One of the attractive features of the great classical ethologists was their readiness to ask different kinds of questions about behavior - and to do so without muddling the answers. Niko Tinbergen, for instance, was interested in the evolution of behavior. But he also had interests in the present-day sur vival value of a behavior pattern and in the mechanisms that control it from moment to moment. Broad as his interests were, he clearly separated out the problems and recognized that questions about the history, function, control, and development of behavior require distinct approaches - even...