Tuesday, March 21, 2006


Blonde Extinction

(Via Neil Gaiman) A few weeks ago I came across an article online that advanced the theory that blonde hair had been a selective advantage 10K years ago, but that in short order the gene would be extinct. And I'm ashamed to say I bought it hook, line, and sinker. Via Gaiman's blog I discover that the good people of Snopes have called bullshit, with the full weight of their authority behind them. What's fascinating, though, is that they trace this particular myth back to the nineteenth century.

I heard about the blonde extinction rumor some years back, and it never made much sense. Recessive genes don't just disappear from a population; the Hardy-Weinberg law of genetics ensures that. And natural blondes can lighten their hair just as easily as brunettes, if not more so. The only reason the gene might decrease in frequency would be something like increased susceptibility to skin cancer due to having fair skin (a factor never even suggested in the rumor), and even that probably wouldn't matter much, since it doesn't usually kill people until after after they've already reproduced.
What I don't know about genetics is, embarrassingly, a lot. But what was interesting to me in reading the history of the myth that the Snopes folks had put together was that the counter argument to the myth was advanced in the 19C: instead of blondes going extinct because bottle-blondes were edging them out, it was because brunettes were considered more attractive. Either is equally impossible, as you point out, but it's amusing to see how the rationalization for the myth has changed with shifting fashions and tastes.
Just to clarify: the idea that the gene for blond hair offered a selective advantage 10,000 years ago is *not* a myth. According to recent reports, genetic analysis indicates that the gene for blond hair is of recent origin, and for it to have become relatively common in such a short timespan, it must have offered some advantage. The precise nature of that advantage is unclear.

What is a myth is the idea that blond hair will disappear simply because it's a recessive gene (as cited in the rumor). This means that in order for you to have blond hair, the gene must be present in both your father's family and your mother's family. By contrast, if dark hair is a carried by a dominant gene, you can have dark hair even if dark hair is present in only one of your parent's families. Some people think that this means recessive genes will gradually disappear. This is incorrect, as shown by Hardy and Weinberg. In the absence of other factors, recessive genes will remain in the population, in the same proportions, indefinitely.

If someone were to identify a link between the gene for blond hair and, say, early death due to a congenital heart defect, then the gene might become less frequent over time (assuming the absence of medical care). But there's no possible way it could happen in only 200 years. You might as well say it would happen by next Tuesday.
Did I hear, and is it correct, that the gene for six fingers is actually a dominant gene?

Speaking of, I knew a girl with six toes but her parents cut the extra toes off when she was born. Provided they didn't stick out at odd, shoe-unfriendly angles, I would have felt violated had I lost toes this way.
I couldn't help but reply to this blogg for two reasons. Those being blonds and the other six toes.
I have almost black hair and all three of my children have white blond hair, not just muddy blond or gold blond but white.
My mother and great grandmother had 6 toes, which actually my mother's was removed when she was a baby.
I am very interested in the blond gene as my children are so blond and I am trying to work out why being as dark as I am that they inherited my husbands blond hair, even though I have the dominant gene.
ted have you never heard of The Pill? harvey-weinberg never accounted for that.
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