Cooperation in a Social Network : This diagram illustrates how a single act of kindness can spread between individuals and across time. Cooperative behavior spreads three degrees of separation: if Eleni increases her contribution to the public good, it benefits Lucas (one degree of separation), who gives more when paired with Erika (two degrees of separation) in period 2, who gives more when paired with Jay (three degrees of separation) in period 3, who gives more when paired with Brecken in period 4. The effects also persist over time, so that Lucas gives more when paired with Erika (period 2) and also when paired with Lysander (period 3), Bemy (period 4), Sebastian (period 5), and Nicholas (period 6). The effect also persists at two degrees of separation, as Erika not only gives more when paired with Jay (period 3), but also when paired with Harla (period 4) and James (period 5). All the paths in this illustrative cascade are supported by results in the experiments, and it is important to note that if Eleni decreases her initial contribution then her uncooperative behavior can spread and persist as well.
Credit: Courtesy James Fowler, UC San Diego
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