Sexy son hypothesis

The sexy son hypothesis is a concept from evolutionary biology, proposed by P. J. Weatherhead and R. J. Robertson in 1979. [ Weatherhead, P. J., and R. J. Robertson. 1979. Offspring quality and the polygyny threshold: 'The sexy son hypothesis'. "American Naturalist" 113:201-208.] It posits that a female animal's optimal choice among potential fathers is a male whose genes will produce male offspring with the best chance of reproductive success. In particular, the sexy son hypothesis implies that a potential mate's capacity as a caregiver or any other direct benefits the male can offer the female (eg. nuptial gifts, good territory) are irrelevant to his value as potential father of the female's offspring.

The sexy son hypothesis has been suggested as the origin of some aspects of human sexual behavior. In particular, it has been shown that human females are more attracted to traditionally masculine men ("cads") during the most fertile times of their menstrual cycles, and more attracted to relatively feminine men ("dads") during the remainder of the cycle. However, the methodology of these claims are disputed. [ [http://news.bbc.co.uk/2/hi/science/nature/376321.stm BBC NEWS | Science/Nature | Women's choice of men goes in cycles] ] These observations have led to the conclusion that infidelity is a natural occurrence in women, and evolutionarily advantageous, on the grounds that it will enable them to secure both the best genes and the best caregiver for their offspring. [ [http://www.ncbi.nlm.nih.gov/pubmed/17619174?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum NCBI "Sexy son" model] ] [ [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2197213 Male phenotypic quality influences offspring sex ratio in a polygynous ungulate] .]

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