Adaptation or happy coincidence?
By Katy Love

It was the year that “A Streetcar Named Desire” won the Pulitzer Prize. But in 1948, Dr. Alfred C. Kinsey was interested in a less dramatic look at desire as he released his study “Sexual Behavior in the Human Male.” It sold more than 200,000 copies when it was released. The follow-up, “Sexual Behavior in the Human Female” became a best-seller when it was released in 1953 – the same year Playboy published its first issue. This post-war era marked the beginnings of the current open discourse about sex. From Cosmo to Kiegels, sex is a hot topic in our society; a constant source of conversation, fascination and research. But there are still some mysteries about human sexuality, and one of the most enduring is why women evolved to have orgasms.

“The adaptive value in men is real straight forward – a great experience when you deliver gametes,” says Randy Thornhill, distinguished professor of evolution at the University of New Mexico. “The question is, why do women orgasm?”

Theories about the adaptive value of the female orgasm are prolific and include the possibility that female orgasm might not be an adaptation at all. Some think orgasm creates a pair bond, giving the female motivation to become emotionally involved with her partner. At the point of orgasm, the hormone oxytocin is released into the brain creating sensations of pleasure and possibly bonding the beneficiary on the person that created that pleasure. Another idea, the “pole axe” holds that women need to assume a prone position in order to help insemination occur. As such, the orgasm is there to create feelings of fatigue so that the female feels the need to rest afterwards, allowing time for insemination to occur. Yet another theory, the “upsuck” hypothesis, suggests that the orgasm actually helps pull the sperm up into the reproductive tract with muscle contractions.

The “upsuck” hypothesis is currently the most well accepted by scientists like Robin Baker, an evolutionary biologist at the University of Manchester, whose research shows that the timing of the female orgasm to the male orgasm can either help or hinder sperm retention, which will either help or hinder fertilization. Taking Baker’s work a step further, Thornhill showed that females have the ability to make the sperm-retaining effects work towards selecting a better mate. He found that women will orgasm more often with partners that have bilateral symmetry. This physical trait has been found to be an indicator of such things as higher growth rate and better immune systems, qualities that a woman would want to pass on to her children. Thornhill suggests that this shows that the female orgasm is a way for women to help the sperm from “higher quality” mates reach the point of fertilization. “We’re talking about something that’s not a passive reproductive tract,” he says.

Symmetry is also a characteristic of attractiveness, points out Don Symons, emeritus professor of anthropology at the University of California at Santa Barbara. The more symmetrical the body and face, the more attractive it is. Symons finds the fact that women have more orgasms with more symmetric men unsurprising. “If a guy is better looking, the more sexually excited the woman is and the more likely she is to orgasm. Why wouldn’t there be a link?”

Perhaps the female orgasm is just a byproduct of the fact that men and women are developmentally similar, suggests Don Symons. “Males have nipples,” Symons says. “Does that mean that natural selection specifically favored male nipples?” According to Symons, the default position for men and women is to have the same body plan. Every change from that plan comes at a cost that must be balanced by a reciprocal benefit. There’s no benefit to balance the developmental cost of eliminating nipples in men, so men have nipples even though there’s no adaptive value to them. Similarly, Symons thinks that because natural selection created a link between the genitals and the brain that causes orgasm, giving men their “great experience” as incentive to inseminate women, women simply share the same connection without it serving a specific function. His argument is bolstered by the fact that the penis and the clitoris stem from the same organ within the embryo – it is only after the organ receives a dose of certain hormones that it will begin to develop into either a penis or a clitoris.

A major failing of the adaptation hypotheses is that they are based on the assumption that the female orgasm has an adaptive value to begin with, according to Elisabeth Lloyd, Tanis Chair of History and Philosophy of Science at Indiana University, because they’re biased. “They go in with a loaded question ‘What is the adaptation’ instead of the neutral question ‘Is it an adaptation at all?’” says Lloyd. Similar to the premise of innocent until proven guilty, a trait or feature cannot be assumed to be adaptive until it has been shown that it was shaped by natural selection to fulfill a specific function – that the fit between the design and the solution of a specific problem is so close, that it could not have arisen by chance. The human eye, for instance, is so specific in design that there’s no question that it was shaped over evolutionary time for the purpose of sight. The case is not so clear with orgasms.

According to Lloyd, one of the main arguments against female orgasm being an adaptation is that not only is it not required for conception, it’s not even guaranteed through intercourse. As Kinsey’s 1953 study found, less than half of women always or almost always orgasm through intercourse. More current studies put the average around the 30 to 40 percent mark. Lloyd considers this strong evidence that female orgasm is not an adaptation. “If it were an adaptation, it would have evolved to fixation, it would universally appear,” says Lloyd. As Kinsey and his successors have shown, this is not the case.

So far, none of the theories set forth have proven that the female orgasm is an adaptive feature. But the lack of adaptive value, does not make orgasm any less important on a cultural level. Nobody argues that the ability to read and write is an adaptation, Symons points out. It’s just something that humans do, but that doesn’t devalue it in anyway. The ability to read and write is similar to the female orgasm, he notes, “it’s not trivial or unimportant, it just may not occur spontaneously. You have to work toward it.”