Infidelity will have a clear effect on a relationship and evolutionary psychologists argue that it triggers an emotional state within an individual as it is a perceived threat to the relationship. Buss et al (1992) argue that this naturally leads to the showing of any behaviour which would reduce or eliminate the threat. This could include aggressive or violent behaviour. According to Cascardi and Vivian (1995), when asking participants to explain aggression, jealousy is the most commonly attributed cause.
To support this, Canary et al (1998) argue that couples with relationship problems commonly reported that anger and jealousy was contributed to aggression. Whilst it could be considered that jealously and anger are socially learnt emotions (supporting the nurture viewpoint of the nature v nurture debate) equally they can be directly associated to evolutionary perspectives such as parental uncertainty. Brunk et al (1996) suggest that for the male infidelity brings both intense sexual jealousy and uncertainty of paternity.
However for the female who becomes pregnant after an act of infidelity, the associated sexual jealousy is influenced by the lack of time, support and economic resources that are given to her offspring by her mate. For both males and females, infidelity can be adaptive. For a male, additional sexual partners increase reproductive success. For a female, mating with another male with better genes than her current mate can lead to an improvement to the quality of her offspring. Most significantly, males appear to be more aggressive when presented with the threat of paternity uncertainty, particularly as fertilisation in humans is internal.
In terms of reproductive success, infidelity is more threatening to a male than a female (whose offspring will definitely carry her genes). This provides further explanation for guarding behaviours, which may also involve aggression or violence. Daly and Wilson (1996) note how men from different cultures have developed ways in which to increase paternal certainty, by restricting other men from getting close to their females. For example, female circumcision, infibulations and women having to wear vales in some Muslim countries, and not being allowed to travel without a male.
Some cultures even practise violent ‘punishment’ for adultery, like being stoned to death. Furthermore, the threat of sexual infidelity will trigger sexual jealousy for both males and females but evolutionary psychologists argue that these cues are different for both genders, as mirrored through ethology. Here, jealousy is considered as the desire to keep one’s mate to permit the continuation of genes. Males show guarding activities which may include showing aggressive tendencies (Buss and Shackelford, 1997) whereas females show these behaviours less frequently.
In two separate studies of partner rivalry, Haden and Hojjat (2006) noted that men were more likely to consider aggressive action against the rival whereas women tended to be more behaviourally and emotionally reactive. There appears to be further evidence that men and women interpret and perceive infidelity in different ways. If we accept evolutionary arguments it would see that jealousy would be stronger in males than in females, due to paternity uncertainty. This has been supported by Daly and Wilson (1988) who compared the motives of men and women who had killed their partners in Canada.
Whilst this research might be criticised for being ethnocentric, due to it gathering data in one Western country, it also holds significant validity in that that it permits a long-term pattern to be considered through a longitudinal study over nine years. Through data collected on spousal homicides the key results strongly highlight the differences between the aggressive tendencies of men and women in response to threats to their relationships. Most notably, there were 812 cases of a husband killing his wife, compared to 248 cases of the wife killing husband.
Jealousy was cited as the motive by 24% of the husbands, in comparison to 7. 7% of females. From a deterministic viewpoint it could be argued that these results underline that even in modern times males are much more pre-disposed to aggression, regardless of social influence that may have nurtured non-aggressive responses. By way of conclusion it is important to note the complexity of understanding human behaviour and its many influences. When considering a widespread behaviour such as aggression, in many areas of human existence there appears to be no direct need for this behaviour.
In other words, in many areas of the world there is no need to still hunt or defend territory as there would have historically been. However, from an evolutionary approach (supported strongly be the biological approach), it is clear that mankind is clearly unable to exist without aggression and violence, suggesting strong support for the nature perspective. Here, evolutionary psychologists conclude that the adaptive and functional benefits of aggressive behaviour must outweigh the possible costs (Buss and Duntley, 2006).
Equally, this approach can be criticised for failing to acknowledge the powerful effects of social influence. Social-psychological approaches place entire emphasis on aggression being a learnt behaviour (such as through social learning theory) or through adapting in social situations (as explained by deindividuation theory). Therefore, a less biologically reductionist approach would have to explain behaviour with the notion that humans (and particularly males) may be more pre-disposed to aggression, yet our social context is critical in determine whether that pre-disposition translates into actual, physical aggression.