Female orgasm evolution

Why do women have orgasms? In a literature review recently published in the Journal of Evolutionary Zoology , a pair of developmental evolutionary specialists posit that as the female reproductive system evolved, so did the role of the orgasm. But similar to vestigial organs like tonsils or appendix, the orgasm remained. The secret lies in ovulation, the mechanism that causes ovaries to discharge eggs for reproduction. In some species, like cats and rabbits, physical stimulation is needed to prompt the egg to be released—a phenomenon called induced ovulation. But in humans, ovulation happens spontaneously without stimulation , often on a regular schedule.

Have scientists solved the mystery of the female orgasm? As a team of researchers pointed out, during intercourse the male orgasm serves an obvious reproductive function: Without it, ejaculation can't happen. But the reproductive role of female orgasm has been much less clear, because ovulation in humans occurs whether a woman has recently had an orgasm or not. So the very existence of the female orgasm in women has long been a physiological mystery.

Billy Crystal may have been shocked when Meg Ryan so effectively—and amusingly—faked an orgasm in a restaurant during the movie When Harry Met Sally , but surveys suggest only one-third of women are regularly fully aroused during intercourse. And although poor partner performance, psychological issues, or physiological shortfalls are often cited as the reason, two evolutionary biologists now offer a provocative new explanation. In a paper published today, they argue that female orgasm is an evolutionary holdover from an ancient system, seen in some other mammals, in which intercourse stimulated important hormonal surges that drive ovulation. And because those hormonal surges no longer confer a biological advantage, orgasms during intercourse may be lost in some women.

The evolutionary explanation of female orgasm has been difficult to come by. The orgasm in women does not obviously contribute to the reproductive success, and surprisingly unreliably accompanies heterosexual intercourse. Two types of explanations have been proposed: one insisting on extant adaptive roles in reproduction, another explaining female orgasm as a byproduct of selection on male orgasm, which is crucial for sperm transfer. We emphasize that these explanations tend to focus on evidence from human biology and thus address the modification of a trait rather than its evolutionary origin.