Why Not Theistic Evolution? Part 4: Does “Darwin Devolves” Survive Criticism?

In "The Edge of Evolution," Michael Behe proposes an eponymous edge of evolution. In "Evolution Unscathed," Behe's colleagues Gregory Lang and Amber Rice give that edge an almost imperceptible nudge.

A number of readers have, in their comments, drawn my attention to critiques of Intelligent Design. I thoroughly agree with one reader’s encouragement to give attention to these:

I do think it’s important to engage with mainstream science’s responses to the ID crowd, many of which strike me as generally persuasive and sincere.

In particular, in response to my last post in my series “Why Not Theistic Evolution?” based on Michael Behe’s Darwin Devolves, I was directed to the following review of Behe’s book by Gregory Lang and Amber Rice, two of his own colleagues at Lehigh University, “Evolution unscathed: Darwin Devolves argues on weak reasoning that unguided evolution is a destructive force, incapable of innovation.”

While there is an entire website dedicated to cataloging the reviews of and responses to the reviews of Darwin Devolves, this review is exemplary of what two biologists, Behe’s own colleagues, think is an adequate rebuttal of his work.

In commenting on this as a philosopher, one accusation will be that I lack the scientific qualifications to be informed on these fundamental matters of biology. However, in reading this review of Behe’s book, I was struck by the consequences that a lack of philosophical training has for these evolutionary biologists. As biologists, they are well-equipped with empirical knowledge of biology and microbiology, in particular. But, in their evaluation of the kind of evidence necessary to determine whether unguided evolution is sufficient to account for all of life, a kind of philosophical naïveté is revealed.

The age-old question of whether the evidence of biology permits a materialist explanation cannot be decided by a handful of examples. As a result, the effect of Lang and Rice’s review is to showcase several examples of evolution right at Behe’s identified “edge of evolution.” What the review does not do is persuade that Neo-Darwinian evolution is capable of creative work and the generation of original genetic information. Likewise, while Lang and Rice persuade that not all mutation is degradative, they do not persuade that any mutation is truly generative. Evolution is shown to produce many neutral genetic changes, shuffling the existing genetic cards, but the deck itself is left unexplained.

In The Edge of Evolution and Darwin Devolves, Michael Behe proposes an eponymous “edge of evolution.” In “Evolution Unscathed,” Lang and Rice give that edge an almost imperceptible nudge. The line remains at the biological taxon of the family, and evolution remains a bounded and limited biological force, incapable of the generation of original forms of life.

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Table of Contents:

1. Neo-Darwinian Evolution: Degradative, Neutral, or Generative?

2. The Evolution of Irreducible Complexity: Erasing or Nudging the Edge of Evolution?

3. The Evidence of Evolution and the Need for Philosophy

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1. Neo-Darwinian Evolution: Degradative, Neutral, or Generative?

Lang and Rice begin by critiquing an impression they suppose Darwin Devolves is designed to leave: That a majority of the genetic mutations that result from Neo-Darwinian processes are degradative or loss-of-function mutations. Over several paragraphs, they object that a great many mutations are neutral and do not involve loss-of-function, the deletion of functional genetic material. As a result, they at best correct an overemphasis on Behe’s part. But in so doing, they effectively concede that Neo-Darwinian processes have no positive, generative power.

One of Behe’s main points in Darwin Devolves is that Neo-Darwinian evolution, which has been demonstrated to occur at the level of species and genus, often works by providing a variation that is advantageous relative to the organism's environment, but which is the result of a loss of functional genetic material. A great example is the polar bear’s mutation of a gene that is shared by many (all?) mammals, up to and including humans. The APOB gene is involved in fat metabolism, and its loss in other species is shown to lead “to high levels of cholesterol and heart disease” (Behe, 17). The polar bear’s mutation of this gene proves advantageous under its extreme environmental conditions, allowing it to have a diet much higher in fat than its relative, the brown bear, with whom the polar bear shares a common (bear) ancestor. Again, in terms of genetic information, the mutation is a loss; but by the accident of the polar bear’s environment, the mutation is actually adaptive.

Lang and Rice point out that degradative mutations like this one are only predominant in cases of what is known as “experimental evolution.” Experimental evolution is what occurs “where selective pressures are high and conditions are constant, or nearly so.” I gather that the polar bear’s extreme, Arctic environment made for a paradigmatic case of experimental evolution.

However, most evolution does not occur under such constant and high-pressure conditions. In these other situations, “loss-of-function mutations account for only a small fraction of natural genetic variation”:

In humans only ∼3.5% of exonic and splice site variants are putatively loss-of-function, and a survey of 42 yeast strains found that only 242 of the nearly 6000 genes contain putative loss-of-function variants.

These distinctions, between different kinds of evolution and mutations, are helpful and provide a corrective to Behe’s apparent overemphasis on the degradative force of Neo-Darwinian evolution.

