In a recent study by The Journal of Experimental Zoology, authors Mihaela Pavlicev and Gunter Wagner look back 150 million years to better understand the development of the female orgasm. For men, an orgasm directly coincides with ejaculation—meaning it is more or less encouragement to pass along semen. For women, however, it’s more complex—as an orgasm is not a requirement for fertilization. The authors propose that this is due to the development of the ovulatory cycle—something that occurred in only a few mammals. Our ancient mammal ancestors would ovulate when triggered by sex (as some still do today), but with a shift toward living in social groups, ovulation became monthly, and the clitoris slowly shifted away from the uterus.