Against unifying homology concepts: Redirecting the debate.

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 Lankester's celebrated 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.

Historicizing the homology problem.

There is widespread agreement that "homology" designates something of fundamental biological importance, but no consensus as to how precisely that "something" should be defined, recognized, or theorized. Philosophical observers of this situation commonly focus on tensions between historical and mechanistic explications of homological sameness by appeal, respectively, to common ancestry and shared developmental resources. This paper uses select historical episodes to decenter those tensions and challenge standard narratives about how they arose. Haas and Simpson (1946) influentially defined "homology" simply as "similarity due to common ancestry." They claimed historical precedent in Lankester (1870) but seriously oversimplified his views in the process. Lankester did prioritize common ancestry, but he also raised mechanistic questions that resonate with contemporary evo devo work on homology. The rise of genetics inspired similar speculations in twentieth-century workers like Boyden (1943), a zoologist who engaged Simpson in a 15-year debate over homology. Though he shared Simpson's devotion to taxonomy and his interest in evolutionary history, he favored a more operational and less theoretical homology concept. Their dispute is poorly captured by current analyses of the homology problem. It calls for further study of the complex relationship between concepts and the epistemic goals they serve.

Experience Modulates the Reproductive Response to Heat Stress in C. elegans via Multiple Physiological Processes.

Natural environments are considerably more variable than laboratory settings and often involve transient exposure to stressful conditions. To fully understand how organisms have evolved to respond to any given stress, prior experience must therefore be considered. We investigated the effects of individual and ancestral experience on C. elegans reproduction. We documented ways in which cultivation at 15°C or 25°C affects developmental time, lifetime fecundity, and reproductive performance after severe heat stress that exceeds the fertile range of the organism but is compatible with survival and future fecundity. We found that experience modulates multiple aspects of reproductive physiology, including the male and female germ lines and the interaction between them. These responses vary in their environmental sensitivity, suggesting the existence of complex mechanisms for coping with unpredictable and stressful environments.