The origins of (a culture of) cooperation
研究了时间不一致的精英与非精英之间的投资互动，发现消费风险增大或投资回报减少会促进风险共担和合作文化积累，而有限投资回报则推动精英包容性政治与非精英强互惠规范。基于美索不达米亚44个城邦公元前3050-1750年的数据验证了预测。
Abstract We study an investment setting involving time-inconsistent elites and non-elites. The latter embrace norms that provide an intrinsic return on cooperation and may switch to a risk-sharing activity yielding a higher marginal intrinsic return. A more severe consumption risk and/or a smaller investment return increase the profitability of risk-sharing and, in turn, foster cultural accumulation. A limited investment payoff, instead, pushes the elites to enact an inclusive political process to incentivize the non-elites and the latter to reciprocate with strong norms signaling cooperation despite its limited return. These predictions are consistent with data on 44 Mesopotamian polities observed between 3050 and 1750 BCE. While the diffusion of interest-free loans of agricultural products and major irrigation infrastructures was negatively related to the harvest value, the spread of formal merchant institutions was linked to the distance to the trade circuits. Moreover, major irrigation projects were implemented where the climate was more erratic.