Female orgasm may have evolved from a trigger for ovulation

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What’s the evolutionary origin of the female orgasm? A study that involved giving antidepressants to rabbits has lent support to the idea that the female orgasm may have originated from a reflex that makes some female mammals ovulate during intercourse.
There are multiple theories regarding the function of female orgasms. Some studies have found that contractions of the uterus experienced during orgasm help transport sperm towards the egg. However, many women don’t orgasm during intercourse, and it is also common for women to conceive without climaxing.

 

There are also simpler explanations, including that sexual pleasure encourages women to have more sex, making them more likely to conceive, or motivates them to form committed relationships, which may be beneficial for raising children.                    

But how did the female orgasm evolve? Mihaela Pavlicev, currently at the University of Vienna in Austria, and her colleagues think that animals that ovulate during intercourse may hint at the answer.
While women release an egg roughly every month, ovulation in some other mammals such as rabbits is triggered by copulation. Pavlicev and her team think the hormones and brain circuitry involved in such reflex ovulation could also be involved in generating a pleasurable climax.

Evolving a new function

In 2016, they analysed 41 species of mammal. Of these, 15 species, including cats, koalas and camels, have reflex ovulation. The way these species are related across the mammal family tree suggests that this system is likely to have been present in the earliest mammal ancestors.
In their latest study, the team exploited the finding that the antidepressant fluoxetine, which is sold as Prozac, reduces people’s ability to orgasm. They found that, after giving rabbits fluoxetine for two weeks, the rate of ovulation during copulation fell by a third.

 

This supports the idea that the same hormones and brain circuitry could be involved in both sex-triggered ovulation and orgasm, says Pavlicev. It could be that both events happened in our mammalian ancestors – or perhaps the brain circuitry was once used for triggering egg release and has since evolved into a mechanism for triggering orgasm.

“Selection can take something and shape it for a new function,” says David Puts of Pennsylvania State University, who wasn’t involved in the work. “Our ear holes were gill slits originally. Functions evolve over time.”
One clue would be whether female rabbits and other animals with reflex ovulation also experience orgasms. “That’s a hard question – we can’t talk to them,” says Pavlicev.