Blackwell Publishing

The units of selection - Can natural selection favor altruistic actions?


What is the condition for natural selection to favor altruism?

If the altruists dispensed their aid indiscriminately to other individuals it would be received by other altruists and by selfish individuals in the same proportion as they exist in the population: natural selection will then favor the selfish types, because they receive the benefits but do not pay the costs. If altruism is to evolve, it has to be directed preferentially to other altruists. How do altruists recognize each other?

In practice it is usually (maybe always) impossible for altruism only to be directed to other altruists, because they cannot be recognized with certainty. It may be possible, however, for altruism to be directed at a class of individuals that contains a disproportionate number of altruists relative to their frequency in the population. This is true when altruism is directed toward genetic relatives: if a gene for altruism is in an individual, it is also likely to be in its relatives.

Social insects, such as these worker ants pictured opposite, are genetically much closer related than most members of a species: it has been suggested that this explains the high levels of altruism found among them.

W.D Hamilton discusses the evolution of altruism.

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