Tens of thousands of years ago, the rise of humanity as we know it began. Modern humans spread from Africa to Europe and Asia, which were already populated by older Neanderthal cultures. The two groups interbred, adding some Neanderthal DNA to our present-day genes. The relatively sophisticated humans flourished, while their Neanderthal counterparts disappeared, going extinct in Europe somewhere between 39,000 to 41,000 years ago. But the timeline, in many places, is still foggy. By identifying a pair of ancient teeth as conclusively human, a team of scientists think they've managed to clear things up a little — and helped settle a debate about how different human and Neanderthal cultures might have been.
"From 45,000 up to 40,000 [years], we have several cultures that suddenly appeared in Europe," says University of Bologna researcher Stefano Benazzi, co-author of a paper that appears today in Science. One of those cultures was the Protoaurignacian, which developed in southern Europe around 42,000 years ago. The Aurignacian culture that followed marked a turning point in modern humanity: among other things, it gave us the world's earliest known musical instruments, the earliest known wall art, and potentially the first representation of a human figure. Protoaurignacians themselves are known for making personal ornaments, small stone blades, and other things that are "quite typical of modern humans." But while their artifacts have been left behind, it's hard to conclusively prove that the Protoaurignacians actually were human.
Only two teeth and a bone fragment have been found in Protoaurignacian sites
In fact, only three remains have ever been recovered from known Protoaurignacian sites: a fragment of fetal bone from France and two teeth, found in different parts of northern Italy in 1976 and 1992. It was widely expected that they came from humans, Benazzi says, but they couldn't rule out the possibility that Neanderthals had managed to develop a strikingly modern culture. "It would mean that Neanderthals had exactly the same skill as modern humans," says Benazzi, and could weaken the theory that humans had survived by outcompeting them.
In order to test this, Benazzi and his team examined the two tooth samples. First, they checked the enamel of one against a range of newer human teeth. Neanderthal teeth have comparatively thin enamel layers, and even heavily worn down, the Protoaurignacian tooth was closer to human measurements. For the second tooth, they managed to extract mitochondrial DNA, which sits outside a cell's nucleus and is passed down only through the mother. Checked against the DNA of 54 present-day humans, 10 ancient modern humans, and 10 Neanderthals, along with another extinct species of human and a chimpanzee, it fell squarely within the modern human range.
3D models of the two teeth. (Daniele Panetta, CNR Institute of Clinical Physiology)
Unfortunately, because mitochondrial DNA comes only from the mother, the team can't get a full picture of the genetics. "From enamel thickness and the mitochondrial DNA, we cannot exclude interbreeding," says Benazzi. The mother of whomever owned the second tooth was human, he says, "but if the father of this child was a Neanderthal, we don't know." His team hopes to later extract nuclear DNA, which contains both parents' genes, but that's a more difficult proposition. Even if it turns up conclusively human, the study is limited by the fact that there are only two samples. Considering that it's taken nearly 40 years to find even these two, they can't count on having another one turn up.
Based on the estimated age of the two teeth, these humans lived in southern Europe at least 41,000 years ago, around the time Neanderthals went extinct. Though it's only speculative, Benazzi believes this supports the idea that modern humans contributed to their demise, whether through direct measures or some kind of indirect competition. No matter what, he thinks they've demonstrated that the Protoaurignacian culture can be traced back to modern humans — not, at least exclusively, highly skilled Neanderthals.