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Edmund Becher Wilson's Early Contributions to the Chromosome

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Edmund Becher Wilson's Early Contributions to the Chromosome Philosophy Study, September 2015, Vol. 5, No. 9, 431-443 doi: 10.17265/2159-5313/2015.09.001 D DAVID PUBLISHING Edmund Becher Wilson’s Early Contributions to the Chromosome Theory of Heredity: A Case Study of Instrumentalism in Science Lilian Al-Chueyr Pereira Martins University of São Paulo The chromosome theory of inheritance was established during the three first decades of the 20th century. During the early stage of its substantiating, there were lots of puzzles and little evidence that could validate it. The cytological processes were obscure and several scientists maintained serious doubts concerning the existence of a connection between Mendel’s principles and the behaviour of chromosomes during cell division. It was vital to associate an external, observable characteristic of the organism to a specific chromosome, and this was achieved when sex was connected to special chromosomes. At that time, however, some important scholars refused to accept or delayed acceptance of the conception that the hereditary factors (later called genes) were physical entities located along the chromosomes. Such was the case of Thomas Morgan (1866-1945) and William Bateson (1861-1926). Their attitudes could be explained by considering the doubtful ground of the hypothesis at that time. It is more difficult, however, to understand the attitude of Edmund Beecher Wilson (1856-1939). Being an expert in cytology he was acquainted with all the difficulties concerning the chromosome hypothesis. Nonetheless, from 1905 onward, he attributed little weight to the problems and dedicated a notable effort to obtaining evidence that could have grounded it. This paper analyses Wilson’s attitude focusing on his studies from 1900 to 1915 and the scientific context of this period. This study led to the conclusion that Wilson’s attitude could be explained in methodological terms by the adoption of an instrumentalist attitude, while Bateson and Morgan adopted a realistic perspective. Keywords: history of genetics, philosophy of biology, chromosome hypothesis/theory, Wilson, Edmund Beecher, instrumentalism 1. Introduction The chromosome theory of inheritance was established during the first three decades of the 20th century. It assumed that the factors (the bearers of hereditary characteristics) were material entities located along the nuclear chromosomes and attempted to establish a parallel between the behaviour of chromosomes during cell division (cytological or microscopic level) and the results of experimental crossings (macroscopic level). The first cytological hints favourable to this idea were presented by Theodor Boveri (1862-1915) and Lilian Al-Chueyr Pereira Martins, Prof., Dr., Department of Biology, University of São Paulo, Campus Ribeirão Preto, Brazil; main research fields: History and Philosophy of Biology mainly focusing on Classical Genetics and Evolution. Acknowledgements: The author is grateful to the Brazilian National Council of Scientific and Technological Development (CNPq) and to the São Paulo State Research Foundation (FAPESP) for supporting this research. Besides that, she is also grateful to Prof. Dr. Anna Carolina Regner for her comments and criticisms that contributed to the improvement of this paper. 432 A CASE STUDY OF INSTRUMENTALISM IN SCIENCE Walter Sutton (1877-1916), in 1902 and 1903. Their work seemed to show that the chromosomes preserve their individuality during all the phases of cell division (Sutton), and that different chromosomes play different roles in the development of the organism (Boveri). However, they did not obtain any evidence of the association of specific chromosomes to any observable characteristic of the organisms they had studied. During the early stage of the substantiation of the chromosome theory, there were lots of puzzles and little evidence that could validate it. The cytological processes were obscure and several scientists maintained serious doubts concerning the existence of a connection between Mendel’s principles and the behaviour of chromosomes during cell division. The individuality and constancy of chromosomes were still doubtful. Without assuming the individuality and constancy of the chromosomes, it was difficult to explain the constancy of Mendel’s factors and the purity of the gametes. It was vital to associate an external, observable characteristic of the organism to a specific chromosome. This was achieved when sex was connected to special chromosomes. Historians of science, such as Garland Allen and Ernst Mayr, considered that important contributions to the problem of sex determination came in 1905 with the independent work of Edmund Beecher Wilson and Nettie Maria Stevens (Allen 1978, 129; Mayr 1982, 751). At that time, however, some important scholars refused to accept or delayed acceptance of the conception that the hereditary factors (later called genes) were physical entities located along the chromosomes. Such was the case