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 be psychological or objectively beneficial in the sense that they prolong life or improve the material well-being of the beneficiary of the action. Similarly, the costs to the donor may be psychological or objectively verifiable as posing risk to life or limb. Altruistic acts can include affirmative acts of assistance as well as restraint where preemptively harming another might prevent or reduce the risk of attack from the individual harmed.
Humans are potentially dangerous to one another, and since they care about their own survival we might expect them to attack others when it is potentially beneficial for them to do so. Yet this is more the exception than the rule, a reality consistent with a wide range of experimental evidence showing that many humans are prepared to cooperate in one-shot or one-time prisoner's dilemma games. In such games, an actor has two choices: He or she can either defect or cooperate. Defecting can be understood here as engaging in preemptive attack, a strategy considered strictly dominant because if the other player cooperates, one is better off defecting, and if the other player defects, one is also better off defecting.
But to choose defect is to preclude any possibility of continuing mutually beneficial interaction. Cooperation, on the other hand, is altruistic in the biological sense, and arguably in a morally philosophical sense, because it provides a benefit to one's counterparty at potential cost to oneself. If both players cooperate, of course, the outcome that is most beneficial jointly results, and it is this strategy profile alone that opens the door to additional plays of the game.
Although it remains quite controversial, the most straightforward explanation of the origin of human predispositions to refrain from attacking nonkin (as well as our weaker inclination to provide affirmative assistance) is that human evolutionary history has been influenced by selection at multiple levels, including levels above the individual organism. Such an evolutionary account, which can be made completely consistent with the proposition that genes are the ultimate loci of selection could also explain our inclinations to devote disproportionate energy to detecting violators of social rules and engage in costly punishment against violators.
The complex of behavioral inclinations that enables human society to interact also has a dark side: in addition to underlying our ability to make peace, it also is behind our ability to wage organized war. In conjunction with the ease with which humans can define some as members of their own group and others as outsiders, altruistic behavior on behalf of other members of one's group may also entail preemptive violence against a feared other, thereby providing a biological underpinning for genocide. The fluidity with which the boundaries between the in group and out group can alter or be altered, however, gives hope that the frequency of genocide may be reduced. Genocide is not inevitable, and biology leaves intact our responsibility for all harms visited upon others.
Keller, Laurent, ed. (1999). Levels of Selection in Evolution. Princeton, N.J.: Princeton University Press.
Sober, Elliott, and David Sloan Wilson (1998). Unto Others: The Evolution and Psychology of Unselfish Behavior. Cambridge, Mass.: Harvard University Press.
Alexander J. Field