Can irrational behaviour maximise fitness?

Behavioural models for both humans and other animals often assume economic rationality on the part of decision makers. Economic rationality supposes that outcomes can be assigned objective values within a stable valuation framework and that choices are made to maximise a decision maker's expected payoff. Yet, both human and animal behaviour is often not economically rational. Here, we compare economically rational making strategies with a strategy (trade-off contrasts) that has been proposed to account for decision-making behaviour in humans that departs of axiomatic rationality. We model the fitness of these strategies in a simple environment where choices are made on repeated occasions, there is stochastic fluctuation in the choices available at any given time, and uncertainty about what choices will be available in the future. Our results show that, for at least some of the model parameter space, non-rational decision strategies achieve higher fitness than economically rational strategies. The differences were comparable in magnitude to selection differentials observed in nature.