Flying in the face of nature.

Functional explanations of animal behaviour are based on the idea that decisions will maximise fitness. It is not straightforward to investigate functional explanations by means of laboratory experiments. Animals are not expected to use general mathematical principles to achieve optimal behaviour. Instead, they are likely to follow rules that evolved to perform well in a particular environment that may be significantly different from the environment provided in the lab. A consequence is that there is no guarantee that an attempt to replicate an environment in the lab will result in appropriate behaviour. The exact way in which the environment is instantiated in the lab may be critical. Environments with the same formal description are not necessarily equivalent. After giving examples in which the same description is instantiated on different scales, I focus on attempts to use the marginal value theorem to predict behaviour.