Evolutionary Explanations of Aggressive Behaviour: Sexual Jealousy and Infidelity

Whilst on the face of it, aggression may not seem like an adaptive
response as to be aggressive runs the risk of serious physical injury
or even death, it must serve some adaptive value as it was present
in our evolutionary past and continues to be present.

One of the reasons most often cited for aggressive behaviour is
sexual jealousy and infidelity. By sexual jealousy we mean being
jealous of the fact that our partner may be having a sexual
relationship with another person. Infidelity is when we are certain
that our partner has cheated on us.

When looking at sexual jealousy and infidelity it becomes clear that there are gender differences in terms of how men and women react in these situations. Men are more likely to be physically aggressive than women when confronted with situations of sexual jealousy and infidelity. 

There is an evolutionary explanation for this gender difference. Remember that the key idea of the evolutionary explanation is that our sole purpose in life is to ensure that our genes are continued and all behaviours we demonstrate serve that purpose.

As females carry their offspring during gestation they can always be 100% that the child is theirs. Men on the other hand have no such guarantee and run the risk of being cuckolded – bringing up another man’s child as their own. This is something they will not want to do according to evolutionary theory as they will want to put all of their energies and resources into ensuring the continuation of their own genes.

Sexual jealousy has therefore evolved to help a man protect the continuation of his genes and to ensure that any investment he is making in offspring will be to his benefit (i.e. to ensure that his genes are successfully passed on). 

There are two types of aggression that a man might show to ensure he is not being cuckolded. On the one hand he may show aggression as a form of ‘mate guarding’. This may take the form of being aggressive to the rival male or being aggressive to his partner (e.g. by threatening her if she sees the other man). 

The second type of aggressive behaviour involves killing the female mate. This may seem counterproductive as by doing this the male is killing off the possibility of this woman helping to pass on his genes. However, by doing this, the man is also ensuring that the woman will not be used to pass on the genes of rival men.

Issues and Debates

A limitation is that this explanation is very deterministic. It states that we are slaves to our biology. It states that men will behave aggressively in response to sexual jealousy and infidelity. This is obviously not always the case. The majority of men have the capacity to stop themselves showing aggression and so demonstrate free will in this respect.

Another limitation is that this explanation is socially sensitive. This is because it seems to legitimise aggressive acts towards women. It sees male aggression towards women as an adaptive response, the implication being that this is a normal behaviour and of no real concern. This is obviously not the case and so this explanation does nothing to highlight and solve the problem of domestic abuse. 

Supporting Research

Daly and Wilson (1982) – They took a sample of 80 murders where
the victim and murderer were married or living together. The
victims were 44 husbands and 36 wives. 29% of the conflicts arose
as a result of sexual jealousy. What is interesting about these
statistics is that they show more husbands murdered by their wives
than vice versa. Evidence from these cases however, points to the fact that the conflict was instigated by the husband and that the wife killed him in self defence.
Why is this relevant? This study can be used as support for the evolutionary explanation of the link between sexual jealousy and aggression as sexual jealousy was the motivating factor behind many of the murders.
Problems with this study…..Nevertheless, it is unlikely that other factors didn’t contribute to the murders such as alcohol, drugs and low socio-economic-status. This means that the evolutionary explanation cannot give a complete answer as to why the aggression occurred. 

Daly and Wilson (1985) – In another study Daly and Wilson looked at 214 cases of murder and found that sexual jealousy was the motivating factor in 58 of the cases.
Why is this relevant? This supports the evolutionary explanation for aggression as it does show that sexual jealousy can lead to an extremely strong aggressive drive.
Problems with this study…..Nevertheless, as with the previous study it should be remembered that factors other than sexual jealousy undoubtedly contributed to the murders. 

Miller (1980) – This study was carried out on 44 battered wives living in a women’s hostel in Ontario, Canada. 55% of the women said that the reason for their husbands aggressive behaviour was jealousy. Actual infidelity on the part of the woman was the reason for the assault in eleven of the cases but the beatings were often motivated by suspicion or fear of adultery.
Why is this relevant? This study shows us that jealousy is a motivating factor for male aggression and so supports the evolutionary theory.
Problems with this study…. This was a limited sample and so generalisations are difficult.

Further Evaluation

A further limitation concerns the fact that the evolutionary approach cannot explain why females sometimes show aggressive behaviour towards their male partners in response to sexual jealousy. The evolutionary explanation would have it that females should not show aggressive behaviour towards their mates as they need them for resources to ensure the survival of their offspring. Nevertheless, females often do show extreme violence and indeed murder in response to sexual jealousy. This explanation can therefore take some of the blame in terms of upholding the misconception that males are never victims of domestic violence.