Strong reciprocity
A drive to reward kindness and punish unfairness even at a net cost to yourself.
What it means
A behavioral disposition combining a willingness to cooperate with those who cooperate and to punish those who violate cooperative norms, both at personal expense and even toward strangers one will never meet again. It goes beyond reciprocal altruism, which ultimately serves self-interest through future return, because strong reciprocators act this way in one-shot, anonymous settings where no payback is possible. Proponents argue it evolved through gene-culture coevolution and group-level selection, and that it is essential to explaining cooperation in large, anonymous human societies. It matters because it offers a unified account of generosity, fairness enforcement, and altruistic punishment that pure self-interest cannot.
Examples
A traveler tips fairly and reports a cheating vendor in a city they will never return to, acting on principle rather than payoff.
In the ultimatum game, people routinely reject a small share of real money from a stranger they will never meet again, paying out of pocket to punish an unfair offer.
An employee serving her final week still writes a thorough handover for a successor she will never meet, and files a complaint about the manager who bullies juniors.
First described in Gintis (2000); Fehr, Fischbacher & Gächter (2002).