The Naked Ape by Desmond Morris

Breezy comparison of humans to other primates; while not as fun as you might think (we need more grooming time ;), it has some neat tidbits: some people can orgasm just via earlobe manipulation, and piercings that padlock vaginas (both in chapter 2, Sex).

It is interesting that amongst children of pre-school age, the more intelligent ones tend to sleep less than the dull ones. After the age of seven, this relationship is reversed, the more intelligent schoolchildren sleeping more than the dull ones... Amongst adults, by contrast, there appears to be no relationship between brilliance and the average amount of sleep.
-- Chapter 3, Rearing