Scientists delve into its evolutionary history.
Aristotle was baffled by the female orgasm more than 2,000 years ago, when he observed that females could conceive without it. Unlike the male orgasm, which is required for ejaculation and sperm transfer, the function of the female orgasm was not so clear.
Some argue that the female orgasm does, in fact, induce physiological changes that improve the odds of conception, but so far there is no evidence to support this claim. Others believe the female orgasm is simply a fortunate consequence of the shared developmental origins between the clitoris and penis.
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Gunter Wagner and Mihaela Pavličev from the Center for Prevention of Preterm Birth at Cincinnati Children's Hospital wanted to dig a bit deeper. "Prior studies have tended to focus on evidence from human biology and the modification of a trait rather than its evolutionary origin," said Wagner in a press release.
The female orgasm is not only mysterious, but it’s also hard to define. It is sometimes described as a “climax, followed by a sudden discharge of major sexual arousal,” the researchers write in their article published in the journal JEZ-Molecular and Developmental Evolution. But to understand its origins, they needed to find some aspect of the female orgasm that they could compare across species. They focused on a physiological trait that accompanies human female orgasm — the discharge of the hormones prolactin and oxytocin.
Ovulation in humans is spontaneous, not requiring external triggers. In some other mammals, however, this hormone discharge reflex actually induces ovulation.
A comparative analysis of female genitalia revealed that as spontaneous ovulation evolved, the clitoris — often key to the female orgasm — relocated, moving outward from its ancestral position inside of the vaginal canal. Its new position means that the human clitoris is often deprived of the penile stimulation required to induce the orgasm during intercourse.
For the researchers, a clear picture began to emerge. Perhaps the female orgasm initially evolved as an adaptation with a direct reproductive role: inducing ovulation. But over evolutionary time, the reflex became superfluous, as it was no longer needed for reproduction.
“We suggest that the ancestral trait that evolved into human female orgasm had an ancestral function in inducing ovulation,” the authors write. However, they believe that with the evolution of spontaneous ovulation, the female orgasm “was freed to gain secondary roles, which may explain its maintenance, but not its origin.”
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