In biology an altruistic act increases the reproductive fitness of a member of the same species (a conspecific) while reducing the reproductive fitness of the one committing the act. Reproductive fitness refers to the differential ability of an organism to influence gene frequencies in future generations. Altruism is distinguished from mutualistic behavior, which increases the reproductive fitness of others as well as the actor. Altruism also is distinguished from selfishness, which benefits the actor and either does not benefit or harms others' reproductive fitness.

In characterizing behavior as biologically altruistic, the issue of intention is not relevant as it is in the related but not identical meaning in moral philosophy, in contrast, an altruistic act is defined as one undertaken with the intention of helping another with the anticipation that it will incur or risk harm to the actor. In principle, the benefits rendered may...