PAGE 1 A professor sent holiday cards to perfect strangers, and the response was amazing. The great majority of those who returned a card never inquired into the identity of the unknown professor, and the rule for reciprocation is one of the most potent weapons of influence around us. The rule for reciprocation is pervasive in human culture and may be a unique property of human culture. It allows humans to divide labor, exchange different kinds of goods, and exchange different kinds of services, and create a web of interdependencies that bind individuals together into highly efficient units. PAGE 2 A sense of obligation made an enormous difference in human social evolution because it allowed one person to give something to another without actually giving them away. This led to sophisticated and coordinated systems of aid, gift giving, defense, and trade. Five thousand dollars of relief aid was sent from Mexico to Ethiopia in 1985, but the aid went in the opposite direction, to Mexico City, to help the victims of the earthquakes there. I was puzzled by Ethiopia's action, but after learning that Mexico had sent aid to Ethiopia in 1935, I was no longer puzzled. The reciprocity rule had triumphed. Human societies derive a competitive advantage from the reciprocity rule, and members are trained to comply with and believe in it. However, we are often taken advantage of by individuals who stand to gain from our indebtedness. PAGE 3 To understand how the rule for reciprocation can be exploited, we should examine an experiment performed by Professor Dennis Regan of Cornell University.5 In this experiment, Joe, a posing fellow subject, did a small favor for the true subject in some cases, but not in others. After the paintings had all been rated, Joe asked the subject to do him a favor. The subjects who had received his earlier favor bought twice as many tickets as the subjects who had not been given the prior favor. The Rule Is Overpowering One of the reasons reciprocation can be used so effectively as a device for gaining another's compliance is because the rule possesses incredible strength. This strength can overpower the influence of other factors that normally determine whether a request will be complied with. PAGE 4 When subjects were given a Coke by Joe, the relationship between liking the requester and compliance was completely wiped out. They felt an obligation to repay Joe, and they did, whether they liked him or not. The Hare Krishna Society, an Eastern religious sect with centuries-old roots traceable to the Indian city of Calcutta, experienced a remarkable growth in the 1970s, funded in part by requests for donations from passersby in public places. Although highly effective as a technique for gaining attention, this form of fundraising did not work especially well because the average Ameri- can considered the Krishnas weird, to say the least, and was reluctant to provide money to support them. The Krishnas switched to a fund-raising tactic that made it unnecessary for target persons to have positive feel-ings toward the fund-raisers. This strategy involved giving a "gift" to the target person before a donation was requested, and this strategy was wildly successful for the Hare Krishna Society. PAGE 5 The reciprocation rule has begun to outlive its usefulness for the Krishnas, because we have found ways to prevent them from using it on us. Airports have started to restrict the Krishnas' soliciting activity to certain areas and announce their presence through signs and the public address system. The Krishnas' gift giving tactic is too strong for us to want to violate the reciprocity rule. The reciprocity rule is a powerful political tool that has been used by many presidents to get programs through Congress. Jimmy Carter had difficulty getting his programs through Congress because he was indebted to no one there.