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« Sen. Carl Levin: Iraq’s leaders are too slow forming unity government | Main | Could an Iraq civil war be a good thing? »

February 27, 2006

Comments

Nicholas

Nit pick: we are currently in an ice age interglacial period. The transition 10 000 years ago you are referring to was from the glacial period to the inter-glacial period.

I believe that, when the planet is not in an ice age, there's virtually no ice at all, even at the poles.

See here for more information.

jj mollo

Blondness may well be an adaptation related to fair skin in order to improve access to sunlight in northern latitudes. Humans require vitamin D, which is catalyzed under the skin by sunlight. The hair color may be an accidental co-evolved feature related to fair skin, or it may provide additional solar exposure. Blondness is also an avertisement for youth since it, as well as red hair color, tends to disappear with age. In a male-sparse environment, male preferrences will dominate, giving relative advantage to younger women. The genetic outcome will be that women will tend to remain blond longer (neoteny).

I would bet that the prevalence of genes for blondness are actually increasing in the population, but may not be expressed as often due to the fact that the feature is recessive. At any rate, the article on Wikipedia claims that the disappearance assertion is a myth. The young lady pictured appears to me to have a selective advantage in any environment.

Stephen Cobb

To JJ Mollo's excellent comment I will add the clarification that it is unlikely that blondes have more estrogen than non-blondes, but rather that young blondes have more than old blondes.

This is just one of many theories for the purpose of blond hair. The one I like concerns "paternal confidence": men prefer a woman with a combination of dominant and recessive genes such that a child is likely to resemble the father. It has been shown that blue-eyed men prefer blue-eyed women, but no other combination produces a preference.

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