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The substantial literature on charitable giving–a prototypical pro-social behavior–commonly faces constraints on sample size, diversity, or experimental design, resulting ina fragmented understanding of factors that influence charitable giving and theirinteractions. We developed a game that co-varies multiple factors that influencegiving—akin to running thousands of experiments. Over 2.7 million decisions, someincentivized, from 257,000 participants in 203 countries were collected. Helping at least 3or 6 strangers, on average, surpassed even the strongest effects of giving to oneself or arelative, respectively. This finding holds cross-culturally. Further, we found substantialheterogeneity from experimental stimuli in all main factor effects (e.g., identifiable victimeffect), often reversing direction. Our findings paint a more comprehensive and promisingpicture of human prosociality.