It may be evolutionary—or not.
Sex is about more than just the orgasm—but it’s hard to resist the satisfaction of a climax. Unfortunately, though, orgasms aren’t always as easily achieved for some people as others: a 2017 study of cis-gendered participants found that bisexual and straight women were about 20% less likely to orgasm when sexually intimate than lesbian women, and even less likely to climax than men of all sexual orientations. The female orgasm can be a mysterious phenomenon—and not just to potential bedfellows. After all, science can’t quite explain exactly why people with vaginas orgasm.
The biological basis for a penile orgasm is pretty obvious, even if, the majority of the time, ejaculation doesn’t lead to pregnancy. But female orgasms don’t appear to play a role in reproduction. One theory about why women orgasm, according to a 2016 study, is that it's an evolutionary holdover from more primitive mammals, who experienced induced ovulation (aka, an egg is released only during sex), as opposed to the spontaneous ovulation that humans and other complex mammals experience, Stat News reported. At one point in the development of modern humans, a response much like the female orgasm could have been key to procreation. “Female orgasm is an evolutionary vestige like the appendix,” one of the researchers, Günter Wagner, an evolutionary biologist at Yale University, said.
Another popular theory is that the female orgasm exists because both the penis and the vagina develop similarly in the womb, before differentiating after about six weeks of gestation, The Conversation reported. But not everyone agrees with this theory, either. As Popular Science reported, a 2011 study surveying twins about their rate of orgasm found that twins (both identical and fraternal) of opposite sexes had zero correlation in this regard—which led researchers to say that this evolutionary view doesn’t quite hold up.
There’s still more disagreement, though: Popular Science reported that Kim Wallen, a behavioral neuroendocrinologist at Emory University, said that the 2011 study’s methodology of comparing rates of orgasm between opposite-sex twins was like comparing apples to oranges—they’re just not similar enough for the data to translate so neatly.
There is one more theory that can explain female orgasm: the phenomenon serves as a reward for engaging in intercourse (a biological imperative for reproduction) and also helps partner bonding. There may be some basis in this line of thinking: We do know that orgasms lead to the release of dopamine, serotonin, and oxytocin, the latter of which is known as “the love hormone,” which does play an important role in intimacy.
Science may not yet have a firm answer on the reason behind the female orgasm, but if anything’s clear, it’s that this phenomenon is seriously beneficial, and whether or not it plays some kind of evolutionary advantage, it’s well worth experiencing.