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When Humans and Other Animals Behave Irrationally

The field of comparative cognition has been largely concerned with the degree to which animals have analogs of the cognitive capacities of humans (e.g., imitation, categorization), but recently attention has been directed to behavior that is judged to be biased or suboptimal. We and some of our colleagues have studied several of these and have found that pigeons too show similar paradoxical behaviors. In the present review I will discuss three of these behaviors: sunk cost, justification of effort, and unskilled gambling. Sunk cost is the tendency to decide to spend more on a losing project because of the amount already invested. Pigeons show similar effects even when there is no ambiguity about the results of continuing versus changing alternatives. Justification of effort is the added value one often gives to a reward based on the effort exerted to obtain it. Pigeons too prefer stimuli that signal outcomes that they have had to work harder to obtain. Humans engage in unskilled gambling, like lotteries and slot machines, in which the return is typically less than the investment. And pigeons show a similar tendency to choose a low-probability, high-payoff alternative (gamble) over a more optimal, high-probability, low-payoff alternative. The fact that animals such as pigeons show behavior thought to be unique to humans suggests that the basis for such behaviors is not likely to result from culture or social mechanisms and may have basic behavioral origins.