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Abstract
Conceptual change often accompanies the development of scientific knowledge over time. Scientists also frequently disagree about what exactly their core concepts mean and how they should be applied. Why is this the case, and what makes these dynamic concepts work as well as they do? This dissertation addresses that larger problem by way of a smaller one involving a particularly important biological concept. Homology relates corresponding parts in different organisms—for instance the human arm, bat wing, and whale flipper are all vertebrate forelimbs despite their differences in form and function. Biologists have specified the nature of this relationship quite differently over a period of more than 150 years, and they continue to do so today. How can such a central concept be so difficult to pin down?
Philosophical analyses of ‘homology’ typically collapse its many contemporary variants into two or three major theoretical accounts of what makes homologous body parts “the same.” By examining four key historical episodes, I argue that a much richer characterization of the concept is necessary to make sense of its formation and subsequent development. Richard Owen’s original definition was just one part of a complex research program that provided cohesion to later and otherwise quite diverse studies. A mid-twentieth century conflict over Owen’s legacy decisively altered the conceptualization of homology in evolutionary biology. G. G. Simpson and Alan Boyden disagreed as to whether the evolutionary explanation of homologous resemblance belonged in the definition of the concept. More recently, differences over how to determine, represent, and interpret homology have rent a small group of systematists who identify themselves as intellectual descendants of Willi Hennig. Finally, ongoing attempts to resolve avian wing digit homology challenge any simple association between disciplines and accounts of homology.
My analysis of the homology case motivates a novel general model of conceptual change according to which certain scientific concepts are essentially dynamic. Scientists initially adopt such concepts because they identify a phenomenon worth studying and consolidate promising epistemic resources for that study. These resources are both material and cognitive in nature. In addition to theoretical definitions of the concept, they may include specialized techniques, sources of data, operational criteria, and known examples. The coordination of these resources represents a valuable achievement or exemplar for the ongoing use of the concept. Change and variation in its use follow naturally from the epistemic complexity of scientific research and from the spatiotemporal complexity of the systems it targets. The course of subsequent research also depends on the aims of individual scientists and the development of new techniques and methods in their wider fields of study. My model suggests approaches to the study of conceptual change that are likely to apply to other concepts in biology and perhaps beyond.
