Group SelectionGroup Selection in Predator-Prey Communities. M. E. Gilpin

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Abstract
It is useful to distinguish as sharply as possible the processes of kin and group selection. The terms group selection should be confined to cases in which the group (deme or species) is the unit of selection. This requires that groups be able to reproduce by splitting or by sending out propagules and that groups should go extinct. The origin of an altruistic trait (but not its maintenance) requires that the groups be small or that new groups be established by one or a few founders. Kin selection requires only that relatives should live close to one another. The division of the population into groups, permanently or for part of the life cycle, may favor the operation of kin selection but is not a necessary feature. Group selection can maintain altruistic alleles, i.e., alleles which reduce individual fitness but increase the fitness of groups carrying them. The conditions under which this can happen are stringent, so that the main debate concerns whether the process has had evolutionarily important consequences. The main function of models is to indicate the circumstances in which group selection can be important. For one large class of models the condition for the maintenance of an altruistic allele by group selection is M < 1, where M is the expected number of successful migrants carrying the selfish allele produced by a group during the whole period from the moment when it was first infected by a selfish immigrant to the times of its extinction. The features favoring group selection are small group size, low migration rates and rapid extinction of groups infected with the selfish allele. The ultimate test of the group selection hypothesis will be whether populations having these characteristics tend to show self-sacrificing or prudent behavior more commonly than those which do not.