Should attractive males have more sons?

It is often argued that females with attractive partners should produce more sons because these sons will inherit their father's attractiveness. Numerous field and laboratory studies have addressed this hypothesis, with inconsistent results, but there is surprisingly little theoretical work on the topic. Here, we present an extensive investigation of the link between male attractiveness and offspring sex ratios, using evolutionary, individual-based computer simulations. In situations where sexual selection leads to the stable exaggeration of a costly male trait and a costly female preference, we find that females with attractive partners produce more sons than females with unattractive partners. This same qualitative pattern is seen for a wide range of different models, with discrete or continuous variation in the male trait, under Fisherian or good-genes sexual selection and for abrupt or gradual sex ratio adjustment. However, in all simulations, it takes a huge number of generations to evolve, suggesting that selection acting on sex ratio adjustment is weak. Our models ignore many potential costs and constraints associated with manipulation, which implies that selection may be weaker still in natural populations. These results may explain why published evidence for sex ratio bias in relation to male attractiveness is mixed. Copyright 2007.attractiveness; Fisherian runaway; good genes; handicap principle; individual-based simulation; sex allocation; sex ratio; sexual selection; Trivers--Willard hypothesis