Before Neanderthals went extinct some 30,000 years ago, they interbred with our human ancestors, and now, thanks to a Neanderthal toe bone, scientists have been able ot put a number on exactly how much of our genetic legacy comes from these romps. According to two new research papers simultaneously published in Nature and Science, about 1 to 4 percent of our DNA originates from Neanderthals, reports Ed Yong for National Geographic.
Previously, writes Carl Zimmer for the New York Times, Neanderthal remains failed to produce an accurate genome. But with the data from the toe bone, scientists could finally figure out how much Neanderthal is still present in our own genetic code.
The authors of the two studies went about this in different ways: one team directly compared the Neanderthal genome to genomes of around 1,000 people living today, while the other team first picked out suspect mutations in genomes of modern Europeans and Asians, and then traced those mutations back to the Neanderthal genome.
Neanderthals' contributions to our own evolution turns out to be a mixed bag of pros and cons, as Scientific American describes:
Those genes with the highest Neandertal ancestry are associated with keratin, a protein found in skin and hair. The Neandertal variants of these genes may well have helped early modern humans adapt to the new environments they found themselves in as they spread into Eurasia.
But the researchers also found that people today carry Neandertal genes that are associated with diseases including Crohn’s, type 2 diabetes and lupus.
As Carl Zimmer points out on National Geographic, scientists still haven't settled on answers to basic questions about Neanderthals, including whether or not they were a different species, a sub-species or the same species as Homo sapiens. Based on evidence from the new studies—which showed, for example, that some hybrid Neanderthal-human male offspring were sterile—it looks like there were some significant issues with reproduction between the two groups, which has implications for Neanderthals' standing as a separate species. As Zimmer explains:
Many genes from Neanderthals appear to have reduced the number of offspring that hybrids could have. That would explain why big segments of the human genome are free of Neanderthal DNA.
There are no known reproductive barriers between any living humans, no matter how distantly related they are to each other. These barriers are crucial to the origin of new species (although they can still allow some populations to interbreed even after millions of years). So perhaps we can say that Neanderthal, while not a separate species, were well on their way to separating.