A new study in Evolutionary Psychology suggests that sex within romantic relationships can be driven by obligation as well as desire, with duty-based sex appearing more often among those who fear infidelity, view their partner as more desirable, or exhibit higher emotional instability. The researchers say duty sex may act as a relationship-maintenance tactic when couples sense their bond is at risk.
Duty sex is defined as consensual sexual activity motivated by a sense of obligation rather than personal desire. It is considered distinct from broader sexual compliance, which covers consensual sex one does not actively want, by focusing specifically on obligation to one’s partner to maintain the relationship, protect feelings, avert an argument, or deter a partner from leaving.
While not uncommon, duty sex is linked to emotional downsides, particularly lower sexual satisfaction among women. The researchers note that sexual satisfaction often correlates with overall relationship well-being. They reference prior work showing women with histories of nonconsensual sexual experiences reporting more frequent duty sex and greater sexual pain than others.
The study’s author, F. Sid Dougan, a doctoral candidate in the Buss Evolutionary Psychology Lab at the University of Texas at Austin, collaborated with Kate B. Metcalfe and Cindy M. Meston, who previously conducted related work. Dougan described his motivation to explore the question of why people engage in duty sex, asking what ultimate evolutionary function such behaviour might serve.
From an evolutionary viewpoint, partner loss posed a heavy cost to our ancestors, incentivising mate-retention tactics designed to keep a partner invested. The researchers classify these tactics into two broad categories: cost-inflicting behaviours aimed at discouraging a partner from leaving, and benefit-provisioning behaviours designed to make the relationship more rewarding. They propose that duty sex fits the latter, potentially helping to preserve investment in the relationship when it feels threatened.
If duty sex functions as a form of mate retention, individuals should be more likely to use it when relationship threat is perceived. Infidelity remains a central risk, but the researchers also consider mate-value disparities—where one partner is judged more desirable than the other—as a key factor that might prompt duty sex as a way of maintaining commitment.
Neuroticism, characterised by emotional instability and anxiety, was another factor of interest. The team hypothesised that people scoring higher on neuroticism would report more duty sex, driven by heightened sensitivity to rejection and fears about losing a partner. Unlike some prior work, the study aimed to test these associations across both men and women.
The researchers recruited 252 sexually active university students aged 18 to 24, with an average age of about 19. The sample comprised 176 women and 76 men, all currently dating at least one partner and having engaged in vaginal, anal, or oral sex within the past four weeks. Roughly three-quarters were in committed relationships, while the rest were casually dating, and the average relationship length was just under 15 months.
Participants completed a 45-minute online survey that assessed their motives for sex, perceptions of their relationship, and personality traits. Duty sex was measured with a four-item questionnaire, scored from 4 to 20, where 4 indicated rarely engaging in duty-based sex. They also estimated the likelihood of their partner’s infidelity on a 0 to 100 percent scale across five behaviours, rated both their own and their partner’s desirability on a 7-point scale, and undertook a brief neuroticism assessment.
Across the combined sample, duty sex was reported infrequently, with women averaging 5.24 and men 4.76 on the 4-to-20 scale; there was no statistically significant gender difference in overall frequency. Dougan noted this was surprising given cross-cultural expectations of higher male sex drives, which could have made duty sex a more effective retention tactic for women with male partners.
When the data were pooled, the three main predictions held true: greater concerns about a partner’s infidelity correlated with more duty sex, and this pattern persisted when analysed separately for women and men. Women, on average, estimated an 11 percent risk of partner infidelity, compared with just under 10 percent for men, and higher perceived infidelity risk aligned with higher duty sex scores.
“Sex isn’t always motivated by desires for physical and emotional pleasure,” Dougan said. “People have sex for all sorts of reasons, and our findings suggest that one of these reasons is to prevent their romantic partners from straying elsewhere.”
The study’s conclusions also align with recent PsyPost coverage of related research showing that triggering fears of cheating can elevate jealousy and prompt both affectionate and controlling mate-retention strategies in the subsequent month.
Desirability gaps also played a role. Perceiving oneself as less desirable than one’s partner was associated with higher duty sex scores overall, particularly among women. Although this link did not reach statistical significance within the male subgroup alone, there was no significant difference in the strength of the association between the sexes.
The authors note that this pattern mirrors other work on desirability gaps and sexual behaviour, including studies suggesting that women who see their partner as more desirable are more inclined to engage in behaviours aimed at keeping them satisfied.
Neuroticism emerged as a concurrent influence for both sexes, with higher neuroticism associated with more duty sex. The researchers emphasise that the effect size was modest, and the finding held even after accounting for fears of infidelity and mate-value gaps.
Relationship length did not predict duty sex, while being in a committed relationship was linked to more duty sex in the combined sample and among men, potentially reflecting higher stakes in long-term investments. The authors caution that the gender difference should be interpreted cautiously due to smaller numbers in the dating group.
Overall, the model explained about 29 percent of the variation in duty sex scores across participants.
Dougan stressed that the findings should not be interpreted as endorsement of the behaviour. “Duty Sex shouldn’t automatically be viewed as something negative or dysfunctional,” he said. “We often assume that people should only engage in sex when they’re experiencing sexual desire, but sexual behaviour can serve functions beyond immediate sexual gratification. Consensually engaging in sex to strengthen bonds within a romantic relationship might be a perfectly understandable response to the possibility of losing a valued partner.”
The study also carries several caveats. The cross-sectional design means causality cannot be established, and the sample—young university students in relatively new relationships—limits generalisability to older adults or long-married couples. Other potential influences, such as emotional manipulation or abuse, were not measured, and some measures, including a two-question neuroticism scale, had limited reliability. The researchers call for future work to separate passive duty sex—acquiescing to a partner’s request to avoid a fight—from active duty sex, where a person initiates sex to sustain the relationship.
Looking ahead, Dougan suggested that distinguishing between active and passive duty sex could yield important insights into wellbeing and relationship stability, and inform clinical contexts.
The study, “Who Engages in Duty Sex?—Infidelity Concerns and Mate Value Discrepancies,” was authored by F. Sid Dougan, Kate B. Metcalfe, and Cindy M. Meston.
