groups is quite widespread, but it rarely leads to death. The frequent fighting between males is most often ­limited to intimidation be­hav­ior. While certainly frightful, it is rarely fatal. ­There is one exception, however: our closest cousins, the chimpanzees! Ethological studies have shown animals to be capable of forming complex ­political alliances. ­English primatologist Jane Goodall made a major discovery on this subject when she revealed an unsuspected dark side in chimpanzees.

In 1974, when Goodall was studying the be­hav­ior of chimpanzee colonies in Gombe, Tanzania, she observed a social divide between two groups in one of the communities. The first group, called the Kasakela community ­because they occupied the north part of the park bearing this name, was composed of eight adult males and twelve adult females, as well as their young. The second group, called the Kahama community, consisted of six adult males, an adolescent male and three adult females.

The hostilities began in an extremely violent way when a male from the Kasakela group killed Godi, a male from the Kahama group. The rage of the Kasakelas continued to plague the Kahamas for the next four years, during which time six more males ­were killed. As for the Kahama females, two dis­appeared and three ­were beaten by a gang of violent males.

The end of this "four-­year war" resulted in the Kasakela community taking over the Kahama's territory. It was a short-­lived victory, however, since another community of chimpanzees living nearby managed to scare the Kasakelas away. 

Goodall recounted her poignant memories of this war in her memoir "Through a Win­dow: My Thirty Years with the Chimpanzees of Gombe." She recalls, "For several years I strug­gled to come to terms with this new knowledge. Often when I woke in the night, horrific pictures sprang unbidden to my mind — ­Satan [one of the apes], cupping his hand below Sniff's chin to drink the blood that welled from a great wound on his face; old Rodolf, usually so benign, standing upright to hurl a four-­pound [1.8 kilograms] rock at Godi's prostrate body; Jomeo tearing a strip of skin from Dé's thigh; Figan, charging and hitting, again and again, the stricken, quivering body of Goliath, one of his childhood heroes." 

Related: Chimps use military tactic only ever seen in humans before

Jane Goodall is not the only one to be haunted by the bloody images of murders between groups of chimpanzees. American researchers reported similar scenes of vio­lence among chimpanzees in Kibale National Park in Uganda. ­These primates' fierce ­battles ­were instigated by co­ali­tions of adult males, with the sole aim of extending their territory. The areas where the fighting took place corresponded to the land conquered by force. 

Are ­these primates ­really at "war"? If we define war as being lethal vio­lence ­organized against members of another group, then the answer is clear. Like ­humans, chimpanzees have the capacity to wage war. Before the fighting began in Kibale National Park, the males carried out systematic patrols. The location of the corpses confirms the importance of the territory as a motivation to fight: these chimpanzees had breathed their last breath in this coveted neighboring area. ­These wars ­were fraught with the terror of infanticide between rival gangs, atrocities also committed by ­humans.

Three such attacks ­were reported by anthropologists from Ohio University and the University of Michigan in the International Journal of Primatology. The researchers recounted how on differ­ent occasions, while on patrol, the adolescent and adult males of the Ngogo chimpanzee community attacked the ­children of a rival gang, killed them, and cannibalized one of them.

Although ­there are cultural disparities between our ways of waging war and ­those of chimpanzees, certain similarities are striking. Both ­humans and chimpanzees ensure that assassinations can be committed by several individuals without major risk to the assailants, and both have motivations for ­these killings (gaining territory, hierarchical position, access to resources, ­etc.). In fact, some researchers are now using the "chimpanzee model" to explain the emergence of war in ­humans.

But aggression in chimpanzees does not only manifest itself when faced with a rival community. American anthropology professor Jill Pruetz and her team at Iowa State University recounted the 2013 murder committed by several males of a member of their own group at Fongoli in Senegal. While the researchers did not witness the massacre as it took place, which was in the darkness of night, they did hear the blood curdling cries. In the morning, they discovered with horror the corpse of Foudouko, a 17-­year-­old former alpha male, who had been stripped of his status in 2007 by a gang of young chimpanzees. 

Condemned to exile and isolation, the pariah regularly attempted to rejoin the group, imposing himself as dominant, which the new alpha males did not like. The research team speculated that if his entrance had been more submissive, the outcome would prob­ably not have been fatal. ­These lethal attacks recorded in chimpanzees, rare but incredibly cruel, were not linked to a ­human presence near their communities (as some scientists had presumed) but to a hierarchical tension within the group and prob­ably to intense competition for access to females. 

But what disturbed scientists the most was how the gang treated Foudouko's body the day ­after his death. Most likely to make sure they had nothing left to fear, the murderous gang dragged the body across the ground, sniffed it repeatedly, ripped out its genitals, bit it all over, and tore its flesh and… ate it!

Murder and cruelty are therefore not unique to H. sapiens. And the animal world has not finished surprising us ­either. 

Excerpted from The Beast Within: Human as Animals, by Jessica Serra. Copyright 2024. Published with permission of Johns Hopkins University Press.

A man caught a rare but potentially lethal infection after being wounded by wild monkeys in a Hong Kong park and is currently in critical condition, health officials report.

The infection was caused by B virus, which is commonly found in the saliva, urine and stool of macaques, monkeys that live in various locations in the city, according to the Centre for Health Protection (CHP), an agency of the Department of Health in Hong Kong. The monkeys themselves usually are either asymptomatic or show only mild symptoms of infection, the Centers for Disease Control and Prevention (CDC) notes.

According to the infected man's family, he'd encountered the monkeys during a visit to Kam Shan Country Park — home to an area nicknamed "Monkey Hill" — in late February. His case is thought to be the first human infection with B virus in Hong Kong, the CHP noted.

B virus, also called monkey B virus or herpesvirus simiae, rarely infects people. From its discovery in 1932 to 2019, the virus sickened about 50 people, 21 of whom died of the infection, according to the CDC. Most of the affected people had been bitten or scratched by a monkey or were infected when the tissue or bodily fluids of a monkey had made contact with broken skin. There's only one known case of an infected person spreading B virus on to another person, the CDC notes.

Related: 11 (sometimes) deadly diseases that hopped across species

The first known human case of B virus in China was reported in 2021, in a veterinary surgeon in Beijing who'd dissected two dead monkeys and died of the infection about a month later.

In the current case in Hong Kong, the infected 37-year-old man was admitted to Yan Chai Hospital on March 21 "due to fever and decreased conscious level." As of Wednesday (April 3), he was being treated in the intensive care unit. A sample of the fluid that surrounds the brain and spinal cord tested positive for B virus.

The initial symptoms of B virus are flu-like and include fever, chills, muscle ache, fatigue and headache. Additional symptoms include shortness of breath, nausea, vomiting, abdominal pain and hiccups. (Hiccups may potentially be related to the virus invading the nervous system.) People may also develop small blisters on the part of their body a monkey scratched or made contact with.

In its late stages, the infection can cause inflammation of the brain and spinal cord. This can lead to sensations of pain, numbness or itching near the wound site, as well as muscle coordination issues and brain and nerve damage. Breathing problems and death can occur within one day to three weeks after initial symptoms appear, the CDC notes. The infection is typically treated with antiviral drugs and supportive care to maintain a person's vital signs.

