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This project aims to understand whether players are affected by evolutionary forces when making decisions in a two-player contest. Indeed, the experimental literature shows that contestants almost systematically invest more effort in the contest than predicted by the Nash equilibrium. One possible explanation is that there are evolutionary forces that cause this paternal overbidding. However, testing the predictions of evolutionary game theory requires a very long-time horizon which is not really possible to transcribable in the lab. Therefore, we have imagined an experimental design that we believe is capable of understanding how evolutionary forces impact the decisions of participants in the lab. To do so, we start from the "evolutionary" vision of equilibrium as defended by Maynard Smith: evolutionarily stable equilibrium (ESS) corresponds to a situation in which the introduction of a new strategy (called "mutant") into a population does not change the dynamics of the game. Thus, we will expose participants in a traditional two-player contest game to "mutants", i.e. to computers potentially having a completely different strategy than "human" players. By testing the stability of the equilibria to this "mutant invasion", we test the evolutionarily stable character of the choices made by the participants. Our experimetantion consists on 4 sessions (one baseline and three treatments) and we detail the hypotheses we want to test : H1 : in the baseline, we expect bids to be higher than those predicted by the Nash equilibrium. H2 : in the treatment 1, we expect bids from unconstrained players to increase once some players have been constrained to play the evolutionarily stable strategy. H3 : in the treatment 2, a) We expect bids from unconstrained players to increase once some players have been constrained to play the evolutionarily stable strategy. b) We expect the increase in bids from unconstrained players to be larger and/or faster when the share of players constrained to play the evolutionarily stable strategy increases (comparison between treatment 1 and treatment 2). H4 : in treatment 3, we expect that the bids of unconstrained players will not change significantly once some players have been constrained to play the Nash strategy. Variables We manipulate the number of subjects forced to play a strategy: - 4 subjects playing the evolutionarily stable strategy; - 8 subjects playing the evolutionarily stable strategy; - 8 subjects playing the Nash strategy. Measured variables The only outcome variable will be the bid made by each subject. It is a variable that can take integer values between 0 and 60. In addition, we will use responses to a demographic questionnaire, a CRT questionnaire and a questionnaire on subjects' motivations in their decision-making as control variables (see the questionnaires on the instructions - in French). Finally, during each round, we ask subjects to estimate the choices made by their opponents. This will help us understand how subjects anticipate the actions of others. Data collection procedure Each subject will participate to 30 rounds of a simple Tullock contest game and will receive 60 ECU at the beginning of each round. The payoff for one round is equal to the initial dotation + the probability (depending of relative effort) of getting the prize of value 60 ECU minus the cost of effort between 0 and 60 ECU. The final individual payoff in ECU is given by the sum of payoffs over the 30 rounds. The conversion rate is 100 ECU for 1 euros. There will be also a CRT with three questions with each good answer paid 0.5 euros. The sessions will last about 20 minutes and we expect an average individual gain between 15 and 17 euros, without the show-up fee of 6 euros. Sammple size Our target sample size is 160 participants. Sample size rationale We used the Stata software to conduct a power analysis. Our goal was to obtain .80 power to detect a medium effect size of 2.8 points at the standard .05 alpha error probability. Study design Between subjects design with one factor (bids in a lotery contest) and 3 treatments (4 players forced to play the evolutionarily stable strategy ; 8 players forced to play the evolutionarily stable strategy ; 8 players forced to play the Nash strategy.

Supplemental material, Response-Referee2-FINAL for Group cooperation against a hegemon by Guillaume Cheikbossian in Journal of Theoretical Politics

In this paper, I study the ability of group members to cooperate against an incumbent in a repeated rent-seeking game and where group members and the incumbent have di¤erent valuations of the prize. I …rst consider that group members use Nash Reversion Strategies (NRS) to support cooperative behavior and show that full cooperation within the group is more easily sustained as a Stationary Subgame Perfect (Nash) Equilibrium (SSPE) as either group size, or the heterogeneity in the valuation of the prize, increases. In turn, I show that full cooperation within the challenger group can also be sustained as a Weakly Renegotiation-Proof Equilibrium (WRPE). Yet, an increase in group size makes it more di¢ cult to sustain within-group cooperation but an increase in the relative valuation of the prize by group members still facilitates group cooperation.

We provide an evolutionary explanation for the well-established evidence of the existence of in-group favoritism in intergroup conflict. Using a model of group contest, we show that the larger the number of groups competing against one another or the larger the degree of complementarity between individual efforts, the more likely group members are altruistic towards their teammates under preference evolution.

We revisit the group size paradox in a model where two groups of different sizes compete for a prize exhibiting a varying degree of rivalry and where group effort is given by a CES function of individual e¤orts. We show that the larger group can be more successful than the smaller group if the degree of complementarity is sufficiently high relative to the degree of rivalry of the prize.

In a two-stage game with three firms and two countries, we study the profitability of a domestic merger in the context of an international oligopoly game with differentiated products and in a strategic trade policy environment. In contrast to a completely unregulated economy, we show that the domestic merger under Cournot competition is always profitable to the host country irrespective of the degree of product differentiation. Furthermore, it is also profitable to the competing country - hosting one firm only if products are sufficiently differentiated. Under Bertrand competition the merger is always profitable to both countries independently of the product range rivalry. But in a strategic trade environment it is more profitable to the country in which the merger occurs than to the other country.

