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A new study examines "orgasmability" to determine whether it serves a purpose or is just an evolutionary accident

By Jennifer Abbasi
Posted 09.21.2011 at 1:40 pm

Climax Benjamin Rondel / Getty Images

There may be few questions of human sexuality more rancorous than those about the female orgasm. Scientists agree that women probably started having orgasms as a by-product of men having them, similar to how men have nipples because women have them. As Elisabeth Lloyd, a philosopher of science and theoretical biologist at Indiana University put it in her 2005 book The Case of the Female Orgasm: Bias in the Science of Evolution: “Females get the erectile and nervous tissue necessary for orgasm in virtue of the strong, ongoing selective pressure on males for the sperm delivery system of male orgasm and ejaculation.” But why we ladies still have orgasms is hotly debated.

Male orgasms exist, it’s widely believed, to encourage men to spread their seed. On face value, it would be easy to say that women orgasm for the same reason: to encourage them to have sex and make babies. But in practice, compared to male orgasm, female orgasm is very difficult to achieve. There's a lot of variation even within individual women, and 10 percent of women never have them at all. And, unlike male orgasm, female orgasm isn’t a prerequisite for pregnancy.

So why do women have orgasms at all? There are two firmly opposed camps on this question. The first group proposes that it has an adaptive function in one of three categories: pair bonding, mate selection and enhanced fertility. I’ll break these down. The pair-bonding theory suggests that female orgasm bonds partners, ensuring two parents for the offspring, while mate selection offers that women use orgasm as a sort of litmus test for “quality” partners. The enhanced fertility theory, meanwhile, proposes that uterine contractions during female orgasm help to “suck up” sperm into the uterus.

The by-product camp, on the other hand, claims that female orgasms are to this day an incidental by-product of male orgasm, not an evolutionary adaption. “There’s no documented connection between women who have orgasm at all, or faster, having more or better offspring,” Lloyd says.

The schism between the two camps deepened this month with the publication of a new study of twins and siblings in Animal Behavior that seems to rule out the by-product theory of female orgasm. Researchers Brendan Zietsch at the University of Queensland in Australia and Pekka Santtila at Abo Akedemi University in Finland asked 10,000 Finnish female and male twins and siblings to report on their “orgasmability” (their word, not mine). They looked for similarities in orgasm function between female and male twins. If the by-product theory of female orgasm is true, they say, this similarity should exist. Due to the inherent differences in orgasm between women and men, females were asked to report how often they had orgasms during sex and how difficult they were to achieve, while males were asked how long it took them to reach orgasm during the act and how often they felt they ejaculated too quickly or too slowly.

Zietsch and Santtila found strong orgasmability correlations among same-sex identical twins, and weaker yet still significant similarities between same-sex non-identical twins and siblings. However, they found zero correlation in orgasm function between opposite-sex twins. “We show that while male and female orgasmic function are influenced by genes, there is no cross-sex correlation in orgasmic function -- women’s orgasmability doesn’t correlate with their brother’s orgasmability,” explains Zietsch. “As such, there is no path by which selection on male orgasm can be transferred to female orgasm, in which case the by-product theory cannot work.”

Zietsch says he doesn’t have a favorite theory on the evolutionary function of female orgasm, but if forced to guess he’d say that it provides women extra reward for engaging in sex, thus increasing frequency of intercourse and, in turn, fertility. (There’s no proof of this yet, though, as Lloyd points out.) Zietsch continues: “I’ve shown in another paper, though, that there is only a very weak association between women’s orgasm rate and their libido, so the selection pressure on female orgasm is probably weak -- this might explain why many women rarely or never have orgasms during sex.”

Lloyd and other proponents of the by-product theory agree that weak selection pressure could be acting on female orgasm, but not enough to maintain it over the eons of human evolution. Rather, if female orgasm bestows any reproductive benefits onto the human race, it would be by happy accident. Unsurprisingly, Lloyd has a lot of bones to pick with the recent study. Comparing different orgasm traits in women and men is a textbook case of apples and oranges, she says.

