1 it was a leap of faith to test whether females might choose males based on asymmetry between the left and right sides of the body. Such asymmetry had been known to correlate with stress and other environmental factors, but not to mate selection.
M?ller is a strong proponent of the "good genes" model of sexual selection, 2,3 which holds that certain characteristics, for example, the tail feathers of a peacock, signal the presence of genes that will be beneficial to offspring, and therefore make an individual more attractive to potential mates. M?ller began to think that perhaps more subtle signals of a mate's quality, such as tail symmetry, also mattered.4 He used to measure only the length of one side of the tail, but he says, "There was one year that the swallows came back from Africa and there were lots of individuals that were asymmetric." ...
