Tinbergen suggested there are four major aims or questions in ethology. All of these contribute to the larger single question of why animals behave as they do. Here, I emphasise one aim, to understand the evolution of behaviour. Using studies of sexual communication in túngara frogs (Physalaemus pustulosus) I attempt to illustrate how an analysis of the past evolution of behaviour can contribute to our understanding of its current function and the details of the mechanisms guiding it. I argue that integration of Tinbergen's four questions not only give us a more complete understanding of the biology of behaviour, it might be necessary to give us a correct understanding.