International Journal of Comparative Psychology

This paper

is a response to Campbell and Hodos' continuing critiques of the field of comparative psychology. Their opinion to the contrary, I show that anagenesis is still a useful concept to evolution scientists and that anagenetic analysis provides a viable and fruitful approach to theory development in comparative psychology. Anagenesis suggests improvement with evolution and the idea of complexity as an indicator of evolutionary progress is discussed. Finally, the paper discusses the utility of a modified form of the Scala naturae, namely the concept of integrative levels by showing how T. C. Schneirla has used this idea as the foundation of his significant theoretical contributions to comparative psychology