BEAUTY, the saying has it, is only skin deep. Not true. Skin is important (the cosmetics industry proves that). But so is what lies under it. In particular, the shape of people’s faces, determined by their bone structure, contributes enormously to how beautiful they are. And, since the ultimate point of beauty is to signal who is a good prospect as a mate, what makes a face beautiful is not only an aesthetic matter but also a biological one.