Evolution: the role of dGRNs (Evolution)

by David Turell , Saturday, July 27, 2024, 18:29 (117 days ago) @ David Turell

In experimental gene studies:

https://evolutionnews.org/2024/07/on-developmental-gene-regulatory-networks-the-scienti...

"...over 100 years of mutagenesis experiments show that mutations in genes regulating development are invariably deleterious (or in some cases have only trivial effects). Meyer summarizes: “This generates a dilemma: major changes are not viable; viable changes are not major. In neither case do the kinds of mutation that actually occur produce viable major changes of the kind necessary to build new body plans.”

"We see these deleterious effects particularly in experiments on developmental gene regulatory networks (dGRNs), complex networks of gene-interaction which regulate the expression of genes early in development as an organism’s body plan begins to grow. After reviewing experimental work on dGRNs, Meyer finds that, “These dGRNs cannot vary without causing catastrophic effects to the organism.”

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"...if changes to dGRNs are lethal to an embryo, how can they be modified to explain how new body plans evolve? Meyer’s writes in the book: “The system of gene regulation that controls animal-body-plan development is exquisitely integrated, so that significant alterations in these gene regulatory networks inevitably damage or destroy the developing animal. But given this, how could a new animal body plan, and the new dGRNs necessary to produce it, ever evolve gradually via mutation and selection from a preexisting body plan and set of dGRNs?”

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"Meyer was justified in making these arguments. The work of the late Caltech developmental biologist Eric Davidson, an eminent expert in the field of evo-devo, shows that mutations in genes that affect body plan characteristics (which tend to be expressed early, as the body plan is being put in place) don’t lead to new body plans — they lead to dead embryos.

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" [Davidson:] Interference with expression of any [genes in the dGRN kernel] by mutation or experimental manipulation has severe effects on the phase of development that they initiate. This accentuates the selective conservation of the whole subcircuit, on pain of developmental catastrophe.

"This intolerance of body plan-affecting dGRNs to fundamental perturbations indicates that they could not have evolved by undirected mutations. Many coordinated mutations would be needed to convert one functional dGRN that generates a particular body plan into a different dGRN that generates a different body plan."

Comment: careful DNA studies show no way to have major evolutionary advances in phenotype by specific mutations affecting dGRNs. There is another viewpoint from ID folks in this article:

"What we do know from experience, however, is that large increases in functionally specified information — especially information expressed in an alphabetic or digital form — are always produced by conscious and rational agents. So the best explanation for the explosion of information necessary to produce the Cambrian animals (whether that explosion occurred during or before the Cambrian period) remains intelligent design."
Darwin’s Doubt, p. 448

I agree.