Researchers shed light on evolutionary mystery: Origins of the female orgasm

Oxytocin
Spacefilling model of oxytocin. Created using ACD/ChemSketch 8.0, ACD/3D Viewer and The GIMP. Credit: Wikipedia.

Female orgasm seems to be a happy afterthought of our evolutionary past when it helped stimulate ovulation, a new study of mammals shows.

The role of female orgasm, which plays no obvious role in human reproduction, has intrigued scholars as far back as Aristotle. Numerous theories have tried to explain the origins of the trait, but most have concentrated on its role in human and primate biology.

Now scientists at Yale and the Cincinnati Children's Hospital have provided fresh insights on the subject by examining the evolving trait across different species. Their study appears Aug. 1 in the journal JEZ-Molecular and Developmental Evolution.

"Prior studies have tended to focus on evidence from human biology and the modification of a trait rather than its evolutionary origin," said Gunter Wagner, the Alison Richard Professor of Ecology and Evolutionary biology, and a member of Yale's Systems Biology Institute.

Instead, Wagner and Mihaela Pavličev of the Center for Prevention of Preterm Birth at Cincinnati Children's Hospital propose that the trait that evolved into human female orgasm had an ancestral function in inducing .

Since there is no apparent association between orgasm and number of offspring or successful reproduction in humans, the scientists focused on a specific physiological trait that accompanies human female orgasm—the neuro-endocrine discharge of prolactin and oxytocin—and looked for this activity in other placental mammals. They found that in many mammals this reflex plays a role in ovulation.

In spite of the enormous diversity of mammalian reproductive biology, some core characteristics can be traced throughout mammalian evolution, note the researchers. The female ovarian cycle in humans, for instance, is not dependent upon sexual activity. However, in other mammalian species ovulation is induced by males. The scientists' analysis shows male-induced ovulation evolved first and that cyclical or spontaneous ovulation is a derived trait that evolved later.

The scientists suggest that female orgasm may have evolved as an adaptation for a direct reproductive role—the reflex that, ancestrally, induced ovulation. This reflex became superfluous for reproduction later in evolution, freeing female orgasm for secondary roles.

A comparative study of female genitalia also revealed that, coincidental with the evolution of spontaneous ovulation, the clitoris was relocated from its ancestral position inside the copulatory canal. This anatomical change made it less likely that the clitoris receives adequate stimulation during intercourse to lead to the neuro-endocrine reflex known in humans as orgasm.

"Homologous traits in different species are often difficult to identify, as they can change substantially in the course of evolution," said Pavlicev. "We think the hormonal surge characterizes a trait that we know as female orgasm in humans. This insight enabled us to trace the evolution of the trait across species."

Such evolutionary changes are known to produce new functions, as is well established for feathers, hair, or swim bladders, etc., which originated for one purpose and were coopted into secondary functions later.


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More information: JEZ-Molecular and Developmental Evolution, DOI: 10.1002/jez.b.22690
Provided by Yale University
Citation: Researchers shed light on evolutionary mystery: Origins of the female orgasm (2016, August 1) retrieved 22 October 2019 from https://phys.org/news/2016-08-evolutionary-mystery-female-orgasm.html
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Aug 01, 2016
This research is basically devoid of any facts and is mostly a compilation of just-so stories that speculate wildly as to how the female orgasm supposedly "evolved".
Since there are no direct observations and documentation showing this supposed "evolution" the only thing that these researchers can do is take wild guesses.
There is NOT ONE fact that can be verified by going back into the past or even by direct observation in the present. The "research" is completely non-science.
For instance, take this vacuous statement:
Such evolutionary changes are known to produce new functions, as is well established for feathers, hair, or swim bladders, etc., which originated for one purpose and were coopted into secondary functions later.

The only way this can be "well-known" is by uni-lateral agreement among evolutionary believers, otherwise it's a pure myth from a real-life factual point of view.


Aug 01, 2016
This comment has been removed by a moderator.

Aug 01, 2016
If some orgasm hormones are important for conception, why it didn't work at the case of another species? I'd guess it would rather something to do with https://en.wikipe...zations.

Wow... a Wiki citation for something most would have never thought of...

Aug 01, 2016
I note that Rh negative blood was a mutation produced 40,000 y ago. If the age of this mutation can be tracked down would it be 40,000 y ago also? Would it also be found primarily linked to women from the British Isles, Spain and the Basque region where Rh negative blood is as high as 50%?

