If you're not African, the odds are you're a Neanderthal. Ok - 4% Neanderthal, anyways. A study of human and amplified Neanderthal DNA by renowned paleo-geneticist Svante Paabo finds that virtually all human populations outside of Africa have a small but significant Neanderthal ancestry.
He has been studying this for a long time, and this discovery is notable because it contradicts all of his previous research. In 1997, Svante Paabo began his efforts to study the DNA of Neanderthals. By this point in time, it was clear that the fossil record could only tell us so much about Neanderthals, so Paabo decided to study DNA extracted from bones found in the Neander valley a century earlier. His early efforts were fraught with difficulty: only one percent of the DNA extracted was human (most of it was bacteria), and some of that DNA was modern human contamination, and not Neanderthal.
Over time, he refined his techniques, and most importantly, began to collect specimens in a way that prevented contamination by Homo Sapiens. As his team began to study the DNA and map the Neanderthal genome, they began to make some startling discoveries - most importantly, they discovered that Neanderthals possessed the genetic equipment for language, which anthropologists had predicted for years would not be the case. This dovetailed with paleontological discoveries, which began to discover that Neanderthals had made art, and had made sophisticated glues that not even their Homo Sapiens counterparts had discovered.
But the initial clues from the DNA seemed to point to another mystery: comparisons of human and Neanderthal DNA initially suggested no introgression by Neanderthals into the human population. Mitochondrial DNA of modern humans was exclusively modern - no maternal lineage back to Neanderthals existed. Initial studies of the cellular DNA seemed to point to the same thing. So how could this be? It is very difficult to imagine two human communities living in close proximity with similar intellectual capabilities, and not seeing each other as potential mates.
We now know they did.
The dam broke last week, when an analysis of modern human DNA suggested by a team lead by N.M. Hunley found that people from outside Africa seemed to possess some unexpected genetic diversity, that could be explained by two introgressions from an archaic hominid species.
This week Paabo announced that a study of five modern humans and recovered Neanderthal DNA suggested much the same thing. All humans originating outside of Africa carry about 4% Neanderthal DNA.
That's the equivalent of your great, great, great grandfather, as John Hawks points out. Most of the introgressions are believed to be neutral - neither conferring advantage upon nor disadvantaging the groups that gained them. The work was done in the opposite direction from his previous efforts - modern humans were compared to those Neanderthal sequences they clearly had, and they mapped out how different the modern people were from the Neanderthal sequence. On average, the three people not from Africa were significantly less distant from the Neanderthal sequence than the African people sampled were.
Hawks suggests the contradicting evidence of Neanderthal MT DNA extinction is not surprising; evidence already suggested that modern humans had recently gained a mitochondrial mutation that was metabolically advantageous. The first women with Neanderthal MT DNA would have been disadvantaged and selected against. However, men with Neanderthal DNA were not similarly disadvantaged, and passed forward the Neanderthal DNA.
The Leipzig group’s interbreeding theory would undercut the present belief that all human populations today draw from the same gene pool that existed a mere 50,000 years ago. “What we falsify here is the strong Out-of-Africa hypothesis that everyone comes from the same population,” Dr. Paabo said.
In his and Dr. Reich’s view, Neanderthals interbred only with non-Africans, the people who left Africa, which would mean that non-Africans drew from a second gene pool not available to Africans. Dr. Reich said that the known percentage difference in DNA units between African and non-African genomes was not changed by his proposal that some of the non-African DNA is from Neanderthals.
What the existence of Neanderthal DNA in European and Asian genes does tell us - leaving aside the salacious implications of interspecies sex - is that when moderns first encountered Neanderthals in the middle east 100,000 years or so ago, they recognized them as human to the point of intimacy. It is probably no longer possible to recognize Neanderthals as an inferior animal - another human species was once our equal, and regarded as such by our ancestors.
(BTW - sorry for not being around lately. I got kind of crabby as a person, and I think it was politics that was doing it. So I took a break!)