In some primates the degree of sperm uptake has been linked to contractions associated with female orgasm. During climax, the release of the hormone oxytocin causes the uterus and oviducts to contract resulting in the ‘upsuck’ of sperm, which significantly accelerates their passage to the egg. A study of captive Japanese macaques, Macaca fuscata, found that females are more likely to achieve orgasm-like responses when mating with high-ranking, socially dominant males, suggesting preferential sperm uptake for these males.