However, the rest of the mutations that Lang and Rice describe as much more prevalent than loss-of-function variations are, relative to the introduction of novel genetic material, merely neutral. The three they mention are “gene duplication, horizontal gene transfer, and introgression.” Gene duplication involves the introduction of an extra copy of an existing gene into the resulting genome. Horizontal gene transfer is the relocation of a gene to a different point in the genome. Introgression is the introduction of genetic material from a different species or population via inter-breeding.

About these three forms of genetic mutation, Lang and Rice say: “Gene duplication, horizontal gene transfer, and introgression balance out gene loss, providing a source of new genetic material.”

But this is a generous use of the term “new genetic material.” 

If I took a work of Shakespeare and duplicated or moved around its parts, or inserted portions from other works of Shakespeare, would any new, dramatic prose be produced? How we answer that question determines our verdict on the theory of universal common descent by Neo-Darwinian evolution.

Let’s imagine that a line of Shakespeare was duplicated and repeated successively. Even if it was copied without error, its unnecessary repetition might be thought to damage the flow and meaning of the text. Nevertheless, using Lang and Rice’s standard, we could admit that the text had not been degraded, just rearranged. And the same for moving a line “horizontally” within the text. Introducing text from another drama would certainly involve new, dramatic prose relative to this drama; but of course, that other line was equally the creative work of Shakespeare and is also likely to interrupt and damage the text.

Of course, it is possible that repeating a line of the drama, shifting a line to a different point in the text, or inserting a line from another drama could, on rare occasions, fit into and slightly change the plot or, at least, the dialogue. If this occurred, we could say that “new, dramatic prose” has been produced. But for other reasons, we might want to maintain that no new, dramatic prose had been produced, because the novelty arises merely by the (accidental) rearrangement of prose that required a human author in order to be produced in the first place.

At this point, we realize that we lack the categories to distinguish different levels or kinds of novelty and of dramatic prose. These processes are capable of producing new prose that is a permutation of existing prose. These permutations of Shakespeare’s text by a copying mechanism are limited and shaped by the original text the mechanism is given. So-called “artificial intelligence” might even be able to produce an imitation Shakespearean drama, by an advanced and not entirely random, but mechanical process. However, given the necessity of informational input to the mechanism or A.I., we must distinguish the kind of text such a mechanism can produce from that which it must be given.

The same goes for genetic information. The kind of genetic information on which Neo-Darwinian processes can work is categorically different than the kind of genetic information they can produce. Another theorist of Intelligent Design, William Dembski, has proposed and defended a theory of the kind of information that requires a designer: Information that is both specified and complex. (He elaborates the theory in his books The Design Inference and No Free Lunch.)  But even his theory fails to distinguish between the genetic information Neo-Darwinian processes can produce and that which they require to get started. (Fortunately, his theory indicates that both require design as an explanation.)

So, to the theory of Intelligent Design, I offer my own contribution, the distinction between original and mutative information. For Shakespearean text, a copying mechanism might be able to produce novel, mutative dramatic prose. But it will produce no original dramatic prose. Likewise, for genetic information, Neo-Darwinian processes are able to produce novel, mutative genetic information. But they are incapable of producing novel, original genetic information. The question is not, then, of novelty, but of originality.

Behe’s claim was that Neo-Darwinian processes are powerfully degradative to genetic information. Lang and Rice retort that, in most evolutionary circumstances, “Gene duplication, horizontal gene transfer, and introgression balance out gene loss, providing a source of new genetic material.” My response is that these processes indeed produce new mutative genetic material. But the question for evolution is really of the possibility of the production of original genetic information. Behe’s claim about the devolutionary power of Neo-Darwinism is, likewise, not primarily about the degradation of mutative genetic information, but of original genetic information, like that in the APOB gene, shared by many mammals, which the polar bear lost, on account of the unique diet its environment required.

Accordingly, concerning original genetic information, the verdict must be that Lang and Rice highlight processes that are, at best, neutral with respect to such information, neither degradative nor creative. But the verdict that Lang and Rice require is that: “the data (only some of which we present here) are more than sufficient to convince any open-minded skeptic that unguided evolution is capable of generating complex systems.” What Lang and Rice have actually shown is that, given complex, self-reproducing systems, unguided evolution is capable of producing non-degradative variations to such systems. They have not provided data that supports unguided evolution’s capacity to generate complex systems.

2. The Evolution of Irreducible Complexity: Erasing or Nudging the Edge of Evolution?

However, later in the piece, Lang and Rice attempt to do just that, to demonstrate evolution’s ability to generate complex systems. A hallmark of Behe’s original argument for Intelligent Design, from his book Darwin’s Black Box, is irreducible complexity, a feature of systems that require all their parts in order to function, like Behe’s famous mousetrap. A step-wise theory of the generation of systems must overcome the obstacle that function is not gradually improved by the accumulation of parts, but is absent until all the parts are present in the required arrangement.

The Neo-Darwinian response to Behe has always been that there are step-wise evolutionary paths to such systems, in which each individual part serves a function different from that of the eventual whole. The irreducibly complex system is an unforeseen, but happy result of independent adaptations, that previously served other functions (or may continue to do so). Lang and Rice provide just such an example.

