Cooperation in Evolving Social Networks

Abstract

We study the problem of cooperative behavior emerging in an environment where individual behaviors and interaction structures coevolve. Players not only learn which strategy to adopt by imitating the strategy of the best-performing player they observe, but also choose with whom they should interact by selectively creating and/or severing ties with other players based on a myopic cost-benefit comparison. We find that scalable cooperation--that is, high levels of cooperation in large populations--can be achieved in sparse networks, assuming that individuals are able to sever ties unilaterally and that new ties can only be created with the mutual consent of both parties. Detailed examination shows that there is an important trade-off between local reinforcement and global expansion in achieving cooperation in dynamic networks. As a result, networks in which ties are costly and local structure is largely absent tend to generate higher levels of cooperation than those in which ties are made easily and friends of friends interact with high probability, where the latter result contrasts strongly with the usual intuition.networks-graphs, theory, games-group decisions, simulation

Conformism and cooperation in a local interaction model

“…Marsili et al (2005) highlight the importance of the clustering degree for sustaining cooperation. Zimmermann et al (2004), Fosco and Mengel (2008) or Hanaki et al (2007) among many others explain cooperation through exclusion of non-cooperators in a dynamic network setting. The role of a conformist bias in imitation has been examined by Ellison and Fudenberg (1993) to study the spread of an efficient technology in a one person decision problem.…”

Network Economics and the Environment: Insights and Perspectives

“…Interestingly, a careful examination of these feedbacks has lead to results that are at odds with previously shared wisdom on what type of social structure promotes cooperation. In particular, Hanaki et al (2007) have shown how the survival of a cooperating population requires sparse networks, little local clustering, and the possibility that agents unilaterally cut unprofitable ties. This findings are at odds with the prior wisdom that cooperation would develope in closed and dense communities of cooperators (see Axelrof, 1984, Coleman, 1988.…”

Chapter 21 ACE Models of Endogenous Interactions

“…If, however, the population starts being relatively indifferent with respect to tags (b = 2.00), and there are no search costs, then the population may or may not evolve into one that cares about tags (see and lines in Figure 12). Hanaki et al (2004): trust Hanaki et al (2004) study a repeatedly played one-shot version of a standard Prisoner's Dilemma (PD) game. Just as Ashlock et al (1996), they start from the observation that defection is the dominant strategy, and ask the question whether cooperation could be sustained with endogenously determined local interactions, with the individual agents choosing their (number of) partners.…”

“…That is, although the agents update their trust levels, they do not learn on which interactions they should base their trust. Hanaki et al (2004) present an extensive analysis for a wide range of parameter values. Figure 14 shows the relative frequency distribution of average cooperation levels reached in 10 000 runs of 10 000 periods for a population of 1000 agents, with the other parameter values sampled randomly from pre-specified ranges.…”