He is equally sober in his discussion of the strengths and weaknesses of the ‘model systems’ approach so beloved by most contemporary developmental biologists while extremely effective as a paradigm for exple ration of basic and common developmental processes, such. an approach may have considerable liabilities and biases when employed in a comparative context. To Raff, comprehensive investigation of the relation between evolution and development requires that one’s phylogenetic analyses be as rigorous and appropriate as analyses of developmental process and mechanism.