http://www.eurekalert.org/pub_releases/2010-03/uoc–if030510.php
“UC San Diego and Harvard deliver first experimental findings on spread of cooperation in a social network”
“In a study published in the March 8 early online edition of the Proceedings of the National Academy of Sciences, researchers from the University of California, San Diego and Harvard provide the first laboratory evidence that cooperative behavior is contagious and that it spreads from person to person to person. When people benefit from kindness they “pay it forward” by helping others who were not originally involved, and this creates a cascade of cooperation that influences dozens more in a social network.”
