Friday, 28 May 2010

Many Species of Homo: Update from the Neanderthals

Recently, new scientific research has contradicted my earlier statements: that while we likely interbred with Neanderthals, very few of their genes were passed on (highlighting the difference between ancestry and gene lineage). However, Svante Pääbo’s team from the Max Planck Institute for Evolutionary Anthropology in Leipzig, suggest that perhaps 4% of some peoples’ genes are from Neanderthals. Homo sapiens and Homo neanderthalis did interbreed. The conclusions come from comparing uncontaminated Neanderthal DNA to living humans, and chimpazees. Surprisingly, Neanderthals and non-African humans share some distinct markers, not found in either chimps or Africans, suggesting interbreeding. The researchers also stress that these where only “genetic markers”, DNA regions supposed not to have any function. If they do not have any function, then Natural Selection can’t work upon them. So, we don’t know if the DNA contributes in any way meaningfully to non-African humans. Any negative traits that Neanderthals may have passed on in their hybrid children, would presumably have been selected against and become extirpated from the gene pool long ago.

(See an amazing interactive website of the neanderthal genome at the Science)

It is amazing to think of two species of humans, first separated over 300 000 years ago, and coming in such (literally) intimate contact again. How many other humans were there? The recent DNA extracted from a 30 – 50 thousand year old finger in a Siberian cave is neither human nor Neanderthal, but something else from its contemporaries. There is also the supposed Homo floresiensis “Hobbit”, indicating that maybe as little as 13,000 years ago, the prehistorical landscape was abloom with many different species of humans. How, I wonder, and what did they think of each other? Did they have such separate lifestyles and separate ecological niches, enabling them to co-habitat the same geographic area, like Pygmy’s and other Africans? Did they raid, trade and communicate with each other? Perhaps. But the Neanderthals quick demise upon the advent of modern H. sapiens upon the North suggests competitive exclusion, and maybe perhaps even violent confrontation.

I can’t help but think what this study means for the perennially touchy issue of “race” among H. sapiens. Probably it means nothing. Regardless of the minor, and apparently non-functional genetic variation introduced by H. neaderthalis, H. sapiens are still remarkably homogeneous in our genes. Most genes came from a few, closely spaced “out-of-Africa” outbursts, starting 70,000 years ago.

Instead of bolstering racist arguments, this study rather helps to lay to rest an even more controversial theory, the Multiregional Hypothesis, which tried to explain how some minor features, like the mandibular cavity, seems to show a continuity from earlier hominids in Europe and Asia to their respective modern humans, by hypothesizing H. sapiens evolved indigenously and in parallel from earlier Hominids who’d already populated Eurasia many millions of years ago. This study by Pääbo gives us a way to reconcile the Multiregional evidence with the Out-of-Africa evidence, that these features common to certain modern “races” and earlier hominids are a result of interbreeding, not separate speciation, and that our genes mostly come through one species from Africa.
I hope they will look for other functionally relevant markers, though racially sensitive, one can easily imagine what a Northern-adapted Neanderthal could offer the northward expanding African humans. But then again, the Neanderthals clearly didn’t have such a great advantage.

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