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Social Networks Can Be Used to Increase Human Cooperation

Social Networks Can Be Used to Increase Human Cooperation

David G. Rand

The Conundrum of Cooperative Behavior

Cooperation is central to the success of human societies and it is widespread, but social and biological scientists have long pondered how it can persist in the face of possible exploitation. One answer involves networked interactions and population structure. People often have control over whom they interact with, and interaction patterns change over time. This creates a new form of conditional action: people can change their network structure, not just their own cooperation behavior.

Reciprocity has traditionally been conceptualized as the emergence of concordant behaviors within dyads. For example, the “tit-for-tat” strategy means only cooperating if the opponent cooperated in the previous round. But this kind of behavioral reciprocity is problematic in larger group interactions: if the only way to sanction defectors is to defect, one must also harm the cooperators in one’s group in order to punish a defector.

Strategic tie formation and dissolution in dynamic networks offers a solution to this problem by providing players with an additional method of responding to the past actions of others. Not only can they change their cooperation behaviors, players can respond by creating or dissolving ties. In short, cooperators can establish and maintain links with other cooperators, but sever connections with defectors, engaging in ëlink reciprocity.’

Novel Methods

Our work evaluates theoretical predictions by leveraging new tools for running economic games online to conduct a series of large-scale behavioral cooperation experiments using dynamic networks. Subjects play a repeated cooperative dilemma with other subjects in an artificial social network created in the virtual lab.

In these online experiments, each subject interacts with her neighbors by choosing a single action simultaneously towards all neighbors: cooperation (C or blue dots in the figure) or defection (D or red dots in the figure). Prior to making a decision whether to cooperate, which involves paying 50 units for each neighbor (who will thus gain 100 units), subjects are reminded of their number of neighbors and the neighbors’ previous decisions (C vs. D). At the end of each turn, subjects are informed about the decisions of their neighbors, along with their own payoff. We examine three kinds of network conditions. In the ëRandom’ condition, the social network is randomly re-generated after every round. In the ëFixed’ condition, the network is static and remains in its initial conformation for the duration of the experiment. In the strategic link updating conditions, each cooperation round is followed by a ‘rewiring’ round in which subjects choose whether to alter their network connections, either relatively infrequently (‘viscous’ condition) or more frequently (‘fluid’ condition).

Results of Network Rewiring on Competition

In random and fixed network conditions, cooperation declines steeply over time, re-creating the classic ‘tragedy of the commons.’ In the viscous dynamic network condition, where 10% of connections update each round, we again see that cooperation decreases over time. Subjects cannot update their partnerships quickly enough to incentivize cooperation. But in the fluid dynamic network condition, where 30% of connections update each round, we see a qualitatively different outcome: cooperation is robust and stable (see figure).

We also find that links between two cooperators are much more stable than either cooperator-defector or defector-defector links. And cooperators have more connections than defectors, on average. Examining the mechanism behind these results shows that subjects preferentially break connections with defectors and make new connections with cooperators, confirming ‘link reciprocity.’

We provide novel empirical evidence regarding cooperation in dynamic networks, confirming the predictions of a family of evolutionary game theoretic models. Allowing subjects to dynamically update their social network connections can stabilize cooperation in groups, where cooperation is otherwise difficult to maintain through changes in cooperative behavior alone. Thus, dynamically updating social networks can support cooperation in large groups. When social ties are fluid, people need not abandon cooperation in order to punish free-riders. Instead we can shun them, excluding them from the benefits of future cooperation and dis-incentivizing defection. It pays to cooperate today, lest you find yourself alone tomorrow.