How (not) to test an optimality model.

The controversy over the use of optimality models in the investigation of adaptation is long-standing. Nonetheless, little or no attention has been paid in this debate to the most important question to be asked about such models: how should the test of an optimality model be structured if the local optimality of the trait is to be assessed? Here we answer this question and describe how such a test can contribute to a test of adaptationism.