The practice of making an appropriate return for a benefit or harm received from another. Reciprocal altruism is the system whereby a benefit received is returned with a benefit; under a wide range of conditions, groups practising it will flourish better than those practising unbridled self-interest. Reciprocity was a moral imperative in the Homeric world, essential to the creation of binding relationships between otherwise independent warriors. However that code allowed quite indiscriminate orgies of retaliation in face of an insult or provocation (similarly the God of the Old Testament). With the emergence of the polis individual reciprocities become less important than action on behalf of the city which also reserved to itself the business of appropriate retaliation. This is the germ of the idea of acting under an impartial law, See also Justice, retributive; rule of law; tit for tat.