Blueprints for the complexity of life

A new theory – Embryo Geometry – provides an explanation for how vertebrates develop and evolve

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According to the Neo-Darwinian view of evolution, new species – and indeed, entire genera – emerge as a result of the accumulation and selection of random mutations over time. In fact, many of its proponents have argued that the Neo-Darwinian framework can account for all of biological complexity.

But today, the explanatory power of this view is increasingly being challenged, not by creationists or purveyors of so-called “intelligent design” pedaling all-too familiar, impoverished arguments of decades past, but by serious biologists who have legitimate qualms about the role of natural selection in the emergence of radically new forms of life over evolutionary time.

After nearly 20 years of work, we offer a new mechanically-based hypothesis – Embryo Geometry – to account for the origin of vertebrate form, both during development and over the course of evolution. This new framework is presented in Progress in Biophysics & Molecular Biology.

When a fertilized egg divides, it initially forms a ball of cells called the blastula. Mechanical deformation of the blastula eventually produces the embryo. As the cells comprising the blastula proliferate, the ball increases in volume and surface area, altering its geometry.

We show how the blastula might plausibly maintain the geometry of the original eight cells produced by the first three divisions of the egg, ultimately defining the three axes of the vertebrate body. Though cellular and molecular processes clearly have a role in determining the fate and behavior of cells, we suggest that it is the global mechanical deformation of the growing blastula that is largely responsible for vertebrate form, both during individual development and in the course of evolution.

We look at the vertebrate body as principally a product of geometric constraints and mechanical principles, rather than solely the result of the accumulation of fortuitous mutations selected incrementally over time. We believe this view offers a viable alternative approach to the problem of biological complexity.

As much as it challenges Neo-Darwinian orthodoxy, it is important to understand that our view also represents a strong refutation of creationist and intelligent design arguments based on the notion of irreducible complexity.

Formation of the alimentary and musculoskeletal systems. a. Egg; b–e. Cleavage; f. Blastula; g–n. Gastrulation. (This image features in the <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0079610716300542">original research article</a> by Edelman, David <em>et al</em> published in <em>Progress in Bioscience and Molecular Biology</em>.)

Examining embryos

Anatomists have long held that complexity can be seen to arise during development of the embryo (embryogenesis). But despite detailed descriptions of the embryonic stages of all major types of animal, the evolution of complexity during development remains a mystery.

Evolutionary biologist Stephen Jay Gould encouraged one of us (S. Pivar) to look for a possible solution to this problem. Unfortunately, years of preliminary attempts were met with strong opposition by the most ardent proponents of the Neo-Darwinian view.

But now, our team of researchers and scientific illustrators from the University of San Diego, Mount Holyoke College, The Evergreen State College and Chem-Tainer Industries, Inc. gives an account of vertebrate morphogenesis, conveyed through detailed schematic illustrations, that provides a plausible solution to one of the most vexing problems in biology.

Morphogenesis of the skull. (This image features in the <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0079610716300542">original research article</a> by Edelman, David <em>et al</em> published in <em>Progress in Bioscience and Molecular Biology</em>.)

In 24 figures, we show how the musculoskeletal, cardiovascular, nervous and reproductive systems form through the mechanical deformation of geometric patterns. These illustrations demonstrate how the vertebrate body might plausibly arise from a single cell, both during individual embryogenesis and in the course of evolution.

<strong>The cardiovascular system</strong>. a. Blastula; b. Enlargement of endoderm layer; c. Separation of the artery and vein precursors; d-e. Onset of gastrulation; f–h. Reassembly of artery-vein configuration; i–k. Schematic depiction of heart formation; l. fully formed cardiovascular system. (This image features in the <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0079610716300542">original research article</a> by Edelman, David <em>et al</em> published in <em>Progress in Bioscience and Molecular Biology</em>.)

Although any challenge to the tenets Neo-Darwinism is still met with intense resistance, it is encouraging that an increasing number of prominent biologists – most notably Denis Noble and James Shapiro – have begun to question the explanatory power of Neo-Darwinian theory in accounting for the rise of new forms of organisms. In this light, we believe that Embryo Geometry may offer a possible way forward. At the very least, we hope it will stimulate further investigation by researchers across a wide swath of biology.

We are also applying this theory more widely. The embryo has a peculiar shape, with puzzling limb buds and segments called somites. We are now considering how this shape could be a transient form that results from a kind of springing back – or “elastic recoil ” – of the layers of tissue in the blastula. This recoil could happen after the blastula bursts along its midline, releasing it from a compressed state. If corroborated experimentally, this would represent an important addition to the mechanical account of the development and evolution of the vertebrate body plan we have already provided.

In addition, we have recently completed a paper on the origin of the form of the flower and fruit, which we will submit for publication shortly. You can read more about this on our website.

<strong>Origin of the nervous system</strong>. a–c. Separation of the afferent-efferent nerve primordia; d. Subductive gastrulation; e–g. Formation of the brain; h. Assembly of the afferent-efferent nerve pattern; i–l. Brain morphogenesis. (This image features in the <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0079610716300542">original research article</a> by Edelman, David <em>et al</em> published in <em>Progress in Bioscience and Molecular Biology</em>.)

Read the study

Elsevier has published this article open access:

Edelman, David et al: “Origin of the vertebrate body plan in the conservation of regular geometrical patterns in the structure of the blastula,” Progress in Biophysics and Molecular Biology (July 2016)


The journal

Progress in Biophysics & Molecular Biology covers the ground between the physical and biological sciences. It indicates to the physicist the great variety of unsolved problems awaiting attention in the biological sciences. The biologist and biochemist will find that this journal presents new and stimulating ideas on structural and functional problems of the living organism. This journal will be of particular interest to biophysicists, biologists, biochemists, cell physiologists, systems biologists, and molecular biologists. This journal is published by Elsevier.


Co-authors of the study

Mark McMenamin, PhDDr. Mark McMenamin is Professor of Geology at Mount Holyoke College. He is author or co-author of several books and numerous research articles that consider the origin of animals, the origin of land plants, and the Snowball Earth glaciation; his most recent book is Dynamic Paleontology: Using Quantification and Other Tools to Decipher the History of Life. In 2008, as director of the Keck Geology Consortium project to study the rocks of the Boston Basin, Dr. McMenamin received a teaching award from Southern Utah University for student project excellence. In 1988 he received a Presidential Young Investigator Award from the National Science Foundation, and in 1992-1993 he was named a Sigma Xi National Lecturer. Mark named the supercontinent Rodinia in The Emergence of Animals. In 1994, Mark and Dianna McMenamin introduced the Hypersea theory to explain the diversification of life forms on land.

Peter Sheesley, BSSpanning arts and science, Peter Sheesley has worked for over a decade as a scientific illustrator while making his own fine art oil paintings and studying biology. His interests include human anatomy, developmental biology, and microbiology. He is currently doing research on bacteriophage in the cow rumen, and painting murals for pediatric offices in Centralia, Washington. Sheesley has a BA in English Literature from Wheaton College, Illinois, an MFA in Figurative Painting from the New York Academy of Art and most recently a BS in Biology from The Evergreen State College, Washington.

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