Tuesday, November 20, 2007

Brown eyed girl?   posted by Razib @ 11/20/2007 02:27:00 PM

Peter Frost states:
I suspect there is some incipient sex-linkage, i.e., European women may be somewhat likelier to have non-brown eyes and non-black hair. If this sex-linkage is mediated by prenatal estrogenization there may also be some impact on personality and temperament. But I really don’t know, and unfortunately there are still more questions than answers.

I've read Peter's book, Fair Women, Dark men, and it is a great collection of data. Also, he has theorized that European color variation is a byproduct of selection selection. So I have been primed to look for a trend where women seem to express blondism or light eye color at higher frequencies. But I just haven't found anything like that. In fact, I've found data which goes in the other direction, that is, females have a higher frequency of brown eyes! But this really clinched it for me:

The source is this paper, Genetic determinants of hair, eye and skin pigmentation in Europeans. Note that women tend to score higher on skin sensitivity toward sun, which implies that they do have ligher skin. And as for hair color, well, perhaps there is a difference in how one judges blonde vs. brunette for males and females? I don't know. But the eye color data I've seen elsewhere and just dismissed it as small N or something like that. At this point my assumption is that there isn't really the sexual dimorphism in eye color that there is most definitely is in skin color. As for hair, I'm more open to this since it seems that it is subject to more genes, and there could be some hormonal factor as the tendency toward greater blondism in children and females is noted among Australian Aboriginals as well.

Anyway, forget visual inspection. Here's the associations taking sex into account (from Table 4 of supplementary info):

The authors don't want to make a judgment based on these data. But I'm not religious about 0.05 P values. And it looks like there's some action on KITLG anyhow.

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