Modern humans and Neanderthals: Did they or didn't they? The sordid truth is out, and its not what scientists expected. The closest-ever look at the Neanderthal genome reveals that yes, we did interbreed. But scientists are still fuzzy on the where, the when, and the why.
If you watched Becoming Human when it premiered this fall, you might be feeling some scientific whiplash. At the time, genetic analysis suggested that modern humans and Neanderthals kept to themselves and didn't share their, ahem, genetic material. So why the sudden turnaround? The first time around, scientists based their conclusions on mitochondrial DNA. This time, researchers looked at nuclear DNA, which provides a more sensitive comparison to the DNA of modern humans.
So, our ancestors made babies with Neanderthals. But that's not the whole story: Only some modern populations have Neanderthal parentage. Africans don't seem to have any distinctively Neanderthal DNA. So what does that tell us about where and when modern humans and Neanderthals decided to commingle?
It must have been after some populations left Africa. Archeologists think that humans and Neanderthals lived side by side in Europe for about 15,000 years, until the Neanderthals died out about 30,000 years ago, so it seems reasonable to think that over the course of fifteen millennia these two populations would have done some canoodling.
But here's the weird part: The genetic clues point much farther back, between 60,000 and 100,000 years ago, when modern humans were settled in the Middle East and European and East Asian populations hadn't split yet. There is still no scientific consensus on whether Neanderthals and modern humans shared territory during this time. But dating DNA divergence is a complicated statistical game, so some archeologists and paleontologists, who are used to working with the kind of evidence you can hold in your hand--not the kind that comes chugging out of a computer algorithm--are skeptical.
But this research isn't just a high-tech paternity test. By comparing modern DNA with Neanderthal DNA, scientists can also uncover genes that are distinctively human. So far, the team has found about 100 genes that appear in modern humans but not in Neanderthals. They are involved in everything from skin to cognition to metabolism.
As Ian Tattersall, a paleontologist at the American Museum of Natural History, told the New York Times, "This is probably not the authors' last word" on the ties that bind us to Neanderthals.