In that social networks are thought to influence the evolution of cooperation amongst individuals, James H. Fowler, from University of California/San Diego (UCSD; California, USA), and colleagues explored how cooperative and uncooperative behaviors spread among people.  The team found that when study participants played a game in which they had an opportunity to cooperate with one another, people who received a donation of money were more likely to donate money to other people in future games. The resulting domino effect spread one person's generosity onward, whereby the influence persisted for multiple periods and spread up to three degrees of separation (from person to person to person to person). The researchers observe that: “The results suggest that each additional contribution a subject makes to the public good in the first period is tripled over the course of the experiment by other subjects who are directly or indirectly influenced to contribute more as a consequence. These results show experimentally that cooperative behavior cascades in human social networks.”