Deviant generations, Ricardian equivalence, and growth cycles

Two equilibrium possibilities are known to obtain in a standard overlapping-generations model with dynastic preferences: either the altruistic bequest motive is operative for every generation (in which case, Ricardian equivalence obtains) or it is not, for any generation. Dynamic equilibria, where the bequest motive is occasionally operative, cannot emerge. This paper studies bequest-giving behavior and out-of-steady-state bequest and growth dynamics in a Ak model with intra- and inter-generational consumption externalities. These externalities, by their very presence, do not destroy Ricardian equivalence. They may, however, give rise to deviant generations—generations that do not leave a bequest having received an inheritance, and vice versa—and that seals the fate for Ricardian equivalence. Consumption externalities may also generate interesting indeterminacies and endogenous growth cycles that did not exist otherwise.     

Learning and evolution of altruistic preferences in the Centipede Game

Several studies show that evolution favors non-selfish preferences only if preference types are observable. We present a new evolutionary scenario applied to the Centipede Game, where we adopt self-confirming equilibrium to capture behavior. We show that altruism may be evolutionarily successful even if preferences are unobservable.     

Preference aggregation with randomized social orderings

We show that every binary and Paretian method for passing from preference profiles to lotteries over preferences is associated with a subadditive function on the set of coalitions of individuals. This function gives the power of each coalition to secure its preference for any x over any y.     

Optimality and Natural Selection in Markets

We ask if natural selection in markets favors profit-maximizing firms and, if so, is there a difference between the predictions of models which assume all firms are profit maximizers and the predictions of models which explicitly take account of population dynamics in the market. We show that market selection favors profit maximizing firms, but we also show that the long-run behavior of evolutionary market models is nonetheless not consistent with equilibrium models based on the profit-maximization hypothesis. Dynamic equilibrium paths with market selection are not Pareto optimal, nor even asymptotically optimal. The discrepancy arises because the dynamics created by firm evolution causes prices to vary over time and the resulting dynamical system need not have stable steady states.     

Preference Evolution,Two-Speed Dynamics,and Rapid Social Change

We present a dynamic analysis of the evolution of preferences in a strategic environment. In our model, each player's behavior depends on both the game's payoffs and his idiosyncratic biases, but only the game's payoffs determine his evolutionary success. Dynamics run at two speeds at once; while natural selection slowly reshapes the distribution of preferences, players quickly learn to behave as their preferences dictate. We establish the existence and uniqueness of the paired trajectories of society's preferences and behavior. While aggregate behavior adjusts smoothly in equilibration games, in coordination games aggregate behavior can jump discretely in an instant of evolutionary time. Journal of Economic Literature Classification Numbers: C72, C73.     

Incomplete preferences and rational intransitivity of choice

Do violations of classical rationality theory imply that agents are acting against their self-interest? To answer this question, we investigate whether completeness and transitivity necessarily hold when agents choose outcome rationally—that is, their choice sequences do not lead to dominated outcomes. We show that, because of the danger of money pumps and other manipulations, outcome rationality implies that agents must have transitive psychological preferences. Revealed preferences, on the other hand, must be complete since agents can be forced to choose from any set of options. But these justifications of transitivity and completeness cannot be combined. We show that if psychological preferences are incomplete then revealed preferences can be intransitive without exposing agents to manipulations or violating outcome rationality. We also show that a specific case of nonstandard behavior, status quo maintenance, is outcome-rational in the simple environments considered in the experimental literature, but not in more complex settings.     

Evolutionary stability of discrimination under observability

We study the evolution of preferences under perfect and almost perfect observability in symmetric 2-player games. We demonstrate that if nature can choose from a sufficiently general preference space, which includes preferences over outcomes that may depend on the opponent's preference-type, then, in most games, only discriminating preferences (treating different types of opponents differently in the same situation) can be evolutionary stable and some discriminating types are stable in a very strong sense in all games. We use these discriminating types to show that any symmetric outcome which gives players more than their minmax value in material payoffs (fitness) can be seen as equilibrium play of a player population with such strongly stable preferences.     

