Sexy Son Hypothesis - Good Genes Theory

Good Genes Theory

"Good genes" theory proposes that females select males seen to have genetic advantages that increase offspring quality. Increased viability of offspring provides compensation for any lower reproductive success that results from their being "picky". The good-gene hypothesis for polyandry proposes that when females encounter better males than their previous mates, they re-mate in order to fertilize their eggs with the better male's sperm.

Significant sire effects on egg to adult viability and son’s pre-productive survival, as well as moderate to high coefficients of additive genetic variation for these traits have been found in Dung Beetles. Beetles who have selected mates with better genetics tend to have offspring that survive longer and are more able to reproduce than those that do not pick mates with genetic quality. This suggests that carefully choosing a mate is beneficial.

Another study notes that Pronghorn females engage in an obvious and energetically expensive mate sampling process to identify vigorous males. Though each female selects independently, the outcome is that a small proportion of the herd's males sire most young. Offspring of attractive males were more likely to survive to weaning and to age classes as late as 5 years, apparently due to faster growth rates. Because pronghorn males do not have costly ornaments, the authors conclude that female choice for good genes can exist in the absence of obvious sexual selection cues such as elaborate antlers.

The sexy son hypothesis is closely related to the good genes assumption and the Fisherian runaway selection process. Like good genes, the sexy son hypothesis assumes the existence of indirect genetic benefits that are able to compensate any inferior direct reproductive success (i.e., fewer offspring). The main difference between good genes and the sexy son hypothesis is that the latter assumes an indirect effect due to the attractiveness of the sons, whereas good genes focus on the viability of both sons and daughters. However, "attractiveness" is not narrowly defined, and can refer to every trait that increases a male's probability to become polygynous.