Comment: Masturbating to a novel pornstar increased ejaculate volume and motile sperm. Also, the time it took to ejaculate decreased significantly. The Coolidge effect is characterized as greater reward circuit activity when exposed to a novel sexual partner. Here, sexual novelty also translates into better sperm and faster ejaculation, making any “extra-pair couplings” more efficient, and more costly.

Evolutionary Psychological Science

June 2015

Paul N. Joseph,  Rakesh K. Sharma, Ashok Agarwal, Laura K. Sirot


Males in many species differentially allocate sperm and seminal fluid depending on certain social variables, including perceived sperm competition and female reproductive status. In some species, males reduce their investment in sperm quantity or quality upon repeated matings with the same female and increase such investment when mated to a novel female. We tested for effects of stimulus habituation and novelty on ejaculated semen parameters in humans. We analyzed ejaculates produced through masturbation with stimulation from sexually explicit films. When males were exposed successively to the same female six times, we saw no change in ejaculate parameters between the first and sixth exposures to the same female. However, ejaculate volume and total motile sperm count significantly increased when males were exposed to a novel female. Time to ejaculation also decreased significantly upon exposure to a novel female. Thus, our results suggest that human males ejaculate more quickly and invest more in ejaculates with novel females.



Study by Wooster Scientists Shows Promise for Enhancing Male Fertility

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Student-faculty collaboration offers hope for couples trying to conceive

18 June, 2015 by John Finn

WOOSTER, Ohio — When couples have trouble conceiving, it’s often the woman who endures the greatest scrutiny, but a new study by scientists at The College of Wooster suggests that male infertility might be consistently overlooked and that men can actually boost their sperm numbers.

Paul Joseph, a 2014 Wooster graduate, and Laura Sirot, an assistant professor of biology at Wooster, together with researchers at the Cleveland Clinic’s Center for Reproductive Medicine, collaborated on the project, which considered the “Coolidge Effect,” a phenomenon seen in mammalian species whereby the quality and quantity of a male’s sperm would decrease with repeated exposure to images of the same woman but subsequently increase upon exposure to images of a new woman The research indicates that men, like males in other animal species, invest more (i.e. produce greater ejaculate volume with a greater number of motile sperm) when a little variety is introduced. Their findings are published in the June issue of Evolutionary Psychological Science.

Joseph and Sirot simulated mating scenarios with familiar and novel women using various images and then analyzed the different semen samples. “Our results revealed that when exposed to images of a novel woman, men ejaculated at a faster rate with higher volumes of semen that contained higher numbers of motile sperm,” says Joseph. “This suggests that the men were able to differentiate between the two women they saw and produce larger ejaculates with more sperm for the depictions of a novel woman.”

The findings also provide new insights for the fields of evolutionary biology and human evolutionary psychology, but the applications for male fertility medicine are particularly promising, say the two scientists. “Male infertility may be under-diagnosed since the ejaculates produced for analysis and for procreative purposes are generated under two different scenarios,” says Joseph. “Ejaculates produced for procreative purposes are usually generated with a familiar woman, while those that are analyzed in a clinical setting are usually generated while viewing images depicting a novel woman. Thus, the ejaculates produced in fertility clinics may be of higher quality than usual, which may conceal any potential fertility problems experienced in the bedroom.”

Joseph and Sirot hope that the results will provide insight into ways to improve the diagnosis and treatment of fertility problems, thus boosting chances for conception, while sparing women invasive diagnostic and treatment procedures.


Why New Sex Gives Men A Faster Orgasm

Aug 3, 2015 04:01 PM By Lizette Borreli

Healthy sperm isn’t always a given for men. Quantity, movement, and structure all contribute to sperm health, and according to a recent study published in the journal Evolutionary Psychological Science, these traits may change with new sex partners.

“Our findings are the first to demonstrate that men’s ejaculate behavior and composition change in response to a novel female stimulus,” the researchers, from the College of Wooster in Ohio, wrote.

Male physiology and behavior are known to be influenced when they’re exposed to new partners. In a 2000 study, for example, men found repeated exposure to an erotic stimulus to be not only less sexually arousing, but also as less appetitive and absorbing. Self-reported arousal, and therefore penile circumference, increased when men were exposed to new female stimuli after becoming accustomed to the same female stimulus. These findings are linked to man’s innate physiology, which works to boost virility in the face of new mates, thus improving his chances of producing offspring.

For the current study, researchers sought to uncover whether men’s ejaculate traits changed in response to familiar or new female stimuli. A total of 21 heterosexual men between the ages of 18 and 23 were recruited to watch seven sexually explicit videos in a private room every 48 to 75 hours for 15 days.

The first six videos depicted the same actress and actor, while the seventh film had a different actress but the same actor. Each video consisted of a three-minute clip from a longer 20-minute video and was played on repeat until the men ejaculated.

The men were instructed to record what time they began watching the film, what time they ejaculated, and whether all of their ejaculate was deposited into a collection cup. The researchers also assessed time of ejaculate volume and the number of motile sperm from each participant. If some of the ejaculate didn’t make it into the cup, it was not included as part of the data.

The findings revealed that the time it took participants to ejaculate ranged between four and 21 minutes. When it came to the first six films, there was no habituation effect, which means repeatedly viewing the same woman did not increase or decrease the time to ejaculation. However, they ejaculated faster and with a higher quality when viewing the seventh film, which included a new woman.

The researchers suspect these men were more likely to produce higher quality sperm for a new female stimulus for two reasons. First, they believe that hypothetically, the men had already fertilized the egg(s) or had their sperm stored by women they mated with. Second, these findings are linked to the concept of sperm competition, which refers to the competition between the sperm of two different men to fertilize a single woman’s egg. This occurs more in extra-pair copulations — when people have sex with others other than their mate.

Casual sex sheds light on more than just a person’s  desire to have sex with more than one other person. It also affects how male infertility is diagnosed and may assist in reproductive techniques. Promoting behaviors that are more similar to normal sexual scenarios, for example, can improve the accuracy of male infertility diagnoses, while using new female stimuli may improve the outcome of assisted reproductive techniques.


Joseph, PN, Sharma, RK, Agarwal, A., & Sirot, LK. Men Ejaculate Larger Volumes of Semen, More Motile Sperm, and More Quickly when Exposed to Images of Novel Women. Evolutionary Psychological Science. 2015.

Koukounas E and Over R. Changes in the magnitude of the eyeblink startle response during habituation of sexual arousal. Behavior Research and Therapy. 2000.