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Still No Basis for Stretched-Rubbery Theory of Body-Plan Origins: An Exchange with Vincent Fleury


We’ve already devoted two past articles to analyzing claims by a French team to have illuminated the origin of animal body plans. See here:

Now one of the researchers, Vincent Fleury of the French National Centre for Scientific Research, has responded to us with a post of his own ("Reply to Evolution News"). Despite some intemperate name-calling, Fleury deserves a response, and perhaps even a commendation for engaging in substantive debate. He writes:

Now that you have read the article, you seem to find some merit to this work (3), and realize that it is based on experimental work on actual embryos, and not experiments on rubber as you seem to have thought.

Actually our original post fully recognized that they did experimental work on chick embryos. It provided a lengthy quote from a press statement that said:

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.

Fleury writes:

Nowhere in our article is Darwinism questioned, and nowhere in our article is Lamarckism put forward.

We never claimed the article questions Darwinism. And if he were advocating Lamarckism, that wouldn’t necessarily mean he was questioning Darwinism. Darwinism is a theory of evolution. Lamarckism is a theory of inheritance. The opposite of Lamarckism is much closer to Mendelism than it is to Darwinism. Darwin himself didn’t fully reject all aspects of Lamarckism. As he wrote in the Origin of Species, "I think there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited." Indeed, biologist Denis Noble recognizes:

As Mayr (1964) points out, there are as many as 12 references to the inheritance of acquired characteristics in The Origin of Species (Darwin, 1859) and in the first edition he explicitly states ‘I am convinced that natural selection has been the main, but not the exclusive means of modification’, a statement he reiterated with increased force in the 1872, 6th edition.

In any case, the author doesn’t seem to understand what we’re saying: that if their theory of embryonic folding and buckling is a correct description of how new body plans arise, an evolutionary model would still need to explain how those folding mechanisms could become encoded in the DNA. According to conventional neo-Darwinian thinking, an organism’s development is encoded, somehow and somewhere, in the DNA. Their press release states clearly:

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.

Fleury’s team is welcome to propose that model. But if their model is correct, then something at the genetic level has to change "in a single step" to allow these radical changes in embryonic development. They provide no explanation of how this might happen. Absent such an explanation, we felt it was fair to ask "why their theory is not Lamarckian," as it seems to assume that changes in body plan can somehow become heritable in the DNA. Again, they give no account of how this might happen.

Fleury writes:

I do not even understand what you mean by Lamarckism in this instance.

That is apparent. But we can explain it one more time.

Lamarckism is a largely debunked theory of heredity that says changes acquired during the lifetime of an organism may be passed on to the next generation. The Fleury team’s model of the evolution of development must explain how any developmental changes become heritable. Because they only discuss change to the embryo, and not how those changes are heritable or produced by information in genetic molecules like DNA, his model has a Lamarckian flavor to it.

Fleury writes:

We are addressing the movements in a blastula, at an early developmental stage. Movements at the blastula stage do not occur by free will of the blastula, nor is anyone pulling on the ectoderm "from the outside". Movements in the blastula at any generation occur by the live activity of the blastula at that generation, as defined by the molecular content at that moment, in particular the genetic content. All the examples and challenges which you suggest (such as your volvox example) are completely nonsensical.

Again, they are welcome to propose whatever model they like. But the challenge is not nonsensical. In fact, he all but admits this when he writes, "Movements in the blastula at any generation occur by the live activity of the blastula at that generation, as defined by the molecular content at that moment, in particular the genetic content." In saying "as defined by the molecular content at that moment, in particular the genetic content," he has conceded that any movements of the blastula ultimately need to be casually connected to information in the genome. Can you suddenly encode these complex movements "in a single step" at the genetic level? He never says.

His post clarifies that their theory is not Lamarckian. That doesn’t help his case, though. On the contrary, he said any movements in the blastula must be "defined by … the genetic content," but then failed to describe or account for any of those necessary genetic changes. From this, it seems that his theory has not been demonstrated as biologically viable.

