Optimistic and realistic perspectives on cognitive biases

•Different definitions of cognitive bias are identified and discussed.•Various authors have failed to explain the evolution of cognitive biases.•We can understand cognitive biases by incorporating internal costs into models.•It is possible to have adaptive explanations for sub-optimal behaviours.

Numerous papers have tried to explain cognitive biases, such as optimism and overconfidence, from an evolutionary perspective. The attempts have met with mixed success. I identify why some approaches are more successful than others in explaining sub-optimal behaviours. I conclude that some evolutionary explanations of cognitive biases can be successful; the relevant explanation will depend on the particular bias being studied. In particular, I highlight the need to incorporate internal costs when considering the evolution of mental mechanisms, and how this can provide adaptive explanations of sub-optimal behaviours.