Any theory that attributes human brains, bipedality or nakedness to sexual selection has got to face up to a major difficulty. There is no evidence that one sex is brainier than the other, nor that one sex is more bipedal than the other. It is true that one sex tends to be more naked than the other, and Darwin made use of this in his own sexual selection theory of the loss of human hair. He supposed that ancestral males chose females rather than the other way around as is normal in the animal kingdom, and that they preferred hairless females. When one sex evolves ahead of the other (in this
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