A possible explanation for one of the biggest secrets of biology, female orgasm, has been reinforced by research showing that rabbits receiving antidepressants release fewer eggs during sex.
Human orgasm has long been interesting, with no obvious purpose but pleasure.
Researchers have previously suggested that it may have its evolutionary roots in the reflex associated with the release of eggs during sex – a mechanism that exists today in several animal species, including rabbits.
Because people have spontaneous ovulation, according to theory, female orgasm can be an evolutionary hangover. They say the new experiment supports this idea.
"We know that there is a reflex [in rabbits]but the question [is] can it be the same one that lost function in humans? "- said Dr. Mihaela Pavličev, a researcher at the University of Cincinnati who is the co-author of the study.
To investigate the question, the team gave twelve female rabbits a two-week course of fluoxetine (the trade name Prozac) – an antidepressant known for reducing women's orgasm – and looked at the number of eggs released after animals had sex with a male rabbit named Frank.
The results, published in the Proceedings of the National Academy of Sciences, showed that rabbits receiving antidepressants released 30% less eggs than nine rabbits who were not given Prozac but who were associated with Frank.
Further experiments confirmed the theory that the drug affects ovulation through a mechanism involved in copulation and involving the nervous system, instead of acting directly on the ovaries or other pathways.
The team said the results fit their theory that rabbits must experience something similar to orgasm to achieve hormonal growth and ovulation, although it is unknown whether this gives animals sexual pleasure.
They also said that their theory was supported by an earlier finding that animals that rely on sudden hormonal increases associated with ovulation usually had a clitoris – the body behind a female orgasm – in a position that meant it was more likely to be stimulated during sex
Pavličev said that it is not known exactly how Prozac affects the reflex of rabbits, and that further experiments with other animals are necessary.
She added that even if the theory is correct, the important question was why the body is still there – could it be that it obtained another function, that it was a function on women's health?
Elisabeth Lloyd, a professor of biology at the University of Indiana and author of The Case of Female Orgasm, praised this study and said she offered support for team theory.
She said questions remain about whether the same muscles and nerve fibers involved in the rabbit reflex were present in the female orgasm.
She also noted that ovulation and orgasm are associated with various hormones in humans, although it was not clear why – if female orgasm has its roots in ovulation – orgasms in men and women show so many overlapping features.
She said such traits are generally thought to support the theory that orgasm has evolved to reward men for fertilization, with female orgasm simply being a bonus based on the way in which embryos of different sexes develop from a common form.
Lloyd and Pavličev said that perhaps theories can be reconciled, one of which potentially explains the origin of female orgasm, and the other indicates why it still exists.
Pavličev added that understanding the role of female orgasm remained important. "Maybe he can put a little more friendly emphasis on female sexuality than just being in [the] childbirth service, "she said.