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May 24, 2005

Altruistic punishment

Dienekes recently drew attention to an important forthcoming article on altruistic punishment. The article has now appeared: James H. Fowler: Altruistic punishment and the origin of cooperation, Proc. National Academy of Sciences, May 10 2005, vol. 102, 7027-49. It is available as a free pdf download here.

So what is altruistic punishment and why is it important?

One of the central problems of human evolution is to explain the widespread existence of cooperation. Such cooperation often produces a benefit for social groups as a whole, but at a cost to the cooperating individuals. So there is an advantage for ‘free-riders’ who take the benefits but avoid the costs. Why then does cooperation not break down?

The problem can obviously be solved if free-riders are punished. But those who do the punishing incur a cost in doing so (e.g. the risk of retaliation), greater than their individual gain, hence the term ‘altruistic punishment’. So why should anyone punish?

Again there is an obvious solution if failure to punish is itself punished. We can avoid an infinite regress of special rules about punishment by adopting a general social rule to the effect ‘punish all breaches of social rules’. Since this is itself a social rule, failure to punish is also a breach of a social rule, which must therefore be punished, and so on.

Such a rule is an evolutionarily stable strategy provided a large enough proportion of the population are already following it. But it is difficult to see how the rule could become established in the first place. Several theorists have resorted to an explanation by group selection: in small groups a large proportion of ‘punishers’ may be established by chance, and these groups then spread at the expense of other groups.

Group selection should be regarded as an explanatory last resort. The importance of Fowler’s paper is that it provides an alternative explanation of altruistic punishment based on individual selection. If the only strategies allowed are ‘cooperate’, ‘free ride’, and ‘cooperate and punish’, then ‘cooperate and punish’ will be more costly than the alternatives when it is rare, and it cannot spread by individual selection. The crucial feature of Fowler’s model is that it allows another strategy: individuals can opt out of group activities when the benefit of cooperation is lower than that of individual activity. If there are too many free-riders, more individuals will opt out and ‘do their own thing’. But when most of the population have opted out, the strategy of ‘cooperate and punish’ may have an advantage over ‘opt out’, which allows it to spread even when it is rare. The strategy ‘cooperate’ (but not punish) will spread more quickly at first, but once ‘cooperate and punish’ has passed a certain critical frequency (which depends on the parameters) it gains over ‘cooperate’ until it becomes the prevalent strategy. So ‘cooperate and punish’ cannot spread when it is rare in a population consisting only of ‘cooperators’ and ‘free-riders’, but the existence of the ‘opt-out’ strategy gives it an entry point.

Fowler considers a number of possible objections to his model. I am not sure that the model is very plausible, but it is no worse in this respect than the group-selectionist alternatives. It does at least mean that the groupies can no longer claim there is no alternative.

Personally I think that both approaches are misconceived. The basic flaw is encapsulated in the first sentence of Fowler’s paper: ‘Human beings frequently cooperate with genetically unrelated strangers whom they will never meet again, even when such cooperation is individually costly’.

Well, no, they don’t. Even in modern, well-regulated societies such cooperation is unusual. (When did you last do it?) In hunter-gather societies, which prevailed for most of human evolutionary history, it is practically unknown. But I will expand on my objections in another post.

Posted by David B at 11:56 AM