Evolutionary stability of discrimination under observability

We study the evolution of preferences under perfect and almost perfect observability in symmetric 2-player games. We demonstrate that if nature can choose from a sufficiently general preference space, which includes preferences over outcomes that may depend on the opponent's preference-type, then, in most games, only discriminating preferences (treating different types of opponents differently in the same situation) can be evolutionary stable and some discriminating types are stable in a very strong sense in all games. We use these discriminating types to show that any symmetric outcome which gives players more than their minmax value in material payoffs (fitness) can be seen as equilibrium play of a player population with such strongly stable preferences.     

Proper scoring rules for general decision models

If a decision maker whose behavior conforms to the max-min expected utility model is faced with a scoring rule for a subjective expected utility decision maker, she will always announce a probability belonging to her set of priors; moreover, for any prior in the set, there is a scoring rule inducing the agent to announce that prior. We also show that on the domain of Choquet expected utility preferences with risk neutral lottery evaluation and totally monotone capacities, proper scoring rules do not exist. This implies the non-existence of proper scoring rules for any larger class of preferences (CEU with convex capacities, multiple priors).     

Law of the jungle: firm survival and price dynamics in evolutionary markets

In this paper I develop a simple, and general model of supply and demand within which almost any theory of consumer and producer behaviour may be integrated by varying parameters. I then investigate the dynamics of this model and its implications for the theory of market evolution, and show that it unifies a number of insights from evolutionary economics. I extend upon these evolutionary theories and also characterise the distribution of prices across the market and investigate its evolution over time.     

Improving the performance of an economic system: Controlling chaos

In this paper we use a simple model of evolutionary market dynamics to illustrate how chaotic behavior can be controlled by making small changes in a parameter that is accessible to the decision makers. This approach is commonly referred to as `targeting' – one can easily switch from a chaotic evolution of the market to any desired regular motion. We show that complex dynamics leads to inferior performance in our model and that an application of such a correction mechanism by the decision makers of the firms yields a considerable improvement in the system's economical properties in terms of profits and profitability. We present numerical simulations in order to illustrate the effectiveness of this method.     

On the rationalizability of observed consumers’ choices when preferences depend on budget sets and (potentially) on anything else

We prove that defining consumers’ preferences over budget sets is both necessary and sufficient to make every fully informative and finite set of observed consumption choices rationalizable by a collection of preferences which are transitive, complete, and monotone with respect to own consumption. Our finding has two important theoretical consequences. First, assuming that preferences depend on budget sets is illegitimate under the scientific commitments of revealed preference theory. Second, as long as consumers’ preferences are not defined over budget sets, we can assume that preferences depend on observable objects other than own consumption without compromising the logical possibility to reject the model against observation. We however point out that, despite this logical possibility, in practice it can be almost impossible to reject a model where preferences are defined over objects that depend on budget sets. As an example of this we show that if preferences are defined over consumption choices of other individuals then rationalization fails only in cases of negligible practical interest.     

Matching soulmates

We study iterated matching of soulmates (IMS), a recursive process of forming coalitions that are mutually preferred by members to any other coalition containing individuals as yet unmatched by this process. If all players can be matched this way, preferences are IMS-complete. A mechanism is a soulmate mechanism if it allows the formation of all soulmate coalitions. Our model follows Banerjee, Konishi, and Sönmez, except reported preferences are strategic variables. We investigate the incentive and stability properties of soulmate mechanisms. In contrast to prior literature, we do not impose conditions that ensure IMS-completeness. A fundamental result is that, (1) any group of players who could change their reported preferences and mutually benefit does not contain any players who were matched as soulmates and reported their preferences truthfully. As corollaries, (2) for any IMS-complete profile, soulmate mechanisms have a truthful strong Nash equilibrium, and (3) as long as all players matched as soulmates report their preferences truthfully, there is no incentive for any to deviate. Moreover, (4) soulmate coalitions are invariant core coalitions—that is, any soulmate coalition will be a coalition in every outcome in the core. To accompany our theoretical results, we present real-world data analysis and simulations that highlight the prevalence of situations in which many, but not all, players can be matched as soulmates. In the Appendix we relate IMS to other well-known coalition formation processes.     

