Dr. Michael Tobler and Dr. Zach Culumber at Kansas State University examined 112 species of live-bearing fish (Poeciliidae) and have made some interesting discoveries about their evolution. Their analyses included information on body shape, fin size, where the species are found and information on global climate. What they discovered is that the evolution of female fish is influenced by natural selection as well as the environment, whereas sexual selection plays a larger role in the evolution of males. In addition, the body shape of male fish was also found to be evolving faster than in females. According to Dr. Tobler, "The assumption that people often make is that on a broad evolutionary scale, natural selection and adaptation drive most of the patterns in the evolution of traits. That's true for females in our case, but not for males. Male morphological evolution is really more of a consequence of achieving high mating success." In contrast, generation of new species appears to be driven in large part by variations in the environment. Their findings were recently published in Nature Ecology & Evolution.
Lead study author Dr. Tobler stated, "In the big picture, this means that males and females are different and that matters not only within species but also in terms of shaping broad-scale evolutionary outcomes. Acknowledging that the sexes are different really affects how we make inferences about how evolutionary change has actually unfolded."
Culumber ZW, Tobler M. Sex-specific evolution during the diversification of live-bearing fishes. Nature Ecology & Evolution. 2017. doi:10.1038/s41559-017-0233-4
natural selection is not evolution