BIO150Y: Evolution of Cooperation Introduction

Theory
Background to the Evolution of Cooperation

Social behaviour
Animals who live in groups have evolved social behaviours such as cooperative hunting and predator defense. These hyaenas have hunted together to capture their prey. An especially interesting form of cooperative behaviour is called "altruism" where it costs the individual performing the behaviour and benefits the recipient. Such "charitable" behaviour appears to go against Darwinian notions of evolution by natural selection on individual success, since cooperation should only evolve if the individual gets more out of it than they put in.

Kin selection
Examples of apparent altruistic behaviour, such as the worker bees that forfit their chance to breed to help the queen raise more sisters were once explained as acts for "the good of the species". These so-called "group selection" arguments have generally not been supported, and instead kin selection is invoked. W.D. Hamilton reasoned that "individual success" should be thought of in terms of passing on genes to the next generation not simply in direct descendants but also in relatives who share the same genes. By helping a relative you are helping your own fitness.

Reciprocal altruism
Kin selection likely explains much cooperation in social groups but what about apparent cooperation between unrelated individuals, such as between species? An example of these mutualisms is this wrasse fish which picks skin parasites off other fish. Typically the fish are large enough to eat the wrasse but instead they sit quietly and allow it to clean their skin. R.L. Trivers proposed that in these cases, individuals behave altruistically to another individual in the expectation that they in turn will reciprocate the favour and be altruistic to them.

Game theory
In interactions where there is a delay between reciprocating, then individuals can cheat and not reciprocate the altruistic act. Individuals are actually playing a game, and game theory can be used to model the possible moves and outcomes. In game theory, cooperative behaviours such as the cleaner fish behaviour is called a non-zero-sum game; both individuals have a shared interest of survival. By contrast, ice hockey or predator-prey interactions, where one wins at the expense of the other, is a zero-sum game.

"A non-zero-sum game which appears to approximate some of the reciprocal behaviours in nature is a popular puzzle called the Prisoner's Dilemma game. Let's find out about it... "



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