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”

Background

Natural selection will have made animals that make choices that maximise their fitness. Animals often must decide whether to contest a resource (such as food) with another individual, which often involves a risk of injury or death. However, the gains from winning - such as access to mates - are large so we would expect natural selection to make animals that have as efficient weapons and fighting styles that can best kill opponents. However, we see in nature that animals actually have ritualised fighting that is usually harmless, such as the antler pushing in deer. The accepted explanation was that this ritualised fighting is for the survival of the species, but this does not makes sense, because any individual that decided to kill opponents would win every time, and its genes would quickly spread.

Findings

Game theory can be used to find the ‘evolutionarily stable strategy’ (ESS). A population of individuals using the ESS cannot be 'invaded' by an initially rare mutant adopting any other strategy. A computer simulation was used to find an ESS assuming that every individual tried to maximise its own fitness. These showed that the best behaviour is to have limited aggression with low chance of injuring opponents. ‘Hawks’ that always tries to injure goes extinct, because other animals will avoid fighting and avoid being killed, whereas hawks do not survive long.

Implications

Natural selection on individuals explains why animals rarely try to kill members of their own species, because such super aggressive animals would get injured, whereas more limited fighting wins in the long run. Animals can gradually escalate contests which enables them to work out which one is likely to win if the fight became dangerous. In deer, the males do lots of posturing and bellowing before even locking horns, because this enables all individuals to avoid pointless and dangerous fights.

Subject

Behavioural ecology


Subject Group

Zoology and Ecology


Keywords

game theory

ESS

Prisoner's dilemma

fighting

sexual selection


Posted by

AndrewDHigginson

on Fri Oct 27 2017


Article ID

FKSUH25NZ


Details of original research article:

Maynard Smith J, Price GR. The logic of animal conflict. . Nature . 1973;246: 15-18.

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