From machine-theory to entelechy: Two studies in developmental teleology

Abstract

The 1880's and 1890's were exciting decades for a young embryologist. At the outset, Wilhelm Roux announced his program of Developmental Mechanics (Entwickelungsmechanik ) ,' designed to seduce investigation away from endless comparative descriptions of embryos into an experimental analysis of developmental events. Eduard Pfluger, Gustav Born, and Oscar Hertwig, to name a few, championed the same experimental approach in embryology at nearly the same time. By the 1890's the ranks of experimenters had swelled to include Hans Driesch, Curt Herbst, T. H. Morgan, and many others. It was a time when certain techniques developed in plant physiology and cytology converged onto embryology to broach questions about the activities within the cleaving egg -questions, more specifically, about the role of the nucleus in heredity and development, about the formative influences exerted by some cells upon other cells or by external stimuli, and about the regenerative capacities of experimentally altered embryos. Amphibians and echinoderms were the chief martyrs in these quests, but roundworms, gastropods, even protozoa, served embryology too. There were almost as many explanations of development and heredity as experimental animals, and often the choice of the latter determined the tenets of the former. Yves Delage, at the turn of the century, described over thirty general theories of heredity, most of them contemporary and many of them arising directly from experimental embryology.2