An eye is for seeing, a nose is for smelling. Many aspects of the human body have obvious purposes. But some defy easy explanation. For biologists, few phenomena are as mysterious as the female orgasm. While orgasms have an important role in a woman’s intimate relationships, the evolutionary roots of the experience – a combination of muscle contractions, hormone release and intense pleasure – have been difficult to uncover.
For decades, researchers have put forward theories, but none are widely accepted. Now two evolutionary biologists have joined the fray, offering a new way of thinking about the female orgasm based on a reconstruction of its ancient history.
Last week, in the Journal of Experimental Zoology, the authors conclude that the response originated in mammals more than 150 million years ago as a way to release eggs to be fertilized after sex.
Until now, few scientists have investigated the biology of distantly related animals for clues to the mystery.
“For orgasms, we kept it reserved for humans and primates,” said Mihaela Pavlicev, an evolutionary biologist at University of Cincinnati College of Medicine and an author of the paper. “We didn’t look to other species to dig deeper and look for the origin.”
The male orgasm has never caused much of a stir among evolutionary biologists. The pleasure is precisely linked to ejaculation, the most important step in passing on a male’s genes to the next generation.
For women, the evolutionary path is harder to figure out. The muscle contractions that occur during an orgasm are not essential for a woman to become pregnant. And while most men can experience an orgasm during sex, it’s less reliable for women.
“My gut instinct is that something that matters so much at an emotional level – the intense pleasure of orgasm – would seem to have reproductive consequences,” said David Puts, an evolutionary anthropologist at Pennsylvania State University.
Many hypotheses have been put forward. Puts and his colleagues have carried out studies to test the possibility that orgasms increase the odds that a woman’s eggs are fertilized by a genetically attractive male.
Elisabeth Lloyd, a philosopher at Indiana University, isn’t buying it. In 2005, she published a book called The Case of the Female Orgasm, in which she reviewed 18 published theories about its function.
None had strong evidence in its favour, she concluded, and many were undermined by other findings about human sexuality. Lloyd thinks the best explanation for the female orgasm is that it hasn’t served any evolutionary purpose at all. It’s nothing more than the byproduct of the development of the male orgasm. The orgasm is to women, she believes, as nipples are to men.
But now Pavlicev and her colleague, Gunter P. Wagner of Yale University, are making the case that the human female orgasm has a deep evolutionary history that reaches back to early mammals.
They began by getting better acquainted with the sex lives of other animals, poring through obscure old journals to gather information on species ranging from aardvarks to koalas.
They noted that many female mammals release oxytocin and prolactin during sex – the hormones released by women during orgasms. What’s more, in many of those species, females use a radically different kind of reproduction. While women release an egg each month, other female mammals, such as rabbits and camels, release an egg only after mating with a male.
Those early mammals developed a clitoris inside the vagina. Only in mammals that evolved ovulatory cycles did the clitoris move away. Based on these findings, Pavlicev and Wagner argue that the female orgasm first evolved as a reflex to help females become pregnant.
When early mammals mated, the clitoris could send signals to the brain, triggering hormones that released an egg. Once the egg became fertilized, the hormones may have helped ensure it became implanted in the uterus.
For more news visit:
www.v4vartha.com
