PHILADELPHIA -- Whether it is barn-raising or crafting a business plan, humans are among the few creatures that are able to work well cooperatively. According to an evolutionary psychologist at the University of Pennsylvania, our success at cooperation results from three distinct personality types.  

"In any given group of people, youl find three kinds of people:  Cooperators, Free Riders, and what we call Reciprocators. Cooperators do the most work and Free Riders do as little as possible, but most of us are Reciprocators.  We hold back a bit to determine the chances of success before devoting our full energy to a project," said Robert Kurzban, an assistant professor in Penn's Department of Psychology.  "We found that these traits remained fairly stable among people, and you could reliably predict how a group might perform if you know the percentage of each type of person in that group."

Kurzban and Daniel Houser of George Mason University present their findings this week in the Online Early Edition of the Proceedings of the National Academy of Sciences.  The researchers used a computer-based experiment to assess the range of cooperative behaviors among people.  While they cannot offer a complete explanation of how these traits might have evolved, they point to reciprocity as an important motive in human societal behavior.   According to Kurzban, it could also provide a simple lesson on the power of internal communications to managers and group leaders.  

"Our findings show that the vast majority of people, about 63 percent, are Reciprocators, and in any group you are likely to have a substantial number of Reciprocators," Kurzban said.  "The simplest way to make use of a Reciprocator potential is to keep everyone apprised with information about the successful contributions of others within the group.  This way you show them that there is something to gain from their efforts."

More than 80 subjects participated in the experiment in which they were given 50 tokens that they could choose to keep or place in a group pool.  Tokens placed in the group pool doubled in value and, at the end of the time period, were distributed equally among members.   About 17 percent of the participants could be classified as Cooperators, taking the most risk almost immediately.  Free Riders, who prefer not to cooperate, made up 20 percent.   

"Overall, these personality traits remained strong through different games no matter which combinations of people were used.  Granted, if people are stuck working with a bunch of Free Riders, even the most highly cooperative among them will tend to take the 'wait-and-see' approach," Kurzban said.

Kurzban and Houser are now replicating their experiments to determine if distributions of cooperative types are similar across cultures.  If those similarities are found, it might help clarify the origins of these distinct personality types.

  The Russell Sage Foundation and the International Foundation for Research in Experimental Economics provided support for this research.