10.10 What’s up with the human female orgasm?

Considering that it happens all the time across the world, scientists are fairly clueless about the female orgasm. Among the most tantalizing of questions is, “what is the evolutionary significance of the female orgasm?”

It is widely thought that the male orgasm exists to encourage males to spread their sperm (i.e. genetic material) as much as possible. Some argue that females orgasm for the same reason: to encourage procreation. But in practice, compared with the male orgasm, female orgasm is extremely difficult to achieve and nearly 10% of human females never have an orgasm in their lifetime. Furthermore, unlike the male orgasm, which is coupled with the release of sperm and other ejaculates necessary for reproduction, the female orgasm appears to serve no similar role. So then what is the purpose of the female orgasm? Few questions regarding human evolution have been more difficult to answer than those regarding the female orgasm and for the most part there are two firmly opposed arguments for this phenomenon.

One hypothesis harkens back to a concept we previously discussed- human females orgasm simply because males do; in other words, female orgasm occurs because of selection on males. This answer is similar to the reason why males have nipples because females use them to feed their children. Because males and females share a similar developmental pathway, whatever structure or process appears in one sex will necessarily appear in the other. Females develop similar erectile and nervous tissue that is necessary for orgasm in virtue of the strong and ongoing selective pressure on males for releasing sperm via coupled orgasm and ejaculation.

While most scientists agree that females probably started having orgasms as a by-product of males having them, why females still have orgasms is hotly debated. Some people think that this holdover from development continues to be the reason that females experience orgasm. The holdover camp claims that female orgasms are an incidental by-product of male orgasm, and that’s it.

Another evolutionary holdover hypothesis involves ovulation. In some species, like humans, ovulation is spontaneous. In other species, females actually do not ovulate until stimulated to do so through hormonal surges during and after copulation. Scientists have recently proposed that human females orgasm because of an evolutionary holdover from closely related species that used orgasm as an ovulation-triggering event. In other words, human females orgasm not because of a holdover from male development, but because of a holdover from our early female ancestors.

Many scientists think the female orgasm serves an adaptive purpose. This group of scientists has proposed three broad categories for why human females orgasm: pair bonding, mate choice, and enhanced fertility. The pair-bonding hypothesis suggests that female orgasm facilitates the bond formed between sexual partners, aiding in mate retention and bi-parental care. Others propose that females can judge the quality of potential long-term mates by whether or not orgasm is achieved during their sexual interaction. This last hypothesis states that the female orgasm actually does aid in reproductive success. Referred to as the “upsuck theory”, the idea is that during orgasm, muscles contracting and relaxing in the uterus and vagina create suction that moves sperm up the female reproductive tract, resulting in enhanced fertility.

We may never know the exact reason why human females orgasm from an evolutionary perspective, but simply pondering the question is interesting. Much of the fun for researchers is returning to scientific questions with new methods and with fresh eyes!