In the film Pay it Forward people do good deeds for other people, who in turn do favours for others and this spreads throughout a whole network of people. Researchers from the University of California, San Diego and Harvard tested this theory out in a series of experiments in which people had the opportunity to cooperate or do each other down as part of a game. The participants in the study were all strangers and never played twice with the same person. The study found that - just as in the film - those who received money in the first game were more likely to give money away in subsequent games even though they were playing with completely different people. Uncooperative behaviour also spread in this way but no more quickly or powerfully than acts of generosity.
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