indirect fitness

Indirect fitness refers to an organism's genetic success through the reproduction of relatives, rather than its own offspring. This concept is central to the theory of inclusive fitness, which posits that natural selection favors genes that increase reproductive success, whether directly through an individual's own offspring or indirectly by aiding the survival and reproduction of close kin.123

Hamilton's rule (r × B > C) quantifies the conditions under which altruistic behavior, which benefits others at a cost to oneself, can evolve. Here, B is the benefit to the recipient, C is the cost to the donor, and r is the genetic relatedness between them. Altruism is favored when the benefit to relatives, weighted by their genetic relatedness, outweighs the cost to the altruist. This principle helps explain cooperative behaviors and sociality in many species, particularly among relatives.213