Contrary to Mendel, who introduced hybridization as a methodology for the study of selected discrete traits, de Vries conceived of organisms to be composed of discrete traits. This introduced into genetic research the dialectics of reductive analysis of genes as instrumental variables versus that of genes as the material atoms of heredity. The latter conception gained support with the analysis of mutations and eventually with high resolution analysis at the genetic and biochemical levels, as achieved in fungi and later in (...) bacteria and their viruses. Attempts to reduce "classical" genetics to "molecular" genetics turned out to be futile. However, this did not necessarily imply that these were two distinct theoretical approaches. On the contrary, it is argued that molecular genetics is an extension of phenomenological deduction, rather than being induction from molecular (DNA) causes to effects. Although conceptually systems direct development, methodologically individual inputs must be studied. (shrink)
Developments in the sequencing of whole genomes and in simultaneously surveying many thousands of transcription and translation products of specific cells have ushered in a conceptual revolution in genetics that rationally introduces top-down, holistic analyses. This emphasized the futility of attempts to reduce genes to structurally discrete entities along the genome, and the need to return to Johannsen's definition of a gene as 'something' that refers to an invariant entity of inheritance and development. We may view genes either as generic (...) terms for units of inheritance whose referents are pragmatic ad hoc and context-dependent, or as (epistemologically) representing entities of cell functions. It is cellular functions that determine the structural referents along the DNA. Structures that happened to secure specific functions that were essential for or conducive to the survival of cells were selected for. With natural selection being the etiological background of genes as functions, genes obtain again their theoretical role as intervening variables, abstractive variables that purely 'summarize' characters. The importance of DNA sequences is that of all possible phenotypes these are the most basic ones from which we can read off the genotype directly. (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)
Advances in molecular biological research in the last forty years have made the story of the gene vastly complicated: the more we learn about genes, the less sure we are of what a gene really is. Knowledge about the structure and functioning of genes abounds, but the gene has also become curiously intangible. This collection of essays renews the question: what are genes? Philosophers, historians, and working scientists re-evaluate the question in this volume, treating the gene as a focal point (...) of interdisciplinary and international research. This book is unique in that it is the first interdisciplinary volume solely devoted to the quest for the gene. It will be of interest to professionals and students in the philosophy and history of science, genetics, and molecular biology. (shrink)
In 1941/42 Konrad Lorenz suggested that Kant''s transcendental categories ofa priori knowledge could be given an empirical interpretation in Darwinian material evolutionary terms:A priori propositional knowledge was an organ subject to natural selection for adaptation to its specific environments. D. Campbell extended the conception, and termed evolution a process of knowledge. The philosophical problem of what knowledge is became a descriptive one of how knowledge developed, the normative semantic questions have been sidestepped, as if the descriptive insights would automatically resolve (...) them. This came at a time when the traditional concept of knowledge as universally true, justified beliefs had been challenged by subjectivist, intercommunicative coherence frameworks. Much of the literature on evolutionary epistemology claimed that knowledge in general, and science as its epitome in particular, evolved along lines analogous to organic biological evolution. I refer here only to the view of knowledge as an extension of material biological evolution. These theories of evolutionary epistemology, contrary to the relativist notions of naturalized epistemology, adopted strict realist positions.Although there is no contention with the claim that biological evolution provided the raw material and the constraints for human knowledge, cognition is not knowledge and knowledge is not constrained by it beyond some trivial truisms. The view that sees evolution as a knowledge/cognition process is coercing a loosely defined term into the status of a phenotypic trait on which selection could act. This disregards the intricate many-to-many relationship between correlates of knowledge and biological capacities. But even if we grant the correlates of knowledge the status of selectable traits, the heritability of alternative phenotypes would be low and unpredictable due to the high, open-ended environmental malleability of such complex characters in the course of development. Such concepts are therefore biologically inconsequential. (shrink)
Mendel's work in hybridization is ipso facto a study in inheritance. He is explicit in his interest to formulate universal generalizations, and at least in the case of the independent segregation of traits, he formulated his conclusions in the form of a law. Mendel did not discern, however, the inheritance of traits from that of the potential for traits. Choosing to study discrete non-overlapping traits, this did not hamper his efforts.
The encounter between the Darwinian theory of evolution and Mendelism could be resolved only when reductionist tools could be applied to the analysis of complex systems. The instrumental reductionist interpretation of the hereditary basis of continuously varying traits provided mathematical tools which eventually allowed the construction of the Modern Synthesis of the theory of evolution.When genotypic as well as environmental variance allow the isolation of parts of the system, it is possible to apply Mendelian reductionism, that is , to treat (...) the phenotypic trait as if ti causally determined by discrete genes for the trait. howeverm such a beanbag genetics approach obscures the system's eye-view. The concept of heritability, defined as the proportion of the total phenotypic variance due to (additive) hereditary variation, asserts that genetic elements have discrete effects; but by relating to the genotypic variance, it avoids the trap of reffering to genes for characters. (shrink)