In 1829, part of the skull of a Neanderthal child was found in a cave near Engis, Belgium. It was the first Neanderthal fossil ever found, though the skull wasn’t recognized as belonging to a Neanderthal until decades later.

Quarry workers cutting limestone in the Feldhofer Cave in Neandertal, a small valley of the Düssel River near the German city of Düsseldorf, uncovered the first identified Neanderthal bones in 1856.

Anatomists puzzled over the bones: Included among them was a piece of a skull which looked human, but not quite. The Neanderthal skull included a prominent, bony brow ridge and large, wide nostrils. The Neanderthal body was also stockier and shorter than ours.

In a 1857 paper, German anatomist Hermann Shaafhausen posited that the Neanderthal fossil belonged to a “savage and barbarous race of ancient human.” Seven years later, Irish geologist William King concluded that the Neanderthal fossil was not human and that it belonged to a separate species he named Homo neanderthalensis.

Fossil evidence suggests that Neanderthals, like early humans, made an assortment of sophisticated tools from stone and bones. These included small blades, hand axe and scrapers used to remove flesh and fat from animal skin.

Neanderthals were skilled hunters who used spears to kill large Ice Age mammals such as mammoths and wooly rhinos.

Little is known about Neanderthal culture and customs, though there’s some evidence that Neanderthals might have made symbolic or ornamental objects, created artwork, used fire and intentionally buried their dead.

Genetic analysis shows that Neanderthals lived in small, isolated groups that had little contact with each other.

Neanderthals had bigger brains than humans, though that doesn’t mean they were smarter. One recent study found that a large portion of the Neanderthal brain was devoted to vision and motor control.

This would have come in handy for hunting and coordinating movement of their stocky bodies, yet left relatively little brain space compared to modern humans for areas that controlled thinking and social interactions.

Most researchers agree that modern humans and Neanderthals interbred, though many believe that sex between the two species occurred rarely.

These matings introduced a small amount of Neanderthal DNA into the human gene pool. Today, most people living outside of Africa have trace amounts of Neanderthal DNA in their genomes.

People of European and Asian descent have an estimated 2 percent Neanderthal DNA. Indigenous Africans may have little or no Neanderthal DNA. That’s because the two species did not meet—and mate—until after modern humans had migrated out of Africa.

Some of the Neanderthal genes that persist in humans today may influence traits having to do with sun exposure. These include hair color, skin tone and sleeping patterns.

Neanderthals had been living in Europe and Asia for hundreds of thousands of years when modern humans arrived. Neanderthals were already adapted to the climate of Eurasia, and some experts think Neanderthal DNA may have conveyed some advantage to modern humans as they exited Africa and colonized points north.

Neanderthals went extinct in Europe around 40,000 years ago, roughly 5,000 to 10,000 years after first meeting Homo sapiens. There are several theories for their extinction.

Around 40,000 years ago, the climate grew colder, transforming much of Europe and Asia into a vast, treeless steppe. Fossil evidence shows that Neanderthal prey, including wooly mammoths, may have shifted their range further south, leaving Neanderthals without their preferred foods.

Humans, who had a more diverse diet than Neanderthals and long-distance trade networks, may have been better suited to find food and survive the harsh, new climate.

Some scientists believe that Neanderthals gradually disappeared through interbreeding with humans. Over many generations of interbreeding, Neanderthals—and small amounts of their DNA—may have been absorbed into the human race.

Other theories suggest that modern humans brought some kind of disease with them from Africa for which Neanderthals had no immunity—or, modern humans violently exterminated Neanderthals when they crossed paths, though there’s no archeological evidence that humans killed off Neanderthals.

Homo neanderthalensis, Smithsonian National Museum of Natural History.
New insights into differences in brain organization between Neanderthals and anatomically modern humans, Proceedings of the Royal Society B.
The contribution of Neanderthals to phenotypic variation in modern humans, American Journal of Human Genetics.