In natural populations there are almost always differences between population members. For almost any trait there are genetic differences. Furthermore, for most behavioural traits differences in experience during development leads to additional variation at the phenotypic level. Game theoretical models often ignore differences between individuals. In many cases this may not matter, as the solution of the game with no differences may give a good approximation to what evolves when individuals differ. However, there are many cases in which differences are not innocuous noise, but can fundamentally change the nature of a game. I believe this is an important and underexplored topic.
Differences promote the need to have extensive interactions to find out about a partner, so changing the strategy set and hence the outcome of the interaction. These ideas apply to a whole range of phenomena considered by behavioural ecologists and, I believe, render their modelling predictions unrealistic at best. Differences mean that it may be worth taking risks that a partner is cooperative, and can completely reverse the direction of evolution in a simple prisoner’s dilemma game. Differences promote choosiness, and the co-evolution of choosiness and cooperativeness can lead to high levels of cooperation when repeated interactions with the same partner are possible. Finally, differences in personality promote social sensitivity; and once individuals are socially sensitive this changes the selection pressure on those individuals that are observed, and can maintenance personality differences.
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