Indirect reciprocity is defined here as "I help you and somebody else helps me."

Indirect reciprocity has only been shown to occur in humans.

A generalized exchange involves indirect reciprocity between three or more individuals.

The calculations of indirect reciprocity are complicated, but again a simple rule has emerged.

The efficient interaction of indirect reciprocity and costly punishment.

Lévi-Strauss emphasizes this a system of generalized exchange based on indirect reciprocity.

Indirect reciprocity can stabilize cooperation without the second-order free rider problem.

Reputation allows evolution of cooperation by indirect reciprocity.

Evolutionary theories of indirect reciprocity and costly signaling may be useful to explain large-scale cooperation.

This has found gossip to be an important means by which people can monitor cooperative reputations and so maintain widespread indirect reciprocity.

Individual acts of indirect reciprocity may be classified as "upstream" or "downstream":

Both indirect reciprocity and costly signaling depend on the value of reputation and tend to make similar predictions.

As predicted, gossip promoted indirect reciprocity.

Religion serves as a means of communicating the commitments that serve as the psychological mechanism for establishing indirect reciprocity.

Indirect reciprocity is based on knowing the other player's reputation, which is the player's history with other players.

Indirect reciprocity.

In the standard framework of indirect reciprocity, there are randomly chosen pairwise encounters between members of a population; the same two individuals need not meet again.

In “SuperCooperators,” Nowak argues that two of his mechanisms, indirect reciprocity and group selection, played an important role in human evolution.

Indirect reciprocity can only promote cooperation if the probability, q, of knowing someone's reputation exceeds the cost-to-benefit ratio of the altruistic act:

Panchanathan K. & Boyd, R. (2003) A Tale of Two Defectors: The Importance of Standing for the Evolution of Indirect Reciprocity.

Milinski, Semmann & Krambeck (2002) have demonstrated, through the use of public goods games and indirect reciprocity games, that humans are less likely to interact with those who have a reputation for not equivalently returning the favour.

In his 1987 book The Biology of Moral Systems, Richard Alexander explored the consequences of what he called "indirect reciprocity"-- when individuals in a population observe other members of the population interacting with each other.

In a paper in Science in 2006 Nowak enunciated and unified the mathematical rules for the five understood bases of the evolution of cooperation (kin selection, direct reciprocity, indirect reciprocity, network reciprocity, and group selection).

Another example of a hidden benefit is indirect reciprocity, in which a donor individual helps a beneficiary to increase the probability that observers will invest in the donor in the future, even when the donor will have no further interaction with the beneficiary.