Recently, several journalists have contacted me about my article on the diversity of hair and eye color in European populations. They weren't interested in eye color. Nor were they interested in hair color diversity as such (red hair, brown hair, black hair, …). They wanted my opinion on blond hair.
They also wanted a summary that their readers could understand. Something short and sweet.
Well, I thought and thought. This is what I came up with:
Over most of Ice Age Europe, the main food source was wandering herds of reindeer. To exploit this food source, hunters had to cover long distances on foot, thus increasing the male death rate and reducing the ratio of men to women.
Meanwhile, this steppe-tundra environment offered no alternate food source that women could exploit. Women were thus less self-sufficient and only the ablest hunters could provide for a second wife. Not only were there fewer men, but also fewer were polygamous. Women had to compete more intensely for mates and the more successful tended to be those who could "stand out from the crowd." There was thus selection for hair and eye colors that deviated from our species norm of black hair and brown eyes.
One journalist answered: "…the parts of your quote about food and hunting are not relevant. The point is blondes had an edge over their darker-hair counterparts due to the rarity of that color."
I wrote back: "Blondes did not have an edge simply because blonde hair was less common. They had an edge because fewer men were available and because fewer of them were polygamous. When there are enough men to go around, there is no competition for mates and no "edge."
I got a response to the effect that something would be put in about competition … if space permits.
Most people seem to think that sexual selection is about preference. They're wrong. It's about choice. Choice is what you get when preference hits the brick wall of reality. If the numbers of mateable men and women are roughly equal, your preferences will not be fully reflected in your final mate choice. You'll have to compromise. The more favorable the sex ratio, the less trouble you'll have translating your preferences into your final mate choice and, ultimately, into the physical appearance of your descendants.
Conditions were unusually optimal for sexual selection of women among Ice Age Europeans. Men were in a position to translate very subtle preferences into mate choice. In most human populations, these preferences exist only as an unrealized potential.