Both the CDC and CHP advise the public to stay away from wild monkeys and avoid touching or feeding them. If a person is wounded by a monkey, they should wash the wound and then immediately seek medical attention.

As of April 4, CHP has not released additional information about the ongoing case.

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

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Scientists have discovered a universal pattern of brain waves in multiple primate species, including humans.

This pattern of electrical activity is seen in the six layers of tissue that cover the outside of mammals' brains, known as the cerebral cortex. In primates, higher frequency waves of electrical activity dance through the most superficial layers while slower waves bubble in layers below.

The ubiquitousness of these brain waves was revealed in a recent study, published in January in the journal Nature Neuroscience. And previous research conducted by some of the same researchers suggests that the distinct activity patterns may reflect how the brain consciously switches focus from one piece of information to the next.

The slower brain waves in deeper portions of the cortex act as gatekeepers, dictating which bits of information enter and remain in conscious thought, said senior study author André Bastos, an assistant professor of psychology at Vanderbilt University. The fast waves, which reflect those conscious thoughts, are called gamma rhythms and range between 50 and 150 hertz. The slow waves, meanwhile, are called alpha-beta rhythms and run about 10 to 30 hertz. 

"You have information coming in that can get represented by gamma bursts and spikes," Bastos told Live Science. "And then you can have another mechanism for saying, 'I don't care anymore, turn that off." That's the alpha-beta waves' job — to yank one thought off stage to let another on.

Related: Most detailed human brain map ever contains 3,300 cell types

While previously a postdoctoral student at the Massachusetts Institute of Technology (MIT), Bastos led a number of monkey studies to reveal how this mechanism works in some parts of the cerebral cortex. Now, in the January paper, "we showed the universality of those patterns," he said. The scientists found that the pattern consistently cropped up in 14 different regions of the cortex, not just a handful. 

"What we have shown here is that it's not just present in one area or another area, but it's really present throughout," Bastos said. And the researchers also showed that it appears in three different primates: macaques (Macaca), marmosets (Callithrix jacchus) and humans.

Scientists across four institutions — Vanderbilt, MIT, the Netherlands Institute for Neuroscience and the University of Western Ontario in Canada — collaborated to gather this trove of brain data from monkeys and people. They used devices called multicontact laminar probes to record activity from all the layers of the cortex at once. The probes were surgically embedded in different parts of the cortex — therefore, for the study's human subjects, the devices were implanted in a few people who were undergoing brain surgery for epilepsy or movement disorders.

"Essentially it's just a very micro version of the EEG," or electroencephalogram, a way of recording electrical brain activity, Bastos said. The difference is that EEG most often uses electrodes on the outside of the scalp and thus, through that bone and tissue, it gathers a fuzzier picture of the activity happening in all the cortical layers below.

Laminar probes offer a more high-resolution picture, by comparison. In the study, the data gathered by the devices was fed into an algorithm of the researchers' design that deciphered the cortical layer from which they came. 

In this way, they uncovered a universal pattern of brain activity that shows up throughout the cortex and between species. This pattern is marked by peak gamma activity in layers 2 and 3 of the cortex, closer to the skull, and peak alpha-beta activity in layers 5 and 6, closer to subcortical regions of the brain. There's also a point of crossover in layer 4.

Related: How does the brain store memories?

To check if this pattern popped up in other mammals, the team also looked at mouse brains, but the activity seen in the mouse cortex was not the same.

Based on the prior monkey studies, Bastos and colleagues suspect that the patterns reflect the same mental process in each primate species, in which the slower waves dictate which data enters conscious thought. However, they haven't shown that definitively. 

In the Nature paper, all the primates and humans were resting during the brain recordings, not engaged in a specific task. Future studies could involve having the subjects perform similar tasks while their brains are scanned; the prior monkey research had the animals perform tasks centered around an aspect of cognition called working memory, which involves temporarily holding an idea or piece of data in your mind so you can use it for a task at hand, for instance.

Looking ahead, the researchers hope to study whether conditions that affect the brain disrupt the universal pattern in measurable ways. Alzheimer's and schizophrenia have been connected to abnormal gamma activity in the brain, for instance, so gaining deeper insights into why might help with diagnosis and treatment.

Bastos also anticipates that brain-recording technologies will continue to advance in the future, allowing researchers to record tens of thousands of neurons in different parts of the brain simultaneously. "The hope there is that we can begin to understand in a much deeper way what is the neural basis of thought, for example," Bastos said, "or what is the neural basis for more complex types of cognition, which we haven't really been able to touch yet."

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website! 

Approximately 25 million years ago, an ancestor of both humans and apes genetically diverged from monkeys and lost its tail. No one had identified the genetic mutation responsible for this dramatic change in our physiology — until now.

In a new study published Wednesday (Feb. 28) in the journal Nature, researchers identified a unique DNA mutation that drove the loss of our ancestors' tails. It's located in the gene TBXT, which is known to be involved in tail length in tailed animals.

The impressive discovery began when first study author Bo Xia, formerly a graduate student at New York University who is now a principal investigator at the Broad Institute, injured his tailbone and became interested in the structure's origin. 

"Bo is really a genius because he looked at something that thousands of people, at least, must have looked at before — but he saw something different," said Itai Yanai, scientific director of the Applied Bioinformatics Laboratories at NYU Langone Health and a senior author of the study.

Related: What if humans had tails? 

Jumping genes and "dark matter"

Over millions of years, changes in DNA allow animals to evolve. Some changes involve only a single rung in DNA's twisted ladder, but others are more complex. 

So-called Alu elements are repetitive DNA sequences that can generate bits of RNA, a molecular cousin of DNA, that can convert back to DNA and then insert themselves randomly into the genome. These "transposable elements," or jumping genes, can disrupt or enhance a gene's function upon insertion. This specific type of jumping gene exists only in primates and has been driving genetic diversity for millions of years. 

In this latest study, the researchers found two Alu elements in the gene TBXT that are present in great apes but not in monkeys. These elements aren't in the part of the gene that codes for proteins — the exons — but rather in introns. Introns are DNA sequences flanking exons that have been referred to as "dark matter" of the genome because they were historically assumed to have no function. They are removed, or "spliced," out of the sequence before an RNA molecule gets converted into protein. 

In this case, however, when cells use the TBXT gene to generate RNA, the repetitive nature of the Alu sequences causes them to bind together. This complex structure still gets cut out of the larger RNA molecule but takes an entire exon with it, thereby changing the final code for and structure of the resulting protein.

Related: 10 things we learned about our human ancestors in 2023

"We did a lot of other analyses of other genes implicated in tail length or morphology. And, of course, there are differences, but this was like a lightning bolt," said Jef Boeke, director of the Institute for Systems Genetics at NYU Langone Health and a senior author of the study. "And it was noncoding DNA [introns] that was 100% conserved in all the apes and 100% absent in all the monkeys," he told Live Science.

In human cells, the researchers confirmed that the same Alu sequences appear in the TBXT gene and result in removal of the same exon. They also found that the related RNA molecule can be cut in a variety of ways to generate multiple proteins from the same gene. By comparison, mice make only one version of the protein, so having both versions seems to prevent the formation of tails, the team concluded. 

