Laudan's thesis that conceptual problem solving is at least as important as empirical problem solving in scientific research is given support by a study of the relation between the chromosome theory and the Mendelian research program. It will be shown that there existed a conceptual tension between the chromosome theory and the Mendelian program. This tension was to be resolved by changing the constraints of the Mendelian program. The relation between the chromosome theory and the Mendelian program is shown to (...) be a good illustration of the influence of science itself on the rational standards governing scientific development. (shrink)

Prompted by recent recognitions of the omnipresence of horizontal gene transfer among microbial species and the associated emphasis on exchange, rather than isolation, as the driving force of evolution, this essay will reflect on hybridization as one of the central concerns of nineteenth-century biology. I will argue that an emphasis on horizontal exchange was already endorsed by ‘biology’ when it came into being around 1800 and was brought to full fruition with the emergence of genetics in 1900. The true revolution (...) in nineteenth-century life sciences, I maintain, consisted in a fundamental shift in ontology, which eroded the boundaries between individual and species, and allowed biologists to move up and down the scale of organic complexity. Life became a property extending both ‘downwards’, to the parts that organisms were composed of, as well as ‘upwards’, to the collective entities constituted by the relations of exchange and interaction that organisms engage in to reproduce. This mode of thinking was crystallized by Gregor Mendel and consolidated in the late nineteenth-century conjunction of biochemistry, microbiology and breeding in agro-industrial settings. This conjunction and its implications are especially exemplified by Wilhelm Johannsen’s and Martinus Beijerinck’s work on pure lines and cultures. An understanding of the subsequent constraints imposed by the evolutionary synthesis of the twentieth century on models of genetic systems may require us to rethink the history of biology and displace Darwin’s theory of natural selection from that history’s centre. (shrink)

This paper presents and discusses a series of hybridization experiments carried out by Nils Herman Nilsson-Ehle between 1900 and 1907 at a plant breeding station in Svalöf, Sweden. Since the late 1880s, the Svalöf station had been renowned for its ‘scientific’ breeding methods, which basically consisted of an elaborate system of record-keeping through which the offspring of individual plants were traced over generations while being meticulously described. This record system corresponded to a certain breeding technique and certain theoretical convictions . (...) Inspired by Tschermack’s translation of Mendel’s Pisum-paper, Nilsson-Ehle began his experiments in 1900 and published a first, major synthesis of his findings in 1908. If one compares these experiments as documented in the breeding records, with their representations in print, one encounters discrepancies in terms of procedure and presentation of data. This can be explained by the fact that Nilsson-Ehle was obliged to follow the recording and breeding procedures institutionalised at Svalöf, and these procedures, grounded in a taxonomic discourse, left little room for Mendelian hybridisation experiments. The twists and turns that this story takes are analysed in terms of Bachelardian philosophy of science, where the ‘epistemological obstacle’ functions as a central, analytic category. In contrast to Bachelard, however, I will characterise these obstacles as being of an institutional, rather than mental, nature. Thus characterized, moreover, they turn out to have been prerequisites as much as barriers to scientific progress. (shrink)

The aim of this virtual special issue is to bring together philosophical and historical perspectives to address long-standing issues in the interpretation, utility, and impacts of quantitative genetics methods and findings. Methodological approaches and the underlying scientific understanding of genetics and heredity have transformed since the field's inception. These advances have brought with them new philosophical issues regarding the interpretation and understanding of quantitative genetic results. The contributions in this issue demonstrate that there is still work to be done integrating (...) old and new methodological and conceptual frameworks. In some cases, new results are interpreted using assumptions based on old concepts and methodologies that need to be explicitly recognised and updated. In other cases, new philosophical tools can be employed to synthesise historical quantitative genetics work with modern methodologies and findings. This introductory article surveys three general themes that have dominated philosophical discussion of quantitative genetics throughout history: (1) how methodologies have changed and transformed our knowledge and interpretations; (2) whether or not quantitative genetics can offer explanations relating to causation and prediction; and (3) the importance of defining the phenotypes under study. We situate the contributions in this virtual special issue within a historical framework addressing these three themes. (shrink)

