Nice guys finish first: the competitive altruism hypothesis.

Three experimental studies examined the relationship between altruistic behavior and the emergence of status hierarchies within groups. In each study, group members were confronted with a social dilemma in which they could either benefit themselves or their group. Study 1 revealed that in a reputation environment when contributions were public, people were more altruistic. In both Studies 1 and 2, the most altruistic members gained the highest status in their group and were most frequently preferred as cooperative interaction partners. Study 3 showed that as the costs of altruism increase, the status rewards also increase. These results support the premise at the heart of competitive altruism: Individuals may behave altruistically for reputation reasons because selective benefits (associated with status) accrue to the generous.