Fleury writes:

Now, this being said, at early developmental and evolutionary stage, we assume that masses of living cells were simpler. In effect, vertebrate blastulas are round. It is unlikely that this roundness is controlled by genes. We show that at early developmental stages, cells are organized in rings, much like tree rings. This makes sense, and it is also unlikely that genes control specifically the ring symmetry of the cells. In addition, the cell size varies from the inside towards the periphery. Cells are smaller internally and larger externally. It is also unlikely that such a trend is genetically controlled. It is just an effect of cell crowding.

It may well be true that forces other than genes affect the shape of vertebrate blastulas. So what are those other forces? How are their actions generated through processes driven by inheritable genetic information? Absent any answer to such questions, there is still no biological basis for his theory.

Fleury writes:

Stated otherwise, there is some sort of a "code" if you insist, in the presence of rings, but the algorithm to decipher the code is entirely physical and starts by a hydrodynamic flow (the vectors of the field are not "controlled" locally). This flow continues by a spontaneous spread of mesoderm, and the spread of mesoderm pulls and folds the embryo along the prepatterned boundaries of elastic contrast, locked at boundaries between rings.

It suffices to increase the magnitude of the driving force (mesodermal pull) to generate such animals as cephalochordates, once the buckling threshold is crossed. This work assumes that cell motility increased somehow such that the driving force for morphogenesis reached the buckling level. Of course, this force is genetically coded.

That’s all fine. But since he acknowledges that the force that causes the buckling is "genetically coded," he has to explain how this force is somehow genetically coded in such a finely tuned manner as to generate a proper body plan. Once more, their model never provides such an explanation.

Fleur writes:

However, if you like scientific reasoning, you might be aware of recent work suggesting that the Cambrian explosion occurred as a consequence of raising levels of oxygen in the atmosphere, which favored a metabolism based on respiration, as opposed as a metabolism based on fermentation, which is much less efficient.

In fact, we are quite aware of these proposals, and have responded to them in detail already. See the following:

As Casey Luskin wrote in commenting on these proposals: "The common theme among each of these ‘solutions’ to Darwin’s dilemma is that none of them explains the origin of biological information." How exactly does raising oxygen levels in the atmosphere produce the new genetic (and epigenetic) information needed to yield a body plan? As is typical, our interlocutor offers no answer.

Fleury writes:

In this view, animal morphogenesis may have occurred without specific genetic mutations: everything might have been ready for millions of years when the cell strength became epigenetically large enough to start the Marangoni movements of the rings, which lead eventually to the buckling of the blastula. But I agree this is a speculation, as is any form of reasoning about what happened 600 millions years ago.

This is where his entire model breaks down, revealing the impotence of current materialist attempts to explain the Cambrian explosion. To claim that "animal morphogenesis may have occurred without specific genetic mutations" and simply happened because cell strength became great enough to cause movements of rings in the blastula, which in turn formed body plans, does not explain anything.

Such biological processes must be heritable. They must be encoded in some information-carrying molecule or molecules or patterning-system that are passed down from generation to generation. So unless he can say how these complex folding patterns of embryos became encoded in sources of heritable genetic and epigenetic information, he has cast no real light on how they arose. His theory would then be either (a) completely useless, or (b) Lamarckian, which amounts to the same thing as (a) since Lamarckism is generally wrong, except for a few rare exceptions. He says he’s not promoting Lamarckism, so we’ll go with (a).

Animal body plans develop through a precise, finely tuned coordination of parts, starting with the earliest molecular processes that occur after fertilization which soon designate parts of the zygote to become certain types of cells, and then certain types of cells to become various body parts. This intricate dance involves far more than just the folding of the blastula. These carefully orchestrated developmental processes require immense amounts of new genetic and epigenetic information to guide an organism’s embryogenesis. His model accounts for none of this.

Fleury writes:

To be honest, these questions by the end of your last blog post are as stupid as is arrogant and absurd the sentence: "After a review of the paper, published in European Physical Journal E, we can report that our original coverage was entirely correct."

Attacking us in personal terms, calling us "stupid," "arrogant," and "absurd," is not a response. What would have answered our criticisms is an explanation for how these changes could have become encoded in the DNA. Fleury in his reply does not provide that. At this point it seems safe to assume he cannot.

Image by Chiltepinster (Own work) [CC BY-SA 3.0], via Wikimedia Commons.

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