In a recently-published book, Eric Davidson, â€œthe world's leading expertâ€ in the field of evo-devo, offers his perspective â€œon the gene regulatory networks that control animal developmentâ€. The book is significant because Davidson â€œproposes a scenario to explain how these distinct types of network subcircuits have emerged in animal evolution.â€
The complexity of the gene networks is well known. â€œThese networks consist of huge sets of regulatory genes that control one another's expression as well as the expression of downstream effector genes via so-called cis-regulatory elements (to which the transcription factors bind).â€ The reviewer comments appreciatively on the way Davidson describes the genetic control of development in living animals: â€œIn essence, through a stepwise process, development subdivides the embryo into territories, subterritories, and "progenitor fields" that make up a given body part of the adult animal. This stepwise subdivision is accomplished by gene regulatory network subroutines called subcircuits that consist of small sets of genes and cis-regulatory elements.â€ Something of this complexity can be appreciated by reference to the figure that accompanies the review.
â€œThe final chapter, on the evolution of gene regulatory networks, is the most speculative and most stimulating. Here, Davidson outlines a possible evolutionary origin of kernels â€¦â€. The reviewer refers to three stages of evolution. â€œIn a third stage â€¦ , the animal body parts and, concomitantly, the territorial subdivision of the developing embryo became more and more elaborate until finally the underlying subcircuits were locked down into kernels that could no longer be changed without deleterious consequences. According to Davidson, this "triumph of the bilaterian versions of animal body plans" was in place sometime before the Cambrian and has persisted, constraining metazoan evolution ever since with tremendous success.â€
The concept being developed here can be related to irreducible complexity (although Davidson clearly thinks these IC systems can be constructed by evolutionary processes). The â€œkernelâ€ is a term drawn from information science, referring to the core of an operating system. When these kernels were in place, they could no longer be modified by evolutionary processes, because any change was deleterious and was not preserved.
We thus have the developmental architectures of animals in place sometime before the Cambrian. This is a scenario that is discussed in that much denigrated paper by Steve Meyer (â€œThe Origin of Biological Information and the Higher Taxonomic Categoriesâ€ Proceedings of the Biological Society of Washington 117(2004):213-239.). Meyer writes: â€œCan neo-Darwinism explain the discontinuous increase in CSI that appears in the Cambrian explosion--either in the form of new genetic information or in the form of hierarchically organized systems of parts?â€ Davidsonâ€™s book undoubtedly puts more substance into the argument, spelling out some essential elements of the complexity that has to be in place for the Cambrian Explosion.
The reviewer continues: â€œThe proposed link between the evolution of kernels and the evolution of bilaterian body plans is exciting, but it awaits validation through more comparative analyses of gene networks. As Davidson himself concedes, "for the identification of kernels â€¦ an overwhelming feature of the evidence thus far is its thinness."â€ This seems to be a realistic assessment of the state of knowledge. There is also the significant absence of ancestors of the Cambrian animals, despite continuing discoveries about the Ediacaran fauna. But it seems to me that the convergence between the thinking of Davidson and Meyer is such that it gives strength to the argument of Meyerâ€™s 2004 paper. I wonder if others see the situation like this?
A Kernel Bears Fruit
Science 314, 17 November 2006: 1085-1086.
A review of: "The Regulatory Genome. Gene Regulatory Networks in Development and Evolution" by Eric H. Davidson, Academic Press (Elsevier), Burlington, MA, 2006.
|<< <||> >>|
Evolution has become a favorite topic of the news media recently, but for some reason, they never seem to get the story straight. The staff at Discovery Institute's Center for Science and Culture started this Blog to set the record straight and make sure you knew "the rest of the story".
A blogger from New England offers his intelligent reasoning.
We are a group of individuals, coming from diverse backgrounds and not speaking for any organization, who have found common ground around teleological concepts, including intelligent design. We think these concepts have real potential to generate insights about our reality that are being drowned out by political advocacy from both sides. We hope this blog will provide a small voice that helps rectify this situation.
Website dedicated to comparing scenes from the "Inherit the Wind" movie with factual information from actual Scopes Trial. View 37 clips from the movie and decide for yourself if this movie is more fact or fiction.
Don Cicchetti blogs on: Culture, Music, Faith, Intelligent Design, Guitar, Audio
Australian biologist Stephen E. Jones maintains one of the best origins "quote" databases around. He is meticulous about accuracy and working from original sources.
Most guys going through midlife crisis buy a convertible. Austrialian Stephen E. Jones went back to college to get a biology degree and is now a proponent of ID and common ancestry.
Complete zipped downloadable pdf copy of David Stove's devastating, and yet hard-to-find, critique of neo-Darwinism entitled "Darwinian Fairytales"
Intelligent Design The Future is a multiple contributor weblog whose participants include the nation's leading design scientists and theorists: biochemist Michael Behe, mathematician William Dembski, astronomer Guillermo Gonzalez, philosophers of science Stephen Meyer, and Jay Richards, philosopher of biology Paul Nelson, molecular biologist Jonathan Wells, and science writer Jonathan Witt. Posts will focus primarily on the intellectual issues at stake in the debate over intelligent design, rather than its implications for education or public policy.
A Philosopher's Journey: Political and cultural reflections of John Mark N. Reynolds. Dr. Reynolds is Director of the Torrey Honors Institute at