Sperm competition in marriage: Semen displacement, male rivals, and spousal discrepancy in sexual interest

Abstract

Non-human males attend to the presence of potential sexual rivals in the local environment to assess sperm competition risk, and adjust accordingly the deployment of sperm competition tactics (e.g., performing semen-displacing copulatory behaviors). We extend this research to humans using data from 45 married couples who completed questionnaires in a laboratory. We found that husbands whose wife spent more time with her male coworkers and male friends (i.e., potential sexual rivals) performed more semen-displacing copulatory behaviors at the couple's most recent copulation. We also found that performance of semen-displacing copulatory behaviors correlated with a novel cue to sperm competition risk: the discrepancy between the husband's sexual interest in his wife and her sexual interest in him. We also tested and refuted an alternative hypothesis that men adjust their copulatory thrusting to facilitate their partner's orgasm. Discussion highlights the novel contributions of the current research and notes limitations that can be addressed by future research.