Extra-pair copulations

Extra-pair copulation (EPC) is a promiscuous mating behaviour in monogamous species. Monogamy occurs when one male mates exclusively with one female, forming a long term bond and combining efforts to raise offspring together; extra-pair copulation occurs when one of these individuals mates outside of this pairing. Across the animal kingdom, extra-pair copulation is common in monogamous species, and only a very few pair-bonded species are thought to be exclusively sexually monogamous. EPC in the animal kingdom has mostly been studied in birds and mammals. Possible benefits of EPC can be investigated within non-human species, such as birds. In males, a number of theories are proposed to explain extra-pair copulations. One such hypothesis is that males maximise their reproductive success by copulating with as many females as possible outside of a pair bond relationship because their parental investment is lower, meaning they can copulate and leave the female with minimum risk to themselves. Females, on the other hand, have to invest a lot more in their offspring; extra-pair copulations produce a greater cost because they put the resources that their mate can offer at risk by copulating outside the relationship. Despite this, females do seek out extra pair copulations, and, because of the risk, there is more debate about the evolutionary benefits for females.

Extra-pair copulation in men has been explained as being partly due to parental investment. Research has suggested that copulation poses more of a risk to future investment for women, as they have the potential of becoming pregnant, and consequently require a large parental investment of the gestation period, and then further rearing of the offspring. Contrastingly, men are able to copulate and then abandon their mate as there is no risk of pregnancy for themselves, meaning there is a smaller risk of parental investment in any possible offspring. It has been suggested that, due to having such low parental investment, it is evolutionarily adaptive for men to copulate with as many women as possible, as it will allow them to spread their genes with little risk of future investment. This may therefore lead to more extra-pair copulation in men, as they are able to copulate with other women without the consequences of having to rear new offspring.

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