Magic embryology: forming fetus totally unexplained (Introduction)

by David Turell , Monday, April 16, 2018, 00:50 (2414 days ago) @ David Turell

The original paper is here:

https://www.sciencedirect.com/science/article/pii/S0079610716300542?via%3Dihub

"Abstract
We present a plausible account of the origin of the archetypal vertebrate bauplan. We offer a theoretical reconstruction of the geometrically regular structure of the blastula resulting from the sequential subdivision of the egg, followed by mechanical deformations of the blastula in subsequent stages of gastrulation. We suggest that the formation of the vertebrate bauplan during development, as well as fixation of its variants over the course of evolution, have been constrained and guided by global mechanical biases. Arguably, the role of such biases in directing morphology—though all but neglected in previous accounts of both development and macroevolution—is critical to any substantive explanation for the origin of the archetypal vertebrate bauplan. We surmise that the blastula inherently preserves the underlying geometry of the cuboidal array of eight cells produced by the first three cleavages that ultimately define the medial-lateral, dorsal-ventral, and anterior-posterior axes of the future body plan. Through graphical depictions, we demonstrate the formation of principal structures of the vertebrate body via mechanical deformation of predictable geometrical patterns during gastrulation. The descriptive rigor of our model is supported through comparisons with previous characterizations of the embryonic and adult vertebrate bauplane. Though speculative, the model addresses the poignant absence in the literature of any plausible account of the origin of vertebrate morphology. A robust solution to the problem of morphogenesis—currently an elusive goal—will only emerge from consideration of both top-down (e.g., the mechanical constraints and geometric properties considered here) and bottom-up (e.g., molecular and mechano-chemical) influences."

***

"From conclusion:

The causal account that the model provides for the development of complex vertebrate morphology is necessarily presented by a speculative series of schematic images representing sequences of key mechanical events during embryogenesis, akin to a series of blueprints. The vast—and largely non-pictorial—literature on this subject does not offer a global mechanism to explain the rise of diverse forms of animal phyla. Though highly speculative, the model offered here may suggest just such a mechanism. The homologous morphological resemblance among the phyla may, in fact, be due as much to the inevitable topological trajectory of the confined expansion of a primordial spherical membrane as it is to common ancestry. Accordingly, the choices available to natural selection may be limited to the possible variations in proportions of the body parts of otherwise relatively conservative and invariant phyletic forms, rather than simply provided by random genetic mutations resulting from errors in transcription. Animal form may thus be seen as the product of physical forces—or biases—acting upon cells and populations of cells with very specific and constrained geometric properties, rather than arising solely from the vagaries of chance."(my bold)

Comment: Note the bold. Not Darwin. As can be seen embryogesnesis is not explained. The authors' initial point about their theory:

"Though neither rigorous nor exhaustive in an empirical sense, our model offers an intuitive and plausible description of the emergence of form via simple geometrical and mechanical forces and constraints. The model provides a template, or roadmap, for further investigation, subject to confirmation (or refutation) by interested researchers."