 Despite its eclipse by behaviorism in North America, the study of instinct was rehabilitated in Europe on either side of World War Two by the founders of ethology, Konrad Lorenz and Niko Tinbergen (Tinbergen 1942; 1951; Lorenz 1957 (1937); Lorenz and Tinbergen 1957 (1938)). Ethology was a Darwinian approach to behavior and the direct ancestor of today’s behavioral ecology and sociobiology. It treated an organism’s behavior as simply one more evolved characteristic alongside its skeleton and its digestive system. Innate behavior was thought to be composed of identifiable units – ‘fixed action patterns’ – whose evolution could be studied like that of a bone by comparing the different form taken by the same (homologous) behavior in different species. The evolutionary relationships of birds, for example, were thought by the early ethologists to be reflected in similarities and differences in their courtship rituals as reliably as in similarities and differences in their bones.