The existence of female orgasm is intriguing: On the one hand, female orgasm is not necessary for female reproductive success, & on the other hand, this neuro-endocrine reflex is too complex to be an evolutionary accident

An experimental test of the ovulatory homolog model of female orgasm. Mihaela Pavlicev, Andreja Moset Zupan, Amanda Barry, Savannah Walters, Kristin M. Milano, Harvey J. Kliman, and Günter P. Wagner. Proceedings of the National Academy of Sciences,  September 30, 2019. https://doi.org/10.1073/pnas.1910295116

Significance: The existence of female orgasm is intriguing for 2 reasons: On the one hand, female orgasm is not necessary for female reproductive success, and on the other hand, this neuro-endocrine reflex is too complex to be an evolutionary accident. This led to many proposed evolutionary explanations, most of which have little empirical support. We previously proposed that female orgasm uses a mechanism that originated for inducing ovulation during copulation: A mechanism that still exists in many animals but lost its role in others. Here we provide experimental evidence, strengthening the likelihood that female orgasm evolved from copulation-induced ovulation. This finding helps interpreting otherwise difficult to explain aspects of female sexuality, such as the low rate of female orgasm during intercourse.

Abstract: The ovulatory homolog model of female orgasm posits that the neuro-endocrine mechanisms underlying female orgasm evolved from and are homologous to the mechanisms mediating copulation-induced ovulation in some mammals. This model predicts that pharmacological agents that affect human orgasm, such as fluoxetine, should also affect ovulation in animals with copulation-induced ovulation, such as rabbits. We tested this prediction by treating rabbits with daily doses of fluoxetine for 2 wk and found that fluoxetine treatment reduces the number of ovulations postcopulation by 30%. In a second experiment we tested whether this result was mediated by an effect on the brain or via peripheral serotonin functions. We treated animals with fluoxetine and induced ovulation with a single injection of human chorionic gonadotropin. In this experiment ovulation rate was nominally reduced by only 8%, which is statistically not significant. We conclude that the effect of fluoxetine on copulation-induced ovulation rate supports the ovulatory homolog model of female orgasm, suggesting that female orgasm has very deep evolutionary roots among the early eutherian mammals.

Keywords: fluoxetineinduced ovulationprocess homologyanorgasmiafemale sexuality