Kim Wallen, a behavioral neuroendocrinologist at Emory University and frequent collaborator with Lloyd, explains it thus: “Imagine that I wanted to compare height in men and women. In women I used a measurement from the top of the head to the bottom of the foot. In men I used how rapidly they could stand up. Would I be surprised that each measure was correlated in identical twins within sexes, but uncorrelated in mixed-sex twins? Such a result would be what was predicted and completely unsurprising. Zietsch and Santtila have done the equivalent of this experiment using orgasm instead of height.”

Wallen also points out that previous research has shown that traits under strong selective pressure show little variability, while those under weak pressure tend to show more variability. With human orgasm this bears out in that men report almost always achieving orgasm during sex, while the ability to orgasm during intercourse varies widely among women. (Penis and vagina size – both necessary for reproduction -- show little variability, suggesting they are under strong selective pressure, Lloyd says, while clitoral length is highly variable.) Wallen asserts that Zietsch and Santtila, “chose to compare apples to oranges because the evidence is so strong that men’s and women’s orgasms are under different degrees of selective pressure, the very point they were trying to disprove.” Yikes.

To their credit, Zietsch and Santilla acknowledged the limitations of their study, both in the paper and in Zietsch’s email to me. More work obviously needs to be done. “Figuring out the function of female orgasm, if any, will probably require very large genetically informative samples, fertility data, and detailed information on sexual behaviour, orgasm rate, and the conditions and partners involved,” Zietsch says. “I do have plans, but the debate probably won’t be settled quite some time to come.”

If, at this point, you’re as frustrated as me, you might be wondering what we do know about female orgasm. Well, we’re closer to knowing why they’re so few and far between during sex. In a paper published online this January in Hormones and Behavior, Lloyd and Wallen found that the farther away the clitoris is from the urinary opening, the less likely it is that the woman will regularly achieve orgasm with intercourse. If this holds up in future experiments, Lloyd says, it would establish that a woman’s ability to have an orgasm during sex rests on an anatomical trait that likely varies with exposure to male sex hormones in the womb. “Such a trait could possibly be under selection,” she says, “but this would have to be investigated. So far, no selective force seems to appear.”

Jennifer Abbasi is a science and health writer and editor living in Brooklyn. She has seen every episode of The X-Files. Have a question about the science of sex? Email Jen at

BELOW YOU'LL FIND THE BEST 30 OR SO (IMO, NATCH) OF THE 83 COMMENTS POSTED AS OF 9/28/11 4:56 PM... my seven faves are highlighted in red...

Full disclosure: Several of these comments made shit for sense -- and "mp" only gets better as the comment thread moves along... cheers!

09/21/11 at 2:16 pm
I am not a doctor or scientist. I am just your average human. My best guess why the males and females share common physical, social and psychology traits is we are the same human species. The similarities could just occur because the female in mating is not a kangaroo and the man is not bubble bee.
Yes, male and female human species share like characteristics.
I not surprised.

09/21/11 at 2:35 pm
Ok from a guy who has been with well more than his share of women, I can categorically say that for the most part, a genuine real and hard orgasm for a woman will legitimately change the way she interacts with you. Call it love or devotion or addiction, but she wants that feeling again. There are endorphens released as so on and so forth. Women from a sociobiological standpoint are built to find one or very few mates. Thus it is only logical that she is biologically rewarded for sticking to the same mate. Trust me when I say that when a chick isnt into you, she has a lot harder time getting off. It seems like common sense from where I stand. But I have been with lots of women...

09/21/11 at 5:49 pm
People always forget that 90% of men's sperm is designed to kill off and block all the other foreign sperm inside a woman's vagina. Evolution teaches us that females of our species got into heat and had sex with many partners in a short period of time. This has been happening for hundreds of thousands of years. The males have been competing in hordes to be the one that gets the lady pregnant. This likely explains the popularity of religion. It was devised to keep women as sexual shut-ins that would guarantee a male his offspring. There is no religion that does not seek to control a woman's sex life (that I'm aware of). In this case the males get an orgy and then get to disappear and go hunting or whatever. Meanwhile the woman ends up pregnant and ends up raising the kid by herself. Sound familiar?

