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This paper's main contention is that some basically methodological developments in science which are apparently distant and unrelated can be seen as part of a sequential story. Focusing on general inferential and epistemological matters, the paper links occurrences separated by both in time and space, by formal and representational issues rather than social or disciplinary links. It focuses on a few limited aspects of several cognitive practices in medical and biological contexts separated by geography, disciplines and decades, but connected by long term transdisciplinary representational and inferential structures and constraints. The paper intends to show a given set of knowledge claims based on organizing statistically empirical data can be seen to have been underpinned by a previous, more familiar, and probably more natural, narrative handling of similar evidence. To achieve that this paper moves from medicine in France in the late eighteenth and early nineteenth century to the second half of the nineteenth century in England among gentleman naturalists, following its subject: the shift from narrative depiction of hereditary transmission of physical peculiarities to posterior statistical articulations of the same phenomena. Some early defenders of heredity as an important (if not the most important) causal presence in the understanding of life adopted singular narratives, in the form of case stories from medical and natural history traditions, to flesh out a special kind of causality peculiar to heredity. This work tries to reconstruct historically the rationale that drove the use of such narratives. It then shows that when this rationale was methodologically challenged, its basic narrative and probabilistic underpinings were transferred to the statistical quantificational tools that took their place.

This paper argues that our modern concept of biological heredity was first clearly introduced in a theoretical and practical setting by the generation of French physicians that were active between 1810 and 1830. It describes how from a traditional focus on hereditary transmission of disease, influential French medical men like Esquirol, Fodéré, Piorry, Lévy, moved towards considering heredity a central concept for the conception of the human bodily frame, and its set of physical and moral dispositions. The notion of heredity as a natural force, with a wide ranging capabilities of transmitting differentially both fundamental and accidental characters was generalized by that generation of physicians with the help of contemporary naturalists and physiologists. By 1830 the term hérédité was widespread, and it shared the explanatory and semantic qualities of traditional medical concepts like constitution and temperament. An analysis is given of the main developments that led to the conception of biological (including human) bodies as consisting of a layered, hierarchical organization of characters, differentially affected by the law of conservation (Heredity) and change (Inneity, Variation). The mid-century work of the French physician Prosper Lucas, Traité Philosophique et Physiologique de L' Hérédité Naturelle, is shown to be the culmination of the efforts of several generations of French physicians towards having a feasible, complexly structured notion of how heredity works.

This paper aims to give a causal account of the privileged status of genes in the theory of natural selection. Adding to the arguments that Dawkins (1976, 1982) and Kitcher & Sterelny (1989) have given for a distinction between the role of genes as units of natural selection, and that of other structures and properties from higher levels of organization, it criticizes the hierarchical view of a multiplicity of units for its lack of awareness of a basic causal assymetry between the genic and other levels. Being located at what one might call a Weismannian vertex, genes, it is argued, neatly articulate the two different dimensions of probabilistic causality, the token causality and the type causality. They do not have the passive (book-keeping) role some authors want to give them but are causally (probabilistically) responsible both for the recurrence of features from generation to generation, and for the presence of similar genes in future gene-pools. Heritability, it is also argued, when properly understood, can be seen as the biological property that captures this dual causal role of genes.