Graph Model Suggests Social Diversity Promotes Emergence of Cooperation

July 23, 2008

Three European scientists have introduced the idea of diversity into models of social networks, using graphs in which individuals occupy the vertices while links define group sizes and the social structures of a population. Their mathematical model suggests that acts of cooperation may depend on one's social context or ranking. Diversity becomes associated with meeting the greater good of the group. And an individual's contribution to each act of the public good leads to more altruism.

Evolutionary game theory has long posited that the desires of individuals often trump the need to support group cooperation. Researcher Francisco C. Santos of the Université Libre de Bruxelles, along with Marta D. Santos and Jorge M. Pacheco of the University of Lisbon, has shown that a population's diversity might balance the scales. People, the researchers say, "often cooperate in public goods games and situations ranging from family issues to global warming."

Using heterogeneous graphs, they show that cooperation is promoted by diversity associated with the number and size of the public goods game in which each individual participates and with the individual contribution to each such game. Their results appear in the article "Social Diversity Promotes the Emergence of Cooperation in Public Goods Games," published in the July 10 Nature.

"When social ties follow a scale-free distribution," the researchers write, "cooperation is enhanced whenever all individuals are expected to contribute a fixed amount irrespective of the plethora of public goods games in which they engage."

Their conclusions may help explain the emergence of cooperation in the absence of mechanisms based on individual reputation and punishment. Combining social diversity with the ideas of reputation and punishment could offer clues to community organization and suggest solutions to economic inequality. According to the researchers, cooperation blooms whenever the act of giving becomes more important than the amount given.

Source: Université Libre de Bruxelles, July 10, 2008.