We’ve seen some pretty dead-on-arrival explanations for the origin of new body plans in the Cambrian explosion, but this one takes the cake. Researchers at CNRS in France (Centre national de la recherch� scientifique) have been experimenting with rubber sheets to explain how the first bilateral body plans might have evolved:

A simple physical mechanism that can be assimilated to folding, or buckling, means that an unformed mass of cells can change in a single step into an embryo organized as a typical vertebrate. This is the main conclusion of work by a team involving physicists from the Laboratoire Mati�re et Syst�mes Complexes (CNRS/Universit� Paris Diderot) and a biologist from the Laboratoire de Biologie du D�veloppement (CNRS/UPMC). Thanks to microscopic observations and micromechanical experiments, the scientists have discovered that the pattern that guides this folding is present from the early stages of development. The folds that will give a final shape to the animal form along the boundaries between cell territories with different properties. This work has shed light on the mechanism for the formation of vertebrates and thus how they appeared during evolution. [Emphasis added.]

It’s hard to believe that any biologist can say this. For one thing, it’s Lamarckian; nowhere would this "single step" of folding in an "unformed mass of cells" be preserved in the offspring without the information getting coded in the genes. For another, a vertebrate is so much more than a buckle in a sheet of cells! You might as well explain the Cambrian animals by reference to a circus clown blowing up balloons and twisting them into amusing shapes.

To see that they’re serious, one only has to look at their one and only illustration. It shows a sheet of rubber being stretched by some kind of clasp at one side. Here’s the caption:

Modeling of the fold formation mechanism. A sheet of rubber on which a (stiffer) paper label is stuck buckles along the boundary between the stiff zone and the soft zone when it is stretched. This reproduces the formation of folds along the boundaries between cellular domains.

Let’s check to be sure we’re not dreaming. What is the question they are trying to address?

How has evolution produced a structure as complicated as a vertebrate, organized along an anteriorposterior axis, marked dorsally by the nervous system and ventrally by the digestive tract, and displaying almost perfect left-right symmetry? And how, during embryonic development, does this develop from a mass of round cells into an organized embryo? By working on chicken embryos, a team involving physicists and a biologist has managed to explain this transition by means of a relatively simple physical mechanism.

If you’ve seen the Illustra film Flight: The Genius of Birds you will remember the sequence from egg to chick in 21 days, when the cluster of cells took on its bilateral shape. "What’s right? What’s left? What’s front versus back?" Paul Nelson narrates. "Already these cells are committing themselves, in many cases irreversibly, into the roles they will take on in the adult." It’s a marvelous pictorial display, illustrating the "elaborate dance with thousands of cast members," as Ann Gauger described it.

It seems these French evolutionists want to reduce this process to, "Hey, pull on that ball of cells till it buckles and all the rest will follow." Let’s give them a chance to explain it in their own words:

The scientists worked on chicken embryos because at this development stage, they constitute the model that is closest to human embryos. Furthermore, its flat, disk-shaped structure facilitates the observation and modeling of cell movements. A chicken embryo is made up of four concentric rings. Under the microscope, each ring looks like a series of cells of homogenous size; their size increases from the center towards the peripheral rings, with a "stepped" change from one ring to another. Not only will these cellular domains form different tissues (nervous, muscle, digestive, etc.) but, as discovered by the scientists when filming development of the embryo, it always folds at the boundary between two neighboring rings, as from the second day of its development. These folds will result in a three-dimensional shape, typical of vertebrates.

By measuring the stiffness of the tissues, the scientists were then able to confirm that these boundaries between cell domains display an elastic contrast. The stiffness becomes increasingly marked when the cells are smaller, towards the center of the embryo. Thus as soon as adequate force is applied, the softer, peripheral regions (flanks) "naturally" wrap themselves around the central, stiffer region (the future central nervous system). The force in question is generated by the migration of certain cells, which stretches the embryo lengthwise.

Do they not understand that these forces are pre-programmed in DNA?

Let’s be sure they actually think they are explaining the emergence of a new body plan by a physical stretching of a mass of cells. The ending paragraph says:

These findings thus offer an explanation for the coupling of cell differentiation and morphogenesis (acquisition by the embryo of its shape), so that a well-formed animal containing territories with different and physically separated functions, emerges "naturally". Understanding this process fills a conceptual gap between a shapeless mass of cells and an "animal archetype", and sheds new light on how vertebrates have emerged during evolution.

The scientific paper is behind a paywall, but the Abstract should give the salient points. The title is, "Buckling along boundaries of elastic contrast as a mechanism for early vertebrate morphogenesis."

We have investigated the mechanism of formation of the body of a typical vertebrate, the chicken. We find that the body forms initially by folding at boundaries of stiffness contrast. These boundaries are dynamic lines, separating domains of different cell sizes, that are advected in a deterministic thin-film visco-elastic flow. While initially roughly circular, the lines of elastic contrast form large "peanut" shapes evoking a slender figure-8 at the moment of formation of the animal body, due to deformation and flow in a quadrupolar stretch caused by mesoderm migration. Folding of these "peanut" or "figure-8" motives along the lines of stiffness contrast creates the global pattern of the animal, and segregates several important territories. The main result is that the pattern of cell texture in the embryo serves simultaneously two seemingly different purposes: it regionalizes territories that will differentiate to different cell types and it also locks the folds that physically segregate these territories. This explains how the different cellular types segregate in physically separated domains.

Not much there about "how vertebrates have emerged during evolution." If the paper merely describes the observable, measurable forces that cells in a chicken embryo produce as they differentiate under genetic control, there would be no problem. But if they think this explains the origin of new body plans in the Cambrian explosion (as the news release seems to imply), that’s another matter.

Here’s a more informative experiment they could try. Stretch a spherical multicellular colony like Volvox and see if (1) it remains stretched in a bilaterial shape, (2) the stretching force gets transmitted to the DNA for the next generation, (3) the buckles in the stretch develop into digestive tracts, nervous systems, and circulatory systems, and (4) a vertebrate swims away.

Image: � DC Studio / Dollar Photo Club.