Devin Gouvêa

The term ‘homology’ is persistently polysemous, defying the expectation that extensive scientific research should yield semantic stability. A common response has been to seek a unification of various prominent definitions. This paper proposes an alternative strategy, based on the insight that scientific concepts function as tools for research: When analyzing various conceptualizations of homology, we should preserve those distinguishing features that support particular research goals. We illustrate the fruitfulness of our strategy by application to two cases. First, we revisit E. Ray Lankester’s celebrated (1870) evolutionary reappraisal of homology and argue that his analysis has been distorted by assimilation to modern agendas. His ‘homogeny’ does not mean the same thing as modern evolutionary ‘homology,’ and his ‘homoplasy’ is no mere antonym. Instead, Lankester uses both new terms to pose a question that remains strikingly relevant—how do mechanistic and historical causes of morphological resemblance interact? Second, we examine the puzzle of avian digit homology, which exemplifies disciplinary differences in homology conceptualization and assessment. Recent progress has been fueled by the development of new tools within the relevant disciplines (paleontology and developmental biology) and especially by increasing interdisciplinary cooperation. Conceptual unification has played very little role in this work, which instead seeks concrete evolutionary scenarios that integrate all the available evidence. Together these cases indicate the complex relationship between concepts and other tools in homology research.

Recent philosophical work on biological homology has generally treated its conceptual fragmentation as a problem to be solved by new accounts that either unify disparate approaches to homology or specify sharp constraints on its meaning. I show that several proposed solutions either misunderstand or ignore central features of comparative biological research, despite attempts to capture scientific practice. I conclude that the problem is incorrectly framed and that disagreements about homology may be epistemically fruitful. Empirically tractable debates are more likely to occur among biologists who share theoretical perspectives on homology. Philosophers should consider homology not merely as a generator of inductive generalizations but also as a scaffold for meaningful empirical comparisons.

Analogies between Newtonian mechanics and evolutionary processes are powerful but not infinitely versatile tools for generating explanations of particular biological phenomena. Their explanatory range is sensitive to a preliminary decision about which processes count as background conditions and which as special forces. Here I argue that the defenders of the zero-force evolutionary law are mistaken in defending their decision as the only appropriate one. The Hardy–Weinberg principle remains a viable option that is consistent with the epistemic role of Newton’s own first law, and the strengths and weaknesses of each analogy are sufficiently distinct to justify their continued coexistence