Coalitions, tipping points and the speed of evolution

This study considers pure coordination games on networks and the waiting time for an adaptive process of strategic change to achieve efficient coordination. Although it is in the interest of every player to coordinate on a single globally efficient norm, coalitional behavior at a local level can greatly slow, as well as hasten convergence to efficiency. For some networks, when one action becomes efficient enough relative to the other, the effect of coalitional behavior changes abruptly from a conservative effect to a reforming effect. These effects are confirmed for a variety of stylized and empirical social networks found in the literature. For coordination games in which the Pareto efficient and risk dominant equilibria differ, polymorphic states can be the only stochastically stable states

Shared intentions and the advance of cumulative culture in hunter-gatherers

It has been hypothesized that the evolution of modern human cognition was catalyzed by the development of jointly intentional modes of behaviour. From an early age (1-2 years), human infants outperform apes at tasks that involve collaborative activity. Specifically, human infants excel at joint action motivated by reasoning of the form "we will do X" (shared intentions), as opposed to reasoning of the form "I will do X [because he is doing X]" (individual intentions). The mechanism behind the evolution of shared intentionality is unknown. Here we formally model the evolution of jointly intentional action and show under what conditions it is likely to have emerged in humans. Modelling the interaction of hunter-gatherers as a coordination game, we find that when the benefits from adopting new technologies or norms are low but positive, the sharing of intentions does not evolve, despite being a mutualistic behaviour that directly benefits all participants. When the benefits from adopting new technologies or norms are high, such as may be the case during a period of rapid environmental change, shared intentionality evolves and rapidly becomes dominant in the population. Our results shed new light on the evolution of collaborative behaviours.Comment: 6 pages, 4 figures, 1 table, Supplementary Information not include

Risk Attitudes and Risk Dominance in the Long Run

This paper investigates the role that risk attitudes play in the evolution of conventions in the long run. Risk aversion is shown to be associated with the evolution of maximin conventions, and risk seeking with the evolution of payoff dominant conventions

Stochastic Coalitional Better-response Dynamics and Stable Equilibrium

International audienceWe consider coalition formation among players in an n-player finite strategic game over infinite horizon. At each time a randomly formed coalition makes a joint deviation from a current action profile such that at new action profile all the players from the coalition are strictly benefited. Such deviations define a coalitional better-response (CBR) dynamics that is in general stochastic. The CBR dynamics either converges to a K-stable equilibrium or becomes stuck in a closed cycle. We also assume that at each time a selected coalition makes mistake in deviation with small probability that add mutations (perturbations) into CBR dynamics. We prove that all K-stable equilibria and all action profiles from closed cycles, that have minimum stochastic potential, are stochastically stable. Similar statement holds for strict K-stable equilibrium. We apply the CBR dynamics to study the dynamic formation of the networks in the presence of mutations. Under the CBR dynamics all strongly stable networks and closed cycles of networks are stochastically stable

Market sentiments and convergence dynamics in decentralized assignment economies

International audienceIn two-sided markets with transferable utility ('assignment games'), we study the dynamics of trade arrangements and price adjustments as agents from the two market sides stochastically match, break up, and re-match in their pursuit of better opportunities. The underlying model of individual adjustments is based on the behavioral theories of adaptive learning and aspiration adjustment. Dynamics induced by this model converge to approximately optimal and stable market outcomes, but this convergence may be (exponentially) slow. We introduce the notion of a 'market sentiment' that governs which of the two market sides is temporarily more or less amenable to price adjustments, and show that such a feature may significantly speed up convergence

Integration and Segregation

Individuals prefer to coordinate with others, but they differ on the preferred action. In theory, this can give rise to an integrated society with everyone conforming to the same action or a segregated society with members of different groups choosing diverse actions. Social welfare is maximum when society is integrated and everyone conforms on the majority's action. In laboratory experiments, subjects with different preferences segregate into distinct groups and choose diverse actions. To understand the role of partner choice, we then consider an exogenous network of partners. Subjects in the experiment now choose to conform on the action preferred by the majority. Thus, there exists a tension between two deeply held values: social cohesion and freedom of association

Integration and Diversity

We study a setting where individuals prefer to coordinate with others but they differ on their preferred action. Our interest is understanding the role of linking in shaping behavior. So we consider the situation in which interactions are exogenous and a situation where individuals choose links that determine the interactions. Theory is permissive in both settings: conformism (on either of the actions) and diversity (with different groups choosing their preferred actions) are both sustainable in equilibrium. Our experiments reveal that, in an exogenous complete network, subjects choose to conform to the majority's preferred action. By contrast, when linking is free and endogenous, subjects form dense networks (biased in favour of linking within same preferences type) but choose diverse actions. The convergence to diverse actions is faster under endogenous linking as compared to the convergence to conformity on the majority's preferred action under the exogenous complete network. Thus our experiments suggest that individuals use links to resolve the coordination problem