HALL, B. K.; Dalhousie Univ.: The search for evolutionary developmental mechanisms.

I am grateful for the honor bestowed by the St Petersburg Soc. of Naturalist with the awarding of an Alexander Kowalevsky Medal. Initially, I will outline the contributions to evolutionary embryology/morphology made by Kowalevsky, especially how his research opened up an entirely new theory for the origins of the chordates and vertebrates. Then I will trace my own interests in development and how they transformed into an interest in evo-devo. For me, development contributes to evolution by providing an understanding of evolutionary developmental mechanisms � how can and does development change to effect morphological change � and the processes that underlie the formation of homologous and homoplastic features of the phenotype. Consequently, I am an evo-devoist rather than a devo-evoist. A major challenge for the future is to integrate these two approaches. I will attempt to reconstruct what amounts to the evolution of a developmentalist, to paraphrase de Beer, whose influence on my work has been, and still is, substantial. In hindsight, I can detect a number of pivotal individuals, colleagues, collaborators and students who changed my course. My Ph.D. studies on the differentiation of secondary cartilage sought to answer one of the agenda items outlined by de Beer in �� The Vertebrate Skull �� (1937). An invitation to participate in a 1973 Amer. Soc. of Zoologist symposium on �� Models and Mechanisms of Morphological Change in Evolution,�� organized by Paul Maderson, reoriented my career to the study of the evolutionary consequences of skeletal differentiation. At this time I discovered that I had, been working for eight years on derivatives of the neural crest, now recognized as key to the origin of the vertebrates, a finding akin to Kowalevsky�s discovery of the notochord in the animals we now know as hemichordates.