Theory 06/Selection optimises
Means Optimise, Variances Don't
The claim
Selection optimises the mean of a trait while leaving its variance to drift and mutation, so populations can be well adapted and highly fragile.
01Mechanism
Directional selection moves means; variance is only weakly selected unless it affects fitness directly.
02Prediction
Adapted populations should retain large trait variance.
03Refutation
Variance also optimised would remove the asymmetry.