Wormy logic: model organisms as case-based reasoning

In the past few decades, so-called model organisms have become a cornerstone of research in the biomedical sciences. For the scientists, the model organism is both a practice ground for developing laboratory techniques, and a source of insights into common or even universal biological mechanisms. This paper examines the conceptualization of model organisms as models, and presents a formal account of how they are used to generate knowledge through what can be viewed as a form of case-based reasoning. Case-based reasoning is an epistemic process that is far from straightforward and may seem to fail to allow us to obtain the usual results we expect in science. Meanwhile, a growing literature within the history and philosophy of science on modelling and representation creates a space within which close attention to the principles and practices associated with such models may prove fruitful. Following a brief historical account of the development and use of one model organism, the nematode worm Caenorhabditis elegans, this paper addresses questions about the methodologies underlying work on genetic sequencing and developmental processes in this organism. In particular, what types of reasoning ground the use of experimental organisms when they are being developed and used as model organisms, and how are these models refined over time?