August Weismann is famous for having argued against the inheritance of acquired characters. However, an analysis of his work indicates that Weismann always held that changes in external conditions, acting during development, were the necessary causes of variation in the hereditary material. For much of his career he held that acquired germ-plasm variation was inherited. An irony, which is in tension with much of the standard twentieth-century history of biology, thus exists – Weismann was not a Weismannian. I distinguish three (...) claims regarding the germ-plasm: (1) its continuity, (2) its morphological sequestration, and (3) its variational sequestration. With respect to changes in Weismann’s views on the cause of variation, I divide his career into four stages. For each stage I analyze his beliefs on the relative importance of changes in external conditions and sexual reproduction as causes of variation in the hereditary material. Weismann believed, and Weismannism denies, that variation, heredity, and development were deeply intertwined processes. This article is part of a larger project comparing commitments regarding variation during the latter half of the nineteenth century. (shrink)

Bernard Norton's friends in the history of science have had many reasons for commemorating, with admiration and affection, not only his research and teaching but no less his conversation and his company. One of his most estimable traits was his refusal to beat about the bush in raising the questions he thought worthwhile pursuing. I still remember discoursing at Pittsburgh on Darwin's route to his theory of natural selection, and being asked at the end by Bernard what were Darwin's views (...) on heredity. I answered with the conventional waffle to the effect that the theory concerned the populational fate rather than the individual production and transmission of heritable variation, so that whatever views Darwin had on heredity had only a subsidiary place in his theorizing. Bernard was not fooled. ‘I would have thought’, he said, ‘that in order to understand anyone's theorising about evolution it would be necessary to look at his views on heredity’. (shrink)

Physics matters less than we once thought to the making of Mendel. But it matters more than we tend to recognize to the making of Mendelism. This paper charts the variety of ways in which diverse kinds of physics impinged upon the Galtonian tradition which formed Mendelism’s matrix. The work of three Galtonians in particular is considered: Francis Galton himself, W. F. R. Weldon and William Bateson. One aim is to suggest that tracking influence from physics can bring into focus (...) important but now little-remembered flexibilities in the Galtonian tradition. Another is to show by example why generalizations about what happens when ‘physics’ meets ‘biology’ require caution. Even for a single research tradition in Britain in the decades around 1900, these categories were large, containing multitudes. (shrink)

T. H. Morgan, A. H. Sturtevant, H. J. Muller and C. B. Bridges published their comprehensive treatise "The Mechanism of Mendelian Heredity" in 1915. By 1920 Morgan 's "Chromosome Theory of Heredity" was generally accepted by geneticists in the United States, and by British geneticists by 1925. By 1930 it had been incorporated into most general biology, botany, and zoology textbooks as established knowledge. In this paper, I examine the reasons why it was accepted as part of a series of (...) comparative studies of theory-acceptance in the sciences. In this context it is of interest to look at the persuasiveness of confirmed novel predictions, a factor often regarded by philosophers of science as the most important way to justify a theory. Here it turns out to play a role in the decision of some geneticists to accept the theory, but is generally less important than the CTH's ability to explain Mendelian inheritance, sex-linked inheritance, non-disjunction, and the connection between linkage groups and the number of chromosome pairs; in other words, to establish a firm connection between genetics and cytology. It is remarkable that geneticists were willing to accept the CTH as applicable to all organisms at a time when it had been confirmed only for Drosophila. The construction of maps showing the location on the chromosomes of genes for specific characters was especially convincing for non-geneticists. (shrink)

Cytogenetics was born of the confluence of two so-far independent fields: cytological studies and breeding studies, which merged through the identification of genes with chromosomes. In this paper I argue that genes were introduced as functional entities. Functional explanations are presented here as a subclass of inferences to the best explanation and I argue that abductive arguments do not offer conclusive proof for the existence of the entities postulated through them. However, functional explanations usually follow a scheme laid out by (...) Fodor (1968): there is a first phase where hypothetical entities are postulated and individuated through their effects; there is a second phase where the physical structures responsible for these effects are sought. I analyze the development of both phases in the construction of the chromosome theory of Mendelian inheritance. I will argue that first-phase theories are important to set conditions of identification for the functions played by a certain structure in a given containing system. (shrink)