This paper challenges the common assumption that some phenotypic traits are quantitative while others are qualitative. The distinction between these two kinds of traits is widely influential in biological and biomedical research as well as in scientific education and communication. This is probably due to both historical and epistemological reasons. However, the quantitative/qualitative distinction involves a variety of simplifications on the genetic causes of phenotypic variability and on the development of complex traits. Here, I examine three cases from the life (...) sciences that show inconsistencies in the distinction: Mendelian traits, Mendelian diseases, and polygenic mental disorders. I show that these traits can be framed both quantitatively and qualitatively depending, for instance, on the methods through which they are investigated and on specific epistemic purposes. This suggests that the received view of quantitative and qualitative traits has a limited heuristic power—limited to some local contexts or to the specific methodologies adopted. Throughout the paper, I provide directions for framing phenotypes beyond the quantitative/qualitative distinction. I conclude by pointing at the necessity of developing a principled characterisation of what phenotypic traits, in general, are. (shrink)

I call an experiment “crucial” when it makes possible a decisive choice between conflicting hypotheses. Joharmsen's selection for size and weight within pure lines of beans played a central role in the controversy over continuity or discontinuity in hereditary change, often known as the Biometrician-Mendelian controversy. The “crucial” effect of this experiment was not an instantaneous event, but an extended process of repeating similar experiments and discussing possible objections. It took years before Johannsen's claim about the genetic stability of pure (...) lines was accepted as conclusively demonstrated by the community of geneticists. The paper also argues that crucial experiments thus interpreted contradict certain ideas about the underdetermination of theories by facts and the theory-ladenness of facts which have been influential in recent history and sociology of science. The acceptance of stability in the pure lines did not rest on prior preference for continuity or discontinuity. And this fact permitted a final choice between the two theories. When such choice is characterized as “decisive” or “final”, this is not meant in an absolute philosophical sense. What we achive in these cases is highly reliable empirical knowledge. The philosophical possibility of drawing (almost) any conclusion in doubt should be distinguished from reasonable doubt in empirical science. (shrink)

This paper aims to give an impression of how biologists, at the turn of the twentieth century, came to conceptualize and define the hidden entities presumed to govern the process of hereditary transmission. With that, the stage was set for the emergence of genetics as a biological discipline that came to dominate the life sciences of the twentieth century. The annus mirabilis of 1900, with its triple re-appreciation of Gregor Mendel’s work by the botanists Hugo de Vries, Carl Correns, and (...) Erich Tschermak, can be seen as the watershed after which theorizing about heredity and experimentation—selecting pure lines and Mendelian crossing—became tightly connected. As to concepts before this, this paper will analyze Carl von Nägeli’s ‘idioplasm’, Hugo de Vries’s ‘pangenes’, and August Weismann’s ‘germ plasm’. Carl Correns’s Anlagen and Wilhelm Johannsen’s ‘genes’ would replace them in the decade after 1900.Keywords: Idioplasm ; Pangenes ; Germ plasm ; Anlagen ; Gene; Genotype. (shrink)

In addition to his experiments on selection in pure lines, Wilhelm Johannsen performed less well-known hybridisation experiments with beans. This article describes these experiments and discusses Johannsen’s motivations and interpretations, in the context of developments in early genetics. I will show that Johannsen first presented the hybridisation experiments as an additional control for his selection experiments. The latter were dedicated to investigating heredity with respect to debates concerning the significance of natural selection of continuous variation for evolution. In the course (...) of the establishment of a Mendelian research program after 1900, the study of heredity gained increasing independence from questions of evolution, and focused more on the modes and mechanisms of heredity. Further to their role as control experiments, Johannsen also saw his hybridisation experiments as contributing to the Mendelian program, by extending the scope of the principles of Mendelian inheritance to quantitative characters. Towards the end of the first decade of genetics, Johannsen revisited his experiments to illustrate the many–many relationship between genes and characters, at a time when that relationship appeared increasingly complex, and the unit-character concept, accordingly, became inadequate. For the philosophy of science, the example shows that experiments can have multiple roles in a research programme, and can be interpreted in the light of questions other than those that motivated the experiments in the first place. (shrink)

