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Sun Sep 30, 2012, 12:47 PM

Rethinking "Out of Africa"

Rethinking "Out of Africa"

At the moment, I'm looking again at the whole question of a recent African origin for modern humans—the leading idea over the last 20 years. This argues that we had a recent African origin, that we came out of Africa, and that we replaced all of the other human forms that were outside of Africa. But we're having to re-evaluate that now because genetic data suggest that the modern humans who came out of Africa about 60,000 years ago probably interbred with Neanderthals, first of all, and then some of them later on interbred with another group of people called the Denisovans, over in south eastern Asia.

If this is so, then we are not purely of recent African origin. We're mostly of recent African origin, but there was contact with these other so-called species. We're having to re-evaluate the Out-of-Africa theory, and we're having to re-evaluate the species concepts we apply, because in one view of thinking, species should be self-contained units. They don't interbreed with other species. However, for me, the whole idea of Neanderthals as a different species is really a recognition of their separate evolutionary history—the fact that we can show that they evolved through time in a particular direction, distinct from modern humans, and they separated maybe 400,000 years ago from our lineage. And morphologically we can distinguish a relatively complete Neanderthal fossil from any recent human.

You could argue that they're an extreme variant of Homo sapiens, but a very different 'race' from anyone alive today, or, as I prefer to argue, they're a separate species, with a separate evolutionary history. But I've never actually said that that meant they were completely reproductively isolated from us. We know that many closely related species in primates, for example, can interbreed. Various species of monkey can interbreed and have fertile offspring, and so can our closest living relatives, Bonobos and common chimpanzees.

In my view the Neanderthals were closely related and probably potentially able to interbreed with modern humans, but until recently I considered that while there could have been interbreeding forty or fifty thousand years ago, it was on such a small scale that all trace of it vanished in the intervening years. But it now seems from Neanderthal genome studies that that was not so. We do have a bit of Neanderthal in us, you and I—it's a small amount, but certainly not negligible..

lots more and video here -> http://www.edge.org/conversation/rethinking-out-of-africa

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