XV.6 Sexual selection apparently plays an important role in human evolution

A great many authors, including Darwin himself (Darwin 1909)assume that a many human traits were fixed by sexual selection. These traits include both morphological traits, for example loss of body hair, and some patterns of behavior, for example altruism.

            However, there is mostly no specific evidence for these hypotheses. Nonetheless, some facts are, at the very least, suspicious. For example, two strikingly different human races occur on the Japanese Islands, typical black-haired Japanese with most of their traits identical with those of the inhabitants of the nearby Asian continent, and also the Ainu people, light-haired individuals that tend to be similar to Europeans. The Ainu people were considered to be the original inhabitants of the Japanese Islands and it was anticipated that their origin would differ substantially from that of other Japanese. However, molecular biology studies have overturned these concepts. Genetically, the Ainu people are not very different from the rest of the Japanese population and most probably came to Japan together with the rest (Cavalli-Sforza, Menozzi, & Piazza 1994). The simplest explanation of the fact that the Ainu people differ strikingly from the rest of the population in their external appearance, i.e. a large number of external, apparently selectionally neutral traits, and simultaneously do not differ in their other traits, lies in the assumption that their unique appearance was fixed by intense action of sexual selection.

            The degree to which sexual selection was a factor in human evolution is not yet clear. However, it is quite certain that the effectiveness of environmental selection is constantly decreasing with the development of civilization, so that the relative importance of sexual selection is gradually increasing. It is probable that especially various types of behavioral traits, i.e. various patterns of behavior, could be very readily and quite rapidly fixed through sexual selection.s

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.