Sperm competition in humans

Try out PMC Labs and tell us what you think. Learn More. 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.
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Human sperm competition

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Sperm Competition in Humans: Mate Guarding Behavior Negatively Correlates with Ejaculate Quality

William F. McKibbin, Michael N. Pham, Todd K. Sperm competition theory has been used to generate the hypothesis that men prefer to view pornographic images suggesting the presence of a rival male, over images which do not. Raters coded a random sample of pornographic DVDs from a population of 49 , which were then analyzed using multiple regression. Consistent with the hypothesis generated from sperm competition theory, the number of images on a DVD cover and screenshots depicting 2 or more men interacting with 1 woman suggesting the presence of sperm competition predicts DVD sales rank, whereas the number of images on a DVD cover and screenshots depicting 2 or more women interacting with 1 man suggesting the absence of sperm competition does not predict DVD sales rank. Discussion addresses limitations and future directions, including using penile plethysmography to avoid relying on correlational analyses.
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Sperm Competition in Humans: Mate Guarding Behavior Negatively Correlates with Ejaculate Quality

Sperm competition is a form of post-copulatory sexual selection [1] whereby male ejaculates simultaneously physically compete to fertilize a single ovum. Sperm competition is not exclusive to humans, and has been studied extensively in other primates, [5] [8] [9] as well as throughout much of the animal kingdom. 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.
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In the context of sexual reproduction, natural selection is generally thought of as a pre-copulation mechanism. We are drawn to features of the human body that tell us our partner is healthy and will provide us a fighting opportunity to carry on our genetic lineage. But a new article appearing in the February issue of Current Directions in Psychological Science suggests that the human male has evolved mechanisms to pass on his genes during post-copulation as well, a phenomenon dubbed "sperm competition. In their article, Todd Shackelford and Aaron Getz at Florida Atlantic University describe sperm competition as "the inevitable consequence of males competing for fertilizations.
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