Person:

Hauser, Oliver

Preserving global public goods, such as the planet’s ecosystem, depends on large-scale cooperation, which is difficult to achieve because the standard reciprocity mechanisms weaken in large groups. Here we demonstrate a method by which reciprocity can maintain cooperation in a large-scale public goods game (PGG). In a first experiment, participants in groups of on average 39 people play one round of a Prisoner’s Dilemma (PD) with their two nearest neighbours on a cyclic network after each PGG round. We observe that people engage in “local-to-global” reciprocity, leveraging local interactions to enforce global cooperation: Participants reduce PD cooperation with neighbours who contribute little in the PGG. In response, low PGG contributors increase their contributions if both neighbours defect in the PD. In a control condition, participants do not know their neighbours’ PGG contribution and thus cannot link play in the PD to the PGG. In the control we observe a sharp decline of cooperation in the PGG, while in the treatment condition global cooperation is maintained. In a second experiment, we demonstrate the scalability of this effect: in a 1,000-person PGG, participants in the treatment condition successfully sustain public contributions. Our findings suggest that this simple “local-to-global” intervention facilitates large-scale cooperation.

Cooperation is abundant in the world around us, spanning all levels of biological and social organisation. Yet the existence and maintenance of cooperation is puzzling from an evolutionary perspective because the costs borne to cooperating individuals put them at an evolutionary disadvantage. We thus require an understanding of mechanisms and institutions that can enable cooperation to thrive and be maintained. In this dissertation, I discuss three issues that have presented, or currently present, a challenge to the sustenance of human cooperation. The first chapter addresses an issue of much contemporary debate – inequality. I ask how the well-documented, widespread lack of knowledge of income inequality in society affects the use of costly punishment and costly reward in maintaining public cooperation. When income inequality in a group is not known, the poorest group members are punished (for their low absolute contributions) while the richest are rewarded (for their high absolute contributions). Conversely, when income inequality is revealed, this outcome reverses: the poorest are rewarded (for their high percentage of income contributed) and the richest are punished (for their low percentage contributed). In my next dissertation chapter, I turn to study the emergence of large-scale cooperation. How can cooperation arise and remain stable in large groups? Although it has been argued that the standard reciprocity mechanism weakens in large groups, a simple, scalable intervention—dubbed “local-to-global” reciprocity—successfully maintains public cooperation in groups orders of magnitude larger than previously studied. Local-to-global reciprocity works to maintain group-level cooperation because individuals withhold cooperation from defectors in pairwise interactions as a form of punishment. In the last chapter, I investigate how we can cooperate with future generations: people today face the challenge that they must pay the cost of cooperation now to benefit people in the future who cannot reciprocate their actions. When people decide individually, the renewable resource quickly depletes leaving future generations empty-handed. When decisions today are made by majority vote, however, the resource is sustained for many generations. Voting works because it allows a cooperative majority to restrain a minority of present-day defectors.

We report results from a large online randomised tax experiment in Guatemala. The trial involves short messages and choices presented to taxpayers as part of a CAPTCHA pop-up window immediately before they file a tax return, with the aim of priming honest declarations. In total our sample includes 627,242 taxpayers and 3,232,430 tax declarations made over four months. Treatments include: honesty declaration; information about public goods; information about penalties for dishonesty, questions allowing a taxpayer to choose which public good they think tax money should be spent on; or questions allowing a taxpayer to state a view on the penalty for not declaring honestly. We find no impact of any of these treatments on the average amount of tax declared. We discuss potential causes for this null effect and implications for ‘online nudges’ around honesty priming.

Direct reciprocity is a powerful mechanism for the evolution of cooperation on the basis of repeated interactions. It requires that interacting individuals are sufficiently equal, such that everyone faces similar consequences when they cooperate or defect. Yet inequality is ubiquitous among humans and is generally considered to undermine cooperation and welfare. Most previous models of reciprocity do not include inequality. These models assume that individuals are the same in all relevant aspects. Here we introduce a general framework to study direct reciprocity among unequal individuals. Our model allows for multiple sources of inequality. Subjects can differ in their endowments, their productivities and in how much they benefit from public goods. We find that extreme inequality prevents cooperation. But if subjects differ in productivity, some endowment inequality can be necessary for cooperation to prevail. Our mathematical predictions are supported by a behavioural experiment in which we vary the endowments and productivities of the subjects. We observe that overall welfare is maximized when the two sources of heterogeneity are aligned, such that more productive individuals receive higher endowments. By contrast, when endowments and productivities are misaligned, cooperation quickly breaks down. Our findings have implications for policy-makers concerned with equity, efficiency and the provisioning of public goods.