Our four case studies—penis, clitoris, breasts, and buttocks—do not exhaust the body's complement of sexual ornaments. Because they are sexually differentiated, they are especially informative about male mate choice and female mate choice. However, they are relatively minor contributors to physical attractiveness compared with the face, and with overall body height, proportions, and condition. Our lack of body hair, our long head hair, and our sex differences in musculature are also important signs of sexual choice. Nancy Etcoff's Survival of the Prettiest and Desmond Morris's Bodywatchinghave discussed these charms in great detail.
However, I would like to note a few features of the human head that put the human brain in its bodily context. The head is a major target of sexual choice in both sexes. It is rich in fitness information because it is such a complicated piece of the body to grow, and so many things can go wrong. The front of the head has evolved a convoluted shape because evolution tends to pile sense organs up at the front of the body, where they are best placed to sample that part of the environment toward which we are headed, and from which signals can reach the brain quickly. This is why we have eyes, ears, noses, and tongues all huddled together, rather man spread around the body more evenly. The orifice for ingesting food also evolved to be near the brain so that we could efficiently control what we eat and how we chew. The result of evolution assembling the mourn and sense organs so close to the brain is called the face.
An alien biologist might consider such an unseemly concentration of organs on one tiny area of the body rather disgusting, so it is striking that we consider faces so crucial to physical beauty. If the alien did not understand fitness indicators, he or she (or it) might be puzzled that we pay so much attention to the one part of the body that is too complicated for anyone to grow in a perfect form. Wouldn't we find it easier to focus on thighs or backs, which are so easy to get right? Yes, it would be easier, but it would not give us the fitness information we want. Instead of averting our eyes from the unsightly front of another person's head, where harmful mutations show themselves most readily as unusual proportions and asymmetries, we are sometimes so rude as to stare at it, instead of their penis or their breasts. Have we no courtesy? Indeed, we pick the one part of the body where fitness differences are most manifest, and regard that as the seat of personhood. Where mutations show their effects most readily is where we direct our sexual judgment and social attention. A portrait of a human implies a representation of the face.
Much of this book applies the same fitness-indicator argument to the brain as well. Whereas we can perceive facial form visually, we can perceive a brain efficiency only indirectly, through a person's courtship behavior. Beauty is no longer skin-deep in our species. Sexual choice reached behind our faces to tinker with our minds. Mostly, it did so by connecting our brains in a unique way to our mouths, so that we could talk instead of just chewing and grunting. The attention we pay to faces and brains in sexual choice, our obsession with just those body parts that are most difficult to grow perfectly, is powerful evidence for the fitness-indicator view of sexual selection.
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