Sperm Competition in Humans: Mate Guarding Behavior Negatively Correlates with Ejaculate Quality
Sperm competition - Wikipedia
Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg  during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase males' chance of reproductive success. Sperm competition is often compared to having tickets in a raffle ; a male has a better chance of winning i.
Performed the experiments: SL. The authors confirm that all data underlying the findings are fully available without restriction. In species where females mate with multiple males, the sperm from these males must compete to fertilise available ova. Sexual selection from sperm competition is expected to favor opposing adaptations in males that function either in the avoidance of sperm competition by guarding females from rival males or in the engagement in sperm competition by increased expenditure on the ejaculate.
Sperm competition is a form of post-copulatory sexual selection  whereby male ejaculates simultaneously physically compete to fertilize a single ovum. Physiological evidence, including testis size relative to body weight and the volume of sperm in ejaculations, suggests that humans have experienced a low-to-intermediate level of selection pressure for sperm competition in our evolutionary history. Evidence suggests that, among the great apes, relative testis size is associated with the breeding system of each primate species. The volume of sperm in ejaculates scales proportionately with testis size and, consistent with the intermediate weight of human males testis, ejaculate volume is also intermediate between primates with high and low levels of sperm competition. Researchers have suggested that males produce more and higher quality sperm after spending time apart from their partners, implying that males are responding to an increased risk of sperm competition,  although this view has been challenged in recent years.