Suicidal altruism under random assortment

Abstract

Questions: Can there be a selective explanation for suicide? Or are all suicides evolutionary mistakes, ever pruned by natural selection to the extent that the tendency to perform them is heritable? Model: A simple variant of trait group selection (where a population is divided into mutually exclusive groups, with the direct effects of behaviour limited to group-mates), employing predators as the mechanism underlying group selection. Predators evaluate groups to avoid potentially suicidal defenders (which, when present, limit a predator’s net return), thus acting as a group selection mechanism favouring groups with potentially suicidal altruists. Conclusion: The model supports contingent strong altruism (depressing one’s direct reproduction – absolute fitness – to aid others) without kin assortment. Even an extreme contingent suicidal type (destroying self for the sake of others) may either saturate a population or be polymorphic with a type avoiding such altruism. The model does not, however, support a sterile worker caste, where sterility occurs before life-history events associated with effective altruism; under random assortment, reproductive suicide must remain contingent or facultative.