Understanding the interactions between individual animals requires appreciating that they have flexible responses to each other, rather than have fixed behaviour


The foundation of our understanding of how animals interact is evolutionary game theory, which uses game theory to predict the outcome of natural selection on animal behaviour. When animals interact their fitness (e.g. number of offspring) often depends on the behaviour of others, so their own behaviour should change if other’s behaviour changes. For example, parent birds can reduce their feeding effort if their partner puts in more effort. These interactions are usually studied by assuming that each individuals chooses a single action that depend on the single action of its partner. However, this is unrealistic, because animals often have the opportunity to respond to each other in real time, and so can ‘negotiate’ how much each does.


Studies using evolutionary games should assume instead that animals have a sequence of interactions in which the partners negotiate the final outcomes. This is because natural selection will not lead to fixed decisions, but to good rules for negotiating. This rule is the best rule given the rule of the other individuals. For example, parent birds may instinctively respond to how much feeding their partner does. This should happen provided there is some variation among individuals of population, no matter how small the variation is, as it will be worth responding if the partner is putting in less effort.


The behaviour we predict that we will see can be very different if we assume rules rather than fixed decisions. This suggests that previous evolutionary game theory models will make predictions that are not supported by the evidence. Future models of interactions between individuals should instead take the flexibility of real animals into account.


Behavioural ecology

Subject Group

Zoology and Ecology





game theory

flexible behaviour

Posted by


on Fri Oct 27 2017

Article ID


Details of original research article:

McNamara JM, Gasson CE, Houston AI. Incorporating rules for responding into evolutionary games. Nature. 1999;401:368-371.

Preceded by:

Conflicts between animals are usually settled without injury, but such ritualised harmless fighting has evolved because it is good for individuals, not for the “survival of the species”

Posted by: AndrewDHigginson Posted Fri Oct 27 2017

Followed by:

Cooperation evolves readily if individuals can walk away from uncooperative partners

Posted by: AndrewDHigginson Posted Fri Jun 26 2020

Skills —— one of the important factors determining fighting ability

Posted by: AndrewDHigginson Posted Tue Mar 17 2020


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