Before getting into this one, I want to make it clear that this is not an invitation to debate the merits of the theory of evolution. For the purposes of this post, it is assumed that evolution, specifically that humans evolved from ancient apes (NOT modern apes--humans are not descended from any modern ape). As for the "it's only a theory" argument, a theory is as close to fact as you can get in science. We don't discount Einstein's theory of relativity or Newton's gravitational theory because they are "only theories", so neither should we reject the theory of evolution on those grounds. If evolution wasn't as close to fact as science will get then it would be the conjecture of evolution, not the theory.
Anyway, continuing on now from the assumption that evolution is a fact:
Do you ever wonder why, if our distant ancestors were hairy apes, we have lost almost all of our body hair? Even stranger to me is how long the hair on our heads grows; I know of no other animal that grows the hair on its head to such ridiculous lengths. (If there is one, please enlighten me.)
In pondering this, we must understand that natural selection does not select for any traits. In fact, it selects against traits that are reproductively disadvantageous. Two big words--maybe I should clarify: suppose there are two possible traits in a critter, a red chest or a brown chest. Further suppose that, all other things being equal, those critters with a red chest have a much worse time hiding from predators and, therefore, tend to die younger (some even before they have a chance to reproduce at all) than those with a brown chest. Natural selection is at work here, selecting against red-chested critters, giving you more descendants of brown-chested critters, possibly until there are no more red chests in the critter population.
Going back to body hair, the question I find myself asking is, "why was it a disadvantage for our ancestors to have thicker body hair?" All other land mammals seem to get along just fine with more body hair in all environments. What was different about human ancestors? There is the possibility that the mutation that causes less body hair just never occurred in any other evolutionary line, but that seems unlikely to me. And why is it that we still have thick hair in certain places? What's special about an arm pit that the "less body hair" gene left that alone?
Along the same vein, why do women tend to have less body hair than men (even when they don't shave it off)? Clearly, some evolutionary force selected against women with much body hair. Nowadays, that could be seen because most men (in our culture, anyway) are more attracted to women with little body hair, but is that what started it all? If that was the selective factor, where did that attitude come from in the first place?
A similar question goes for head hair: "what was the disadvantage for not being able to grow long hair on the head?" Those who have had long hair can tell you the disadvantages of same: it takes a long time to dry; it gets tangled and is hard to maintain; it can get caught on things (which seems like a distinct disadvantage to a primitive ape to me); etc. Perhaps the two things are related; longer head hair had to come with less body hair for some reason (or vice versa).
Finally, why do men tend to grow facial hair, but women don't? (I'm speaking in generalities here, and not talking about a little "peach fuzz" on the upper lip.) What possible evolutionary factor could there have been to select against males with no facial hair, but against females with facial hair? Perhaps, again, we're looking at what specific mutations did or did not occur, but why affect males and females differently? Maybe it has something to do with the second X chromosome, seeing as the Y chromosome doesn't have as many genes on it. (I do know that this is the source of some male-female differences, such as pattern baldness, which is a recessive gene but occurs on the X chromosome and not on the Y. A woman with the gene might well have the dominant gene against pattern baldness on the other X chromosome. That's an oversimplification, I'm sure, but it's the basic idea as I understand it.)
I'm afraid I don't have the answers to any of these questions, but they have been occurring to me off and on for years. Please feel free to educate me if you know, or even share if you have a theory. I'd love to know what other people think, especially about the reduced body hair question.
Hey, not all my posts can be deep and meaningful. :-)