This way of making different proteins from the same gene is called "alternative splicing," and it is one of the reasons human physiology is so complex. But this is the first time Alu elements have been shown to cause alternative splicing. 

"Mutations like this have often been thought to be of limited consequence in evolution. Here the authors show that such a mutation has had a profound impact on our species," said Kirk Lohmueller, a professor of ecology and evolutionary biology and of human genetics at the University of California, Los Angeles who was not involved in the study. 

"It is exciting to think of how many other complex mutations like this could have generated important traits throughout human evolution," Lohmueller told Live Science in an email. 

Bipedalism and birth defects

The researchers experimented with inserting these same jumping genes into mice, and they found that the mice lost their tails. 

Notably, evolutionary biologists hypothesize that the loss of the tail allowed humans to become bipedal, according to a 2015 review. "We are the only paper that has ever put together a plausible scenario for how it happened," Yanai told Live Science. 

"We're now walking on two feet. And we evolved a big brain and wield technology," he said. "All from just a selfish element jumping into the intron of a gene. It's astounding to me."

Interestingly, the researchers found that the mice that had lost their tails showed a greater prevalence of spina bifida, a birth defect that affects the neural tube, an embryonic structure that gives rise to the spinal cord and brain. The condition affects approximately 1 in 1,000 human births, according to the Centers for Disease Control and Prevention. 

"It may be a sort of unintended consequence that TBXT deficiency gives you a short tail … but it makes it more likely that you don't get that complete neural closure," meaning a hole is left in the neural tube, Boeke said.

"No one ever thought that, by just following our curiosity, we would make a mouse lose their tail by putting in the same mutation … and then we see the mouse also has a neural tube defect," Yanai added. 

The discovery of this type of alternative splicing will likely influence the whole field of genomic analysis in the future. 

"I think there's going to be more of them out there," Boeke said of these influential Alu elements. Therefore, he added, there's probably alternatively spliced proteins out there that are actually the root cause of some evolutionary change in our traits.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website! 

Wildlife tourism thrives on our fascination with animals and primates are particularly attractive animals to tourists. With their human-like faces, complex family dynamics and acrobatic antics, they are a joy to behold.

But recent stories have emerged that portray monkeys in a more sinister light. Reports of "monkey attacks", "devil monkeys," or even "face-ripping, bone-biting monkeys" have become common in the media. Have our primate cousins turned on us?

The recent monkey attacks involve a variety of species in different countries. They include the long-tailed macaque and the pig-tailed macaque in Thailand, Japanese macaques in Japan, and Hanuman langurs in India.

Most of these species are macaques, which are a diverse group of monkeys. But all macaques are sociable, intelligent, relatively large (between 4 kg and 9 kg [9 and 20 pounds]), and comfortable traveling on the ground. They have a flexible diet, but prefer fruit. They also have cheek pouches that allow them to gather food quickly and carry it to a safe place to eat.

Over-habituation

Regardless of species or location, a major factor in monkey bites and attacks is "over-habituation." Habituation is a process used by animal researchers to gain animals' trust so they can follow and record their behavior, with limited impact of the researchers' presence.

But animals can become unintentionally habituated. Squirrels in a city park who have grown accustomed to handouts are one example, but others include urban foxes in the UK, bears in North America, and, in many parts of the tropics, monkeys.

When animals lose their fear of humans and become a nuisance, they are over-habituated. In nearly all cases of over-habituation, the main factor is human food. What people eat is irresistible to wildlife. It is nutrient-dense, easy to digest and is available in rubbish bins, unattended backpacks, or even directly from people.

From an ecological point of view, animals have every incentive to take advantage of this high-quality resource. So, it's no surprise that animals will adjust their fear and natural behaviour accordingly.

While over-habituation due to associating tourists with food is certainly the main driver for the reported monkey attacks, that does not mean that every person bitten or threatened by a monkey is guilty of feeding or teasing them.

Monkeys are very smart, have a long memory and learn from each other. Many groups have grown so accustomed to human foods that they have learned to harass tourists to get it. Some monkeys have become so adept at this that they know which items are valuable to tourists, which they will "trade" for food. In other words, they'll steal your mobile phone but then drop it when you throw them some food.

Another important factor in monkey attacks at tourist sites is an unawareness of the animals' body language, facial expressions and vocalisation. Even highly habituated monkeys will normally give a warning before attacking someone. But people inexperienced with monkey behaviour will often misinterpret a threatening facial expression for a friendly one. This can lead to dangerous encounters.

Advice

Wildlife tourists cannot be expected to understand every species' typical expressions and body postures. But some things can help tourists be more safe and responsible, regardless of the primate species they are viewing.

1. Give them space. According to the International Union for Conservation of Nature, a network of environmental organisations, keeping a distance of seven meters (23 feet) from the animals is recommended. This helps the animals not feel threatened and also reduces the risk of disease transmission.
2. Do not stand between the animals and their route to safety, or between adults and young.
3. Avoid direct eye contact or showing your teeth because monkeys may perceive this as aggressive.
4. For many primate species, common threats include bared teeth (including some yawns), direct stares with a lowered head, and short lunges or slapping the ground with the hands. If an animal does any of these things, quietly back away.
5. Do not feed the monkeys.

Wildlife tourism contributes more than US$100 billion (£786 billion) per year to the global economy. It is also immensely rewarding and can offer many benefits to wildlife and the communities of people who live near them. But we should all be responsible tourists.

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

Scientists in China have successfully cloned a rhesus monkey by providing the cloned embryo with a healthy placenta. The innovative technique could significantly increase the success rate of cloning, the researchers say.

The monkey, named ReTro, is now three and a half years old and still "doing well and growing strong," study co-author Qiang Sun, a primate neuroscientist at the Chinese Academy of Sciences' Center for Excellence in Brain Science and Intelligence Technology, told Live Science in an email.

Researchers have cloned rhesus monkeys before, but this is the first success using a method known as somatic cell nuclear transfer, which involves replacing the nucleus of a fertilized egg cell with a nucleus extracted from another individual's somatic cells. (Somatic cells include every cell in the body except reproductive cells.) A previous attempt to clone a rhesus monkey using somatic cell nuclear transfer resulted in a live birth, but the infant died just 12 hours later. 

Rhesus monkeys (Macaca mulatta), also called rhesus macaques, are commonly used in laboratory experiments and medical research because they are genetically very closely related to humans. Creating clones of these monkeys "can help us to obtain non-human primate models with identical genetic backgrounds and genotypes [to each other] in a short time," Sun said. This would help researchers filter out any effects of genetic variation between models when testing drugs, for example.

Related: Scientists want to clone an extinct bison unearthed from Siberian permafrost. Experts are skeptical.

The successful cloning, which was described in a new study published Tuesday (Jan. 16) in the journal Nature Communications, is a step toward improving cloning efficiency in primates and other mammals, Sun said.

Scientists have used somatic cell nuclear transfer to clone a range of different mammal species, such as other monkeys, sheep (including Dolly the sheep), cattle and dogs. Most cloned embryos don't survive to birth, however, often due to defects in the development and structure of the placenta. Between 1% and 3% of attempts result in a live birth using conventional cloning methods, according to the study, although the success rate is slightly higher in cattle (5 to 20%). 

