Article excerpt. Rebecca Newberger Goldstein. Philosopher, Novelist; Recipient, 2014 National Humanities Medal; Author, Plato at the Googleplex; 36 Arguments for the Existence of God: A Work of Fiction.

Our impression is that symmetrical faces and bodies are beautiful. Symmetry, it turns out, is a good indicator of health and, consequently, of mate-worthiness. It’s a significant challenge for an organism to coordinate the production of its billions of cells so that its two sides proceed to develop as perfect matches, warding off disease and escaping injury, mutation and malnutrition. Symmetrical female breasts, for example, are a good predictor of fertility.

As our own lustful genes know, the achievement of symmetry is a sign of genetic robustness, and we find lopsidedness a turnoff. So, too, in regard to other components of human beauty – radiant skin, shining eyes, neoteny (at least in women).

The upshot is that we don’t want to mate with people because they’re beautiful, but rather they’re beautiful because we want to mate with them, and we want to mate with them because our genes are betting on them as replicators.