No direct relationship between human female orgasm rate and number of offspring

The evolutionary basis of women's orgasm is unknown, but the most favoured theory involves putative physiological processes that accompany orgasm and increase the likelihood of fertilization during intercourse. In a sample of over 8000 female twins and siblings, we show a substantial genetic basis to both orgasm rate and number of offspring. While there was a very weak but significant phenotypic correlation between the two variables, there was no corresponding genetic correlation, suggesting the involvement of environmental confounders. Controlling for relationship length and frequency of sexual intercourse eliminated the significant phenotypic correlation between orgasm rate and number of offspring, which suggests no substantive causal relationship between orgasm and fertility. These results cast doubt on the predominant functional theory of female orgasm. (C) 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.