But before looking at one of their examples, consider the significance of this design constraint from an engineering perspective. Imagine having to design an irreducibly complex mechanical system to serve a particular function. Then, you are told that each individual part of the system must serve a function on its own, a function distinct from, but not entirely unrelated to that of the whole system. (The parts of a molecular system may serve functions distinct from that of the molecular system, but still related to the functioning and health of the whole organism.) That alone would be a significant design constraint. I would be hard-pressed to think of any artificial system that has been produced according to this constraint.

But the evolutionary bar is actually much higher since the entire system must survive and propagate via natural selection. This means that a part that could serve a function but wasn’t necessary to the organism could very well be eradicated. And again, this all depends on parts of mechanisms arising more or less randomly, based on genetic mutations. (And the randomness of genetic mutations has, I think, been overstated; what mutations and variations are possible is constrained by the genetic code itself.)

For the theory of universal common descent by unguided evolution to be plausible, it must be demonstrated that all kinds of biological systems could arise, without intention, with these restrictive and demanding design constraints that human engineers would struggle to follow. And, it must be argued that it is not improbable that this did occur within the time allotted by the fossil record.

Do Lang and Rice do this? No. What they do offer is an example of a biomolecular system that requires four different protein variations in order to serve the function of binding a new kind of protein. Fortunately, each of the four proteins improves the existing function of the molecular system before enabling “in an all-or-none manner” the system to bind to a new protein, serving a new function. Lang and Rice conclude:

While adapting along a step-wise evolutionary path of improved binding to LamB, the J protein was able to acquire the ability to bind to a new receptor—to evolve a novel protein-protein interaction that was dependent upon four mutations acting in an all-or-none manner, well beyond Behe's “edge of evolution.”

This is an interesting example and indeed demonstrates the development of an irreducibly complex system by a step-wise, unguided evolutionary path. Along with one other example of a biomolecular system, Lang and Rice succeed in demonstrating that, at a rather low level of complexity, a system that is irreducibly complex may arise.

While they say that this is “well beyond Behe’s ‘edge of evolution,’” it barely moves the needle. We can remember Aristotle’s criterion for identifying events caused by chance: That they happen rarely. Likewise, these molecular examples exhibit a low level of complexity; their probability, while small, is not prohibitively so. Accordingly, rather than relocating Behe’s edge of evolution, they, at best, shift it imperceptibly.

Returning to the Shakespeare example, the evolution of this new interaction is like four mutations to the text leading to a new, mutative paragraph, that oddly makes sense. While unlikely, this is not so improbable as never to occur. But the fact that it did does not make it probable that an entirely new Shakespearean drama could be produced in that fashion; in fact, it does not even make it possible, on account of the distinction between original and mutative dramatic prose. Likewise, the fact that functioning, self-replicating bacteria can evolve novel functions in an unguided way does not indicate that bacteria itself could have come to be by Neo-Darwinian processes. It shows that bacteria may evolve (i.e., change), not that anything else could evolve into a bacterium.

3. The Evidence of Evolution and the Need for Philosophy

Earlier, I wrote that Lang and Rice show competence in the empirical work of biology, but they lack philosophical competence. Another way of saying this is that they are very competent to gather evidence; they lack the competence to determine what the evidence is evidence of.

This shows up in their review in a discussion of different standards of evidence: “Darwin Devolves accepts as evidence only de novo protein evolution, a restriction Behe uses to…claim that ‘Darwinian evolution is self-limiting.’” Given that they state in the review that their examples are examples of “novel genetic information,” it seems that they implicitly accept a distinction between the “novel” and the “de novo,” which presumably maps onto something more than the linguistic difference between English and Latin. In my terminology, this is the distinction between the merely new, and the original.

My question to Lang and Rice would be how they can be so confident “that unguided evolution is capable of generating complex systems,” if “de novo protein evolution” is too high a bar for them to demonstrate.

If Behe was inclined to overemphasize the degradative force of Neo-Darwinism, and if he overlooks some cases of the unguided arising of irreducibly, minimally-complex systems, then Lang and Rice have corrected those errors. What they have not done is met the correctly high evidential bar of demonstrating that it is not only possible but not improbable that all irreducibly complex systems arose by unguided, Neo-Darwinian processes. Instead of erasing the “edge of evolution,” Lang and Rice have helped Behe draw it a hair to one side: Not only can Neo-Darwinian processes diversify an existing biological kind into new genera and species, remaining within the same, existing biological family, it can also lead to new protein functions every now and then.

While Lang and Rice insist that “the data (only some of which we present here) are more than sufficient to convince any open-minded skeptic that unguided evolution is capable of generating complex systems,” I propose a different vision of open-mindedness: Our minds should be at best agnostic concerning the capacity of unguided evolution to generate complex systems. To decide between an unguided evolutionary, a teleological evolutionary, and a creationist view of biological origins requires much thought. Whether the unguided evolution of all biological organisms and systems is possible is at least an open question; at most, it is hardly imaginable, and adherence to the view that evolution is a closed question is based on scientistic gullibility and an ideological commitment to methodological naturalism in historical science.

But more on those next time.