I've been wondering about head hair, facial hair in particular. Human males can grow very extensive beards should they choose to not shave - however you do not really see this in our chimpanzee cousins! Yes, they have little pseudo-beards, but the difference being that they do not shave, that is just the length they reach. Whereas in humans we can grow to our hearts content (*this may not be the case, see this question).
I can't really see why this would have been selected, unless it's simply that (evolutionarily speaking) women like men with long beards?
So my question is: why can humans perpetually grow head hair, yet we have lost the majority of our body hair, in comparison to chimpanzees and other ape family members?
Answer
Wheeler (1992; and previous) discusses the evolutionary loss of "non-functional" hair in hominids from the perspective of water balance.
Wheeler's hypothesis is that naked, bipedal hominids could have tolerated higher ambient temperatures as well as elevated metabolic heat production. Naked skin would confer higher levels of evaporative cooling, but would have entailed more water loss.
Wheeler argues that bipedalism necessarily would have preceded loss of hair, which seems to agree with Carrier's (1984) hypothesis that early hominids were distinguished not by large brains but by upright, bipedal postures with striding gaits. Humans are unique among similarly sized mammals in their capacity for endurance running.
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