This paper analyzes how the stability of the tacit cooperation within a fringe of sev- eral identical ?rms is affected by the presence of a more e¢ cient ?rm which does not take part in their cooperative agreement. The model assumes that the ?rms of the fringe adopt ?stick and carrot?strategies à la Abreu (1986, 1988) to support cooperation, while the outside ?rm plays its one-period best response function to these strategies, regardless of the history of play. Assuming a linear demand function and constant marginal costs, we then obtain conditions for the coopera- tion within the fringe to be sustainable and focus on the most cooperative symmetric punishment (MCSP) that sustains cooperation. We show that the MCSP is harsher when the number of ?rms involved in the agreement is relatively large or when their relative cost disadvantage is relatively small. However, both a larger number of ?rms and a larger cost disadvantage make it more di¢ cult to sustain the cooperation.

This paper analyzes the problem of international environmental cooperation as a coalition formation game. For this purpose, we develop a simple model with three countries of unequal size. Strate- gic interactions between those countries come from the imperfect competition among producers in global markets and from the transboundary pollution generated by the ?rms. To capture e¢ ciency gains from coordinating policies, countries can join a coalition and sign an international environmental agreement. The equilibrium coalition structure then depends on the country-size asymmetry and on the marginal environmental damage. Interestingly, we show that the grand coalition is less likely to emerge as an equi- librium outcome once two countries form a subcoalition. Furthermore, the further enlargement of the initial subcoalition can be blocked either by the outsider or by the insiders.

This paper analyzes the ability of group members to cooperate in rent-seeking activities in a context of between-group competition. For this purpose, we develop an infinitely repeated rent-seeking game between two groups of different size. We first investigate Nash reversion strategies to support cooperative behavior in a given group before analyzing double-edge trigger strategies which have the property that cheating on the cooperative agreement in a given group is followed by non-cooperation in this group and cooperation in the rival group. The main conclusion is that the set of parameters for which cooperation can be sustained within the larger group as a subgame perfect outcome is as large as that for which cooperation can be sustained in the smaller group. Hence, in contrast with Olson’s (1965) celebrated thesis but in accordance with many informal and formal observations, the larger group is as effective as the smaller group in furthering its interest.

Law enforcement is decentralized. It is so despite documented interjurisdictional externalities which would justify its centralization. To explain this fact, we construct a political economy model of law enforcement. Under decentralization, law enforcement in each region is in accord with the preferences of regional citizens, but interjurisdictional externalities are neglected. Under centralization, law enforcement for all regions is chosen by a legislature of regional representatives which may take externalities into account. However, the majority rule applies for decisions made by the central legislature and this implies that the allocation of enforcement resources may be skewed in favour of those who belong to the required majority. We show that the choice between centralization and decentralization depends on the technology of law enforcement and the nature of the interjurisdictional externalities.

We present a model of endogenous public good provision and group rent-seeking influence e.g. lobbying. Specifically, two groups with different preferences over public good consumption and different sizes engage in rent-seeking activities to influence policymaking in their preferred direction. When there is within-group cooperation in lobbying, both groups neutralize each other in the political process. Without within-group cooperation, the free-rider problem in lobbying makes the smaller group politically influent. In both cases, rent-seeking by each group is increasing in the degree of preference heterogeneity and in membership size of both groups.

In the presence of spillovers, decentralized provision of local public goods may lead to a higher surplus than centralized provision even if localities have identical preferences. Indeed, free-riding costs associated to decentralization may be larger than the costs of lobbying activities under centralization.

The integration of PECO's in UE The Central Eastern European trade represents a little amount of total European trade : it is less than 1 % of French and German gnp. But in some sectors, the export of Eastern Europe can reach 10 %-20 % of total European import. Thanks to the trade liberalisation process, a significant trade reorientation has taken place, but barriers remain in the sensitive sectors, where the Central Eastern European countries (CEEC's) may have comparative advantages. Although positive (new markets do not compensate for the CMEA trade collapse), the disintegration cost of cmea is decreasing. The analysis of trade at a disaggregated level reveals the sectors where CEEC's have comparative advantages. By estimating the factor content of Eastern European exports, it can been shown that they embody more labour than imports from Western Europe.; Le poids total des peco dans le commerce européen est aujourd'hui faible : il est inférieur à 1 % des PIB français et allemand. Mais dans certains secteurs, les ventes d'Europe de l'Est peuvent atteindre 10 à 20 % des importations totales. Si les mesures de libéralisation se traduisent déjà par une réorientation progressive des échanges vers les marchés occidentaux, des barrières se sont maintenues dans les secteurs sensibles, où précisément les PECO ont des avantages comparés. Bien que positif (les débouchés nouveaux ne compensent pas la perte des marchés garantis par le CAEM), le coût de la désintégration du caem est décroissant. Une analyse du commerce désagrégé permet d'identifier les secteurs où les peco ont des avantages comparés, et de calculer le contenu facto- riel des importations en provenance des PECO : ces importations incorporent plus de travail que les exportations de l'Europe de l'Ouest.