The existence of human female orgasm has posed a much-discussed challenge to evolutionary biologists and broader. What is its role? The evidence for any direct reproductive effect is lacking: women readily conceive without ever experiencing orgasm, and penetrative sex without additional clitoral stimulation is not the primary trigger of orgasm for females. To address the question, we focused on physiological proxy- the neuroendocrine hormonal surge that accompanies human female orgasm. Remarkably, this surge is similar to the neuroendocrine reflex which triggers ovulation in copulation-induced mammals, such as rabbits, ferrets or cats. This suggests that human female orgasm may be a vestige of an evolutionarily older reflex inducing ovulation, which lost its role with the evolution of endogenously regulated ovulatory cycle. Apart from endocrine similarities, two types of evidence support this idea. The first is that copulation-induced ovulation evolutionarily precedes spontaneous ovulation. The second is that female genital anatomy has changed to remove clitoris from copulatory canal concurrent with the evolution of spontaneous ovulation.

Apart from the particular work, I would like to invite everyone to discuss more general issues in evolutionary biology that are beautifully manifested in the discussions about female orgasm, such as the distinction between modification and origin of traits, the importance of function for demonstrating adaptation, and the focus on homology.