Upstream reciprocity in heterogeneous networks

TL;DR

This study demonstrates through numerical simulations that heterogeneous contact networks significantly promote upstream reciprocity, leading to increased cooperation and altruism in social dilemma scenarios.

Contribution

It provides the first numerical evidence that network heterogeneity enhances upstream reciprocity and altruistic behavior in social networks.

Findings

Heterogeneous networks promote cooperation in upstream reciprocity.

Generous strategies occupy hubs and spread helping behavior.

Enhanced altruism resembles dynamics in the Prisoner's Dilemma.

Abstract

Many mechanisms for the emergence and maintenance of altruistic behavior in social dilemma situations have been proposed. Indirect reciprocity is one such mechanism, where other-regarding actions of a player are eventually rewarded by other players with whom the original player has not interacted. The upstream reciprocity (also called generalized indirect reciprocity) is a type of indirect reciprocity and represents the concept that those helped by somebody will help other unspecified players. In spite of the evidence for the enhancement of helping behavior by upstream reciprocity in rats and humans, theoretical support for this mechanism is not strong. In the present study, we numerically investigate upstream reciprocity in heterogeneous contact networks, in which the players generally have different number of neighbors. We show that heterogeneous networks considerably enhance cooperation in a game of upstream reciprocity. In heterogeneous networks, the most generous strategy, by which a player helps a neighbor on being helped and in addition initiates helping behavior, first occupies hubs in a network and then disseminates to other players. The scenario to achieve enhanced altruism resembles that seen in the case of the Prisoner's Dilemma game in heterogeneous networks.