Sperm Competition

Sperm competition is a form of intrasexual competition in which the sperm of two or more males concurrently occupy the reproductive tract of a single female and compete to fertilize an available ovum. As a nonmonogamous species, humans have been subject to selection pressures associated with sperm competition. Consequently, human males have evolved a variety of anatomical, physiological, and psychological adaptations to address associated adaptive problems. Some of these adaptations motivate avoidance of sperm competition by engaging in precopulatory intrasexual competition, which may limit the risk of exposure to sperm competition. Other adaptations promote engagement in sperm competition during copulation or postcopulation and function not by avoiding sperm competition but by increasing the likelihood of winning the competition and siring offspring. For example, men facing a perceived increase in risk of sperm competition are more likely to demonstrate an increased interest in sex with their long-term partner. We summarize previous research on adaptations to sperm competition in humans, and highlight several directions for future research.