Out-of-America Theory and the Race Debate

The topic outlined in the title of this post is huge and I can’t give justice to it at this moment. But considering how dramatic of a revision of modern human evolutionary history the out-of-America theory is offering, it is important to provide a direction where this revision will likely take the so-called “race debate.” In a nutshell, by the “race debate” I mean the unabated discussions taking place across academic and public spheres regarding if and to what extent modern genetics supports “racial” divisions within the human species hypothesized on the basis of some perceptually distinct phenotypes. Recently, an informative quote from Luca L. Cavalli-Sforza has surfaced in an online forum:

“Edwards and Lewontin are both right. Lewontin said that the between populations fraction of variance is very small in humans, and this is true, as it should be on the basis of present knowledge from archeology and genetics alike, that the human species is very young. It has in fact been shown later that it is one of the smallest among mammals. Lewontin probably hoped, for political reasons, that it is trivially small, and he has never shown to my knowledge any interest for evolutionary trees, at least of humans, so he did not care about their reconstruction. In essence, Edwards has objected that it is not trivially small, because it is enough for reconstructing the tree of human evolution, as we did, and he is obviously right.”

It logically follows from this statement that the continental population that shows the largest between-population fraction of variance should be considered the oldest. The bad news for Cavalli-Sforza is that he and Edwards championed a quantitative phylogenetic approach to human evolution (see Edwards, A. W. F. “Statistical Methods for Evolutionary Trees,” Genetics 183 (1): 5-12) that quickly resulted in the practice of rooting the trees of human evolution in Africa and identifying the basal branches of the human tree by their similarity to chimpanzee genetic sequences, while the actual data at hand shows that between-population diversity among humans is the highest outside of Africa, especially in the New World, Papua New Guinea and such isolated island territories as Taiwan. Current phylogenetic trees of human populations make African foragers such as San Bushmen and Pygmies look closer to a non-human, chimp outgroup than other humans, while populations such as Amerindians look like a subset of Asians. These trees reinforce simultaneously two kinds of prejudice: medieval cosmologies that did not account for America because it was not yet “discovered” (see more here) and 19th century racial classifications that plotted human groups on an imaginary scale from more ape-like to more advanced groups.

In reality, however, the “racial” divides, if statistics such as Fst and Gst are taken as measures thereof, are stronger among New World populations and they decrease progressively with geographic distance the closer one gets to Africa and Europe. At the same time, these divides are neutral from the point of view of the relative proximity to “lower,” non-human species because genetic drift likely obliterated those similarities. So, if looked from an out-of-America angle, human evolutionary history is the process of progressive “deracialization” (or detribalization) of human populations and their agglomeration into more cosmopolitan entities. The complete genome of the Denisova individual showed that mid-Pleistocene hominins existed as small, isolated demes characterized by very low intragroup (within-population) and very high intergroup (between-population) diversity. In other words, they were more racialized than anything that is encountered among modern humans. The phenotypical “races” identified by early taxonomists (Negroids, Caucasoids, Mongoloids and suchlike) are, ironically, the most visible outcomes of the genetic deracialization that affected human groups from the Late Pleistocene on.