To overcome this problem, Sun and his colleagues replaced a cluster of cells that normally develops into the placenta from the cloned embryo with the same cells from a normal embryo. These cells, known collectively as the trophectoderm, formed a healthy placenta that provided the cloned embryo with nutrients and oxygen during development. The experiment resulted in the birth of a healthy male rhesus monkey in 2020.

"This approach significantly increased the success rate of cloning by somatic cell nuclear transfer," Sun said, and it could yield "a higher number of cloned animals using a reduced number of oocytes," or egg cells.

"As placental defects are commonly seen in all cloned mammal species, we anticipate that it might be applicable in other mammals and non-human primates," Sun added.

Scientists may have finally solved the mystery of why the largest ape ever to walk Earth went extinct, with new evidence suggesting the giant ape struggled to adapt to climate change. 

In a new study published Jan. 10 in the journal Nature, scientists found that the largest known primate, Gigantopithecus blacki likely died out between 295,000 and 215,000 years ago after it failed to adapt its diet or behaviors to environmental changes that began around 700,000 years ago and put its dense forest habitat in what is now China under threat.

G. blacki first appeared about 2 million years ago. It was identified in 1935 by German paleontologist Gustav von Koenigswald after he stumbled upon molars belonging to the species. Since then, researchers have found thousands of teeth and a handful of partial jawbones — but no complete skeleton has ever been recovered.

The demise of this enormous primate, which grew up to 10 feet (3 meters) tall and weighed up to 600 pounds (270 kilograms), has long perplexed paleontologists as it is one of the few Asian great apes to go extinct in the last 2.6 million years. 

"The story of G. blacki is an enigma in palaeontology — how could such a mighty creature go extinct at a time when other primates were adapting and surviving? The unresolved cause of its disappearance has become the Holy Grail in this discipline," paleontologist and co-lead author Yingqi Zhang, a professor at the Institute of Vertebrate Palaeontology and

Palaeoanthropology at the Chinese Academy of Sciences, said in a statement.

Related: Primates have been masturbating for at least 40 million years

In the new study, the scientists analyzed fossilized teeth remains, pollen records and geological dates to find evidence of the giant ape's demise and establish a detailed timeline of its decline.

Using six different dating techniques to study the fossils and sediments from 22 cave sites in southern China, the scientists were able to date the fossil remains and create a comprehensive chronology for the extinction of the giant ape.

They found that 2.3 million years ago, during the late middle Pleistocene (2.6 million to 11,700 years ago), the giant ape enjoyed a fruit-rich diet and lived in dense canopy forest. However, around 600,000 to 700,000 years ago, this habitat began to change and gradually become open grasslands. Pollen and fossil analysis showed that during this period, the climate and plants became more seasonal and water availability was less consistent as the region began to experience dry seasons.

During this time, G. blacki got bigger, which increased the amount of food it required, and meant it was confined to the forest floor, where it likely ate bark when its preferred fruits were seasonally unavailable. The giant ape also had a reduced geographical range for foraging compared with other great apes.

This habitat change and the ape's inability to adapt ultimately doomed the species, the researchers found.

Previous research suggested that the giant ape went extinct around 200,000 years ago, but the new data show the species was already extinct by this time. By 300,000 years ago, its numbers had plummeted before it vanished altogether between 295,000 and 215,000 years ago.

"We have a much more robust timeline for their life and when they went extinct," co-lead author Kira Westaway, a geochronologist at Macquarie University in Australia, told Live Science. "It seems that G. blacki chose an evolutionary path that it couldn't reverse."

Westaway said understanding the demise of G. blacki is important as there are parallels with environmental conditions on Earth today. "Going back to past unresolved extinctions and determining the causes helps us understand why some species are more vulnerable and why others are more resilient," she said. "This has massive implications for the conservation efforts for our living primates such as modern orangutans and mountain gorillas."

Newborn babies' brains aren't "underdeveloped" compared with those of other primates at birth, a new study suggests.

In the past, scientists typically compared brain development between species by measuring how much each species' newborn brain size differs from its adult brain size. Compared with other primates, human babies' brains are significantly smaller than adults' brains. Meanwhile, newborn and adult primates have a smaller gap, which has led to the popular misconception that human newborns are "underdeveloped" in comparison.

In the new study, published Monday (Dec. 4) in the journal Nature Ecology & Evolution, scientists instead considered how the absolute size of the brain at birth, compared with adulthood, has varied across mammalian evolution. They found that of all mammals with a placenta, humans showed the strongest evolutionary drive toward having a proportionally small brain size at birth. However, this is not because newborn humans' brains are smaller than expected but rather that our adult brains are dramatically larger.

In other words, we're not developmentally behind primates at birth — we just have significantly more growing to do.

"Our study shows that human brains are not substantially less developed than the brains of other primates at birth, and that they simply appear so because we normally compare brain size in newborns with adult brain size, which is much bigger in humans," lead study author Aida Gomez-Robles,  an associate professor of anthropology at University College London, told Live Science in an email.

Related: In rare cases, COVID-19 infection in pregnancy can cause brain damage to fetuses

To better understand how babies' small brains stack up against other newborn animals, Gomez-Robles and colleagues analyzed brain development in modern humans, our extinct relatives the Neanderthals, and various primates, including chimpanzees, bonobos, gorillas and orangutans. In all, the study included 44 primate species, as well as dozens of additional mammals, from rodents to hooved animals and large carnivores.

They found that humans had the smallest relative brain size at birth compared with adulthood of all primates — newborn brains are less than 25% the size of adults.

Researchers believe human babies have relatively small brains because a smaller brain means childbirth is more likely to be successful.

"Classic models assume that human babies are born before they are as developed as other primates because otherwise their brains (and heads) would be too big to go through the birth canal," Gomez-Robles said. This developmental pattern ties into the fact that humans are bipedal, meaning they move around while upright on two feet, which requires a narrow pelvis compared with primates, she said.

However, human baby brains were not significantly underdeveloped compared to age-matched primates, when you consider key steps in early brain development.

When the authors focused specifically on human evolution, they found that only a few of these steps were shifted to occur after birth, instead of in the womb. These processes mainly include the insulation of nerves within brain structures, such as the hippocampus. As this makes nerves more efficient at communicating with each other, it may subsequently play a big role in driving human brain plasticity after birth, the authors wrote in the paper.

The researchers also looked at the time that human babies spend in the womb, and they found that this was no shorter than would be expected for other primates. This suggests that having relatively smaller brains as newborns is not because humans spend comparatively less time developing in the womb.

Most of the authors' results are based on estimates from mathematical models, as they were studying brain development across evolution. For example, when studying our human ancestors, they relied on approximate patterns of brain development inferred from fossilized remains.

"These estimates are valuable because they help us understand general patterns of evolution of brain development, but they are not empirical data, so they are not expected to reflect perfectly the actual ancestral values" in terms of their relative brain size over their life span, for example, Gomez-Robles said.

In future studies, the authors would like to compare these estimates with actual measurements of brain development in newborns across different species. Depending on time and resource constraints, this would be possible to a certain extent in present-day mammalian species but not in extinct species, Gomez-Robles said.

For that, they'll have to go back to the drawing board.

