Natural selection optimizes fitness (see Fitness). Understanding what kin selection optimizes was crucial to its emergence as one of the fundamental tenets of evolutionary theory. W. D. Hamilton was the first to explain this formally in terms of his theory of inclusive fitness in 1964. Hamilton pointed out that when we measure the fitness of a trait we must take into consideration the effect that trait has on the fitness of other individuals as well as the actor who performs the behavior. If a trait has a beneficial effect on carriers of the same gene, then that gene can spread by kin selection. Inclusive fitness therefore is made up of two components - direct fitness (from the production of offspring) and indirect fitness (from aiding the reproduction of relatives). Kin selection explains how a trait can spread by its effect on indirect fitness.
Was this article helpful?