A new study published in the journal Evolutionary Psychology suggests that fear of infidelity is the leading reason why couples engage in "duty sex," a practice where sexual intimacy occurs out of obligation rather than desire. This research aims to uncover the evolutionary underpinnings of this behavior.
Previous studies have identified several factors contributing to duty sex, including relationship maintenance, avoiding conflict, safeguarding a partner's feelings, and preventing abandonment. However, this latest investigation focused on identifying the ultimate evolutionary advantage of such obligatory sexual activity.
"What reproductive advantages might this behavior have provided over our evolutionary history? I wanted to know if duty sex serves an ultimate function, and if so, what that function is," explained lead study author F. Sid Dougan.
The study surveyed 252 participants, consisting of 176 women and 76 men, aged 18 to 24. Most participants identified as heterosexual, and relationship lengths varied from recent beginnings to 84 months. The survey collected demographic information and asked about participants' sexual activity and the frequency with which they engaged in duty sex to protect their relationships.
Researchers evaluated perceived probability of partner infidelity, mate value discrepancy, and neuroticism to predict the likelihood of duty sex. The findings indicated that both men and women engaged in duty sex at equal rates when they feared their partner might be unfaithful. The fear of infidelity emerged as a stronger predictor of duty sex than any other factor examined.
This aligns with earlier research suggesting that couples are more likely to engage in "mate retention" behaviors, such as duty sex, when they perceive a higher risk of infidelity, particularly during challenging periods in the relationship or extended separations. The study posits that when individuals suspect their partner might stray, engaging in sex out of obligation could be an instinctive behavior designed to ensure the partner's continued commitment.
Interestingly, the study found no correlation between relationship length and the frequency of duty sex for either gender. Despite previous research indicating that men generally have higher sex drives, this study found that men and women participate in duty sex at the same rate.
The authors acknowledge certain limitations in their study, including reliance on self-reported data, a relatively small sample size, and a participant pool that was predominantly young and in the early stages of their relationships. Nonetheless, the researchers emphasized the importance of viewing duty sex through an evolutionary lens. "This work highlights how behaviors that appear obligation-based may reflect strategic responses to perceived partner loss risk, offering a foundation for future research on the role of sexual behavior in relationship maintenance," the study concluded.