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Evolutionary explanations of human aggression
Jealousy and infidelity

How can evolutionary pressures and natural selection explain human aggression?

Are men hard-wired to be jealous?

How does gene survival explain aggressive acts such as domestic violence and uxoricide?

The evolution of human aggression
Evolutionary psychologists argue that reproductive challenges faced by our ancestors can explain the aggressive behaviour seen in people today. A man can never be certain that he is the father of his wife’s children unless he prevents her having relationships with other men. This can explain why male sexual jealousy is often cited as a cause of domestic violence. In many countries it is seen as acceptable to murder an adulterous wife or her lover, e.g. among the Nuer people of East Africa, a man who commits adultery is likely to be killed by his lover’s husband, and only 35 years ago in the USA a man who killed his wife’s lover while in the act would have a legal excuse for murder and be unpunished.

Infidelity and Jealousy
According to Daly & Wilson (1988), men have evolved different strategies to deter their partners from committing adultery, ranging from vigilance (watching their every move – e.g. asking who they talk to on the phone, stopping them going out with friends, reading texts etc) to violence. All of these are the result of male jealousy and paternal uncertainty (being unable to be certain he is the father of her children).

If a man’s partner is unfaithful and has a relationship with another man, he runs the risk of cuckoldry (that he may unwittingly invest resources in rearing children that are not his own). Male sexual jealousy may therefore have evolved to prevent infidelity by women and reduce the risk of cuckoldry.
Evolutionary causes of human aggression and domestic violence

Buss (1988) argues that males have developed strategies for mate retention. These include direct guarding (restricting her movements) of the female and negative inducements to prevent her straying (financial control, threat of violence if they are unfaithful or even so much as look at another man, etc).

Wilson et al (1995) found support for the link between sexual jealousy, mate retention and violence. In a questionnaire, women who indicated that their partners were jealous and did not like them talking to other men were twice as likely to have experienced violence from their partners (72% of these needing medical attention).

Shackleton et al (2005) also demonstrated the link between mate retention, jealousy and violence. They surveyed 461 men and 560 women who were all in committed heterosexual relationships. The men answered questions about their use of mate retention techniques, and the women were asked about their partners’ use of mate retention techniques and how violent their male partners were. There was a positive correlation found between men who used mate retention techniques of direct guarding and negative inducements and their use of violence. Men also tended to use emotional manipulation as a mate retention technique. The women’s results confirmed this as there was also a positive correlation between those that had jealous partners and being the victims of violence.

Evolutionary causes of human aggression and domestic violence
If men can prevent female infidelity by giving their partners positive benefits to stay then they are less likely to be violent, but men who are unable to provide positive benefits are more likely to become jealous and violent leading, according to Daly & Wilson (1988), to the unintended killing of the woman (uxorocide – wife killing). However the unintentional nature of uxoricide is challenged by Shackleford et al (2000). They analysed 13,670 uxorocides and found that younger women were most at risk which, as the women were in their reproductive prime, presents a problem for them being unintentionally killed. A better explanation (The Evolved Homicide Module Theory; Duntley & Buss, 2005) might be that when a woman is unfaithful, not only does the man lose a partner, but another man also gains a partner. By killing his partner the man at least prevents his competitor gaining a reproductive advantage over him.

An important implication of research into sexual jealousy and violence is that mate retention techniques (e.g. direct guarding and negative inducements) can be the early signs of a violent man. Educating people in these danger signs can reduce the likelihood of women becoming victims of violence.

The Evolution of Male on Male Homicide
Homicide (murder) is the most extreme form of aggression. The vast majority of murderers and their victims are men (Buss & Shackleford, 1997).

A disproportionate percentage (relative to the normal population) of male murderers and male victims are unemployed and unmarried – a Detroit study found that 43% of victims and 41% of murderers were unemployed even though the population unemployment rates were only 11%. Also 73% of male murderers and 69% of male victims were unmarried. This suggests a lack of resources (unemployment leads to less money, less food, poorer housing etc) and the inability to have a long-term relationship lead to increased social competition and men murdering men.

Another reason that men kill men is to defend their status in a peer group. In our evolutionary past, loss of status could be harmful for survival and reproduction. Even though status is largely irrelevant for survival nowadays, it is an evolved behaviour that is passed on genetically.

Sexual jealousy is a further motivator in male-male homicide. A meta-analysis of 8 studies of same-sex killings involving love triangles found that 92% were male-male and only 8% were female-female (Daly & Wilson, 1988).

If, as is suggested above, homicide is an evolved behaviour then it is very likely that the ability to defend against murder has also evolved, such as being able to read the signs of homicidal intent. This would make homicide a very risky and dangerous behaviour to engage in (Duntley & Buss, 2004), and so it is likely that selection favours the ability of people to deceive others, e.g. the ability to hide homicidal intent from an intended victim.

Also, if homicide has evolved then we would expect all people to behave in a similar way, however 3 different people may react to the same situation in 3 different ways – e.g. one may beat his unfaithful wife, the second may murder her, and the third may just get drunk. And evolution cannot explain why some cultures require violence to attain social status, whereas in others it leads to irreparable reputational damage (Buss & Shackleford, 1997).

Issues debates and approaches (IDA) for evolutionary displays of human aggression
Much research makes use of questionnaires and surveys to collect data
Surveys are a self report method and therefore has inherent difficulties with collecting reliable and valid data. If a man is asked to complete a questionnaire asking how violent he is towards his partner, then it is most likely that he will distort the truth due to his desire to appear more socially desirable than he actually is (social desirability bias). Similarly, a woman may be less likely to accurately report her partner as abusive if she fears recriminations from him, or she may even choose to deny the truth about his behaviour because acknowledging it could mean the end of her relationship with him. Questionnaires and surveys may not therefore reveal the true extent and nature of male jealousy.

Research into infidelity is gender biased
The evolutionary argument for infidelity states that it is something a man must prevent a woman from doing, and does not really acknowledge the fact that men may be just as unfaithful as women. This is heavily gender biased and does not reveal the true nature of male and female infidelity.

Nature nurture debate
Evolutionary explanations argue that behaviour has evolved through gene selection and is therefore biological. If jealousy and uxoricide were really evolved responses to female infidelity and determined by genes, then we would expect all men to behave violently to women, but clearly they do not. There must, therefore, be an alternative explanation that takes into account the fact that men may have naturally aggressive responses to female infidelity, but that also explains why many men do not behave violently and others do. Social learning theory may account for this as violent men may have grown up with violent role models, and have learned to be violent by observing them.

A Level exam tips
Answering exam questions (PSYA3 AQA A specification)
Outline and evaluate research into sexual jealousy as a cause of human aggression (24 marks)
8 AO1 marks come from outlining the evolutionary debate in terms of men never being able to be certain that they are the father of a child, and needing to ensure that they are not subject to cuckoldry. Outline male behaviours to control women. Outline uxoricide as an accidental killing when control has gone too far. Also explain that men may kill other men because of social competition including competition for a mate.

16 AO2 marks come from evaluating and discussing the research. Describe studies supporting the argument that men need to control women and the sort of behaviours they use to do so. Illustrate the link between male jealousy, mate retention and violence using research studies (e.g. Shackleton et al). Discuss the alternative argument to the accidental nature of uxoricide and state why it may be an intentional act. Discuss the problem for the evolutionary argument in that not all men act the same way in the same situation. Remember to build in synoptic links including the problem with questionnaire and survey research, and the gender biased nature of research into infidelity.