How come white people don't all look alike?
Though I recently completed a course in physical anthropology, there is something that I still don't know. How come there seems to be a greater range of variation in the hair color and texture and eye color of Caucasians than in the other three or four races? Caucasian hair goes from practically white to black; eye color, too, can vary from pale blue to black. There aren't as many Caucasians as some of the other races, and they seem to be plenty close together, geography-wise. I know this sounds an awful lot like "all those people look alike," but I'm curious.
I'm glad you have disavowed any unworthy motives in asking this question, because we are dealing here with a highly touchy subject. Nobody knows for sure why Caucasians exhibit a wider range of physical traits than other races, but there are a number of theories, some of them more dubious than others.
But let's clarify a few things first. For one thing, Caucasians don't all live "plenty close together, geography-wise." Even in precolonial times, ethnic groups now classified as Caucasian were spread across Europe, North Africa, the Middle East, and the Indian subcontinent. Given the enormous distances involved, you'd expect considerable variation.
Second, Caucasians don't show the widest variation in all traits, just certain superficial ones--hair color and texture and eye color, as you point out, along with skin color, which varies from very light to almost black. When it comes to something like height, on the other hand, Caucasians lose out to Africans, whose average stature ranges from 4'8" for adult male pygmies to 5'10" for adult male Batutsis. Similarly, other races show greater variation in nose configuration, distribution of body fat, and so on.
Finally, whatever may be said for Caucasians, all major races show substantial variation in coloration, largely because of adaptation to local conditions. For instance, it's generally conceded that skin pigmentation acts as a filter for the sun's ultraviolet rays, and it's possible to plot out a sort of gradient called a "cline" showing that the closer you get to the equator, whether it's in Africa, Europe, or Asia, the darker the characteristic skin color of the locals. Something similar may conceivably apply to eye or hair color.
Still, that doesn't explain why there are no blond, blue-eyed Eskimos. Here's where the theories come in. The least controversial is that Caucasians are the most thoroughly "hybridized" of the major races--that is, they've had the most additions to their gene pool as a result of invasions, migration, slave trade, and so on.
Caucasian "territory," if you want to call it that, spans three continents. It has been repeatedly overrun by Asian tribes such as the Mongols and the Huns. The Romans imported Nubian slaves, and the Moors, with a significant percentage of Negro blood, invaded during the Middle Ages. One might plausibly argue that Negroid and Mongoloid peoples, by contrast, either (a) suffered fewer invasions and other such traumas, or (b) totally annihilated anybody who did try to invade. The trouble with this line of thinking is that it's extremely difficult to document tribal migrations, especially in prehistoric times.
The other theory, which is widely regarded as racist, is that Caucasians show more variation in color because they're the furthest removed from mankind's hominid ancestors, who (some think) were all heavily pigmented. To put it another way, Caucasians are most "advanced," Mongoloids slightly less so, and Negroids least of all. The most elaborate expression of this theory was given by the anthropologist Carleton Coon in the mid-60s. Coon's idea was that there originally were five basic races that evolved separately, in widely differing times and places, from our homo erectus forebears--Caucasians, predictably, being the first.
Coon, I should point out, was not a crackpot, and there is a certain amount of fossil evidence to support his view. But there are some major objections to it as well, the most obvious being that one would expect races that had evolved separately to be unable to interbreed, as all humans today clearly can.
In addition, there's nothing to indicate that our ape grandparents were necessarily all dark-skinned--after all, under their hair, modern chimps are often relatively fair-skinned. And Caucasians are generally hairier than other races, which you would think would be a more primitive trait. Besides, haven't you ever been to a white- boy frat party? You'd swear some of those guys were in trees eating bananas last week.