T. H. Morgan and the Influence of Mechanistic Materialism on the Development of the Gene Concept 1910–1940

Abstract

I am grateful for the opportunity afforded by this symposium to review the role of T. H. Morgan in the development of modern biology. As is almost always the case with such a retrospective glance, I find that I agree with many ofthe points which I made in earlier writings Morgan, as well as disagree?sometimes alarmingly? with others. In general, however, I believe that the major thesis of an earlier series of papers Morgan, as well as of my fulllength biography (Allen, 1978) remains substantially correct. In brief, the thesis was that Morgan and a number of his contemporaries revolted from the older descriptive and speculative biology of the late 19th century as exemplified by the work of Ernst Haeckel (1834-1919), and August Weismann (1834-1914). The younger biologists embraced a new mechanistic and physico-chemical approach to biology championed byjulius Sachs (18321897) and especially Jacques Loeb (18591924). In making this shift, Morgan and his contemporaries not only sought out new biological problems but also new methods for approaching them. They tried to free biology from the overweening influence of morphology, that all-encompassing area of research which attempted to use anatomy, physiology, and embryology as a means of deducing phylogenetic relationships. The younger generation's aim was to make biol? ogy experimental, quantitative, and rigorous?in Morgan's words to put biology on the same footing as physics and chem? istry. Morgan himself never tired of trying to achieve this goal. Indeed, the final major accomplishment of his career was to estab? lish the Division of Biology at the California Institute of Technology (1928) as a monument to experimental, quantitative and physico-chemical biology. In the present paper I would like to explore more deeply one aspect of Mor? gan's work that I only touched upon in my book of 1978: his changing conception of the fundamental unit of heredity, the gene. In the period between 1900 and 1926 Mor? gan's view of hereditary units underwent a profound shift: from opposition to any kind of fundamental particles of heredity (1900) to championing of the discrete, atomistic, Mendelian gene that existed as a definable segment of a chromosome (1925). Behind this change lies an even more profound reorganization of Mor? gan's thought, a reorganization embodied in his changing conception of the field of heredity itself. In this paper I will explore the significance of that change?its bio? logical, philosophical, and sociological implications?and the effect which this changing conception has had contemporary biology. In particular, I would like to argue that the hardening ofthe concep? tion of heredity championed by Morgan and especially his followers, had profound implications for the fields of genetics, embryology and evolution right down to the present day. Behind Morgan's changing conception of heredity, and of the nature of the gene, lay an important philosophical issue: the growth and spread of mechanistic materialism in biology during the early 20th century. Morgan played an important role in the development of mechanistic thought and its application for a variety of biolog? ical problems, particularly in embryology and genetics. In the following section I will discuss briefly Morgan's background and the general outlines of his career. This will set the stage for a discussion of his move from descriptive to experimental and mechanistic biology in the period between 1891 and 1900.