Altruists and envious people who meet in contests are symbionts. They do better than a population of narrowly rational individuals. If there are only altruists and envious individuals, a particular mixture of altruists and envious individuals is evolutionarily stable.

In public good games, voluntary contributions tend to start off high and decline as the game is repeated. If high contributors are matched, however, contributions tend to stay high. We propose a formalization predicting that high contributors will self-select into groups committed to charitable...

This paper presents a formal theory of reciprocity. Reciprocity means that people reward kind actions and punish unkind ones. The theory takes into account that people evaluate the kindness of an action not only by its consequences but also by the intention underlying this action. The theory...

We show that once interfamily exchanges are considered, Becker's rotten kids mechanism has some remarkable implications that have gone hitherto unnoticed. Specifically, we establish that Cornes and Silva's (1999) result of efficiency in the contribution game amongst siblings extends to a setting...

This paper combines several large-scale surveys with different identification strategies to shed new light on the determinants of cooperative behavior. We provide evidence indicating that the well-being maximizing level of trust is above the income maximizing level. Higher trust is also linked...

Allowing for a free choice of the recipient's gender in a dictator game (N = 508), we find that women show a substantial gender biased towards females. Adding a charity recipient to the possible choices, the charity becomes the primary recipient and overall transfers increase. Yet, conditioning...

We report experimental findings on the role of charitable promises in bargaining settings. We vary the enforceability of such promises within variants of ultimatum games where the proposer suggest a split between himself, the responder and a char-itable donation. By reneging on initial pledges,...

Does the cultural background influence the success with which genetically unrelated individuals cooperate in social dilemma situations? In this paper we provide an answer by analyzing the data of Herrmann et al. (Science 2008, pp. 1362-1367), who study cooperation and punishment in sixteen...

To investigate the external validity of laboratory results, we combine a public good experiment with three treatments in a field experiment. One treatment offers the opportunity to free-ride, the other two are placebo treatments. We compare results within subjects. In the free-riding treatment,...

This paper introduces two ideas, emotional state dependent utility components (ESDUCs), and evolutionary perfect Bayesian equilibrium (EPBE). Using a simple extensive form game, we illustrate the efficiency-enhancing role of a powerful ESDUC, the vengeance motive. Incorporating behavioral noise...