"The major challenge is inferring patterns of brain development in fossil hominins," our extinct ancestors, she said.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

An eagle in the Issa Valley of western Tanzania was just about to tuck into a hard-earned meal when an alpha male chimpanzee burst onto the scene and stole its prey — a rare encounter that has been documented by scientists in a new study. 

Chimpanzees (Pan troglodytes) are mostly vegetarian, but their diets include some meat and other animal products. They actively hunt for their meat and, on rare occasions, scavenge from dead carcasses. 

The new study, published Oct. 31 in the journal Primates, highlights chimps' ability to confront other predators and take their food in a behavior called confrontational scavenging. 

Lead author Sam Baker, research coordinator of the Bugoma Primate Conservation Project in Uganda, was following the chimps with Kidosi Raulent Mfaume, a local field assistant, when they saw Imba, an alpha male chimp, run into a patch of long grass. A crowned eagle (Stephanoaetus coronatus) then immediately took flight. Moments later, Imba appeared with a motionless young bushbuck (Tragelaphus scriptus) that the study authors assume the eagle had just caught.

"Like most new, particularly rare experiences, it was surreal and exhilarating in the moment," Baker told Live Science in a message on social media. "These confrontations are rare in the literature, most of which are inferred, so an almost complete observation of events is unique." 

Other chimps tried to steal the carcass and begged Imba to share for around an hour. He gave some to a female chimp and consumed most of the bushbuck himself. After discarding the carcass, other chimps then went and helped themselves to the remains. Eventually, only the skull was left. 

Related: Chimps use military tactic only ever seen in humans before

The encounter is only the second documented example of a chimpanzee stealing food from a raptor. Most accounts of confrontational scavenging involve chimps taking prey from baboons. A 2019 study published in the Journal of Human Evolution found that chimps also steal from leopards (Panthera pardus), even though leopards naturally predate on chimps.

Because chimps are one of our closest living relatives, they offer us a window into the lives of our last common ancestor, which lived around 6 to 8 million years ago, and the evolution of human behavior, Baker said.

Scavenging could have led to increasingly complex social behavior in early humans "like evolutionary stepping stones, passive to confrontational scavenging, to cooperative hunting," he said. 

Mfaume, the field assistant who also witnessed the events, but who was not named in the study, died due to ill health in 2022 at the age of 29. 

Baker said he wished to dedicate the study to Mfaume’s memory. "He was a beautiful, indelible soul passionate about the forest and the chimpanzees there," Baker added. 

Chimps use an ancient military tactic to make decisions and avoid potentially fatal clashes with rival groups, scientists have discovered.

Researchers observed two western chimpanzee (Pan troglodytes verus) communities in Africa take to the hills to carry out surveillance on each other — much like reconnaissance missions used by militaries. They then used that intel to decide when to enter contested territory.

Plenty of animals look out for danger in their environment, but this is the first time scientists have documented a non-human species making elaborate use of elevated terrain to assess risk in a territorial conflict, according to the new study, published Nov. 2 in the journal PLOS Biology.

Related: Primates have been masturbating for at least 40 million years

"It really shows this metacognition ability, so the ability to reflect on your own knowledge and to act on what you don't know to get more information," lead author Sylvain Lemoine, an assistant professor of biological anthropology at the University of Cambridge, told Live Science.

The use of elevated terrain is one of the oldest military tactics in human warfare, according to a statement released by the University of Cambridge.

Chimps live in communities that compete for space and resources, and their normal behavior involves coordinated aggression — including occasional killings.

The border between chimp communities isn't set in stone, and their daily presence in an area is what matters, Lemoine said, adding it is like living in a "constant, low intensity and small-scale state of warfare."

The new study looked at two neighboring chimp communities monitored by the Taï Chimpanzee Project, a research and conservation project based in the Taï National Park in Côte d’Ivoire (Ivory Coast). The team, along with students and local assistants — unnamed in the study — followed the chimps for 8 to 12 hours per day between 2013 and 2016, collecting GPS and behavioral data.

The data showed that chimps were more likely to climb hills when traveling to the borders of their territory than to the center. While on these hills, they quietly rested rather than engaging in activities that would impede their ability to listen, according to the study.

Chimps in the study were more likely to advance from high ground into contested territory when their rivals were far away, suggesting they used the hills to avoid conflict. However, they may also use them to find an opportunity to attack. Lemoine noted that when members of two communities meet, the balance of power — numbers on each side — is an important factor in whether one side escalates violence. The chimps seem able to weigh the cost and benefit of engagement, and the hills help them do that.

"They use the high spots to find the right conditions where they can take the risk — or not — of attacking," Lemoine said.

The new study only looked at chimps in Taï National Park, but Lemoine told Live Science that he assumes other chimps also use this tactic, depending on the terrain. 

In the statement, Lemonie said complex cognitive abilities that help chimps expand their territory would have been favored by natural selection, potentially suggesting these warfare tactics are rooted in evolution. "We are perhaps seeing traces of the small scale proto-warfare that probably existed in prehistoric hunter-gatherer populations," he said.

Wild female chimpanzees in Uganda live well past the point when they can reproduce and probably go through menopause similar to humans, a new study has found. The finding raises fresh questions about why humans experience menopause.

Until now, humans were one of only three animal species known to go through menopause — along with orcas (Orcinus orca) and short-finned pilot whales (Globicephala macrorhynchus). Humans were thought to be the only primates that don't stay fertile for their entire lives.

"How this life history evolved in humans is a fascinating yet challenging puzzle," study lead author Brian Wood, an associate professor and evolutionary anthropologist at the University of California Los Angeles, said in a statement.

That's because the inability to reproduce past a certain age has no obvious evolutionary advantage. To explain it, researchers have previously posited that postmenopausal people may play an important role in caring for their children's children and boosting their survival chances, helping to ensure that their genes will be passed on — an idea known as the "grandmother hypothesis." 

To find out whether menopause occurs in other primates, the authors of a study published Thursday (Oct. 26) in the journal Science investigated the fertility of some of our closest living relatives — eastern chimpanzees (Pan troglodytes schweinfurthii).

Related: Chimps are naturally violent, study suggests

Wood and his colleagues pored over 21 years' worth of demographic and fertility data collected between 1995 and 2016 in Uganda's Kibale National Park, where the Ngogo community of wild chimpanzees lives. The researchers analyzed records for 185 female chimpanzees. They found a decline in fertility from the age of 30 onward and no births after 50, despite several females living long past that point

It turns out that Ngogo female chimps spend one-fifth of their adult lives in a "post-reproductive state" — around half the proportion calculated for modern human hunter-gatherers, such as the Hadza people. Urine samples taken from 66 female chimpanzees in different reproductive phases (ages 14 to 67) also revealed hormonal changes as they got older and stopped having babies — similar to those seen in humans going through menopause.

But unlike many humans, female chimpanzees don't stay with their original tribe to reproduce and instead disperse to other groups, leaving behind their aging mothers. The grandmother hypothesis therefore has no legs to stand on in chimpanzees.

Instead, "the results show that under certain ecological conditions, menopause and post-fertile survival can emerge within a social system that's quite unlike our own and includes no grandparental support," Wood said. 

While the new finding in chimps doesn't rule out the grandmother hypothesis applying to humans, it raises questions about menopause's origins in our species.

