"There is an obligation to give, an obligation to Receive, and an obligation to Repay" – Marcel Mauss Reciprocity is a human rule incorporated in all cultures and that supposedly comes from a significant evolutionary advantage: it allows the division of labor, exchange of goods and services and the creation of structures of interdependence that binds individuals together into larger units and more effective. The press group members to cooperate by threatening a loss of reputation for not working, so we all feel obliged to return (if any) for favors received (in other words, reciprocal altruism and Justice in our commenting Haidt moral). Even we feel obliged to receive (without this, the rule would be weak and fragile evolutionary sense). The simplest option is to offer something and then ask for anything more in return (a classic red cross volunteer regalandote a pin and then asking a voluntary contribution, or first visit to the dentist: no cost review!, or free samples of cheese in the supermarket). The strength of this trend is independent of whether we like or not the donor-petitioner. gree. In addition, the more surprise is in the gift, or in the request, seems to have more favorable response (shorted us the ability to turn the automatic in reflection). A significant problem for most common theme of this blog is, eg when doctors receive gifts from the laboratories (in the U.S. at least, it seems also that psychiatrists are the specialists: the dynamics enters TANSTAAFL (There Is not no such thing as a free lunch).