Cambrian Explosion: It's Just Physics - Evolution News & Views

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Cambrian Explosion: It's Just Physics


Wait till you hear how Stuart A. Newman explains the explosive arrival of animal body plans in the early Cambrian.

With blessings from the journal Science, Dr. Newman, a developmental biologist at the New York Medical College, got ample space to propound a new theory about the Cambrian explosion. His college is promoting it as a "new theory of early animal evolution." PhysOrg's report states that it "challenges basic assumptions." By implication, of course, if the current theory were adequate, he wouldn't need to challenge it.

As charitably as we can briefly describe his new theory, it says that animal body plans arose from layers and cavities that spontaneously emerged in clusters of cells. Since similar cavities form in some nonliving materials, physics alone brought it all about. He calls these cavities and layers "morphological motifs" that are preserved in developing embryos (hints of recapitulation theory?). This makes animal body plans little more than fossilized accidents of physics. Note the giant leap from cavities to human hands:

Animal bodies and the embryos that generate them exhibit an assortment of recurrent "morphological motifs" which, on the evidence of the fossil record, first appeared more than a half billion years ago. During embryonic development of present-day animals, cells arrange themselves into tissues having non-mixing layers and interior cavities. Embryos contain patterned arrangements of cell types with which they may form segments, exoskeletons and blood vessels. Developing bodies go on to fold, elongate, and extend appendages, and in some species, generate endoskeletons with repeating elements (e.g., the human hand).
Newman's paper speaks of "physico-genetic determinants in the evolution of development," but he provides no causal link between the physico- part and the -genetic part. Try to find it in his abstract:
Animal bodies and the embryos that generate them exhibit an assortment of stereotypic morphological motifs that first appeared more than half a billion years ago. During development, cells arrange themselves into tissues with interior cavities and multiple layers with immiscible boundaries, containing patterned arrangements of cell types. These tissues go on to elongate, fold, segment, and form appendages. Their motifs are similar to the outcomes of physical processes generic to condensed, chemically excitable, viscoelastic materials, although the embryonic mechanisms that generate them are typically much more complex. I propose that the origins of animal development lay in the mobilization of physical organizational effects that resulted when certain gene products of single-celled ancestors came to operate on the spatial scale of multicellular aggregates.
Maybe the link is hidden somewhere in Newman's podcast that Science posted.

To all appearances, Newman only found a physical similarity between viscoelastic materials that form cavities and embryos that form cavities as they proceed through the blastula and gastrula stages. Then, somehow, cells "mobilized" to take advantage of "physical organizational effects" in cell aggregates, and "came to operate on them." Perhaps we misunderstand and are selling Dr. Newman's theory short, but the just-so quality of this story leaps out at us. Lava produces cavities, and a sponge or Swiss cheese produces cavities, but that doesn't imply they have any "physico-genetic" relationship. It would be a stretch to call a piece of lava the "body plan" of a sponge.

Newman's theory should be easy to test: put clustering microbes in test tubes, and see if they develop animal body plans. Wait a while and if a trilobite crawls out, Newman might be onto something. His paper offered no way to test the theory (if it can be called a theory).

The centerpiece of Newman's paper is a diagram of a simple spherical cluster of cells that, through cleavage, folding, aggregation and other physical effects, became "morphological motifs" leading to body plans. Naming these pregnant motifs "dynamical patterning modules" (DPMs) doesn't help them give birth. The caption calls these "'proto-eggs,' or eventually fertilized eggs" -- pause now for a gasp! His diagram has arrows out from these motifs to embryos of a chicken, a fruit fly, a comb jelly, a squid, a sponge, a worm, a placozoan, and a sand dollar. There's a lot of detail hidden in those arrows!

That's not all. Newman believes this happened just once, in the early Cambrian. Why should that be? If it's a law of nature, clusters of microbes could co-opt new motifs at any time. Why did it take hundreds of millions of years following the origin of life? Why isn't it happening now? Supposedly this new, assumption-challenging theory explains the Cambrian explosion and the universality of early embryonic development. The physical "motifs" were retained, Newman says, as natural selection took over:

Natural selection, acting over the hundreds of millions of years since the occurrence of these origination events led, according to Newman's hypothesis, to more complex developmental processes which have made embryogenesis much less dependent on potentially inconsistent physical determinants, although the "physical" motifs were retained. As Newman describes in his article, this new perspective provides natural interpretations for puzzling aspects of the early evolution of the animals, including the "explosive" rise of complex body forms between 540 and 640 million years ago and the failure to add new motifs since that time. The model also helps us to understand the conserved use of the same set of genes to orchestrate development in all of the morphologically diverse phyla, and the "embryonic hourglass" of comparative developmental biology: the observation that the species of a phylum can have drastically different trajectories of early embryogenesis (e.g., frogs and mice), but still wind up with very similar "body plans."
Why would Science put about such a fantastic tale? The real point of interest in its publication is that Darwinian evolutionists have nothing better to offer. The Cambrian explosion falsifies Darwinism. Charles Darwin himself knew how contrary the fossil evidence was to his theory (see Chapter 9 of The Origin). He specifically referred to the sudden appearance of animal phyla, but left it to his successors to find all the precursors that must be out there.

DarwinsDilemma-sm.jpgIn the succeeding 153 years, lots of fossils have been found, but the Cambrian explosion has only gotten louder. As biologists Richard Sternberg and Doug Axe explain in the documentary Darwin's Dilemma, embryonic development of animal body plans poses a severe challenge to neo-Darwinian theory. Animal development is not just a result of physical forces; it's the working out of an architectural plan encoded in the genetic blueprint, enacted by molecular machines, with the distant goal of constructing a mature animal. This is intelligent design in action; forces acting on a "viscoelastic material" have nothing to do with it.

Darwinists cannot and will not endure intelligent design, no matter the evidence. They are well aware of how ID advocates have pointed to the Cambrian explosion as a challenge to Darwinism. If they had a more plausible response, Science would surely print it. Newman's paper can be rightly viewed as an act of desperation bordering on pseudoscience. It might better be named, "Psycho-political determinants in the development of evolutionary escape clauses."