Sexual Selection In On The Origin Of Species

Sexual dimorphism describes the often observed phenotypic or behavioral differences between males and females of the same species. Darwin addressed these differences in his first book “On the Origin of Species” and described them as resulting from “sexual selection”. Sexual selection is both different from natural selection and a mechanism of natural selection. Like natural selection, variation in individuals is the driving force behind the differences in their survival and reproductive success. Sexual selection, then, refers to how variation is linked to an individual’s success in obtaining a mate. Like natural selection, sexual selection depends on a the selection of a certain desirable trait and the subsequent, gradual increase in the
In most cases, we see stronger sexual selection on the male of a species than females because the females are usually the sex with the greater parental investment. In other words, the female generally expends more time and energy in producing and caring for offspring than do males (Staftstrom and Hebets, 2013). For example, male and female koalas only associate for mating purposes and have nothing to do with each other otherwise. The female is the one that carries, gives birth to and raises the cub. It also requires more energy to produce eggs than sperm, so in this way, the amount of eggs that a female is capable of producing limits her reproductive success. Sexual selection, therefore, will be felt stronger in the evolution of males than females. There are some exceptions to this rule, however, such as the broad-nosed pipefish (Sygnathus typhle). In this species, the female deposits the eggs in the male’s mouth and the male develops the eggs, thus expending more energy than the female. In this species then, sexual selection acts more strongly on females. Regardless of sex, the individual of a species that is more subject to sexual selection will compete with others of the same sex within the species for access to a mate. The gender subject to weaker sexual selection will be “choosy” (Freeman & Herron,
Many times, toward a predicted goal. Ronald Fisher (2000), in The Genetical theory of Natural Selection, also described sexual selection as unilinear and a “runaway” process. One where the morphological character selected would eventually escalate to an extent that their survival would be in jeopardy because of it. Most of the theories on the development of these