What are the leading theories as to why homo sapiens evolved to have less and less hair except in the pubic area and under the arms? And why the hell does body hair stop growing at a certian, (relatively) uniform length even though head hair grows indefinitely? Are the hair follicles physically different?
Yes they're different. I think some are stronger than others... and that's why we have different lenghts/width's of hairs. (I think the thickest are pubes, and the thinnest... I'm not sure but it's either ... well, forget it) Human hair doesn't normally grow indefinately, they would normally fall out when they reach about 3 feet (If my memory serves me right)... but since people tie it up and stuff, nowdays they don't. Why pubic hairs... I think I read once that at least in females, for hygene... I mean, it is pretty close to the anus, so it's supposed to somewhat prevent bacteria from spreading too much. As for hair under the arms and also pubic hair, they are homes to specific species of bacteria, and we have specific types of sweat glands there, and together they give us odors that help us get mates and stuff... here, read it yourself. I know I suck at explaining. http://zebra.biol.sc.edu/smell/mary-amy/mary_amy_doc.html
AlphaWolf has correctly explained why we have kept some hair. As to why we lost most of it - well that isn't actually true. We still have almost the same number of hairs, it is their thickness and length that has diminished. The most popular theory is that it was favoured by the extensive use of sweat glands to regulate our body temperature.
