Men who knowingly engage in intercourse with a woman who is already in another relationship tend to exhibit different sexual behaviors, according to a new study published in Evolutionary Behavioral Sciences.
The new research is based on the idea that the penis is a “semen displacement device.” In other words, the human penis evolved its unique shape, with an unusually large glans, in order to displace semen left by other men in the female reproductive tract. If this is the case, then men should instinctively thrust deeper and quicker when they suspect they have a sexual rival.
In the study, 643 undergraduates at the State University of New York completed an anonymous online questionnaire regarding their sexual orientation, sexual history, and specific sexual behaviors, including instances of sexual infidelity.
The researchers found that 27.4% of the participants reported cheating on their partner, and 34.3% of these participants reported that the person they were cheating with was also cheating on his or her romantic partner as well. In addition, 26.8% of the sample reported having been the “other” man or woman.
The findings provided evidence that men changed their sexual behaviors when they knew there was a sexual rival. The participants reported that orgasms were easier to have, more intense, and longer lasting when men knew they had sexual rivals. Men also tried harder to satisfy their partner when they knew there was a rival, while women did not.
“Our paper deals with men who are in a committed sexual relationship and cheat with other women. If the other woman is also in a committed sexual relationship, these men unwittingly engage in deeper more vigorous penial thrusting and experience more intense orgasms,” study author Gordon G. Gallup Jr. told PsyPost.
“Such changes in male sexual behavior are thought to represent an ensemble of evolved strategies that function to minimize sperm competition with her committed partner, and thereby increase the likelihood of conception by the rival male.”
The study, like all research, includes some limitations. For instance, the study did not assess motivations for engaging in infidelity or other aspects of the relationship.
“The question asked was whether the participant had sex with someone other than their partner. This leaves open a broad range of reasons and circumstances,” the researchers said. “It is also not clear whether participants were answering sexual questions regarding long-term cheating partners; it is possible that men and women could have long-term sexual relationships outside their primary relationships (e.g., friends with benefits).”
The authors of the study added that “a great deal more research needs to be done in this area. This context by its very nature is complicated, with multiple partners and rivals and multiple relationships of varying duration.”
The study, “The Other Man: Knowledge of Sexual Rivals and Changes in Sexual Behavior“, was authored by Rebecca L. Burch and Gordon G. Gallup Jr.