09/21/11 at 6:18 pm
@Paxalot Good theory, but as humanity is (assumedly) not the only species that orgasms, and is the only species with religion, I doubt a connection.

09/21/11 at 6:58 pm
dont guys have orgasms as well? i often hear guys moan alot.

09/21/11 at 10:32 pm
Men and woman are different in life. I hope you find a match that nurtures all the inspires you in life. We all should learn the concept of nurturing. Just love the one your with.

09/22/11 at 8:09 am
I guess the premise of this article comes from everything that exist in your body, exist for some purpose otherwise it would not be there. From that point of view you can stop and stair at you body and just wonder all day long, why do I have that or this and why do people do this or that?
How to fun to just ponder!

09/22/11 at 2:40 pm
Personally, I'd like to see less articles of this nature in PopSci. It's not that they are not interesting, or that they are not science, but...
I subscribe for the sake of my scientifically-oriented sons. But these young men do not need to be reading about how much protein a person gets from swallowing a man's semen or how the length and location of the clitoris contributes to orgasm statistics.
The first article about sex which I alluded to was offensive, to say the least. This second one about sex, not as much, although it borders on details that should not be published unless someone is researching sex-related material. But...that said...if I see ONE MORE article about sex that is graphically detailed and not suitable, in my opinion, for school-aged scientists-to-be, I am canceling my subscription.

09/22/11 at 3:14 pm
lmao @ KingPatrickVII

09/22/11 at 6:05 pm
I would like to propose what I will call the "Awwwwww Ya!" theory of the female orgasm. It goes like this:
Once upon a time, there was an australopithecine with a random mutation that allowed her to feel real good when doing the nasty. Because this feeling did get in the way of breeding she did, and this trait was passed along to her descendants. Because breeding was rough many women who did not experience pleasure while having sex avoided it, while the women who had more pleasure engaged in it more freely. In addition, orgasms during menstration reduce cramping, and thus led to less homocide. Eventually, most females had some degree of pleasurability during sex, but once again, those that enjoyed it made fewer excuses about not having sex and as a result produced more off-spring, and had happier husbands, who prospered as a result of the symbiosis, allowing him to take care of more children.
If this theory is correct and progressive, in another 100k years you won't be able to look at a women without her having an orgasm, and we will all be filthy rich. Awwwwww ya!

09/23/11 at 12:45 am
The female orgasm requires the rubbing of the vulva with slow and soft strokes and it may take around 15 minutes. The location of the rubbing may have to changed about every 4 minutes as the rubbed area becomes numb. The clitoris should not be touched. There is a similarity between this process and Ravel's Bolero where the tempo is constant, the intensity increases and lasts about 15 minutes and ends in total disaray. There not such a thing as vaginal orgasms.

09/23/11 at 6:49 pm
Ok, people ... just settle down.
I can solve this dillema AND answer all your questions, with authority.
... Just loan me 100 attractive females and I'll get back to you, in a year or two (once my double-blind study is complete). = glad to be able to help ! =

09/23/11 at 7:49 pm
For those who don't care about female orgasms, vinyl partners are available.

09/24/11 at 2:11 pm
Why do men and woman hold hands? Holding hands is not a requirement to procreation. Perhaps the emotional part of us humans to have an organism is in the same context as why we hold hands. It’s just part of our emotional make up and less a biologically function. I love it when my baby ews and ahs… its just beautiful. Oh the word beautiful is not biological too. We humans are really complex and much more than biology and pure chemistry.

09/24/11 at 7:55 pm
My theory is that the point of the female orgasm existance is so females could plausibly fake it if they want. If female orgasms didn't exist, they couldn't fake one ever, because the guy would know that they are lying. So they invented the female orgasm so the guy will think they are actually having one when they fake it.

