Adaptive Illusions: Evolutionary explanations for motivational biases

People often exhibit 'motivational biases' in their judgements about the likelihood of events involving the self. Typically these take the form of unwarranted optimism about the probability of desirable things happening or over-estimation of the self's effectiveness in controlling events. Such biases appear grossly irrational and have been explained in terms of impression management. However, we argue from first principles that where judgements about whether to undertake a task are made under uncertainty, and the benefits of success outweigh the costs of failure, biased reasoning could be directly adaptive. This argument is explored using an agent-based simulation in which organisms play for energy in an uncertain environment. We show that under certain sets of conditions, organisms with motivationally biased decision-making rules can outperform those lacking such biases.