Research on cooperation has shown that people are more generous when they are watched by someone or even when they are exposed to images of eyes (Bateson et al. 2006
; Bereczkei et al. 2007
). Also, the rate of cooperation increases when the identity of the individual is revealed (Andreoni & Petrie 2004
). Considering these findings, generosity and fairness appear to be context-dependent behaviours expressed in the presence of reputational incentives.
One reason why it might pay to be seen to cooperate is indirect reciprocity (Alexander 1987
). Experiments have found that people do indeed prefer to help those who help others (e.g. Milinski et al. 2002
). Moreover, investing in reputation pays in the long run: despite the initial expense, individuals benefit by receiving more cooperation from others in subsequent rounds of indirect reciprocity (Wedekind & Braithwaite 2002
). However, problems remain with indirect reciprocity as a general explanation for reputation building (Roberts 2008
). In particular, indirect reciprocity depends upon cooperation being conditional upon a recipient also being a cooperator, so cannot explain displays of unconditional cooperation.
An alternative theory for reputation formation is that of competitive altruism (CA; Roberts 1998
). This theory stresses the role of partner choice for profitable relationships and is based on a two-stage process in which individuals first have a chance to build up reputations through making generous displays, and secondly choose partners for further interactions. CA postulates that individuals seek to acquire the best cooperators as partners. According to biological market theory, such cooperative pairing will be assortative (Noë & Hammerstein 1994
). Hence, the benefits for cooperative individuals are twofold: first, they are paired with the chosen partner (one of the best cooperators), and second, they gain profits from these highly cooperative partnerships.
In support of CA, research has shown that people were more cooperative when they expected to play a dyadic trust game with a chosen partner later than when they knew they would not be able to choose a partner or when they did not expect to play a further game (Barclay 2004
). Another study demonstrated that participants contributed more when their contributions were to be revealed to others than when they remained anonymous. It also found that status and social prestige increased in proportion to donations made to the group (Hardy & Van Vugt 2006
). Finally, by varying whether contributions were anonymous or public and whether participants had a choice of partner, Barclay & Willer (2007)
demonstrated that participants' contributions were related to the motivation to gain cooperative reputation (see the electronic supplementary material). The study also provided evidence for a preference for the most cooperative players. However, none of these studies has demonstrated net monetary benefits from investing in a cooperative reputation.
Here, we investigate the benefits coming from reputation in the form of partner choice and payoffs from interactions with partners. The study also involves varying the potential gains to be made from a partner to test whether we find an increase in contributions when reputation building is followed by higher potential rewards.
We conducted two experiments referred to as the main experiment and the supporting experiment. The supporting experiment's aim was to demonstrate that (i) public information and (ii) partner choice increased cooperative reputation-building behaviour. Our findings were consistent with those of earlier studies including Barclay & Willer (2007)
and are therefore described in the electronic supplementary material. The main experiment consisted of two stages in which participants first had an opportunity to build up reputation (stage 1) and could then make use of the information about other players' reputations in order to choose partners for further interactions. In stage 2 there were two reward levels in order to vary the incentive to invest in reputation.