Hamiltonian spite

Within the field of social evolution, Hamiltonian spite is a term for behaviours occurring among conspecifics that have a cost for the actor and a negative impact upon the recipient.

W. D. Hamilton published an influential paper on altruism in 1964 to explain why genetic kin tend to help each other. He argued that genetically related individuals are likely to carry the copies of the same alleles; thus, helping kin may ensure that copies of the actors' alleles pass onto next generations of both the recipient and the actor.

While this became a widely accepted idea, it was less noted that Hamilton published a later paper that modified this view. This paper argues that by measuring the genetic relatedness between any two (randomly chosen) individuals of a population several times, we can identify an average level of relatedness. Theoretical models predict that (1) it is adaptive for an individual to be altruistic to any other individuals that are more closely related to it than this average level, and also that (2) it is adaptive for an individual to be spiteful against any other individuals that are less closely related to it than this average level. The indirect adaptive benefits of such acts can surpass certain costs of the act (either helpful or harmful) itself. Hamilton mentioned birds and fishes exhibiting infanticide (more specifically: ovicide) as examples for such behaviours.

Briefly, an individual can increase the chance of its genetic alleles to be passed to the next generations either by helping those that are more closely related, or by harming those that are less closely related than relationship by chance.

Though altruism and spitefulness appear to be two sides of the same coin, the latter is less accepted among evolutionary biologists.

First, unlike the case with the beneficiary of an altruistic act, targets of aggression are likely to act in revenge: bites will provoke bites. Thus harming non-kin may be more costly than helping kins.

Second, presuming a panmictic population, the vast majority of pairs of individuals exhibit a roughly average level of relatedness. For a given individual, the majority of others are not worth helping or harming. While it is easy to identify the few most closely related ones (see: kin recognition), it is hard to identify the most genetically distant ones.

Most terrestrial vertebrates exhibit a certain degree of site fidelity, so levels of kinship tend to correlate negatively with spatial distance. While this may provide some cues to identify the least related individuals, it may also ensure that non-kin rarely if ever meet each other.

...
Wikipedia