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Developing Scaffolds in Evolution, Culture, and Cognition$
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Linnda R. Caporael, James R. Griesemer, and William C. Wimsatt

Print publication date: 2013

Print ISBN-13: 9780262019552

Published to MIT Press Scholarship Online: May 2014

DOI: 10.7551/mitpress/9780262019552.001.0001

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Excitable Media in Medias Res

Excitable Media in Medias Res

How Physics Scaffolds Metazoan Development and Evolution

(p.109) 4 Excitable Media in Medias Res
Developing Scaffolds in Evolution, Culture, and Cognition

Stuart A. Newman

The MIT Press

What are the underlying generative principles that produce multicellular forms, ensure that they are inherited in a type-specific fashion, but also allow for the possibility of evolutionary transformations? This chapter presents the view that the physics of materials of the middle (meso-) scale, acting on embryos at the stage when they consist of dozens to a few hundred cells (blastula, blastoderm, inner cell mass, etc.), provides a functional scaffolding for body plan organization. The specific physical processes and effects that are brought into play at this intermediate “morphogenetic” stage of development depend on the evolutionary-lineage-specific subset of conserved, ancient developmental “toolkit” genes present in a given cell population. This physics-based scaffolding provides the mechanistic basis for the perpetuation from one generation to the next of phylotypic morphological motifs such as multilayering, lumens, segmentation, appendage formation, and so forth. It also accounts for the phenomenon of the “embryonic hourglass” of comparative developmental biology, whereby phyla exhibit extensive morphological variation at stages leading up to, and beyond, the morphogenetic stage, but a high degree of conservation partway through ontogeny.

Keywords:   Developmental genetic toolkit, dynamical patterning modules, egg-patterning processes, embryonic hourglass

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