The true power of kin selection theory is its generality: kin selection can help explain a huge range of social interactions and not just altruistic cooperation. The simplest cases are when interacting individuals are more closely related, they should be more likely to cooperate, show more selfish restraint, and show less aggression. A range of more subtle possibilities arise whenever there is the potential for cooperation or conflict between relatives. A few examples of these are:
• Individuals are expected to be more likely to give warning calls about the presence of predators, if they are in the presence of close relatives, as occurs in ground squirrels.
• In species where cannibalism occurs in response to food limitation, individuals should prefer to eat nonrelatives, as occurs in tiger salamanders and ladybirds.
• In social insects, such as wasps and bees, workers remove eggs laid by other workers, because they are more related to the queen's eggs, than the worker-laid eggs.
• In many insects, related males (brothers) compete with each other for mates (often their sisters), before these females disperse to lay eggs elsewhere. When this happens, mothers produce a female-biased offspring sex ratio, to reduce this competition between brothers.
• If the relatedness between the parasites infecting a host is high, they are expected to prudently exploit that host, causing less damage and mortality (virulence).
In other words, kin selection theory describes when individuals should behave altruistically and also when they should curtail their selfishness. Furthermore, kin selection theory also predicts the existence of spiteful behaviors, where an individual suffers a personal cost (c> 0) in order to inflict harm upon a social partner (b<0) (Table 1). Such behaviors are favored when rb > c is satisfied, which requires a negative relatedness (r < 0) between spiteful actor and victim. Examples of spiteful behaviors include bacteria producing chemicals that kill nonrelatives, or wasp larvae preferentially attacking and killing individuals to whom they are less closely related.
See also: Adaptation; Altruism; Communication; Fitness; Social Behavior.
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