Human Sperm Competition: Playing a Defensive Strategy

Sperm competition is the competition between the sperm of two or more males to fertilize the ova of a single female. Over the past few decades, the extent to which sperm competition has acted as a selective pressure throughout human evolution has been hotly contested. This review aims to assess the current evidence for sperm competition in humans, the limitations of that evidence, and directions for future research. We conclude that humans have primarily evolved defensive adaptations in response to the risk of sperm competition. Thus, men exhibit behaviors that anticipate and address their partner's infidelity, the success of which may have relaxed selection on physiological and morphological adaptations to tackle sperm competition offensively. However, the extent to which humans can perform offensive tactics has been sorely understudied and requires considerable further research before firm conclusions can be drawn. © 2014 Elsevier Inc.