The Coolidge Effect, Explained
Evolutionary biology, lab experiments, and human behavior converge on an uncomfortable truth about how male desire works.
This article was originally published in Le Point on 16.11.2025
Calvin Coolidge wasn’t the first—and, ahem, certainly wouldn’t be the last—U.S. president to have his name indelibly linked to sexual excess. But he is the only one to have a scientifically established sexual phenomenon named after him, a biological fact of male carnal gluttony that researchers are still studying today.
It’s an apocryphal tale, one that seems to have started as a joke made by a long-forgotten sex researcher named Richard Whalen while he was giving a talk at an academic conference nearly seventy years ago. But the legend of the “Coolidge effect,” as it has come to be known, goes something like this.
In the 1920s, the 30th POTUS and his wife Grace were visiting a government-run poultry farm in Kentucky. Shortly after arriving, the President and the First Lady were taken on separate tours.
When Mrs. Coolidge passed the chicken pens, she paused to ask the man in charge if the rooster copulates more than once each day. “Dozens of times,” was the reply. “Please tell that to the President,” Mrs. Coolidge requested. When the President passed the pens and was told about the rooster, he asked, “Same hen every time?” “Oh no, Mr. President, a different one each time.” The President nodded slowly, then said, “Tell that to Mrs. Coolidge.”
Again, apocryphal. Still, Grace was known to be playful and the notoriously reserved President Coolidge was said to have a deadpan sense of humor.
Either way, the story illustrates what most of us eventually come to realize. Men’s sexual response is diminished by repeated exposure to the same person and reignited by new partners. It’s not just roosters and men for which this applies. Back on the farm, bulls that have mated repeatedly with a particular cow will eventually refuse service; providing them with a different female quickly gets their juices flowing again. In the laboratory, the Coolidge effect has been found in everything from male monkeys to male guppies and almost all creatures in between.
Although the details and hypotheses varied, the earliest studies all involved presenting male rats with a single female and leaving them to, well, f*ck until they literally could f*ck no more. How many “intromissions” (copulatory thrusts) and ejaculations before the male reached this state of sexual exhaustion? Calling the female in these rodent mating scenarios “attractive” would be strange, but from the male rat’s perspective, she was just that, having been brought into estrus by injections of estrogen and progesterone. The average male rat in these early studies was vigorously amorous, averaging about 42 intromissions and 7 ejaculations before conking out. (How researchers measure rat ejaculations is another question, but let’s stay focused here.) It appears even rats have their limits. But perhaps, thought these early researchers, it’s not so much a generalized sexual fatigue as it is a stimulus fatigue. Because giving these exhausted males a “fresh female”—their words, not mine—suddenly got them hot and bothered again. “The male performed as if this were the first ejaculation of the test,” as one team of investigators put it.
Conducting such controlled mating experiments with human subjects would strain even the most liberal interpretation of research ethics. It’s more porn plot than lab study. There is evidence, nonetheless, that the Coolidge effect operates in full swing in our species. Some of this evidence is indirect. For example, in one massive study conducted across 52 countries, 6 continents, and 13 islands, the sex difference in desire for sexual variety was ubiquitous: overwhelmingly, men want casual hookups with strangers more than do women. Similarly, men express a desire for more lifetime sexual partners: around 14, they say, sounds about right, whereas the average woman says just two or three is ideal. That’s not to say that women want sex any less than men do, just that they tend to want it more with their regular partner, whereas variety is the spice of life for men. Similar indirect evidence comes from studies on sex differences in sexual fantasizing. A study from those halcyon pre-Internet days showed that, over the course of a lifetime, men cast up to 1,000 different sex partners in the dirty movie theatre of their heads The accessibility of online porn, an industry catering almost exclusively to males, has made all that imaginative work moot; it gets right to the quick of the Coolidge effect with a virtually infinite supply of varied and novel actors.
And then there’s the data on actual infidelity, which is quite messy (often in these surveys, “infidelity” and “cheating” are not clearly defined), but they still find consistently that men more than women have affairs for purely no-strings-attached sexual reasons—otherwise known as “it didn’t mean anything” sex.
