Does society shape individuals? Examining this question is difficult, as individuals influence the collective just as the collective may influence the individual. We use a large-scale field experiment to solve this causality problem and show that groups with stronger community participation render their members generally more altruistic and trusting towards anonymous strangers. Moreover, stronger community participation also causes a boost in trust towards those who reciprocate favours, thus generating stronger implicit punishment for untrustworthy individuals. Increased community participation enhances the strategic sophistication of individuals and raises the prevalence of Machiavellian strategies.