Saturday, March 18, 2006

Blonde hair & blue eyes   posted by Razib @ 3/18/2006 02:28:00 PM

I read Peter Frost's paper on blonde hair and sexual selection awhile ago. I don't have much to say on it that I didn't already say in the previous conversation, I think ascertainments or suppositions in regards to sexual selection in the evolution of the human species and our phenotype(s) will be a lot more fruitful when we have the priors in in regards to the organization of our genome and its deep time history locked down in more detail. I'm posting now because I did think Peter put a lot of interesting data out there, and I am reproduced two of the maps in his paper, which depict the frequency of blonde hair and blue eyes respectively in northwest Eurasia. Nothing surprising, but some concrete percentages for any future discussions on the topic. You'll find it below the fold.

The only substantive point I'd like to add is that Peter points out that the emergence of 30 polymorphisms extant within the European populations on MC1R as a consequence of release of functional constraint is implausible (the locus implicated in melanin regulation which in East Asians and other populations tends to be far less polymoprhic, or nearly monomoprhic, as in Africa). He contends that the current level of hair color diversity in Europe would have taken 850,000 years to develop if one assumes release of constraint was the primary factor, and of course H. sapiens sapiens has been in Europe no longer than 35,000-40,000 years (one assumes that release of constraint would not have occurred prior to leaving the lower latitudes). But, I would like to point out that H. sapiens neanderthalensis was resident in Europe for ~250,000 years. This isn't enough time for a neutral-only model to generate the diversity, but life isn't always an either or scenario, and one could imagine that factors other than in situ mutation or selection upon standing genetic variation might have played a role in the diversification (or perpetuation of diversity) of European color phenotypes.

Update: Greg points out that Neandertal (H. heidelbergensis) precursors might have lived in Europe as early as 800,000 years B.P. So that is a point to consider. Also, I have to add this in the "scientists don't get evolution" files, I recall that one paleoanthropologist posited that Neandertals were dark-skinned because their skeletons seem to exhibit features similar to rickets. At the time (I was 16 when I read this) I wondered how plausible it was that 800,000 years of hominin residence in high latitudes wouldn't have selected against traits which predispose one to rickets. Obviously it isn't plausible.

Credit: Beals et al., An Introduction to Anthropology, 3rd ed.