As outlined by Robert Putnam
, generalized reciprocitry is an outcome of some higher level of social capital
in a society. Basically, generalized reciprocity is the phenomenon of people helping each other not for specific reward, but because they assume they would be helped in a similar way.
Putnam uses the example of a volunteer fire department during a fund drive who print up t-shirts saying "Come to our pancake sale and we'll come to your fire!" The humor is the understanding that the firemen would help you regardless of whether you had helped them.
This mechanism is used by social network theorists to explain why people do apparently altruistic things.