[mannigfaltig]

My guess would be that symmetry is a simple heuristic measure of physical fitness. Visual attraction is basically a strong regularizer that restricts the search space to phenotypes with particular traits. Asymmetry means that the joints wear out more quickly and muscles might not coordinate optimally leading to less strength and a reduced ability to hunt and to fight predators. AFAIK it is also a quite robust predictor of all kinds of diseases because it often means that the growth signalling is out of tune throughout the system. Visual selection basically performs environmental selection more immediately and more effectively: an asymmetric person might still survive, but its offspring has a lower overall chance to survive. The teaching signals of that are much weaker.

[mfrye0]

Good points. Never thought of it that way.