Chimpanzees and humans may have inherited genes inscribing menopause from a common ancestor, according to the study. Alternatively, the trait may have evolved independently in each species.

If that's the case, the new study provides "a solid basis for considering the roles that improved diets and lowered risks of predation would have played" in the evolution of menopause in humans, Wood said.

That's because chimpanzees in Kibale National Park have never had it so good. Hunters wiped out their only predators, leopards, in the 1960s, and humans no longer kill the chimps either. Ngogo chimpanzees also have plenty of fruit and eat more meat than neighboring chimp communities, the researchers wrote in the study.

This good life might explain why female chimpanzees there live long past their fertile years. Although non-reproductive females exist in other wild chimpanzee communities, only a few have lived beyond the age of 50, according to the study.

It's unclear whether the signs of menopause detected in chimps arise solely from "unusually favorable ecological conditions" or the apes evolved that way. Recent environmental changes and disease epidemics shortening their life spans may have, until now, erased the evidence of an evolutionary history that includes menopause, according to the study.

Humans have ape ancestors to thank for their flexible shoulders and elbows, which may have evolved as a natural braking mechanism for tree-scaling.

Scientists made the discovery while watching numerous videos of chimpanzees (Pan troglodytes) and sooty mangabey (Cercocebus atys) monkeys, which are much more distantly related to both chimps and humans, climb up and down trees in the wild. 

In the new study, the researchers noticed that although both animals ascended trees similarly with their shoulders and elbows closely bent toward their bodies as they swiftly reached from one branch to the next, they differed in their techniques for descending.

The findings suggest that chimps and humans may have flexible shoulder and elbow joints as a way to "counteract" the effects of gravity on their heavier lower bodies. The result was a finely calibrated braking system that decreased their risk of falling while they descended downward high in the treetops, according to the study, published Sept. 6 in the journal Royal Society Open Science.

While mangabeys were less flexible, the chimps extended their arms above their heads while descending — similar to the way a person goes down a ladder. This maneuver was a way for the primates to slow their descents as gravity pulled them downward, the team said in a statement. 

"[We] noticed that while both chimpanzees and mangabeys climbed trees in a clipped motion where they didn't fully extend their joints, in downclimbing the mangabeys continued this clipped motion, while the chimps did not," co-author Mary Joy, a biological anthropology major who graduated from Dartmouth University in 2021 and made this her undergraduate thesis, told Live Science. "The two had very different ranges of motions."

Related: Wild chimps and gorillas can form social bonds that last for decades

Human and chimpanzee ancestors diverged approximately 6 million to 7 million years ago, while the mangabey's monkey ancestor diverged from apes around 30 million years ago.

But the study suggests that flexible appendages had evolved by the time of the last common ancestor between chimps and humans, but after apes and monkeys diverged. This flexibility would have proven beneficial for things that involved specific movements like gathering food, hunting and defending themselves, according to the study.

This marks the first time researchers have extensively studied how great apes descended trees; previously, most studies were focused on them climbing.

"We knew generally that chimps had an increased range of motion in their shoulders and elbows, while mangabeys did not," Joy said.

This is because mangabeys and other monkeys are built similarly to quadrupedal mammals like cats and dogs, which walk on all fours and have "deep, pear-shaped shoulder sockets," the team said in the statement. The inner crook of their elbows also protrudes, making the joint resemble the letter "L," according to the statement. These joints may offer stability, but they lack a good range of motion.

Upon analyzing the joints in existing chimp skeletons that were part of museum collections, researchers noticed that the angle of the apes' shoulders was 14 degrees greater when they were descending versus when they were climbing. Their arms also extended outward at the elbow 34 degrees more when the chimps were going down trees, according to the study.

This change in motion not only helped the chimps slow the pull of gravity but also allowed them to decelerate safely.

"Chimps can get out of trees and climb downward without having to keep their shoulder and elbow muscles under tension, which results in the exertion of a lot of energy," Joy said. "As humans, the introduction of this increased range of motion had a lot of benefits, like letting us raise our arms above our heads or throwing a ball. This motion is a legacy of evolutionary pressure on our ancestors, which gave us the ability to do a lot of things."

An ape fossil found in Turkey may controversially suggest that the ancestors of African apes and humans first evolved in Europe before migrating to Africa, a research team says in a new study.

The proposal breaks with the conventional view that hominines — the group that includes humans, the African apes (chimps, bonobos and gorillas) and their fossil ancestors — originated exclusively in Africa.

However, the discovery of several hominine fossils in Europe and Anatolia (modern-day Turkey) has already led some researchers to argue that hominines first evolved in Europe. This view suggests that hominines later dispersed into Africa between 7 million and 9 million years ago.

Study co-senior author David Begun, a paleoanthropologist at the University of Toronto, clarified that they are talking about the common ancestor of hominines, and not about the human lineage after it diverged from the ancestors of chimpanzees and bonobos, our closest living relatives.

"Since that divergence, most of human evolutionary history has occurred in Africa," Begun told Live Science. "It is also most likely that the chimpanzee and human lineages diverged from each other in Africa."

In the new study, the researchers analyzed a newly identified ape fossil from the 8.7 million-year-old site of Çorakyerler in central Anatolia. They dubbed the species Anadoluvius turkae. "Anadolu" is the modern Turkish word for Anatolia, and "turk" refers to Turkey.

The fossil suggests that A. turkae likely weighed about 110 to 130 pounds (50 to 60 kilograms), or about the weight of a large male chimpanzee.

Related: What did the last common ancestor between humans and apes look like?

Based on the fossils of other animals found alongside it — such as giraffes, warthogs, rhinos, antelope, zebras, elephants, porcupines and hyenas — as well as other geological evidence, the researchers suggest that the newfound ape lived in a dry forest, more like where the early humans in Africa may have dwelled, rather than in the forest settings of modern great apes. A. turkae's powerful jaws and large, thickly enameled teeth suggest that it may have dined on hard or tough foods such as roots, so A. turkae likely spent a great deal of time on the ground.

In the new study, the scientists focused on a well-preserved partial skull uncovered at the site in 2015. This fossil includes most of the facial structure and the front part of the braincase, the area where the brain sat — features that helped the team calculate evolutionary relationships.

"I was able to reconstruct and see for the first time the face of an ancestor of ours no one had ever seen before," Begun said.

The researchers suggest that A. turkae and other fossil apes from nearby areas, such as Ouranopithecus in Greece and Turkey and Graecopithecus in Bulgaria, formed a group of early hominines. This may, in turn, suggest that the earliest hominines arose in Europe and the eastern Mediterranean. Specifically, the team contends that ancient Balkan and Anatolian apes evolved from ancestors in Western and Central Europe.

Evolutionary questions

One question these findings raise is why, if hominines arose in Europe, they are no longer there, except for recently arrived humans, and why ancient hominines did not also disperse into Asia, Begun said.

"Evolution is not very predictable," Begun said. "It happens as a series of unrelated and random events interact. We can assume that the conditions were not right for apes to move into Asia from the eastern Mediterranean in the late Miocene, but they were right for a dispersal into Africa."

As for why "we do not find African apes in Europe today, species go extinct all the time," Begun said.

