Humans' propensity to cooperate is driven by our embeddedness in social networks. A key mechanism through which networks promote cooperation is clustering. Within clusters, conditional cooperators are insulated from exploitation by noncooperators, allowing them to reap the benefits of cooperation. Dynamic networks, where ties can be shed and new ties formed, allow for the endogenous emergence of clusters of cooperators. Although past work suggests that either reputation processes or network dynamics can increase clustering and cooperation, existing work on network dynamics conflates reputations and dynamics. Here we report results from a large-scale experiment (total = 2,675) that embedded participants in clustered or random networks that were static or dynamic, with varying levels of reputational information. Results show that initial network clustering predicts cooperation in static networks, but not in dynamic ones. Further, our experiment shows that while reputations are important for partner choice, cooperation levels are driven purely by dynamics. Supplemental conditions confirmed this lack of a reputation effect. Importantly, we find that when participants make individual choices to cooperate or defect with each partner, as opposed to a single decision that applies to all partners (as is standard in the literature on cooperation in networks), cooperation rates in static networks are as high as cooperation rates in dynamic networks. This finding highlights the importance of structured relations for sustained cooperation, and shows how giving experimental participants more realistic choices has important consequences for whether dynamic networks promote higher levels of cooperation than static networks.

A drive-through customer pays for the order of the next customer in line, sparking a cascade of nearly 400 customers paying it forward (Phippen 2014). A farmer helps build a neighbor's barn without payment, confident that neighbors will help him when the need arises, a tradition with roots in colonial America and still practiced in Amish and Mennonite communities (Kadushin 2012). A prisoner shares his drugs with fellow inmates, not knowing whether or when they will reciprocate (Mjåland 2014). A researcher agrees to do a time-intensive peer review, with the understanding-or perhaps hope-that future papers she submits will receive similarly careful reviews. A hunter-gatherer gives meat to others, without 747290A SRXXX10.

prosocial-led groups as a whole are substantially more productive than proself-led groups. Indeed, as predicted, prosocial leaders were even more effective in maintaining large group contributions than the standard peer sanctioning system, where the ability to punish others is distributed equally among all group members. Importantly, these results suggest that prosocial leaders-but not proself leaders-are an effective solution to collective action problems. Therefore, I also address whether group members tend to select prosocials for leadership positions (Study 2a), and whether they are able to identify prosocials when all group members are able to compete for the leadership position by vying to be elected to the role (Study 2b). Results from these studies suggest that people prefer prosocials for the leader position, and that while group members do compete for leadership, both prosocial and proself individuals compete at similar rates, such that vi prosocials remain higher contributors than their proself counterparts. As a result, prosocials are particularly likely to be selected for leadership positions when group contributions are known. Study 2b also demonstrates that groups that hold democratic elections for leadership may induce more cooperative behavior in their members not only once the leader is installed, but even before leadership hierarchies emerge as a result of competition to be elected. Taken as a whole, the findings suggest that putting power and influence in the right hands solves collective action problems and promotes collective welfare. Leadership-specifically, democratically elected, prosocial leadershippromises an effective solution to collective action problems.vii

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Researchers have long argued that religion increases prosocial behavior, but results are equivocal. Recent findings on priming religious concepts seem to show that religion drives other-regarding behaviors. However, here I suggest that some religious concepts may not only be priming religion, but also anticipated rewards. I present the results of a new experiment that primes reward-related and rewardunrelated religious or secular concepts. Results show that priming reward-related concepts positively impacts prosocial behavior (specifically, generosity), regardless of their religious content. Religious cognitions alone are not sufficient to elicit generosity: reward cognitions must be present as well.