Neanderthals (or Neandertals) are our closest extinct human relatives. There is some debate as to whether they were a distinct species of the Homo genus (Homo neanderthalensis) or a subspecies of Homo sapiens. Our well-known, but often misunderstood, fossil kin lived in Eurasia 200,000 to 30,000 years ago, in the Pleistocene Epoch. They started to evolve 300,000 and 100,000 years ago, according to Encyclopedia Britannica.
Neanderthals' appearance was similar to ours, though they were shorter and stockier with angled cheekbones, prominent brow ridges and wide noses. Though sometimes thought of as dumb brutes, scientists have discovered that they used tools, buried their dead and controlled fire, among other intelligent behaviors. It is theorized that for a time, Neanderthals probably shared the Earth with other Homo species.
In 1856, a group of quarrymen discovered remnants of a skeleton in the Neander Valley near Dusseldorf, Germany (hence their name). In a limestone cave, they found 16 pieces of bone, including a skull. Thinking the bones belonged to a bear, the quarrymen gave them to local teacher Johan Karl Fuhlrott. From him, the bones found their way to scientists, and it was eventually determined that they were ancient human relatives. The publication and popularization of Charles Darwin's "On the Origin of the Species" in 1859 helped inform the discovery. Since that day in the Neander Valley, more than 400 Neanderthal bones have been found.
The original cave men
Neanderthals lived during the Ice Age. They often took shelter from the ice, snow and otherwise unpleasant weather in Eurasia's plentiful limestone caves. Many of their fossils have been found in caves, leading to the popular idea of them as "cave men."
Like other humans, Neanderthals originated in Africa but migrated to Eurasia long before other humans did. Neanderthals lived across Eurasia, as far north and west as the Britain, through part of the Middle East, to Uzbekistan. Popular estimates put the peak Neanderthal population around 70,000, though some scientists put the number drastically lower, at around 3,500 females.
Their short, stocky stature was an evolutionary adaptation for cold weather, since it consolidated heat. According to the Smithsonian Institution, the wide nose helped humidify and warm cold air, though this assertion is debated. The American Museum of Natural History states that other differences from other humans are a flaring, funnel-shaped chest, a flaring pelvis, and robust fingers and toes. Approximately 1 percent of Neanderthals had red hair, light skin, and maybe even freckles.
Their brains, however, grew at slower rate than the brains of other humans' and became larger, according to research published in the September 2017 issue of the journal Science. "It took a little bit longer for the brain to grow in Neanderthals than in modern humans," said study co-lead author Antonio Rosas, chairman of the paleoanthropology group at Spain's National Museum of Natural Sciences in Madrid. "We thought our slow way of growing was very specific, very particular, very unique to our species," Rosas said. "What we realize now is that this pattern of slow growth that allows us to have this big brain and mature slowly, with all the advantages involved with that, was also shared by different human species."
Neanderthals lived in nuclear families. Discoveries of elderly or deformed Neanderthal skeletons suggest that they took care of their sick and those who could not care for themselves. Neanderthals typically lived to be about 30 years old, though some lived longer. It is accepted that Neanderthals buried their dead, though whether or not they left carved bone shards as grave goods is debated.
It is not known if they had language, though the large size and complex nature of their brains make it a likely possibility.
Neanderthals used stone tools similar to the ones used by other early humans, including blades and scrapers made from stone flakes. As time went on, they created tools of greater complexity, utilizing materials like bones and antlers. Evan Hadingham of PBS's NOVA reported that Neanderthals used a type of glue, and later pitch, to attach stone tips to wooden shafts, creating formidable hunting spears.
Neanderthals had some control of fire, and it is even theorized that they built boats and sailed on the Mediterranean.
Neanderthals were primarily carnivorous, and the harsh climate caused them to resort occasionally to cannibalism. Recently, however, scientists have found that Neanderthals actually ate cooked vegetables fairly regularly.
Probably the most debated aspect of Neanderthal life in recent years is whether or not they interbred with other human species. The answer remains ambiguous, with scholarly opinions ranging from belief that they definitely interbred to belief that the two groups didn't exist on Earth at the same time.
Neanderthal expert Erik Trinhaus has long promoted the interbreeding hypothesis, but the theory really caught fire when a 2010 study published in Science magazine determined that Neanderthal DNA is 99.7 percent identical to modern human DNA (a chimp's is 99.8 percent identical). Researchers of the Neanderthal Genome Project found that 2.5 percent of an average non-African human's genome is made up of Neanderthal DNA. The average modern African has no Neanderthal DNA. This information could support the interbreeding hypothesis because it suggests that Neanderthals and other species only bred once the other humans had moved out of Africa, into Eurasia, according to a 2012 paper published in the journal PLOS. They could have interbred as recently as 37,000 years ago.
Recent research published in the October 2017 issue of American Journal of Human Genetics found that genomes of modern human groups originating outside Africa contain between 1.8 and 2.6 percent Neanderthal DNA. "Neandertal DNA is one source of variation for many traits in modern humans," study lead author Michael Dannemann, a computational biologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told Live Science. [Your Hair Color and Sleep Habits May Come from Neanderthals]
Another 2017 study by author Kay Prüfer, a paleogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that modern-human DNA entered the Neanderthal gene pool between 130,000 and 145,000 years ago. [You May Be More 'Neanderthal' Than You Thought]
If this interbreeding occurred, why don't modern humans carry more Neanderthal DNA? A possible reason involves the male sex chromosome. Scientists have found that the Neanderthal Y chromosome may have kept the two lineages from successfully interbreeding; the chromosome may have created conditions that frequently led to miscarriages if or when a Neanderthal male and modern human female got together, according to the research published in the April 7, 2016, issue of the American Journal of Human Genetics. In the study, Fernando Mendez, a population geneticist at Stanford University, and colleagues discovered three mutations on the Y chromosome of a Neanderthal male that would have produced molecules that can trigger immune responses from women during pregnancy. Those immune responses are linked to miscarriages.
A 2012 study, however, cast doubt on the interbreeding theory. Researchers re-examined bones from southern Spain that were used in earlier studies with new radiocarbon dating techniques. They discovered that the Neanderthal bones were more than 50,000 years old. Humans aren't believed to have settled in the area until 42,000 years ago, meaning that it may be unlikely that they lived together and interbred.
If humans and Neanderthals didn't interbreed, the similar genomes of humans and Neanderthals could be the result of both groups having a common African ancestor.
No one knows exactly why Neanderthals went extinct and why Homo sapiens survived. Some scholars theorize that gradual or dramatic climate change led them to their demise, while others blame dietary deficiencies. Some theorize that humans killed the Neanderthals. Until recently the hypothesis that Neanderthals didn't go extinct but simply interbred with humans until they were absorbed into our species was popular.
Additional reporting by Alina Bradford, Live Science contributor.