Interests - theory

Theoretical biology has played a central role in our understanding of the evolution of cooperation. Most famously, W.D. Hamilton (1964) developed inclusive fitness (or kin selection) theory that showed how altruism can be evolutionarily advantageous when it is directed at relatives that share an actor' genes. Since then, a vast body of theory has been developed that delves ever deeper in the problem of cooperation in biological systems. Nevertheless, the basic principles identified by Hamilton and his contemporaries hold true and kin selection theory remains the key explanation for altruism and indeed cooperation in general (Foster et al. 2006). That said, there are now several complementary approaches that each bring their own insights to the question of how and when cooperation will evolve, most notably, multi-level or group selection theory. Our work has focused upon two key areas: the tragedy of the commons and the evolution of between-species mutualisms.

The tragedy of the commons

This expression made famous by Garret Hardin (1968) captures the essence of the problem of cooperation. The phrase refers to common land to which many people have rights. Every herdsman knows that putting too many cows upon a pasture will eventually destroy it by overgrazing. However, when pastures are a shared commons, the benefit of adding a cow goes entirely to the owner (the individual) but all herders share the cost (society). The rational solution for an individual is to keep adding cows, even though this leads to the deterioration and possible collapse of the pasture at a large cost for all. Similarly, simple evolutionary models predict that strong selection for competition and selfishness in social groups will cause the collapse of cooperation.

Understanding what solves the tragedy of the commons is closely linked to understanding the evolution of cooperation. But they are not identical questions. In the former, the focus is on whether an individual will perform a particular behaviour (adding a cow) while the latter is concerned with the effect of cooperation and conflict on overall group success (the state of the pasture). Kevin developed a way of thinking about the latter problem using multi-level selection models, which divide the world up into "individual" and "group effects". The trick is then to use the evolved group performance as a measure of the severity of tragedy. Applying this logic to the evolution of social groups shows that diminishing returns reduce tragedy (Foster 2004). It also brings new insight to the crisis of antibiotic overuse in our own societies (Foster and Grundmann 2006). Finally, one can also show that the tragedy of the commons may be weaker in nature than expected by simple microevolutionary models but considering the effects of conflict on extinction. That is, if conflict ridden species are more likely to go extinct than cooperative ones, over evolutionary time we can expect to see cooperation enriched through species-level selection (Rankin et al. 2007)

The evolution of mutualism

Compared to the study of within species cooperation, there has been little work on the evolution of cooperation between species. Particularly, we lack any general theory for the evolution of mutualisms that bears anything like the generality obtained through the work of Hamilton (1964) and others. We developed a simple and general model of mutualisms by extending Hamilton’s rule (1964) using the techniques of Frank (1998). This captures three main feedbacks benefits that favour mutualism (Foster and Wenseleers 2006). First, being mutualistic may mean that an individual tends to associate with the more cooperative genotypes of the other species (cooperator association). Second, when mutualism improves the fitness of a partner species, this may improve it phenotypic ability to return aid (partner-fidelity feedback). Finally, the partner species may have a specific behavioural adaptation that preferentially directs aid to more mutualistic individuals (partner choice). Recently, with Hanna Kokko, this has been extended with a more specific model that investigates the coevolution of partner choice and cooperation in mutualisms (Foster and Kokko 2006).

Spiteful behaviour

As part of Kevin's thesis work with Francis Ratnieks and Tom Wenseleers, he became interested in the evolution of spite. By going back to the original evolutionary definitions of spite from Hamilton and E.O. Wilson, they were able to show that spite is frequently misused as a term, but also that some social insects examples fit the original definitions of spiteful behaviour (Foster et al. 2000, 2001).