Neanderthal skeleton reconstruction G.J. Sawyer and B. Maley photo D. Finnin/AMNH

As evidence from Atapuerca and elsewhere suggests, Europe has been home to a variety of hominid species over the last one million years. Beginning around 200,000 years ago, Europe was occupied by the species known as Homo neanderthalensis: the Neanderthals. This distinctive species was a close relative—and possibly a descendant—of the hominids from Sima de los Huesos in Atapuerca.

The Neanderthals were quite successful, inhabiting Europe for more than 150,000 years—longer than our own species has existed. Around 40,000 years ago, however, a new species arrived in Europe: Homo sapiens. These new hominids—modern humans—possessed astonishing capabilities never before seen. They were sophisticated toolmakers, using a wide array of raw materials for their tools. They also created art and practiced symbolic rituals. The Neanderthals were no match for the newcomers, and by 30,000 years ago, they had vanished, leaving only modern humans.

Since the first Neanderthal fossil was recognized in 1856, paleoanthropologists have found many hundreds of additional bones from this extinct hominid species. Thanks to the extensive evidence available—from both the fossil record and cultural artifacts such as tools—scientists know more about Neanderthals than about any other extinct hominid species.

Neanderthal and Modern Human Skeletons photo D. Finnin/AMNH

Although scientists have never unearthed a complete Neanderthal skeleton, they have reconstructed this one based on numerous partial finds. At first glance, the Neanderthal skeleton above might appear to be just a shorter, bulkier version of a modern human one. But a closer inspection of the two skeletons would reveal important differences between the two species, which led to subtle differences in external traits. For instance, Neanderthals probably walked with a very slightly different gait from modern humans because of the orientation of their pelvis and hip sockets. Neanderthals were once seen as a subspecies of Homo sapiens, but the differences in overall skeletal structure indicate that Neanderthals and modern humans are actually distinct species.

These physical differences most likely reflect separate evolutionary histories—not geographic or other environmental factors. For example, Neanderthals were probably muscular and stocky not only because they led strenuous lives, but also because of their distinct evolutionary past. It is highly doubtful that Neanderthals and Homo sapiens exchanged significant amounts of genetic material over time.