There is much debate about how humans' decision-making compares with that of other primates. One way to explore this is to compare species' performance using identical methodologies in games with strategical interactions. We presented a computerized Assurance Game, which was either functionally simultaneous or sequential, to investigate how humans, rhesus monkeys and capuchin monkeys used information in decision-making. All species coordinated via sequential play on the payoff-dominant Nash equilibrium, indicating that information about the partner's choice improved decisions. Furthermore, some humans and rhesus monkeys found the payoff-dominant Nash equilibrium in the simultaneous game, even when it was the first condition presented. Thus, Old World primates solved the task without any external cues to their partner's choice. Finally, when not explicitly prohibited, humans spontaneously used language to coordinate on the payoff-dominant Nash equilibrium, indicating an alternative mechanism for converting a simultaneous move game into a sequential move game. This phylogenetic distribution implies that no single mechanism drives coordination decisions across the primates, while humans' ability to spontaneously use language to change the structure of the game emphasizes that multiple mechanisms may be used even within the same species. These results provide insight into the evolution of decision-making strategies across the primates.

There is great interest in the evolution of economic behavior. In typical studies, species are asked to play one of a series of economic games, derived from game theory, and their responses are compared. The advantage of this approach is the relative level of consistency and control that emerges from the games themselves; however, in the typical experiment, procedures and conditions differ widely, particularly between humans and other species. Thus, in the current study, we investigated how three primate species, capuchin monkeys, chimpanzees, and humans, played the Assurance (or Stag Hunt) game using procedures that were, to the best of our ability, the same across species, particularly with respect to training and pretesting. Our goal was to determine what, if any, differences existed in the ways in which these species made decisions in this game. We hypothesized differences along phylogenetic lines, which we found. However, the species were more similar than might be expected. In particular, humans who played using "nonhuman primate-friendly" rules did not behave as is typical. Thus, we find evidence for similarity in decision-making processes across the order Primates. These results indicate that such comparative studies are possible and, moreover, that in any comparison rating species' relative abilities, extreme care must be taken in ensuring that one species does not have an advantage over the others due to methodological procedures.cooperation | coordination | comparative behavior | evolution of behavior R ecent advances in the study of economic decision making have fundamentally altered how we view the science of economics. Beginning with experimental economics (1) and continuing in more recently emerging fields such as neuroeconomics (2, 3), there has been a much more scientific approach to understanding how humans make decisions in economic contexts. Most recently, there has emerged an interest in understanding the evolution of human decision making, primarily as studied using a comparative approach. Although studies of rats and pigeons emerged many decades ago, a recent surge with additional species has provided even more data relevant to social scientists interested in decision making.Although game theory has been used independently in behavioral ecology for decades (4), it is only recently that human economic games have been used extensively to address decisionmaking behavior (5, 6) and underlying neural activity (7). There are certainly reasons to think that humans and other primates might be similar in their decision-making abilities. Other primates are our closest living relatives-we share a common ancestor with chimpanzees within approximately the last 6 million y (8)-so there is a high likelihood of homology. Even though this does not mean identical decision making, it implies similarity in the underlying structures. Nonhuman primates also show many of the same cognitive skills, and even biases (9, 10), as humans. Alternately, though, humans are distinct from other primates, and even a few mil...

Allowing players in public goods games to make small incremental commitments to contributing to the good might facilitate cooperation because it helps to prevent players from being “free ridden,” contributing more to the public good than other group members. Two experiments using a real-time version of the voluntary contribution mechanism were conducted to investigate the hypothesis that players are generally willing to contribute public goods conditional on beliefs that others are doing so at similar levels. Experiment 1 provided evidence that affording a strategy of commitment can increase the production of public goods. Experiment 2 provided evidence that most players are willing to contribute to the public good at a level at or slightly above the contribution of the lowest contributor in the group. Both experiments point to inequity aversion as an important element of play in public goods games.

