Blondes seem to attract more than their fair share of attention, both positive and negative. From “Blondes have more fun” to a plethora of “blonde jokes,” there’s something about the fair-haired that draws attention.
So when Canadian anthropologist Peter Frost wrote a paper, published this week in Evolution and Human Behavior, setting forth an explanation for the existence of blondes, it naturally got a lot of press attention…even though it wasn’t really about blondes at all, or at least not only about blondes.
First, a bit about hair colour in general. Your hair colour is basically determined by how much of two pigments, eumelanin and phomelanin, you have in your hair. Eumelanin determines the range from blonde to black: just a little and you have light hair, a lot and you’ll have black hair. Phomelanin determines how red your hair is: the more the redder. A blonde, then, is one with not much pigment of either type, someone with auburn hair has a fair amount of both, and so on.
The genes that code for lots of eumelanin and not much phomelanin are generally dominant, and so the default for humans around the world is brown hair (and brown eyes, for much the same reason). That being the case, how did northern and eastern Europeans get such a variety of hair colours—not just blonde, but strawberry blonde, auburn, and even flaming red?
Frost’s paper is entitled “European Hair and Eye Colour: A case of frequency-dependent sexual selection?” In it, he theorizes that at the end of the Ice Age, 10,000 to 11,000 years ago, women with unusual hair and eye colour stood out as potential mates at a time when there was a scarcity of men.
That man shortage arose, he suggests, because as the Ice Age wound down, northern Europe, still partly ice-covered, had (unlike, say Africa) a shortage of food plants. For the first time, then, food gathering fell almost entirely to males, who had to go off on long, dangerous trips to hunt mammoth, reindeer, bison and other herd animals. Many men died on such trips, reducing the male population. As well, because the men had to provide all the food for their families, they limited themselves to fewer mates. Women who stood out from the crowd were more likely to be chosen as mates, and therefore more likely to reproduce—and thus the recessive genes for non-brown shades of hair and eyes were passed on in greater numbers than they normally would have been.
In newspaper and radio stories, this theory has been boiled down to “Cavemen preferred blondes.”
There are no blondes in my family: rather than the light-haired, on the male side, at least, we run more to the non-haired (though I have thus far evaded this genetic fate).
As it happens, there’s been recent scientific news regarding baldness, too: last September researchers reported in the Proceedings of the National Academy of Science that they were able to genetically engineer hairless mice to grow thick fur.
The hairless mice lack a gene called Hairless that regulates hair growth (oddly enough, it’s the lack of the Hairless gene, not its presence, that makes mice bald). The researchers genetically engineered the hairless mice to produce the protein that Hairless codes for in specific cells within their hair follicles: and presto!, fur.
The hair-growth cycle consists of growth, regression (the hair falls out, destroying the lower part of the follicle), rest (the follicle is dormant), and re-initiation of growth (the follicle repairs itself and grows a new hair).
In the hairless mice, scientists discovered, Hairless turns off another gene that makes a protein called Wise. When Hairless isn’t working, Wise keeps accumulating—and too much Wise prevents follicles from switching back on after the rest phase.
Baldness caused by mutations in the Hairless gene (which humans have a version of) is rare. But the scientists hope that understanding the mechanism involved may point them to ways to deal with more ordinary forms of baldness.
There are still elements of the hair-growth cycle that are puzzling to scientists, just as there are elements of the genetic basis for hair colour (and the evolution of that colour) that are unknown.
Every question science answers simply leads to more questions. It’s enough to make you pull your hair out—
—but don’t.