09/24/11 at 8:56 pm
MommaMidwife is NUTS!
This from a senior lady with four children, a hysterectomy more than 30 years ago and orgasms (still) whenever I wish with or without a uterus, or a cervix and with or without a guy. Good Lord! Ogasmic births! BS! Pregnant ladies RUN. Run very fast in the other direction from this supposed midwife! In response to those discussing anatomic compatibility, that's where it's at, for sure. A good fit matters. You will know it when you feel it. A bad fit is not worth looking for other good traits in a partner for the next 50 years. You will regret settling. Unless you also have other partners...

09/25/11 at 1:19 am
If women have trouble achieving orgasm, it's because they're having sex with men who have never learned anything about female anatomy. Lesbians achieve orgasm with little trouble at all, and are well aware that the clitoris is DEFINITELY touched.

09/25/11 at 2:42 am
Paxalot writes "This likely explains the popularity of religion. It was devised to keep women as sexual shut-ins that would guarantee a male his offspring. There is no religion that does not seek to control a woman's sex life (that I'm aware of)."
I belong to one of those religions that holds that sexual intercourse is for monogamous married couples only. I emphatically do not feel like a sexual shut-in. Far from being oppressed, my husband and I are liberated from sexually transmitted diseases, having our children grow up without a father or mother, jealousy, adultery, and a myriad of other problems that developed with the so-called sexual revolution i.e. free love. We also used natural family planning to space our children five years apart. Our sex life is great because of the deep intimacy we developed over 28 years of a faithful loving committed relationship. And yes we have orgasms when we want, but our sex life is not directed to orgasm being the goal. Being in harmony with God's plan brings a lot more satisfaction sexually and otherwise.

Phil Rubyn
09/25/11 at 3:23 am
I'm not promoting the Bible, just sharing what it says, however whoever said it knew it. Mojoanne, I'm very happy that you believe that your beliefs provide you with such a meaningful sex life. I'm not sure, however, that the historical church was so progressive. Also, a person can have advanced degrees and wisdom in one area, and be totally wrong and deluded in another.

09/25/11 at 3:41 am
Let's start off with this...
It is my hope that the non-same sex twins and same-sex twins are not achieving orgasm together

09/25/11 at 3:53 am
Does "orgasm during sex" mean "during vaginal coitus"? If so, it's true that few woman have such orgasms. But in my experience many women have orgasms, even female ejaculations, during cunnilingus. Freud, as brilliant as he was, was so mesmerized by assuming sex could only be meant for procreation, that he could not understand why women have orgasms or why a woman has a clitoris. I can imagine all too easily some psychodynamic theorist asking "How did coitus become sexualized?" I wonder how the "sex is for procreation" people deal with the fact that God so loved us that She designed men to get powerful orgasms from being anally penetrated. Both oral and anal sex are profoundly pleasurable to both giver and receiver, regardless of gender, and neither causes conception.

09/25/11 at 4:27 am
And this comment...
"...The Catholic Church established the university system, the scientific method, observatories, and more in the pursuit of knowledge..." ...is somewhat wrong in its own right. The University system and the scientific method were created by the Greeks.
Observatories were, at first, created to dispel that there other planets in our solar system, then later looked upon as objects against the Church when they couldn't be twisted in that fashion. In short, if the Church believes that something scientific goes against the Church's established views on the World, Nature, Man, and God, they will denounce it. They have even been known to dispel fictional scientific theories presented in mainstream science fiction. Several "Star Trek: The Next Generation" episodes, especially those dealing with the evolution of life forms and the concept that all bipedal humanoid-type life forms presented in the series came from one Source were denounced and excommunicated by the Church. If they can do this to a show that is set 300 to 400 yrs in the future and is fictional, then they will do it for real theory and real research. Another recent field to come under attack is the research being done by the LHC and its search for the Higgs particle.

09/25/11 at 6:13 am
“As such, there is no path by which selection on male orgasm can be transferred to female orgasm, in which case the by-product theory cannot work.” It may not work now, but that doesn't rule out it worked in the past.