Aug 01, 2016
FTA;
"A comparative study of female genitalia also revealed that, coincidental with the evolution of spontaneous ovulation, the clitoris was relocated from its ancestral position inside the copulatory canal."

A change this drastic would not have happened overnight...

Aug 01, 2016
"The scientists' analysis shows male-induced ovulation evolved first and that cyclical or spontaneous ovulation is a derived trait that evolved later.

The scientists suggest that female orgasm may have evolved as an adaptation for a direct reproductive role—the reflex that, ancestrally, induced ovulation.

This reflex became superfluous for reproduction later in evolution, freeing female orgasm for secondary roles. A comparative study of female genitalia also revealed that, coincidental with the evolution of spontaneous ovulation, the clitoris was relocated from its ancestral position inside the copulatory canal."

Evolution results in the damnedest things:

- Males were initially responsible for both own and female immediate reproductive response.

- Human female biology of clitoris and orgasm is vestigial.

Aug 01, 2016
Evolution results in the damnedest things:

Ain't that the truth...:-)

- Males were initially responsible for both own and female immediate reproductive response.

So... no "was it good for you, too?" stuff?. It was females evolutionary response to gettin' somethin' else out of it besides pregnant? Sounds almost like a choice...

- Human female biology of clitoris and orgasm is vestigial.

Not quite sure what you mean by vestigial...

Aug 02, 2016

Not quite sure what you mean by vestigial...


"Vestigiality refers to genetically determined structures or attributes that have lost some or all of their ancestral function in a given species, but have been retained during the process of evolution."

[ https://en.wikipe...igiality ]

Re: "... the reflex that, ancestrally, induced ovulation. This reflex became superfluous for reproduction later in evolution, freeing female orgasm for secondary roles."

Aug 02, 2016

Not quite sure what you mean by vestigial...


"Vestigiality refers to genetically determined structures or attributes that have lost some or all of their ancestral function in a given species, but have been retained during the process of evolution."

[ https://en.wikipe...igiality ]

Re: "... the reflex that, ancestrally, induced ovulation. This reflex became superfluous for reproduction later in evolution, freeing female orgasm for secondary roles."

So... you're saying situation driven spontaneous ovulation was the norm in earlier times?

Aug 03, 2016
@WG: "The scientists' analysis shows male-induced ovulation evolved first and that cyclical or spontaneous ovulation is a derived trait that evolved later."

I wouldn't know (and I think the scientitss doesn't know either, suggested by the sentence formulation) if and when male-induced ovulation changed to, say, year bound as in most mammals. Maybe males were cyclical early on instead, and no one has bothered to find out which lineages have which mode?

Aug 04, 2016
Any guy knows that his woman's sexual feeling is equal his own and more. It does not take a waste of tax money like what produced the above to know this. Men like sex. So do women, and the more and deeper the better, usually.

Aug 05, 2016
Why doesn't male orgasm have to be explained? Ejaculation and orgasm are not the same thing. They are physiologically distinct. Either can happen independently. So while ejaculation is necessary, why is orgasm necessary in males? Doesn't orgasm in males function as a reward for engaging in the behavior and reinforce the behavior, just as pleasure in eating reinforces that behavior? So wouldn't the same thing be true for female orgasm? It's a reinforcement.

Aug 08, 2016
Wow, the authors are amazingly clueless. They can't put together a simple evolutionary explanation for female orgasms, and so they treat them as a residual and unnecessary trait leftover from earlier ancestors, like an appendix.

Dumb.

There is an evolutionary explanation.

During orgasm, the cervix dips energetically down into the vagina, coming into more direct contact with more semen, if any is present. It also stimulates ovulation, if the timing is right. In both cases, the likelihood of fertilization has increased slightly.

So there is a natural selection impulse going on. Females who are turned on by their partners are more likely - a little - to obtain offspring. Females who are not, are less likely - a little - to obtain offspring. Female orgasms therefore grant women a bit more control over mate selection for their offspring.

Orgasms also make sex more appealing to women. That's a reproductive advantage, too - more kids.

Aug 08, 2016
So: female orgasms are not a relic of old dusty evolution. They're a part of ongoing natural selection.

It's important to grasp that humans are unique among mammals in their sexuality, particularly women's sexuality. In no other mammalian species are the females receptive outside of ovulation. In humans, receptivity is expanded enormously. The reasons are social. We are a highly social species, our children mature very slowly, they need resources from their parents for a long time. The bonding that happens during sex has natural selection advantages.

For sexuality in humans to have departed so far from mainstream mammalian reproductive norms, remnant explanations fail utterly. We're looking at recent and continuing natural selection here.

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