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October 20, 2004

Paradigms (and books) lost....

About six months ago Dr. Henry Harpending expressed to me the opinion in an email that the mtDNA pattern we see (the seed from which genetic Out-of-Africa emerged) is the result of a selective sweep. Since Henry knows this shit, I was pretty troubled. You see, I have half a dozen books on human evolution and cognitive prehistory that I haven't gotten to that are premised on the beautiful simplicity of Out-of-Africa (Damn you Powells!).

A possibility that extremely ancient extra-African genes made their way into modern humans kind of rocks the boat. I know there have been a few genetic studies here and there that stand against Out-of-Africa, and for those "in the know" this might have been on the horizon and not caught them by surprise, but for the interested layperson (like me) it is pretty shocking.

Readers who follow the blog know that I've aired skepticism of the parsimonious appeal of the Great Leap Forward, that supposed cognitive explosion that led to humanity as we know it. If the new research pans out and other studies reproduce it, we might be faced with a phylogenetic as well as palaeoanthropological reworking of the established models. No doubt a Cambrian Explosion of books is just around the corner.

One might wonder if complex and geographically contextualized partial replacement and admixture models become more dominant if the current rhetoric of recent ancestry, ergo, we are all closely related, will fall by the wayside and more space will be given to the idea of interpopulation differences. My honest opinion is that Milford Wolpoff's cant in Race and Human Evolution will be modified, his polemic being that Out-of-Africa + Total replacement implies a genocidal nature for Homo sapiens, while his Multiregionalist model posits more amity and harmonious genetic exchanges between human subpopulations. I await the clever creativity of the sensitivity warriors as they rework partial replacement models into the context of diversity and multisubspecies homonid harmony.

For now, I'll still stick with Out-of-Africa, I'm not going to shift paradigm before the scientists, and I have some books whose subjective value in my eyes would decrease substantially, but my mind is very open to the possibility of change. I will mourn the passing of Out-of-Africa's simplicity if it does pass.

Related: All this is babbling about ancestry and models has to be judged in light of the possible difference between neutral and functional genomic history.

Addendum: I don't think this means we need to go back to the old-style Multiregional conceptions of a worldwide species that stumbles in lockstep toward sapiency. There are, as I suggest above, many points in between old school Multiregionalism and the currently dominant Out-of-Africa + Total replacement model. The Out-of-Africa model was always most well suited to Europe, and Chris Stringer based his ideas on morphological evidence, that is, fossils, which documented the sharp transition between Homo sapiens neanderthalis and Homo sapiens sapiens. In recent years computers have been used to analyze these fossils, so I will hold off on asserting that this sort of assessment is by its nature subjective since my impression is that a great deal of rigor has firmed up the field because of cheap CPU cycles (I have an acquaintance who is a computer science guy working in computational paleontology). But one might conjure up models where Out-of-Africa + Total replacement might hold for region A (Europe) but not for region B (Asia). In The Third Chimpanzee Jared Diamond offers just this model. In Ascent of the Mind William Calvin argued for repeated back-migrations from Eurasia into Africa. The period of the 1980s and 1990s might soon be viewed as a theoretical bottleneck before the diversification of models in this century....

Posted by razib at 02:21 AM