But what exactly is beauty? Trying to define it is difficult, and yet we know it when we see it—or so we think. “Beauty is health,” says one psychologist. “It’s a billboard saying ‘I’m healthy. I can pass on your genes.’” And our awareness of it may start at a very early age. In one set of studies, six-month-old babies were shown a series of photographs. The faces in the pictures had been rated for attractiveness by a group of college students. In the studies, the babies spent more time looking at the attractive faces than the unattractive ones.