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Sexual Coercion
Sexual coercion is forcing mate choice against a partner’s will or preference. Sexual coercion functions to increase the chance of a female mating with a male, and decrease the chance that the female will mate with another male. There are several strategies by which sexual coercion can be achieved. These are harassment, intimidation, and forced copulation (rape).

Thornhill and Palmer’s A Natural History of Rape investigates the evolutionary causes of sexual coercion, particularly of rape, and suggest that such behaviour is a result of sexual selection, rather than Darwinian natural selection. Of 10 hypotheses, they produced two reasonable hypotheses. The first, that rape is a by-product of an adaptation other than rape. The second, that rape as an adaptation (the rape specific adaptation hypothesis), which suggests that rape evolved because it was an adaptive, beneficial behaviour in the environment of evolutionary adaptation.

The 'rape as a by-product' explanation holds that rape behaviour evolved as a by-product of other psychological adaptations in men to obtain many mates. This adaptation not only leads to rape but a number of other behaviours including overrating female sexual interest, a desire for sexual variety, coercion, and sexual arousal which is not dependent on the consent of mate.

The rape specific adaptation hypothesis suggests that rape is an evolved behaviour because it provides direct benefits to the rapist. In this case, the benefit would be a higher chance of reproductive success through increasing mate number. This theory suggests that rape by a man which offers no chance of reproductive success, i.e. the rape of any other person who is not a female of reproductive age, is a maladaptive byproduct of this evolutionary adaptation.

Support for the idea that rape provides males with a way to increase their reproductive success comes from a study by Barbaro and Shackelford, who found that men in committed heterosexual relationships who had committed at least one act of violence/coercion towards their partner in the last month had more in-pair copulations per week.

One of Thornhill and Palmer's rejected hypotheses for why men rape implicates violent pornography. Subscribers to the social science theory of rape purport that one of the main reasons why the human male learns to rape is via learning imitative behaviour when watching violent pornography. However, this fails to explain why if males are likely to imitate behaviour witnessed in violent pornography they would not also imitate the actions of human males in other videos. Furthermore, no explanation is offered into why this behaviour is inspired in some men and not others. It is also limited in its ability to predict valuable variables surrounding why rape occurs (such as who, when or where). For this reason, Thornhill and Palmer argued that “although the removal of violent pornography may be desirable in its own right, it is very unlikely to solve the problem of rape”.

Another of their rejected hypotheses is the 'choosing victim' rape-adaptation hypothesis which suggests that there is an evolved victim-preference mechanism to maximise the reproductive benefits of rape. This hypothesis suggests that men would be most likely to rape reproductive-age females. Research shows that the age of US rape victims correlates slightly better with age of peak fertility than age of peak reproductive potential. However, this explanation does not explain the rape of those with no chance of reproductive success e.g. girls, boys, males and post-menopausal women.

Another hypothesis rejected by Thornhill and Palmer is often referred to as the ‘mate-deprivation hypothesis’, which alludes to the concept that the threshold for rape is lowered in males that lack alternative reproductive options. This idea is supported by the fact that rape is disproportionately committed by men with a lower socioeconomic status. However, Malamuth found a relationship between low socioeconomic status and a rearing environment in which social relationships were not committed, which in turn resulted in a male’s reduced ability to form enduring relationships in later life. This subsequently results in less alternative reproductive options. Therefore, while there is indeed a relationship between a lack of alternative reproductive options and rape behaviour, there are likely to be a number of co-morbid factors affecting this correlation, leading Thornhill and Palmer to conclude that further research need be conducted.

Naturalistic Fallacy
The naturalistic fallacy is the idea that what is natural and evolved is morally correct, but scientists in this field are keen to reiterate that this is certainly not the case. Whilst rape and sexual coercion are natural and evolved behaviours which provided benefits to humans in the environment of evolutionary adaptation, they are not morally sound behaviours in modern civilisation.

Expected Paternal Investment
Elizabeth Cashdan proposed that mate strategies among both genders differ depending on how much parental investment is expected of the male, and provided research support for her hypotheses. When men expect to have to provide a high level of parental investment, they will attempt to attract females by emphasising their ability to invest. In addition, men who expect to invest will be more likely to highlight their chastity and fidelity than men who expect not to invest. Men with the expectation of low parental investment will flaunt their sexuality to females. The author argues the fact the research supports the idea that men expecting to invest emphasise their chastity and fidelity, which is a high cost strategy (because it lowers reproductive opportunities), suggests that that type of behaviour must be beneficial, or the behaviour would not have been selected.

Early Childhood Experiences
A relationship between the early experiences and environment of boys, and their later sexual behaviour, has been drawn by several studies. Research suggests that father absence can lead to an increase in rape behaviour. Research conducted by Malamuth found that men raised in the absence of their father (or where resources were scarce) reported more use of sexual coercion in the past, and were more likely to indicate being more willing to rape, in the event that there was no chance of them getting caught. Research has also found that parental divorce and rape correlate positively.