Spite: Hamilton's unproven theory

Thirty years ago Hamilton showed that spite, an action that harms a recipient at no direct benefit to the actor, could evolve if interactants were negatively related. Wilson later showed that spite could also evolve by indirect benefits to a third party. Since then, many selfish actions that are particularly harmful to the recipient have been called `spite¿ but no convincing examples have been found. Here we discuss three examples of spite from the social insects: worker policing, sex allocation biasing by workers and green beard queen killing in the fire ant. All examples are Wilsonian spite and the last example is also Hamiltonian spite. Spite will be harder to identify in other animals because actions that seem mutually harmful may have delayed reproductive benefits. Spite may prove to be more common at the genetic level than the individual level because negative relatedness can more easily arise. Two possible examples, cytoplasmic incompatibility and maternal-effect lethal distorter genes, are discussed.