A new discovery, announced Monday in the journal Nature, adds a piece to the puzzle. DNA testing of an ancient jawbone has confirmed that a man who lived in Romania about 40,000 years ago descended from a Neanderthal ancestor just four to six generations – less than 200 years – before him.
"To our amazement, this guy had three or four times more Neanderthal DNA than any modern human we had ever looked at," said Svante Paabo, director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and co-senior author of the Nature study. "This is the first time we can say it's dramatically more, and close in the family tree."
Genetic evidence has been the basis of the OOA model of human origins and is usually considered standing in contrast to the physical evidence which supports the Multiregional model.
But some of these new findings (see the other thread: New Type of Ancient Human Found—Descendants Live Today? ) show us that the genetic evidence, when considered in its entirety, is more likely going to end up supporting the MH model than it will the OOA model (which is now as full of holes as Swiss cheese).
I don't see how a population of H. neanderthalensis known to exist at 35k years ago and a population of H. sapiens known to be in the same region at the time conflicts with Out-Of-Africa. What this evidence shows is that the gene flow between the populations may have continued more recently than previously hypothesized.
The issue of interbreeding was discussed in the other thread (linked to in the OP). But basically, the OOA tree model fails to account for the fact that while we carry recent African-origin genetic material we also carry genes of recent non-African origin, which is and always has been the MH position.
The fact that this person's material didn't make it into today's gene pool also supports the MH explanation that the paucity of lineages outside of Africa results from lineage extinctions.
The question now is why, with such recent crossings, is there not more neanderthal DNA in present sapiens populations.
According to the article, the individual in question is not an ancestor of any modern human populations.
The two models have never been mutually exclusive. If about 5% of our genomes are from crossbreeding and the other 95% from our African ancestors, then the MH model explains 5% of our genome and the OOA model explains 95% of our genome.
It's a bit like the "argument" between gradualism and punctuated equilibria. You can have both.
I think MH works fine with the observation that 95% of our genome is African while 5% is from sources outside of Africa.
Where the theories differ is in explaining why that distribution exists. MH explains it as a result of African genes swamping non-African ones (the genes were superior, more numerous, etc.) with little need for the large population movements posited by OOA.
MH works as an explanation for the genetic evidence, to be fair, OOA does too, but MH has the added benefit of explaining the physical evidence and matters such as regional continuity of completely random traits.
The idea of genes moving without any significant movement of populations was sufficient to explain the fact the mtDNA had a recent African origin, but if we're talking more than 90% of the genome it doesn't seem reasonable to think this happened without lots of people carrying these genes.
More than 90% of which genome? The fella in question wasn't 90% African.
The 90% African distribution is the result of millennia of gene flow out of Africa.
But why should the selectively neutral bits of the genome from Africa come to dominate everywhere without being carried by an expanding African population?
Whether the dominance of African genes was brought about by migration or breeding, the evidence rather suggests that the African genes were anything but 'neutral'—they're the genes that won.