Character identity mechanisms: a conceptual model for comparative-mechanistic biology
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Character identity mechanisms: a conceptual model for comparative‑mechanistic biology James DiFrisco1 · Alan C. Love2 · Günter P. Wagner3 Received: 4 May 2020 / Accepted: 17 July 2020 © Springer Nature B.V. 2020
Abstract There have been repeated attempts in the history of comparative biology to provide a mechanistic account of morphological homology. However, it is well-established that homologues can develop from diverse sets of developmental causes, appearing not to share any core causal architecture that underwrites character identity. We address this challenge with a new conceptual model of Character Identity Mechanisms (ChIMs). ChIMs are cohesive mechanisms with a recognizable causal profile that allows them to be traced through evolution as homologues despite having a diverse etiological organization. Our model hypothesizes that anatomical units at different levels of organization—cell types, tissues, and organs—have level-specific ChIMs with different conserved parts, activities, and organization. Relying on a methodology of conceptual engineering, we show how the ChIM concept advances our understanding of the developmental basis of morphological characters, while forging an important link between comparative and mechanistic biology. Keywords Homology · Developmental mechanisms · Comparative biology · Cell types · Characters · Levels of organization
* James DiFrisco [email protected] Alan C. Love [email protected] Günter P. Wagner [email protected] 1
Institute of Philosophy, KU Leuven, Leuven, Belgium
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Department of Philosophy, Minnesota Center for Philosophy of Science, University of Minnesota, Minneapolis, MN, USA
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Department of Ecology & Evolutionary Biology; Systems Biology Institute, Yale University, New Haven, USA
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J. DiFrisco et al.
Wanted: a mechanistic account of morphological homology Throughout the history of comparative biology, there have been repeated attempts to provide a mechanistic account of morphological homology. However, these attempts have foundered on a robust evolutionary pattern: homologous characters develop from different and often diverse sets of causes, appearing not to share any core causal architecture that underwrites trait identity (de Beer 1971; Spemann 1915). This conundrum is related to a longstanding question in evolutionary biology: what is a trait? (Wagner 2001) As Gould and Lewontin (1978) argued, adaptationist reasoning often involves an initial step of decomposing an organism arbitrarily into traits thought to be individually optimized and explaining their modification in a population in terms of natural selection. Yet it is often crucial to understand the developmental mechanisms that control a trait in order to explain how it can be modified evolutionarily. In many cases, what appears to be a trait is only a by-product or intersection of genuinely individualized traits. The human chin, for example, is not a distinct, individualized character, but rather a side effect of the relative sizes of th
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