In this article we report an experiment that examines how demandside bidding can discipline generators in a market for electric power. First we develop a treatment without demand-side bidding; two large firms are allocated baseload and intermediate cost generators such that either firm might unilaterally withhold the capacity of its intermediate cost generators from the market to benefit from the supracompetitive prices that would result from only selling its baseload units. In a converse treatment, ownership of some of the intermediate cost generators is transferred from each of these firms to two other firms such that no one firm could unilaterally restrict output to spawn supracompetitive prices. Having established a well controlled data set with price spikes paralleling those observed in the naturally occurring economy, we also extend the design to include demand-side bidding. We find that demand-side bidding completely neutralizes the exercise of market power and eliminates price spikes even in the presence of structural market power.electric power deregulation ͉ experimental economics T he privatization movement in the electricity industry began in Chile and the United Kingdom in the 1980s and spread to many other countries by the mid-1990s. The U.S. industry joined this trend when California and other states legislated the introduction of competition in the production of electrical energy. This deregulation, however, has dealt most immediately with the wholesale market, not the prices paid by the end-use consumer, whose rates typically are not time-variable throughout the day, week, and season. This has been the crux of the problem, because wholesale energy costs alone vary from peak to off-peak by a factor of 6 or more on normal summer days of high-load demand. Consequently, the local distributor provides a time-average cost buffer, which in effect subsidizes peak consumption while taxing off-peak consumption. In one of our experimental treatments we relax this artificial constraint by introducing price-responsive demand-side bidding, which we use to compare with the usual supply-side auction mechanism both with and without the presence of market power in generation ownership.Market power was an issue in the United Kingdom from the outset of privatization, which created five independent sources of energy: two private generation companies, the nuclear units retained by the Crown, and import competition on transmission lines connecting the United Kingdom grid with France and Scotland. Competition, however, was compromised by three considerations. Capacity on the interconnect lines to Scotland and France was too small to be a competitive factor. Nuclear energy provided only low-cost baseload capacity and was not competitive at the short-run margin. All load following capacity, which represents the critical marginal generator units, was owned by the two new generator companies created by privatization. Finally, no technical provision was made under privatization to mandate or encourage demand-side bidding im...

Compared with other species, exchange among non-kin is a hallmark of human sociality in both the breadth of individuals and total resources involved. One hypothesis is that extensive exchange evolved to buffer the risks associated with hominid dietary specialization on calorie dense, large packages, especially from hunting. 'Lucky' individuals share food with 'unlucky' individuals with the expectation of reciprocity when roles are reversed. Cross-cultural data provide prima facie evidence of pair-wise reciprocity and an almost universal association of high-variance (HV) resources with greater exchange. However, such evidence is not definitive; an alternative hypothesis is that food sharing is really 'tolerated theft', in which individuals possessing more food allow others to steal from them, owing to the threat of violence from hungry individuals. Pair-wise correlations may reflect proximity providing greater opportunities for mutual theft of food. We report a laboratory experiment of foraging and food consumption in a virtual world, designed to test the risk-reduction hypothesis by determining whether people form reciprocal relationships in response to variance of resource acquisition, even when there is no external enforcement of any transfer agreements that might emerge. Individuals can forage in a high-mean, HV patch or a low-mean, low-variance (LV) patch. The key feature of the experimental design is that individuals can transfer resources to others. We find that sharing hardly occurs after LV foraging, but among HV foragers sharing increases dramatically over time. The results provide strong support for the hypothesis that people are pre-disposed to evaluate gains from exchange and respond to unsynchronized variance in resource availability through endogenous reciprocal trading relationships.

to BJW. We thank the editor and two anonymous reviewers for comments that have improved the paper, Megan Luetje for recruiting our human participants, and Jeffrey Kirchner for his software programming.

We compare first-price auctions to an exchange process that we term "multilateral negotiations." In multilateral negotiations, a buyer solicits price offers for a homogeneous product from sellers with privately known costs, and then plays the sellers off one another to obtain additional price concessions. Using the experimental method, we find that with four sellers, transaction prices are statistically indistinguishable in the two institutions, but with two sellers, prices are higher in multilateral negotiations than in first-price auctions. The institutions are equally efficient with two sellers, but multilateral negotiations are slightly more efficient with four sellers.

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