Textbook descriptions of the foundations of Genetics give the impression that besides Mendel’s no other research on heredity took place during the nineteenth century. However, the publication of the Origin of Species in 1859, and the criticism that it received, placed the study of heredity at the centre of biological thought. Consequently, Herbert Spencer, Charles Darwin himself, Francis Galton, William Keith Brooks, Carl von Nägeli, August Weismann, and Hugo de Vries attempted to develop theories of heredity under an evolutionary perspective, (...) and they were all influenced by each other in various ways. Nonetheless, only Nägeli became aware of Mendel’s experimental work; it has also been questioned whether Mendel even had the intention to develop a theory of heredity. In this article, a short presentation of these theories is made, based on the original writings. The major aim of this article is to suggest that Mendel was definitely not the only one studying heredity before 1900, if he even did this, as may be inferred by textbooks. Although his work had a major impact after 1900, it had no impact during the latter half of the nineteenth century when an active community of students of heredity emerged. Thus, textbooks should not only present the work of Mendel, but also provide a wider view of the actual history and a depiction of science as a social process. (shrink)

Genetics was established on a strict particulate conception of heredity. Genetic linkage, the deviation from independent segregation of Mendelian factors, was conceived as a function of the material allocation of the factors to the chromosomes, rather than to the multiple effects (pleiotropy) of discrete factors. Although linkage maps were abstractions they provided strong support for the chromosomal theory of inheritance. Direct Cytogenetic evidence was scarce until X-ray induced major chromosomal rearrangements allowed direct correlation of genetic and cytological rearrangements. Only with (...) the discovery of the polytenic giant chromosomes in Drosophila larvae in the 1930s were the virtual maps backed up by physical maps of the genetic loci. Genetic linkage became a pivotal experimental tool for the examination of the integration of genetic functions in development and in evolution. Genetic mapping has remained a hallmark of genetic analysis. The location of genes in DNA is a modern extension of the notion of genetic linkage. (shrink)

Bateson's belated acceptance of the chromosome theory came in two main stages, and was permanent, although he retained to the end reservations about some implications and extensions of the theory. Coleman's attempt to explain Bateson's resistance in terms of his conservative mode of thought is critically examined, and rejected: the attributes Coleman assigns to Bateson are all either inappropriate, or irrelevant to chromosome theory, or both. Instead, the diverse factors which contributed to Bateson's resistance are enumerated and discussed. These include (...) deficiencies in the evidence then available to support the theory; embryological difficulties; Bateson's aversion to microscopy combined with the lack of a close colleague skilled in cytology; his iconoclastic temperament, and the fact that he found T. H. Morgan, the leader of the Drosophila school, an uncongenial personality. Taken together, these factors suffice to account for his resistance. Bateson's position is contrasted with that of the other most eminent opponent, W. Johannsen, whose organismic outlook was the main obstacle to acceptance. (shrink)

In the early twentieth century, Wilhelm Johannsen proposed his pure line theory and the genotype/phenotype distinction, work that is prized as one of the most important founding contributions to genetics and Mendelian plant breeding. Most historians have already concluded that pure line theory did not change breeding practices directly. Instead, breeding became more orderly as a consequence of pure line theory, which structured breeding programmes and eliminated external heritable influences. This incremental change then explains how and why the large multi-national (...) seed companies that we know today were created; pure lines invited standardisation and economies of scale that the latter were designed to exploit. Rather than focus on breeding practice, this paper examines the plant varietal market itself. It focusses upon work conducted by the National Institute of Agricultural Botany during the interwar years, and in doing so demonstrates that, on the contrary, the pure line was actually only partially accepted by the industry. Moreover, claims that contradicted the logic of the pure line were not merely tolerated by the agricultural geneticists affiliated with NIAB, but were acknowledged and legitimised by them. The history of how and why the plant breeding industry was transformed remains to be written. (shrink)

Laudan's thesis that conceptual problem solving is at least as important as empirical problem solving in scientific research is given support by a study of the relation between the chromosome theory and the Mendelian research program. It will be shown that there existed a conceptual tension between the chromosome theory and the Mendelian program. This tension was to be resolved by changing the constraints of the Mendelian program. The relation between the chromosome theory and the Mendelian program is shown to (...) be a good illustration of the influence of science itself on the rational standards governing scientific development. (shrink)