The Muierii fossils exhibit several Neanderthal-like features, including a bump at the back of the head. Photo courtesy of Erik Trinkaus.
They were first identified in 1856, when scientists unearthed ancient bones in Germany's Neander Valley. Since then, numerous archaeological finds have revealed that Neanderthals, like early modern humans, buried their dead, skinned animals, built fires, and fashioned sophisticated tools from wood and stone. But there were differences, too: Neanderthals were stockier and had bigger noses, brows, muscles, and, curiously, brains.
Fossil evidence places the Neanderthals in Europe and western Asia roughly 230,000 years ago, where they apparently thrived for thousands of years. But about 40,000 years ago, early Homo sapiens began migrating northward, out of Africa and into Europe and Asia. Within 10,000 years, the Neanderthals had vanished from their old haunts; small, isolated Neanderthal populations hung on for a few more millennia in the Iberian Peninsula and then disappeared for good.
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The specifics of the Neanderthal demise is one of the greatest mysteries in anthropology. For decades, many experts have maintained that humans completely replaced the Neanderthals, consistently out-doing them and slaughtering them when they got in the way. Other anthropologists, however, believe that rather than dying out, the Neanderthals assimilated into early human populations through interbreeding, also known as admixture.
In last week's online edition of the Proceedings of the National Academy of Sciences, Erik Trinkaus, an anthropologist at Washington University in St. Louis, and his colleagues in Romania, published a new analysis of early modern human fossils. These 30,000-year-old bones, discovered in the Romanian cave Pestera Muierii in 1952, provide a tantalizingly close glimpse into the transition between Neanderthals and humans. The human remains display some distinctly Neanderthal-like features, suggesting that early humans and Neanderthals may have mated with each other and reproduced.
"The Muierii fossils are just one of several examples from Romania, France, and the Czech Republic, where we have basically modern humans with three or four characteristics that are very reminiscent of Neanderthals," such as a bulge at the back of the cranium, Trinkaus said. "Either they re-evolved these characteristics from their African ancestors, or, more likely, they acquired them through descent from the Neanderthals."
Trinkaus is no stranger to controversial claims. Seven years ago in Portugal, he and several collaborators identified the 24,500-year-old skeleton of a young boy as another likely hybrid. The claim was hotly and publicly disputed by other top anthropologists, most notably Jeff Schwartz of the University of Pittsburgh and Ian Tattersall, curator of anthropology at the American Museum of Natural History, both co-authors of a 1999 commentary dismissing the Portugal fossils as those of a "chunky" human child. Then, as now, Tattersall and Schwartz maintain that Trinkaus's fossils are products of normal variation, not interbreeding between species.
"This stuff conflates the way organisms, especially ones closely related to each other, can vary in similar ways—like being chunky or slender, tall or short—from the things that make them distinct species," Schwartz said, adding that the most reliable defining characteristics of Neanderthal fossils are their large, wedge-shaped snouts and a depression, not a bulge, in the back of their heads.
Via e-mail, Tattersall agreed that the fossils are not evidence of interbreeding: "Though there may have been a bit of Pleistocene hanky-panky, it evidently did not add up to a biologically significant exchange of genes."
To date, the strongest argument against interbreeding between humans and Neanderthals has been genetic evidence.