Begun also cautioned that he did not want this research misinterpreted or misused to suggest that Eurasia was somehow of primary importance in human evolution. Instead, "we need to know where the common ancestor of African apes and humans evolved so that we can begin to understand the circumstances of this evolution," he said. "Between 14 million and 7 million years ago, the areas in which apes were found in Europe, Asia and Africa were different ecologically, just as many regions in these continents differ today. Knowing the ecological conditions in which our ancestors evolved is critical to understanding our origins."

 A different take

This new discovery "expands our understanding of a group that appears closely related to living African apes and humans," Christopher Gilbert, a paleoanthropologist at Hunter College of City University of New York who did not participate in this study, told Live Science.

However, Gilbert noted that recent comprehensive analyses of fossil great apes and early hominins — the group that includes humans and the extinct species more closely related to humans than any other animal — do not support the argument that hominines originated in Europe.

"Many other experts investigating the evolutionary relationships of fossil and living great apes using more modern methods and including more [groups] find that many of the European apes branched off before orangutans, making them likely distant relatives of living African great apes and humans," Gilbert said.

"Furthermore, these more comprehensive analyses suggest that apes like Anadoluvius are just as likely or more likely to be recent immigrants to the Mediterranean from Africa rather than migrating back into Africa," Gilbert added.

Fossil hominines like A. turkae aren't found in Africa largely because "we have a poor African fossil record in general during this time," Gilbert said. "I am reminded of the old paleontological axiom — 'absence of evidence is not evidence of absence.'" 

However, Begun argued that an absence of hominine fossils in Africa was telling and supported the idea that hominines originated elsewhere.

In any case, both Begun and Gilbert noted that future fieldwork in Africa and Eurasia looking for fossil apes would potentially help clarify this matter.

The scientists detailed their findings Aug. 23 in the journal Communications Biology.

A new gene therapy that "resets" the brain's reward system could help treat alcohol use disorder, a new study in monkeys suggests. 

In monkeys who tend to drink heavily when provided lots of alcohol, surgically injecting a gene therapy into the brain increased the production of the so-called feel-good hormone dopamine, the study showed. This, in turn, dramatically reduced the primates' alcohol consumption, the effects of which were sustained over a year. 

If safe and effective in humans, the therapy could provide a "one-time" treatment for alcohol use disorder (AUD), a medical condition in which patients can't stop or control their drinking despite it negatively impacting their daily life. Excessive drinking causes 140,000 deaths a year in the U.S., and although AUD is one of the most common psychiatric disorders, only three drugs for it have been approved by the U.S. Food and Drug Administration (FDA). 

None directly target the underlying brain changes seen with sustained heavy drinking. 

Related: What does alcohol do to the body?

Alcohol boosts the brain's production of dopamine, which leads to feelings of relaxation and improved mood. However, in AUD, the brain adapts by producing less dopamine on its own, meaning people need to drink more to achieve the same positive effects.  

That's also true in monkeys that drink heavily, even during periods when they aren't consuming any alcohol, study lead author Kathleen Grant, a professor of behavioral neuroscience at Oregon Health & Science University, told Live Science.  

In the new study, published Monday (Aug. 14) in the journal Nature Medicine, Grant's team injected a genetically modified virus into the ventral tegmental area — a region in the brain involved in reward processing — of four monkeys as part of a surgical procedure. Those monkeys had been given access to increasingly higher amounts of ethanol dissolved in water over several months to the point where their consumption levels simulated chronic alcohol binge drinking in humans. 

Using a similar approach to what has already been used to treat Parkinson's disease and a rare genetic disorder known as aromatic L-amino acid decarboxylase deficiency, the harmless virus carried a gene that encodes the protein glial cell line-derived neurotrophic factor (GDNF), which helps preserve and regrow neurons. By putting the GDNF gene into cells that make dopamine, the team assumed it would spur them to produce normal levels of the chemical. 

The monkeys reduced their alcohol consumption by more than 90% compared with controls, and their dopamine levels were restored to "normal levels" for at least a year after treatment, roughly equivalent to nine to 12 years in human time, Grant said. Because relapse is such an "integral part of the cycle" of AUD, getting back to levels the animals had before they started drinking heavily is crucial, she emphasized. 

Andrew Mcquillin, a professor of molecular psychiatry at University College London who was not involved in the research, told Live Science in an email that the long-term side effects of this treatment are still unclear. Although brain surgery is "generally well-tolerated" in humans, he said it "seems a somewhat invasive approach for all but the most severe cases of alcohol use disorder."

Grant also urged caution in over-generalizing the findings. "This is only proof-of-principle that it is possible to reverse this behavior in people with drinking disorders that are resistant to all other treatments," she said. "This would not be your first line of treatment, [it] would be appropriate only for very severe cases of alcohol use disorder."

Mcquillin added that future studies will be needed to test the acceptability of this treatment for substance use disorders. The findings could, however, open doors for other treatment options. 

"There is also the possibility that new or existing small molecules that mimic the therapeutic mechanism in this study may represent new treatment targets for substance use disorders," he said.

Adoption is common among humans, who may decide to raise someone else's child for a range of reasons, including fertility struggles or the wish to provide a home for youngsters in need.

But why do animals sometimes adopt the young of others? The act of caring for an unrelated, parentless infant probably emerged because it confers an evolutionary advantage on the foster parent, said Michael Weiss, a behavioral ecologist and research director at the Center for Whale Research in Washington state. For example, adoption may provide valuable caregiving experience for females that lack offspring and increase their future young's survival chances, Weiss told Live Science.

Adoptions can occur within the same species or, in some extremely rare and puzzling cases, between different species. In a 2021 study in the journal eLife, researchers examined the effects of maternal loss on young mountain gorillas (Gorilla beringei beringei) and found that orphans over age 2 forged relationships with other group members, especially with dominant males. 

"A young gorilla would usually share its nest at night with its mother, but if the mother dies or leaves the group, then it will share a nest with the dominant male," study lead author Robin Morrison, a behavioral ecologist at the University of Zurich and an affiliate scientist with the Dian Fossey Gorilla Fund in Rwanda, told Live Science.

Mountain gorillas live in social groups composed of a dominant male and several females with their offspring. Regardless of whether the dominant male fathered the infants, his role is to protect the next generation from infanticide at the hand of rival males. His ability to do so may determine his reproductive success, Morrison said.

"Males that are really good at caring for offspring and do this in front of females are the most popular," she explained. Looking after an orphaned gorilla could earn a dominant male brownie points, thus increasing his chances of mating and of passing on his genes. "It's part of demonstrating their reproductive quality," Morrison said.

Related: What is the maximum number of biological parents an organism can have?

While the females in the group don't necessarily benefit from raising a motherless juvenile, doing so does not come at great energetic cost because infants over age 2 can forage by themselves, Morrison said. "It's also good for the other young gorillas to have a playmate," she added, as it enhances their social skills.

Social bonds and baby obsession

Adoption is also common in other primates and can bridge social groups. In a 2021 study published in the journal Scientific Reports, researchers documented the first known case of great apes adopting infants from a separate group. The team observed two female wild bonobos (Pan paniscus) that appeared to have adopted two infants from another group and posited that the behavior may boost the adults' social status. 

