Human cooperation in changing groups: evidence from a large-scale public goods game

How people cooperate to provide public goods is a major scientific question and crucial for addressing many societal problems. Previous research studied how people cooperate in stable groups in repeated or one-time-only encounters. However, most real-world public good problems occur in groups with a gradually changing composition due to old members leaving and new members arriving. How group changes are related to cooperation in public good provision is not well understood. To address this issue, we analyze a dataset from an online public goods game comprising 1.5 million contribution decisions made by 135 thousand players in 11.3 thousand groups with 234 thousand changes in group composition. We find that changes in group composition negatively relate to cooperation, mainly because newcomers contribute less than incumbents. During the process of moving from newcomer status to incumbent status, individuals cooperate more and more in line with incumbents.