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The Endowment Effect as Blessing

We study the idea that seemingly unrelated behavioral biases can coevolve if they jointly compensate for the errors that any one of them would give rise to in isolation. We pay specific attention to barter trade of the kind that was common in prehistoric societies, and suggest that the “endowment effect” and the “winner's curse” could have jointly survived natural selection together. We first study a barter game with a standard payoff-monotone selection dynamics, and show that in the long run the population consists of biased individuals with two opposed biases that perfectly offset each other. In this population, all individuals play the barter game as if they were rational. Next we develop a new family of “hybrid-replicator” dynamics. We show that under such dynamics, biases survive in the population for a long period of time even if they only partially compensate for each other and despite the fact that the rational type's payoff is strictly larger than the payoffs of all other types.