Images and diagrams were central also for the professional study of heredity. Prior to the establishment of genetics as a scientific field, hereditary factors were still thought of as invisible, germ-like particles. With the rise of Mendelian genetics they turned into computational units in the form of capital letters, and later were transformed into tiny lines residing on dark, worm-like cords (known as chromosomes) inside our cells. Establishing the causal relations between genotype and phenotype, or between genes and their actual impact on human beings, relied heavily on one type of diagram: the pedigree. For the scholars who charted them, the pedigrees’ primary goal was to serve as means for arranging and retrieving medical data and as tools for facilitating scientific reasoning. For those who viewed them, they were the most palpable demonstration of the power of hereditary transmission to shape the fates of individuals, families and communities. Common to both the professional publications of geneticists and the popular exhibitions of eugenicists, pedigree charts therefore became a visual arena where the mechanism of heredity and its meaning were constantly (re)formulated. Studying how pedigrees were constructed in different scholarly communities opens a window into the way biological concepts, social perceptions and aesthetic conventions became entangled, jointly contributing to the formulation of a seemingly neutral scientific method.
In my poster I will explore these relations between scientific and social thought by scrutinizing pedigrees drawn by geneticists and eugenicists in Germany and in the US (1890-1940). I will identify the motivations that prompted individual scholars and entire scholarly communities to prefer one style of diagrammatic presentation over another and unravel the assumptions on the essence of heredity that underlay these methodological preferences. I will also track the lineage of specific pedigrees to highlight the alterations that they went through as they were copied from one scholar’s paper, through another’s textbook, to governmental publications propagating the need to implement eugenic policies. Finally, I will offer some professional reflections on the methodological peculiarities of analyzing pedigrees as historically-situated, scholarly-styled and culturally-loaded analytical devices.