There are also contrasting ideas when it comes to the differentiation of negative and positive norms of reciprocity. "In contrast to a positive norm of reciprocity Gouldner (1960) also suggested a negative norm of reciprocity or sentiments of retaliation where the emphasis is placed not on the return of benefits but on the return of injuries" (Chen, 2009). So there is a slight grey line between what could be considered a positive norm and a negative norm. But both of these reciprocity norms are mechanisms adapted by humans in order to keep a balance among mankind. "Accordingly, both positive and negative norms or reciprocity serve as starting mechanisms as well as stabilizing functions in theta they help initiate and maintain equitable interpersonal exchanges in human evolution" (Chen, 2009).