None of this should be particularly shocking. Alfred Kinsey wrote that “the human male would be promiscuous . . . throughout the whole of his life if there were no social restrictions.” Some theorists have argued that women’s more frequent changing of their appearance (makeup, hairstyles, fashion, even surgical modifications) reflects their unconscious efforts to steer their long-term mate’s attention back to them, a sort of implicit awareness of their knowledge of the Coolidge effect in men.
The most convincing evidence of the foregoing sex difference, in my view, is the experimental data. Although putting random people in a cage and asking them to screw their brains out is a non-starter, this hasn’t stopped a few innovative researchers from testing the primary hypothesis, which is that men, more than women, habituate faster to the same person and lust for novelty. In one experiment, for instance, repeated exposure to photos of the same opposite-sex faces decreased men’s ratings of the women’s attractiveness, whereas seeing the same male face over and over again increased women’s ratings of men’s attractiveness.
Other studies have gotten even more, well, physiological, showing that men’s habituation to an erotic stimulus (repeated exposure to the same nude images, steamy audio, porn clips) leads to a measurable reduction in their “penile tumescence” (aka strength of an erection), with those penises being swiftly brought back to life by new material. The Coolidge effect even seems to function at a gametic level in human males. One study had undergrad students masturbate and ejaculate only to clips of the same porn actress—one who was engaged in a menu of different salacious acts—over the course of two weeks. The researchers examined various “ejaculation parameters” (volume, sperm motility, etc.). These seminal measures basically plateaued over that period. However, in the final study session, the participants saw a video with a different actress. Seeing this novel female not only made these young men ejaculate faster, but led to greater, um, output and healthier swimmers.
The apparent sex differences in the Coolidge effect, with men’s comparatively stronger desire for sexual variety, can really only be understood through the lens of our evolved psychology. There were likely circumstances in which women in the ancestral past might have gotten a reproductive edge by having multiple sex partners within a short succession. For example, being inseminated by different men within a span of a few days may increase the chances of fertilization, with the sperm of multiple males competing so that the “best man” (i.e., the fittest, highest-quality sperm) wins. In general, though, nature wouldn’t have exerted the same pressure on females to seek out novel partners. “Whereas a man has the potential to impregnate an almost unlimited number of women,” explains psychologist Susan Hughes and her colleagues in a recent article in Archives of Sexual Behavior, “women typically have only one child at a time and it takes only one man to impregnate a woman. A woman who has sex with 100 men in 1 year does not necessarily have a reproductive advantage over a woman who has sex with one high-quality man 100 times in 1 year.”
Using that very adaptationist logic, Hughes et al. devised a mating game study, one where (straight) men and women saw a set of 10 photos of opposite-sex faces, and were asked to allocate a limited set of bonks among them. Here’s how it read:
Hypothetical. You have only 10 opportunities to have sex. Please distribute those 10 times across the following 10 individuals by placing a number next to each picture for how many times you would have sex with that person out of the 10. For example, you can have sex with each of them once, you can have sex with one of them 10 times, you can have sex three times with one person and seven times with another person, etc., but your total number must sum to 10. Each box (provided next to each picture) should have a number and a zero indicates you would not have sex with that person.
How would you answer? Basically, the authors reasoned that if you opt for a sample platter of copulating partners over the all-you-can-eat buffet with one, that reveals a stronger Coolidge effect. A person who chose “1” for each of the photos displayed a higher desire for sexual variety than one who put “10” next to one face and “0” for everyone else.
As expected, a clear sex difference emerged on this “mating opportunity task,” with men distributing their bonks among the pictures more than did the women. Even when all 10 photos were of unattractive faces (as judged by a separate panel of independent raters beforehand) this sex difference panned out. The men, but not so much the women, wanted sexual variety. In a second study, Hughes and her coauthors told participants that they would see two faces of opposite sex strangers side by side on a computer screen and were to decide which of the two people they’d prefer to hook up with. After each choice, they saw another pairing—one including the face they just chose, and another novel face—and instructed to choose again. As predicted, the male participants were more likely to choose the novel face, and the female participants more likely to go with the face they’d already been exposed to.
Needless to say, there are some very practical, even clinical, implications for couples in loving relationships hoping to keep that pilot light of men’s libidos flickering over the decades (think, role play, porn priming, sex workers, even open relationships, for those who dare). Understanding and acknowledging the blunt biological reality of the Coolidge effect can allow us to harness it in ways that bring out the better satyrs of our nature.
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