One of biology’s biggest mysteries is the genesis of animal form. Biologists trying to understand the genesis and evolution of life have studied and sought to characterize the embryology of all multicellular animal phyla since the 19th century. Many people believed that by the turn of the twentieth century, this work would have been completed.
Anatomists have succeeded in giving comprehensive descriptions of the musculoskeletal, organ, and neurological systems, ranging from Leonardo Da Vinci and Vesalius through Gray’s Anatomy. However, the genesis of these and other elements of organismal shape remains a mystery. Because the body develops from the embryo, nineteenth-century anatomists logically sought a solution by observing early animal development—or embryogenesis. By the end of the nineteenth century, virtually all major phyla’s embryological phases had been described in minute detail.
Major evolutionary changes, according to Neo-Darwinian theory, occur as a result of the selection of random, fortunate genetic mutations through time. However, other experts argue that this hypothesis fails to account for the emergence of fundamentally diverse living forms and their rich complexity, notably in vertebrates like humans.
The authors beg the reader to suspend skepticism that such a complex and longstanding problem is subject to a solution of relative simplicity. “Embryo geometry”, developed by a team from the University of San Diego, Mount Holyoke College, Evergreen State College, and Chem-Tainer Industries, Inc. in the United States, considers animal complexity in general, and the vertebrate body in particular, to be the result of mechanical forces and geometric laws rather than random genetic mutation.
They offer 24 “blueprints” in their article that illustrate how the musculoskeletal, cardiovascular, neurological, and reproductive systems evolve through the mechanical deformation of geometric patterns. These images show how the vertebrate body might have evolved from a single cell during the evolutionary time and during individual development.
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.
The concept of “embryo geometry” suggests that the vertebrate embryo might be produced by mechanical deformation of the blastula, a ball of cells formed when a fertilized egg splits. As these cells multiply, the volume and surface area of the ball expand, changing its shape. According to the hypothesis, the blastula preserves the geometry of the initial eight cells generated by the egg’s first three divisions, which establish the three axes of the vertebrate body.
The premise that complex animal form arises from mechanical forces acting on geometrically constrained populations of dividing cells in the early embryo provides a new lens through which to view developmental and evolutionary processes, and may pose a significant challenge to the Modern Synthesis’s dictum that evolution proceeds by a selection of adventitious mutations resulting from random mutations.
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.
Origin of the vertebrate body plan via mechanically biased conservation of regular geometrical patterns in the structure of the blastula, David B. Edelman, Mark McMenamin, Peter Sheesley, Stuart Pivar
Published: September 2016, Progress in Biophysics and Molecular Biology