Secondary Sex Characteristic - Evolutionary Roots

Evolutionary Roots

Charles Darwin hypothesized that sexual selection, or competition within a species for mates, can explain observed differences between sexes in many species. Biologists today distinguish between "male-to-male combat" and "mate choice", usually female choice of male mates. Sexual characteristics due to combat are such things as antlers, horns, and greater size. Characteristics due to mate choice, often referred to as ornaments, include brighter plumage, coloration, and other features that have no immediate purpose for survival or combat.

Ornamentation might arise because of some arbitrary female preference that is initially amplified by random genetic drift, eventually being reinforced by active selection for males with the appropriate ornament. This is known as the sexy son hypothesis. An alternative hypothesis is that some of the genes that enable males to develop impressive ornaments or fighting ability may be correlated with fitness markers such as disease resistance or a more efficient metabolism. This idea is known as the good genes hypothesis.