"One possibility is that adoptees could become future allies of the adoptive mothers," the researchers wrote in the study. "Both adoptees were females and female bonobos form strong social bonds and coalitions within their group and sometimes across groups."

Another possibility is that, like humans, female bonobos feel empathy and a fascination with infants, according to the study. "Within primate species, some adults are really baby-obsessed," Morrison said, adding that this zeal can lead to kidnappings and death if the infant is caught in a commotion.

Researchers described the kidnapping of a 3-week-old Tibetan macaque (Macaca thibetana) by a female of the same species in a 2023 study published in the journal Primates. The female had two offspring of her own when she snatched the baby from its mother, including a 1-month-old that she continued to nurse alongside the captive. The kidnapping-turned-adoption may have benefited the female by invoking future social support or favors, such as grooming, the researchers suggested. 

The kidnapping of a 5-day-old yellow baboon (Papio cynocephalus), described in a 1987 study in the American Journal of Primatology, had a less-happy ending: The infant died of starvation or dehydration after a high-ranking female abducted it and carried it around for three days. 

Underwater adoption

Nonhuman primates may feel the same caring instincts as humans do when we see a baby or small animal, which may help to explain these behaviors, Morrison said. And it's not just primates, according to Weiss, who studies orcas (Orcinus orca) in the waters around the Pacific Northwest and western Canada.

"All of the females, and especially the females who haven't had a calf yet, are totally baby-obsessed," he said. "The first year of a calf's life is the absolute center of attention for everyone."

In 2021, researchers in Iceland spotted, for the first time, an orca that appeared to have adopted a baby pilot whale (Globicephala). In June 2023, scientists with the Icelandic Orca Project were baffled by another female showing this behavior. "We are trying to piece together what is happening, but we sure have a lot of questions," they wrote on Twitter.

These cases are "a big mystery" because researchers have never seen adults from these two species socialize, which suggests the orcas may have kidnapped the baby whales, Weiss said. "The abduction case of a killer whale going into a pilot whale group and stealing a calf — while we don't know that's what happened — seems more likely to me," he added. 

A big question also remains over why this may be beneficial for orcas. Producing milk comes at a huge energetic cost, and moms nurse their calves for up to three years, Weiss said. By dividing a female's attention and draining her resources, adoptees could also pose "a bit of an issue" for any existing biological offspring, he added.

Adoptive and biological offspring may compete for attention, and this can lead to negative outcomes. In a 2019 study published in the journal Ethology, researchers documented the case of a melon-headed whale calf (Peponocephala electra) adopted by a female bottlenose dolphin (Tursiops truncatus) with a baby of her own. The adoptee repeatedly pushed the other baby from under the mother's abdomen, potentially contributing to the biological calf's disappearance shortly afterward.

The female dolphin may have felt driven to nurse the calf due to the recent birth of her own, the researchers suggested. "Both calves were approximately the same age, which could have enhanced the mother's tolerance toward a newborn during a sensitive period for establishing mother-offspring bonding," they wrote in the study. Other factors may have contributed to the adoption, such as her "curious and social personality" or her lack of caregiving experience, they added. 

Inexperience may explain why orcas showed interest in pilot whale calves. "It could be misplaced maternal instinct," Weiss said. But it could also be "takeaway lunch" to eat later or play, he added. "I wouldn't be surprised if they saw a cute little baby whale and thought 'Oh! I'll pick that up for a while.'" 

In nonmammal species too, inexperienced moms sometimes make mistakes. Common cuckoos (Cuculus canorus) are brood parasites, meaning females lay their eggs in other species' nests to save themselves the energetic cost of raising them. In a 1992 study published in the journal Behavioral Ecology, researchers found that young great reed warbler (Acrocephalus arundinaceus) females were more easily fooled by cuckoo eggs than older breeders and suggested their indiscriminate behavior could boil down to inexperience.

While evolutionary pressures can explain why animal adoptions emerged and keep happening, they may not shed light on individual cases. "One reason why that behavior might persist and keep getting passed down is because it helps build up the skills for taking care of a calf," Weiss said. "But the females are probably not doing it because they're trying to build up experience." 

Orcas, in particular, are highly intelligent creatures that we may never fully understand. "They've got big, complex brains just like us, and they have instincts and impulses, which means that they'll often do things that are really interesting and don't have an immediate survival or reproductive advantage," Weiss said.

Male rhesus monkeys on a tiny island in Puerto Rico have more sex with each other than they do with females, scientists have discovered. This behavior may be partially rooted in genetics, the team said. 

The researchers also found that male monkeys that had more sex with other males tended to father more offspring, suggesting that same-sex sexual behavior provides a boost when it comes to breeding.

"We find the complete opposite of what people were saying before, which was generally that the more homosexual sex animals have, the less babies they will have," Vincent Savolainen, a professor of organismic biology at Imperial College London in the U.K., told Live Science.

In the 1930s, scientists founded a monkey colony on the small island of Cayo Santiago in Puerto Rico for research purposes. Known locally as Monkey Island, it now has over 1,700 rhesus macaques (Macaca mulatta) living freely there. 

Related: Primates have been masturbating for at least 40 million years

In a study published Monday (July 10) in the journal Nature Ecology and Evolution, researchers were looking at same-sex behavior among males on the island — and found it was extremely common among the 236 male monkeys they observed.

The team logged how often male monkeys mounted, or were mounted by, other males and how often males mounted females over three periods in 2017, 2019 and 2020. This revealed that 72% of males had sex with each other, while just 46% had sex with females. The scientists distinguished between individual monkeys using unique markings that had previously been tattooed onto the animals.

Scientists have previously observed same-sex sexual behavior in a wide range of animals including insects, reptiles, birds and primates, but it is generally thought to be a rare behavior. Researchers previously thought this behavior would reduce the animals' reproductivity, but in an analysis, the team found this behavior boosted reproduction success. 

"We find this behavior between males helps them form coalitions — when they bond by having sex, they fight together against other males [that they are not having sex with]," Savolainen said. "As a result, they probably get an advantage in the group, access more females and end up having more babies."

Because all infant macaques are trapped and genotyped to determine their parentage, the team was able to look at how genetics may influence the likelihood of a male monkey having sex with other males. The researchers compared the DNA sequences in genetic samples collected from the monkeys with their sexual habits and found that genetic factors can help explain 6.4% of the sexual behavior observed, with the remaining differences seemingly down to environmental factors, such as age distribution.

"This is the first time we can show that homosexual behavior in these animals was in part genetically based," said Savolainen. As the behavior is to some extent heritable, this suggests it could be selected for through the process of natural selection, where genes that increase the reproductive success of an animal become more widespread in a population, he said.

The next step will be pinning down exactly which genes might play a role. "We are now going to sequence the whole genome of all these animals to figure that out," Savolainen said. 

The findings, he added, could affect how we view homosexuality among humans. 

"We share an ancestor with rhesus monkeys, and in this study, we argue that maybe in our past, homosexual behavior might have evolved in humans and maybe was also beneficial as we see in the monkeys," he said. "Of course, there are differences between humans and these monkeys but there may be some common ground."

If the findings can help to stamp out stigmatization around same-sex sexual behavior then that would be a positive and important outcome, Savolainen added.