09/25/11 at 12:02 pm
This study isn't very good as it suffers heavily from self report bias, hindsight bias, and it is retrospective study. Also, MALE orgasm isn't a prerequisite for pregnancy, either. Try not to propagate any more myths.

09/25/11 at 1:18 pm
The only explanation why women and men have orgasm is so we can enjoy the procreation experience (not from a religious point of view). Copulating would be a tasking if we didnt have orgasm. We humans are creatures that respond well to rewards.

09/25/11 at 1:58 pm
In Russia men and women both have orgasms all the time, since they have socialism. In the United States the females started getting orgasms after Susan B Anthony fought for the equal rights of women. Now to be politically correct, if men have orgasms, females also need to have orgasms. We live in a society where women are considered equal to men. So without orgasms women may feel inferior. Though there are a lot of fighters fighting for equality among men and women, women still haven't gotten on a level playing field with men. Once women start getting orgasms in 1 minute after the start of sex, then men and women will be on a level playing field.

Jahlee Starks
09/25/11 at 7:09 pm
In a Nutshell, Pun intended, to answer the question,The Function of The Orgasm is wane and wax or Respiratory, to detoxify cells i.e. The Orgasm Formula or Mechanical Tension, Electrical Charge, Electrical Discharge, Mechanical Relaxation, can only work properly as a Biological Function of Meiosis/Mitosis and since dammed-up, undischarged Orgone Energy creates toxicity in the Blood Stream, Orgasm is Nature's Means of Phase Modulation in the Heart since the Orgasm Reflex causes the wave of Pleasure to begin in The Mind as Spirit then it transmutes into muscular undulations commencing in the pelvis,down the legs, up the spine to the brain and down into the heart where the Energy is resolved as Spirit evinced by heavy breathing and panting which release toxicity from the Blood Stream, the Climax, which leads to Relaxation! The Point is Mental Hygiene which helps One build Good Character...The Essence of Beauty!

09/25/11 at 7:30 pm

09/25/11 at 8:04 pm
crackerhead said we were not always ying & yang . we were once unisex , having a-sexual reproduction ! like the worm maybe it would take 2 but both had male and female parts . a mans testicles are a womans ovarys . the vagina is a penis inverted .

09/25/11 at 10:43 pm
My church does not try to control the lives of women. The Church of Cum One Cum All does NOT discriminate.

09/25/11 at 11:08 pm
The reasons women have an organism, is because there was no chocolate available in the house and this is the closest thing available.

Larry Fitz
09/25/11 at 11:22 pm
The modern scientific method was not created by the Ancient Greeks, while they did contribute to it with the Socratic method and Syllogism, the father of the scientific method was a catholic bishop named Robert Grosseteste. While one can make an argument for the Greeks being the forerunners of the University system, once again, advanced education after the Dark Ages was brought to you again by the catholic church. Not liking some of the things the catholic church has done (or even all of the things) does not change facts and you should be more enlightened and skeptical than that. There was also a ridiculous assertion that most people with advanced education were not religious. Seeing as less than 2% of the population of the US are Atheists and significantly more than 35% have degrees, well, that idea shows a distinct lack of research as well.
Studies between fraternal siblings of differing genders would produce no more genetic correlation than studies with siblings who were not twins. Though there might be correlation based on pre-natal hormonal exposure. One explanation of the female orgasm could be as simple as a non-selective trait, like baldness in men, or longevity beyond childbearing years in women.

09/26/11 at 10:24 am
Everyone needs to read Sex at Dawn. Women evolved to have sex with many men in sequence for a longer period of time, that's why they have trouble having an orgasm with one man when the sex only lasts a few minutes. We aren't broken! They also have done studies that show orgasm sucks sperm up into the uterus.
Read Sex at Dawn, really explains alot of things about sex that don't make sense if you listen to the standard narrative.


09/26/11 at 8:00 am
JohnPopSci, I have complained in the past of a scientific study being a waste of tax payer money; you should have heard the wailing, gnashing of teeth and so much whining that all studies are considered necessary in the name of science. I imagine some studies are done to help just pay the bills and less about true science and betterment of humanity.

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