The question of whether female orgasms are essential to the survival of humanity might seem a lot like asking whether puppies really need to be that cute. Who cares? Life is better for having them around.
For a long time, that was pretty much the response to the question of why women can have orgasms during intercourse -- why not? It's tough to even begin to explore the topic from an evolutionary standpoint. We can't ask a female gorilla whether she experiences a period of physical ecstasy at some point during intercourse. Most biologists do believe that male nonhuman primates experience something akin to orgasm, often judging from a marked change in their body language at the time of ejaculation [source: Discover].
The human evolutionary rationale behind the male orgasm is obvious. For males, orgasm and ejaculation go hand in hand. With such extreme pleasure immediately preceding the ejaculation of sperm into the vagina, a male is very effectively encouraged to spread his seed. And, the more mates a male has, the more offspring he creates. A man who experiences orgasm during ejaculation is far more likely to put extraordinary effort into finding sexual partners than the men who ejaculate without any accompanying extreme pleasure.
The physical process of the female orgasm, on the other hand, is far more difficult to explain in terms of evolution. It's not like orgasm is connected to the release of an egg into the uterus. And a female can only get pregnant once in a given period of time, so sheer number of partners is less of an issue in terms of species survival.
So why is the orgasm part of the female sexual experience? Is it in fact an evolutionary adaptation, selected for its contribution to species survival, or is it a lucky break? And if it is an adaptation, what survival advantage does it offer? In this article, we'll explore these questions. We'll take a look at several of the top scientific theories about why women experience orgasms, see what the latest research has to say about it and find out whether the female orgasm could be on its way out.
Before we examine the why, it's helpful to look at the "what." When a woman has an orgasm, what's happening in her body?
Sperm Retention Theory
Men and women experience similar physiological changes during orgasm, the climax of sexual intercourse. It typically lasts less than a minute [source: Discover]. In both sexes, the rectum contracts at intervals of approximately 0.8 seconds; there is less voluntary muscle control; and lots of muscles all over the body start to spasm. And then of course there's the laundry list of pleasure chemicals, like oxytocin, norepinephrine and serotonin, that saturate the brain like a flash flood of indescribable joy. In women, the muscles in the vagina and the uterus go through a series of contractions, as well [source: Discover].
These contractions of the vagina and the uterus are the basis for one of the many evolutionary explanations of the female orgasm -- the sperm retention theory. Some researchers hypothesize that when the vagina and uterus contract, they retain more sperm, possibly due to the way they close up and related to some sort of suction created by the contractions. This suction could reduce the amount of sperm that drips out of the woman's body after sex, meaning more sperm would get a shot at reaching an egg.
Another theory in the sperm-retention realm states that an orgasm tires a woman out, causing her to lie on her back for a long time following sex. This would theoretically cause more sperm to stay inside her than if she were standing up, with gravity taking effect.
Critics point out, though, that there is no proof that either contractions or lying prostrate actually aid in sperm retention. (Some even say that the contractions produce an expulsion force, not a suction force [source: Discover].)
Sperm retention is still a pretty popular theory, although others also have a lot of followers. The most talked-about hypotheses include:
Orgasms encourage women to have sex. The more a woman mates, the more likely it is she'll become pregnant and continue to populate the species.
One interesting piece of evidence for this hypothesis has to do with the way, in some nonhuman primate species, males kill other's young but not their own. Some research suggests that orgasms cause females to mate with as many males as possible, causing confusion as to which baby belongs to whom. Since the males don't know which kid is theirs and which isn't, they won't attack, and the orgasm-experiencing, promiscuous females' genes are passed on more than others [source: Discover].
Orgasms help women choose the best mate. Because most females don't always have orgasms during intercourse, perhaps they provide some sort of selection criteria. Perhaps at one point in human evolution, achieving orgasm during sex indicated the strength, health and attentiveness of a male partner, meaning a female could determine a mate's suitableness by whether or not she had an orgasm.
The orgasm hormone oxytocin causes suction. One of the chemicals released during orgasm is oxytocin, which also is associated with lactation, among other things. In one study, when the uterus was injected directly with oxytocin, it tended to suck up fluid. Perhaps orgasm is a selected adaptation because oxytocin encourages the movement of ejaculate into the uterus, the same end result of the sperm retention theory.
Orgasms encourage pair-bonding. Chemicals released during orgasm, including endorphins and oxytocin, tend to make mates feel closer to each other -- more connected, bonded and happy together (see How Love Works to learn about it). Evolutionarily speaking, this adaptation could cause mates to stay together to care for their children, increasing the chances of survival for their offspring.
These are all possible explanations for why females experience orgasm even though it's not directly connected to conception. One of the latest theories goes in a totally different direction, though: Perhaps there is no evolutionary reason for women to have orgasms. What's their purpose, then?
Pleasure for Pleasure: The Initial Development Hypothesis
The big talk in the scientific community right now surrounds the theory that women have orgasms for no reason at all. It's not an adaptation. It's a wonderful accident stemming from the initial phase of fetal development.
This theory was talked about a lot in the 1970s, and it has recently been revived. The initial-development hypothesis states that women have orgasms because men have orgasms. In the earliest stages of pregnancy, the fetus isn't gendered. The hormones that determine sex haven't kicked in yet, and the nerves laid down for future sex organs in this initial period are exactly the same in all fetuses. When a fetus becomes female instead of male, it still has the nerve pathways that allow for orgasm during sexual intercourse.
If this theory is correct, and the female orgasm isn't an adaptation selected for survival of the species, does that mean it'll be phased out?
There's no consensus on the staying power of the female orgasm. Some say evolution tends to phase out unnecessary traits, so some day, many, many, many years in the future, females might no longer experience orgasms. Perhaps sexual pleasure, short of orgasm, will be enough to keep women getting pregnant.
Others disagree entirely: If it's true that women have orgasms because nerves associated with orgasm are laid down in the initial stages of fetal development, when there's no gender assigned yet, females will have the capacity for orgasm as long as men do. And considering how strongly the male orgasm is selected for in survival of the species, the corresponding female orgasm would be around for a long, long time.
For more information on orgasms, sex, love and related topics, look over the links on the next page.
Related HowStuffWorks Articles
More Great Links
- A Critic Takes On the Logic of Female Orgasm. The New York Times. May 17, 2005. http://www.nytimes.com/2005/05/17/science/17orga.html
- Evolution of the Big O. Discover Magazine. June 1, 1992. http://discovermagazine.com/1992/jun/evolutionofthebi59
- Ogden, Gina, Ph.D. Review: The Technology of Orgasm: "Hysteria," the Vibrator, and Women's Sexual Satisfaction. Electronic Journal of Human Sexuality, Volume 3, Oct.12, 2000. http://www.ejhs.org/volume3/book11.htm
- The Study of O. Amanda Schaffer. Slate Magazine. May 26, 2005. http://www.slate.com/id/2119551/