of Thomas Morgan (1866-1945) and William Bateson (1861-1926). During the first decade of the 20th century, both researchers were sceptical concerning the theory and did not dedicate any effort to the study of chromosomes. It is easy to understand their attitudes: We expect that someone who does not believe that a theory is true will not dedicate much effort to the investigation of that theory—except if he/she intends to refute it (Martins 2002). It is also easy to understand their attitudes during the second decade of the 20th century taking into account their beliefs. Around 1910, Morgan began to accept the chromosome theory of heredity, and from that time onwards, he devoted most of his time to the substantiation of that conception, without giving any more attention to its problems. Bateson was still cautious, pointing out several weighty difficulties of the theory, and did not consecrate himself to its investigation. Edmund Wilson was one of the key actors in the first act of the chromosome theory of inheritance. Sutton’s work was developed in his laboratory, and it was Wilson who publicised this research and associated it to Boveri’s results, proposing the name “Sutton-Bovery chromosome hypothesis.” He also played a main role in the establishment of a relation between sex and chromosomes. Besides his personal contributions, he trained and influenced some young researchers, namely Alfred H. Sturtevant, Calvin B. Bridges, and Hermann J. Muller who brought contributions to the Mendelian chromosome theory of inheritance. Given Wilson’s early role in the development of this theory, one could expect that he had a strong belief in the theory itself and in its fundamental hypothesis from the very beginning. It is surprising, therefore, to find some sceptical comments published by Wilson during this stage, such as this one: … But I hardly need had that this should not be considered as giving more than a tentative point of attack. It is entirely possible that we are on a wrong track, that the so-called sex chromosomes are only associated in a definite way with the sexual characters, and have in themselves no causative influence on sex production. The whole chromosome theory of heredity, for that matter, stands unproven before the judgment seat. I repeat, therefore, that the subject is not yet ripe for discussion; and what we need now is not more theory or discussion, but more observation and experiment. I believe that the chromosome theory as applied to the sex problem presents a sufficiently plausible face to be taken for a time as a guide A CASE STUDY OF INSTRUMENTALISM IN SCIENCE 433 to further examination of the facts. Perchance the true explanation may be found on the way; even should our working hypothesis prove a false leader. (Wilson 1907, 378-9) As it will be shown in this paper, the above citation was not an isolated event—it was typical of Wilson’s attitude. Here we can find a researcher who has serious doubts concerning the chromosome theory of inheritance and the causal association between chromosomes and sex, but who nevertheless dedicates most of his time to the research of those issues. Wilson’s standpoint is clearly different from those adopted by Bateson and Morgan, and it is not a very usual one. The aim of this paper is to analyse and elucidate Wilson’s attitude, especially in the two first decades of the 20th century. 2. The Situation in the First Decade of the 20th Century The main scientific contributions of Edmund Beecher Wilson (1856-1939), up to 1900, were in the field of embryology (Muller 1943, 8-13). At first, he had no specific interest in heredity or cytology. However, in the 1890’s, he dedicated himself to cytology and published two editions of his famous treatise The Cell in Development and Inheritance (1896; 1900). This book contained a detailed discussion about the relation between the cell nucleus and heredity—a subject that was widely discussed at the time. Wilson was favourable to the conclusion that the nucleus contained the physical basis of heredity and that its chromatin (which he identified with the idioplasm postulated by Nägeli’s theory) was the carrier of the hereditary characters (Muller 1943, 32-34). At that time, it was not known whether the chromosomes were permanent bodies or were produced only during the cell division—the only occasion when they were clearly seen. Wilson was well acquainted with the observational difficulties, but he seemed to believe in the individuality of chromosomes mainly grounded in the evidence found by his friend Theodor Boveri in Ascaris (Wilson 1900, 294-304; Martins 1997, chapter 3, 26). He also favoured some of Weismann’s ideas and accepted that during meiosis there occurred a reduction of chromatin. It seemed, at that time, that the chromosomes were united by their extremities, and that the reduction division would be a transversal one (Muller 1943, 35-36). The details of meiosis had not been cleared up. In 1902, Walter Sutton, who was working with Wilson at the Columbia University, published a paper dealing with the spermatogenesis of a grasshopper, Brachystola magna.
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