Sperm competition is "competition between sperm of two or more males for the fertilisation of an ova" (Parker 1970). Sperm competition is often compared to having tickets in a raffle; a male has a better chance of winning (i.e. fathering offspring) the more tickets he has (i.e. the more sperm he inseminates a female with). However, sperm are costly to produce and the energy may be spent elsewhere such as defending a territory to the exclusion of other males; these are called strategies. The optimum amount is the evolutionarily stable strategy (ESS).

Sperm competition may lead to evolutionary adaptations for producing more sperm, such as larger testes. Such adaptations cost and so species with low sperm competition invest in mate competition instead.

In primates Harcourt et al (1981) studied the relative size of testes compared to body mass against the mating system. They found that promiscuous chimpanzees have larger testes compared to polygynous gorillas.

The British biologist Geoffrey Parker proposed the concept of sperm competition in a 1970 paper.

References

• Baker, Robin 1996. "Sperm Wars: The Science of Sex"
• Harcourt, A.H., Harvey, P.H., Larson, S.G., and Short, R.V. 1981. "Testis weight, body weight and breeding system in primates", Nature 293: 55–57.
• Parker, G.A. 1970. "Sperm competition and its evolutionary consequences in the insects", Biological Reviews 45: 525-567.
• Simmons, Leigh W. (2001) "Sperm competition and its evolutionary consequences in the insects" Princeton University Press, ISBN 0-691-05988-8 and ISBN 0-691-05987-X