Humans decide to help others more often in poor environments

Prosocial behaviours are essential for solving global challenges. Typically these behaviours are measured using economic games or tasks where people decide between helping or not. However, in everyday life, current behaviours are interrupted with alternatives. Across three samples, people (total n=510) watched a movie whilst encountering opportunities to interrupt it to benefit another person or themselves. Crucially, participants decided in poor and rich environments where the average reward values of opportunities changed. We demonstrate a robust environmental influence on decisions that benefit others. People were more willing to interrupt their behaviour to help others in poor compared to rich environments. Computational modelling revealed that the opportunity costs of different environments were valued distinctly for others. Factors of utilitarianism, empathy and motivation, captured variability in opportunity costs for others. We show that when we decide to engage in prosocial behaviours depends on the environment which is critical as environments change.