Why do Caucasians differ so much in hair color?

Why do Caucasians differ so much amongst themselves in hair color, while everybody else (with the exception of some blonde Australian Aborigines) has dark brown hair? Here's my theory, which has been getting some favorable responses.

Blonde and red hair are favorable mutations for women because they make men notice them more. Fair hair reflects more light than dark hair, so it catches the eye more. Women like shiny jewelry for the same reason.

But, why then doesn't blonde or red hair become universal? Well, it would lose scarcity value if all women had it. But, also, while it's good for your daughters, under pre-modern conditions it was bad for your sons. It tended to hurt males at hunting and war. I recall attending a golf tournament on a sunny day and standing behind the green when a friend asked, "Which players are coming next?" I glanced at the tee 500 yards away, and said, "I can't tell who all is in the next group, but you can definitely see the sunlight glinting off Greg Norman's hair." The Australian pro Norman, who is no doubt of partial Nordic descent judging by his name and appearance, has extremely blonde hair. Fortunately, by now Northwestern Europeans have largely beaten their swords into golf clubs, but in days of yore, Norman's hair would have served disastrously as a beacon calling attention to his presence. Of course, in the Nordic homelands there aren't many terribly sunny days.

Thus, blonde hair becomes more common the farther in Europe you go north, where the sun is low in the sky and the land heavily forested and therefore shady. Within Northern Europe, red hair becomes more prevalent the farther west you go, where, due to the Gulf Stream, the weather is extremely misty. (I'd guess that the Western Irish are around 1/3 red-haired.) So, in Northwest Europe, you can have lots of blondes and redheads because lack of direct sunlight meant that highly visible hair worked well for women, without much penalizing their men folk when hunting or raiding.

In line with this theory, in movie love scenes, the actress almost always has lighter hair and skin color than the actor. This suggests that we still associate fairness with the fair sex. 12/13/01