Cycles of Learning in the Centipede Game

This paper studies the evolutionary properties of the Centipede Game. For this game, the use of backward induction as a model of rational behavior has been consistently challenged by the experimental evidence. Our claim is that backward induction can still accurately predict the players' behavior, provided that they are given time enough to appreciate the strategic environment in which they operate. We support this claim by proving convergence to the backward induction solution for all continuous-time monotonic selection dynamics. However, we also show that this solution is intrinsically unstable, and how this instability is positively related to the length of the game. Journal of Economic Literature Classification Numbers: C72, C79.     

Learning,Matching, and Aggregation

Fictitious play and stimulus–response/reinforcement learning are examined in the context of a large population where agents are repeatedly randomly matched. We show that the aggregation of this learning behavior can be qualitatively different from learning at the level of the individual. This aggregate dynamic belongs to the same class of simply defined dynamic as do several formulations of evolutionary dynamics. We obtain sufficient conditions for convergence and divergence which are valid for the whole class of dynamics. These results are therefore robust to most specifications of adaptive behavior.Journal of Economic LiteratureClassification Numbers: C72, D83.     

Domestication experiments reveal developmental link between friendliness and cognition

The goal of economics is to understand human preferences. Most research focuses on adult humans and does not take an evolutionary approach. In biology experimental evolution has been able to shift the preferences of animals. As an example, artificial selection for friendly behavior toward humans results in a syndrome of changes that strongly resembles differences between wild and domestic animals. These domestication experiments have revealed precise genetic and neurobiological systems that are altered by the selection and linked through expanded windows of development. Similar evolutionary experiments selecting for a range of social, risk or discounting preferences could push economics toward consilience with biology. Prospects for a unified theory of economic behavior would be drastically improved.     

When is it coevolution?

This paper evaluates the differences between Norgaard's and Winder et al.'s approach to socio-environmental coevolution. Winder et al. emphasize the evolutionary dynamics of coevolutionary change. These were omnipresent in Norgaard's work but they have not been adequately explored by other ecological economists. I argue that Winder et al.'s definition of coevolution is in essence the same as Norgaard's and that their real differences are, how they see coevolution applied and how far they are willing to draw a priori a line between evolutionary and non-evolutionary socio-environmental dynamics. My thesis is that at this stage a more open approach to evolutionary dynamics and coevolution a la Norgaard is a wiser strategy than Winder et al.'s narrower approach.     

Coalitional manipulation and the Pareto rule

This paper examines aggregation procedures that map profiles of individual preferences into choice sets. An aggregation procedure is said to be “manipulable by a coalition” if there is a group of individuals, and a preference profile, such that every member of the group prefers the choice set obtained when they are misrepresenting their preferences, to the one obtained when they are honest. We show that the Pareto rule, which is an aggregation procedure that maps profiles of individual preferences into corresponding sets of Pareto optima, is not manipulable by any coalition of individuals under various behavioural assumptions which relate preferences over choice sets to preferences over alternatives. The non-manipulability of the Pareto rule by a single individual follows as a special case under these behavioural assumptions.     

On the Dynamic Foundation of Evolutionary Stability in Continuous Models

We show in this paper that none of the existing static evolutionary stability concepts (ESS, CSS, uninvadability, NIS) is sufficient to guarantee dynamic stability in the weak topology with respect to standard evolutionary dynamics if the strategy space is continuous. We propose a new concept, evolutionary robustness, which is stronger than the previous concepts. Evolutionary robustness ensures dynamic stability for replicator dynamics in doubly symmetric games. Journal of Economic Literature Classification Numbers: C70, 72.