Hamiltonian spite

Second, presuming a panmictic population, the vast majority of pairs of individuals exhibit a roughly average level of relatedness.

Most terrestrial vertebrates exhibit a certain degree of site fidelity, so levels of kinship tend to correlate negatively with spatial distance.

Many animal species exhibit infanticide, i.e. adults tend to kill the eggs or the offspring of conspecifics, even if they do not feed on them (in the absence of cannibalism).

[9] Thus, tuberculosis-infected European badgers and rabies-infected dogs equally tend to emigrate from their natal ranges before starting to distribute the pathogens.

[10] Throughout human history, war often emerges as a costly form of aggression typically targeting the non-kin enemy.