Evo-Devo Fits Comfortably with Front-loading

Let’s go back to my entry about the New vs. Old views of evolution, as it will help readers get a feel for the solid ground that is developing under the hypothesis of front-loading evolution.

For there are two subtle, but crucial points to grasp: 1) The New view involved a paradigm shift that was not predicted by the theories of the Old view and 2) the New view, known as Evo-Devo, is much more friendly to front-loading.

First, to appreciate the way evolutionary theory used to understand evolution, consider what Sean Carroll passes on:

So what this means is in some ways, some sense, evolution is a simpler process than we first thought. When you think about all of the diversity of forms out there, we first believed this would involve all sorts of novel creations, starting from scratch, again and again and again.

“We first believed this would involve all sorts of novel creations, starting from scratch, again and again and again.” Note carefully that evolutionary theory, at the time, did not prevent biologists from believing the diversity of forms would involve all sorts of novel creations, starting from scratch, again and again and again. On the contrary, Ernst Mayr, who played a significant role in shaping the Modern Synthesis (the synthesis of Darwinian evolution and Mendelian genetics), wrote:

Much that has been learned about gene physiology makes it evident that the search for homologous genes is quite futile except in very close relatives. If there is only one efficient solution for a certain functional demand, very different gene complexes will come up with the same solution, no matter how different the pathway by which it is achieved. The saying “Many roads lead to Rome” is as true in evolution as in daily affairs. – Ernst Mayr, Animal Species and Evolution (Harvard University Press, 1963), p. 609

What led to Evo-Devo was not the gradual unpacking of the Modern Synthesis, but the application of molecular biology techniques to the study of embryonic development. Evolutionary theory, at the time, had not prepared scientists for what they would find as it did not predict what we now know to be true. Consider what Mike Levine says about this study of development:

Maybe the homeotic genes could explain how these related body plans nonetheless become different from each other. He was even so bold to suggest that this bag of genes could distinguish an earthworm, which contains a series of more or less identical body segments, into an animal like a fruit fly or a lobster, that has a series of segments that are all different from each other. Nobody thought that this bag of genes would be conserved in radically different animals like us, like vertebrates.

It led to a change in all of our thinking. When I was a student, there was a sense that all animals did things differently. If a gene was conserved between different animals, or between plants and animals, it was considered to be boring. How could it be interesting, because all animals and plants are different from each other? So, certainly, creating distinct forms of life couldn’t depend on a common set of molecules. And so to see that genes that are doing such profound things in the fruit fly — making head from tail, stomach from back, thorax from abdomen — are conserved, related in other animals … this was just not predicted by anybody. At least nobody that I ever read.

In the case of the discovery of common homeotic genes among all animals, there was a strong sense in the ’70s and the ’80s that embryonic development among different animals involved completely different molecules, completely unrelated. This was such a strongly held view. And so, yes, it came as a huge surprise not only to people like my mother who says, “My God, an earthworm and a mouse? An earthworm and me, sharing things in common?” But it came as a surprise to other scientists that there was this profound conservation of mechanism of building embryos among all these different kinds of animals.

So Evo-Devo represents a mini-paradigm shift in our views about evolution as a consequence of data generated from gene studies in embryos and not some prediction or expectation generated from the Modern Synthesis.

Let’s now turn to the second point.

The Old views of evolution had the blind watchmaker generating all kinds of innovations under the strong selection pressures involved in generating new body plans and structures. That’s why Mayr said, “The saying “Many roads lead to Rome” is as true in evolution as in daily affairs.” If this perspective had turned out to be correct, the hypothesis of front-loading would never get off the ground. If the diversity of forms would have involved all sorts of novel creations, starting from scratch, again and again and again, the connection between the past and the present would be tenuous, at best. How could one design the future through the present if the blind watchmaker behaved in such an unconstrained and wildly creative fashion?

In contrast, Evo-Devo significantly enhances the plausibility of front-loading by more deeply connecting the past to the present (meaning that original designs would remain connected to the future) and showing us that evolution is constrained by the information present in these original states. Consider Carroll again:

We now understand that, no, that evolution works with packets of information and uses them in a new and different ways, and new and different combinations, without necessarily having to invent anything fundamentally new, but new combinations.

That evolution works around ancient packets of information and has no need to invent anything fundamentally new is exactly the pattern we would expect from front-loading.

Again from Sean Carroll:

One general insight from evo-devo that has interested paleontologists a great deal is that the genes required for building new kinds of bodies or structures often long pre-date the appearance of such bodies or structures.

That genes for building bodies or structures predate the appearance of such bodies and structures is exactly what we would expect from front-loading.

And according to Scott Gilbert:

“It’s been said that classical evolutionary theory looks at survival of the fittest,” said Dr. Scott F. Gilbert, a developmental biologist at Swarthmore College. By looking at what sorts of organisms are most likely or impossible to develop, he explained, “evo-devo looks at the arrival of the fittest.”

Arrival of the fittest fits far more easily into a front-loading perspective than mere survival of the fittest.

And Mike Levine again:

And so to see that genes that are doing such profound things in the fruit fly — making head from tail, stomach from back, thorax from abdomen — are conserved, related in other animals … this was just not predicted by anybody. At least nobody that I ever read. So this was very profound. It meant that there could be a common blueprint for all animal life on this planet.

In the case of the discovery of common homeotic genes among all animals, there was a strong sense in the ’70s and the ’80s that embryonic development among different animals involved completely different molecules, completely unrelated. This was such a strongly held view. And so, yes, it came as a huge surprise not only to people like my mother who says, “My God, an earthworm and a mouse? An earthworm and me, sharing things in common?” But it came as a surprise to other scientists that there was this profound conservation of mechanism of building embryos among all these different kinds of animals.

A common blueprint for all animal life and a profound conservation of mechanism of building embryos is exactly what makes front-loading so plausible.

And back to the New York Times:

The development of an organism — how one end gets designated as the head or the tail, how feet are enticed to grow at the end of a leg rather than at the wrist — is controlled by a hierarchy of genes, with master genes at the top controlling a next tier of genes, controlling a next and so on. But the real interest for evolutionary biologists is that these hierarchies not only favor the evolution of certain forms but also disallow the growth of others, determining what can and cannot arise not only in the course of the growth of an embryo, but also over the history of life itself.

Gene circuitry that provides directions to evolution by determining what the blind watchmaker can and cannot see and tweak fits seamlessly within the front-loading perspective.

To summarize, the old views of evolution were very unfriendly to front-loading. In fact, if the old views had born out, front-loading would be a non-starter and the non-teleological perspective would be quite strong (and therefore this blog would not exist). But the new view of evolution, which is not something that was entailed or predicted by the old view, greatly enhances the plausibility of front-loading. For if evolution relies on a common blueprint, if gene circuits control what the blind watchmaker can see, so it is arrival of the fittest more so than survival of the fittest, if genes for building bodies exist prior to the appearance of bodies, and if evolution simply tinkers with packets of information it was handed long ago, then we have a process that can be exploited and used by a designer in an attempt to design the future through the present.

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One response to “Evo-Devo Fits Comfortably with Front-loading

  1. So, if there is a creator, why did he/she/it use so many similar systems. A creator that is versatile and creative enough to make the weird things in space, different elements, and the wide variety of species on this earth would surely be creative enough to make a wide variety of body systems instead of adjusting DNA, bone systems, circulatory systems, etc. The development of organisms over the ages seems like a car company improving on a model over the years. This doesn’t seem like the same creator that could make the universe.

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