Song: "Sexual Selection"
Album: "1994 - Techno Scorpion" -
Darwin conjectured that the male beard, as well as the relative hairlessness of humans compared to nearly all other mammals, are results of sexual selection. He reasoned that since, compared to males, the bodies of females are more nearly hairless, hairlessness is one of the atypical cases due to its selection by males at a remote prehistoric time, when males had overwhelming selective power, and that it nonetheless affected males due to genetic correlation between the sexes. He also hypothesized that sexual selection could also be what had differentiated between different human races, as he did not believe that natural selection provided a satisfactory answer.
Geoffrey Miller, drawing on some of Darwin's largely neglected ideas about human behavior, has hypothesized that many human behaviors not clearly tied to survival benefits, such as humor, music, visual art, verbal creativity, and some forms of altruism, are courtship adaptations that have been favored through sexual selection. In that view, many human artefacts could be considered subject to sexual selection as part of the extended phenotype, for instance clothing that enhance sexually selected traits.
Some hypotheses about the evolution of the human brain argue that it is a sexually selected trait, as it would not confer enough fitness in itself relative to its high maintenance costs (a quarter to a fifth of the energy and oxygen consumed by a human).
The zoologist Richard Dawkins pointed out in 1989 that the loss of the penis bone in humans, when it is present in our nearest related species the chimpanzee, demands some form of evolutionary explanation. He speculates that its loss is probably a form of sexual selection by females looking for signs of good health in prospective mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. Poor erectile function betrays, not only physical states such as diabetes and neurological disorders, but mental states such as stress and depression.