Altruism: its characteristics and evolution.

Altruism is a group phenomenon in which some genes or individuals, which must be presumed to be selfish, benefit others at cost to themselves. The presumption of selfishness and the fact of altruism are reconciled by kin-group selection and by reciprocal altruism. Kin-group selection is clearly visible only in special cases; its role even among social insects may be overestimated; it is probably usually inhibited by competition. However, reciprocal altruism is ubiquitous. All altruism is: (i) potentially reciprocal; (ii) potentially profitable to altruists as well as to recipients; (iii) environmentally determined, usually by position of individuals in group or environmental situations; and (iv) a net-gain lottery. These generalizations are illustrated by four idealized cases; the difficulty of applying them to real cases is illustrated by alarm-calling in groups of birds. Although altruism is a group phenomenon, it evolves by individual selection, by processes equivalent to co-evolutions. Its evolution is: (i) opposed by competition; (ii) costly, complex, and slow, and tending to produce an imprecise flexible altruism rather than a precisely detailed one; and (iii) supplemented by group selection (differential extinction of groups). That altruism in human beings conforms to these generalizations is a good working hypothesis. However, analysis does not "take the altruism out of (human) altruism." Humans do not calculate it, but behave altruistically because they have human altruistic emotions.