Abstract

This study aims to reveal the nature and motivation of human cooperation. By adopting the public goods game paradigm of competition and repetition, and introducing factors such as punishment and heterogeneous contributions, an experiment was conducted at Nanjing University in China, where 224 undergraduate students participated in seven games, including intragroup and intergroup competition. Meanwhile, participants’ social value orientation (SVO) was measured. The results indicated that cooperation (non-zero contribution) was the common choice for participants, but their contributions varied across rounds and games. Individuals generally act as conditional free-riders in intragroup competition games, i.e., they use the “small for big” strategy. In contrast, individuals generally act as conditional cooperators in intergroup competitive games, i.e., they use the “tit for tat” strategy. Although SVO should theoretically be related to contribution, analysis revealed that participants’ contributions were not significantly dominated by SVO, but were primarily driven by self-interest. Specifically, individuals switch back and forth between conditional cooperators and conditional free-riders to seek maximum self-interest. Our results not only reveal the complexity and strategic nature of human behavior in competitive contexts but also highlight the central role of self-interest in driving individual decision-making, reflecting the balance between individuals’ pursuit of self-interest and adaptation to the environment in social interactions.