Is aggression adaptive?

Sticking with the aggression theme from my last post on bullying, I’ve just read an early-view article in Aggressive Behavior by some evolutionary psychologists at Binghamton University which is theoretically very interesting. Gallup, O’Brien and Wilson show that aggression in adolescents appears to be positively correlated with dating success. Based on interviewing college students about both their dating history and their histories of aggressing against or being victimised by same-sex peers, their key findings are as follows:

  • Indirectly aggressive females started dating earlier
  • Aggressive males had more dating partners in total
  • Victimised females started dating later, had more partners in total, and engaged in less flirtation with males

I think this is a really good example of both a great strength and a great weakness of evolutionary psychological studies. The strength is to relate areas of human behaviour that had previously been kept in separate research compartments – in this case, intrasexual aggression and dating behaviour – and provide a sound theoretical rationale for why they are related. The idea here is that aggression against same-sex peers is linked to dating success because adolescents are engaged in a form of reputational competition to determine access to mates. Young men use direct aggressive strategies to display dominance, thus making themselves more sexually attractive to women, whereas young women use indirect aggression to derogate rivals, thus making the latter less likely to form lasting, successful partnerships with men. If this idea is true, it obviously has far-reaching implications for many areas of social behaviour.

Furthermore, if this research project linking aggression and dating strategies had not been done, we would not have seen the intriguing result that victimised females tend to lose out in the dating game, whereas victimised males do not (the authors had predicted that neither sex would do well if victimised). This does look like the sort of result that might vary according to the social context (as many gender effects do), but it would certainly be worth testing whether it applies to other populations – it would get us thinking about when victimisation has serious reputational consequences, and when the consequences may be less severe.

But the big weakness here, I think, is that Gallup and colleagues move a little too easily from observations of aggression to the implications for mating success, without enough consideration of the mediating variables. This is a common flaw of this kind of evolutionary study, which tends to get people tearing their hair out about how evolutionary psychologists obsess about sex and ignore the complexities of human behaviour. It’s also a well-known problem with correlational studies: if you find that A correlates with B, it really tells you very little about causality; even if one thinks that it is plausible for A to cause B but not for B to cause A, one can never really be sure that both A and B are not caused by some unknown variable C.

To be fair, the authors do mention some possible mediating variables in the Discussion section. For example, victimisation may decrease dating success in females by decreasing self-esteem as well as by diminishing reputations directly. They also point out that at a lower level, high levels of testosterone in men may increase their aggressiveness at the same time as making them more attractive to women. But why not include such mediating variables in the research design? Testosterone might be tricky, but there must be a multitude of instruments for measuring self-esteem. And there is one really obvious mediating variable which the authors don’t make enough of: popularity. I would bet money that popularity among same-sex peers correlates strongly with dating success – and surprisingly, perhaps, research has shown that aggressive children can actually be quite popular; Gallup and co. cite an article by Patricia Hawley arguing that the most popular kids are those who can be either aggressive or prosocial, as the situation demands.

Like self-esteem, popularity could have been measured very easily, even in retrospect – e.g. by asking participants how many friends they had at school. Popularity in turn would correlate with social competence: and since both dating and facing up to bullies are social activities, it is not surprising that people who are low in social competence might have problems with both. Perhaps the authors’ defence for ignoring such variables in the research design is that evolutionary psychology is concerned with the ultimal level of causation (the effects on selection of particular behaviours) rather than the proximal level (the mechanisms which generate particular behaviours in the individual organism). But if evolutionary psychology is to convince the mainstream, it needs to find some way of relating these two levels.

So how would I do this sort of research differently? Well, above all I would argue that a developmental perspective is essential. Relating peer aggression directly to reproductive outcomes is short-sighted, because humans aggress against peers long before they reach reproductive age: as I know from my own research on tattling, preschool classrooms are filled with conflict and structured by well-defined dominance hierarchies. The really interesting thing about aggression in adolescence is the way that it changes from earlier patterns, due to hormonal and social changes (in particular, a greater identification with the peer group and a withdrawal from adult authority) – presumably in response to the pressure of having to develop potential sexual relationships with members of the other sex. There is plenty of scope for evolutionary hypotheses in this area, but they should start from a basis of what is known about aggression in childhood, and how this is then transformed by the changes that kids undergo in adolescence.

On the whole though, a fascinating article, and more subtle than many evolutionary approaches.

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