An interesting piece on genetics, intelligence and developmental stability, and rather than focussing on what makes us intelligence, concentrate on those changes and mutations that impact our developmental stability. Quote:
We also inherit — through genes yet to be identified, of course — a trait known as developmental stability. This is essentially the accuracy with which the genetic blueprint is built. Developmental stability keeps the project on track. It reveals itself most obviously in physical symmetry. The two sides of our bodies and brains are constructed separately but from the same 23,000-gene blueprint. If you have high developmental stability, you’ll turn out highly symmetrical. Your feet will be the same shoe size, and the two sides of your face will be identical.
If you’re less developmentally stable, you’ll have feet up to a half-size different and a face that’s like two faces fused together. Doubt me? Take a digital image of your face and split it down the middle. Then make a mirror-image copy of each half and attach it to its original. In the two faces you’ve just made — one your mirrored left side, the other your right — you’ll behold your own developmental stability, or lack thereof.
Both those faces might be better-looking than you are, for we generally find symmetrical faces more attractive. It also happens that symmetry and intelligence tend to run together, because both run with developmental stability. We may find symmetrical faces attractive because they imply the steadiness of genetic development, which creates valuable assets for choosing a mate, like better general fitness and, of course, intelligence — or as Dr. Mitchell might put it, a relative lack of stupidity.