A few days ago I received an email from a reader asking me about the possibility for differentiation of populations because of the postgenomic era, eg., the use of multiple markers to achieve separability. They brought up the near disjoint character of the Duffy antigens between Europeans and Africans (ergo, its historical utility in calculating white admixture into the African American population). One thing I offered is that if a derived allele is near fixation (near 100% in group X), then it will likely be characterized by high frequencies in many other groups and one might find it more worthwhile to search for populations that remain in the ancestral state. In other words, resistence to the acquisition of beneficial alleles by particular local populations, or, more likely, their insulation because of time and space from the region of the origin of a current selective sweep, will be more common than the detection of locally stable clusters of high derived allele frequencies. My hunch is that highly beneficial alleles that emerge within a population will most likely be beneficial in other populations and deme-to-deme gene flow is a powerful force. For example, I think something like lactose tolerance is relatively common, an allele which swept through distinct and varied populations in Eurasia where cattle culture was feasible. This doesn’t people separability is not possible or plausible, obviously Risch’s work falsifies that manifestly, rather, I think that the pairwise comparison of nearly disjoint allele frequencies across populations is going to be a lot less interesting than the richly complex relief of gradients which will track geography and history ways we don’t even understand yet.
