The researchers conclude that human societies can best achieve high levels of cooperative behaviour if their individuals interact repeatedly, and if populations exhibit at least a minor degree of structure.
MORE: http://www.sciencedaily.com/releases/2012/06/120608100557.htm
See also...
The Power of Suggestion: What We Expect Influences Our Behavior, for Better or Worse
http://www.sciencedaily.com/releases/2012/06/120606142818.htm
