Evolutionary game theory is central to a number of themes of this book. Firstly it addresses our concerns over the rationality and common knowledge of rationality (CKR) assumptions used by mainstream game theory. It does this by introducing a more modest assumption that has people adjusting their behaviour on a trial and error basis towards the action which yields the highest pay-off. Many find this more plausible than the pyrotechnics which conventional game theory often seems to demand from its agents under the guise of ‘being rational’ (see the discussion of CKR and CAB in Chapter 2). Secondly it potentially helps with the problem of equilibrium selection (which, as we have seen, has come to haunt the mainstream) by offering an account of the origin of conventions. Finally, the insights of evolutionary game theory are crucial material for many political and philosophical debates, especially those around the State.