Sunday, February 26, 2006

Birth of the Blonde   posted by DavidB @ 2/26/2006 04:42:00 AM

Today's London Sunday Times has an article here about a forthcoming theory on the evolution of blondeness in Northern Europe. The theory is that blondeness become common around the end of the last Ice Age as a result of strong sexual selection on females. Food was short and men had to go on long arduous hunting trips. A lot of them died, leaving a surplus of females, so there was pressure for females to attract mates, resulting in variant hair colour, etc., being selected.

The theory sounds to me like what is technically known as 'a load of bollocks', but hey, what do I know? Actually, what I do know is that women, unless they are very old or seriously ugly, have no difficulty in obtaining mates - all they have to do is to be available. The theory might be more plausible if the society were strictly monogamous, and women found it difficult to get a husband to provide for their children, but very few hunter-gatherer societies are strictly monogamous, least of all if there is a surplus of women.

Added: I see from a Google search that the theory is not that new. The author, Canadian anthropologist Peter Frost, has been touting it in one form or another for some time. I should also say that even in a polygamous society sexual selection on females might operate through the quality of husbands, but I guess this would be a comparatively weak force, and what is needed for the theory is unusually strong selection.

Addendum from Razib: Remember, "beware of British newspapers." The story concludes with this old false story from 3 years ago:

A study by the World Health Organisation found that natural blonds are likely to be extinct within 200 years because there are too few people carrying the blond gene. According to the WHO study, the last natural blond is likely to be born in Finland during 2202.

John Hawks has more. A "recessive" trait like blondness will disappear when the frequency is so low within a panmictic population that the expectation of alleles conferring blondness coming together becomes very low. If you think of it as a monogenic trait (say on MC1R), then it is just a matter of Hardy-Weinberg, p2 + 2pq + q2 = 1, so if q was the frequency of the blonde allele than frequency of blondes would go to q2. As it is, I don't see the process of panmictia in the near future....

Update II OK, I'm going to cut & paste my comment here so everyone sees it. For what it's worth, Dienekes has addressed Frost's thesis and offers his own counter-argument.

re: this theory. props to peter f. for throwing something out there. but, i must say that i am starting to feel that sexual selection is the new deus ex machina in lieu of random genetic drift. ?'s

1) is the asymmetry between Y and mtDNA long term effective population greater in northern/eastern europe than in southern/western europe (the blonde-non-blonde gradient).

2) what about other populations, like eskimos, where this process occurs? since selection can be stochastic it is not inevitable that blondness will be the novel or padaeomorphic cue. could east asian padeomorphism evolve from the same bias?

3) how did blondness increase in frequency among some australian aboriginals? the probability seems high that the trait is endogenous because its transmission mode seems different than that of europeans (though there isn't a perfect coupling between blondness and fair skin, they are connected in europeans via MC1R). i know that blondness is considered attractive among the women and youth there as well.

4) recent work points to selection on non-MC1R loci to generate light skin in europeans. this might have freed up MC1R to explore genetic space and evolve novelty. but, it might be that this process of sexual selection is ubiquitous in many (most) populations and that it stochastically fixed on different traits. (eg., epicanthic fold in asians)

5) is this runaway sexual selection? that implies coupling between the preference and the trait, and extremely fast evolution toward fixation of the trait sans functional/selective constraint. it doesn't seem that blondness has ever fixed, almost no population has a majority of adult female blondes (in c.s. coon he states that only in southern sweden does the intersection of blonde hair and blue eyes exceed 50% of the population).

6) what about traits like blue eyes? that seems unrelated to MC1R.

Here is the link to the abstract.