[Topics: Evolutionary Biology, Logic, Logical Fallacy]

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The Microevolution Fallacy:

Introduction:

Today’s article is fairly straightforward, as it deals with an exercise in philosophy’s bedrock: logic and argumentation. The actual content of what follows concerns the fields of biology and religious apologetics, but you don’t need any background in either in order to understand it. All that is required is an attention to the arguments themselves.

In particular, this article refutes a rebuttal that is present in religious apologetics in response to modern experimental evidence for evolution by natural selection.[1] But I’ll be focusing on the philosophical and logical angle, and leaving most of the relevant scientific responses in the footnotes.

In light of such evidence, one prominent response from those who seek to deny evolution as an account for speciation of all extant life (including humans) is to grant that such evolution occurs without granting that it occurs on a large scale; such an individual would contend that what has been proven is not evolution per se, but merely microevolution. But taking this path means committing a simple logical error by failing to follow a line of thinking to its conclusion.

A Statement of the Creationist Macroevolution Objection:

In order to provide a context for this article, I will now quote a lengthy introduction of the creationist microevolution/macroevolution position from the book I Don’t Have Enough Faith to be an Atheist by Frank Turek and Norman Geisler. But it should not be thought to originate there; this argument crops up everywhere that incredulity regarding evolution can be found today, from online forums to the pages of other contemporary apologia to the minds of wishful biology majors. Here it is:

As an example of “natural selection,” consider what happens to bacteria attacked by antibiotics. When bacteria survive a bout with antibiotics and multiply, that surviving group of bacteria may be resistant to that antibiotic. The surviving bacteria are resistant to that antibiotic because the parent bacteria possessed the genetic capacity to resist, or a rare biochemical mutation somehow helped it survive (we say “rare” because mutations are nearly always harmful). Since the sensitive bacteria die, the surviving bacteria multiply and now dominate.

Darwinists say that the surviving bacteria have evolved. Having adapted to the environment, the surviving bacteria provide us with an example of evolution. Fair enough, but what kind of evolution? The answer we’re about to give is absolutely critical. In fact, outside of the philosophical presuppositions we’ve been exposing, defining “evolution” is perhaps the greatest point of confusion in the creation-evolution controversy. This is where Darwinian errors and false claims begin to multiply like bacteria if not checked by those who believe observation is important to science. Here’s what observation tells us: the surviving bacteria always stay bacteria. They do not evolve into another type of organism. That would be macroevolution. Natural selection has never been observed to create new types.

But macroevolution is exactly what Darwinists claim from the data. They say that these observable micro changes can be extrapolated to prove that unobservable macroevolution has occurred. They make no distinction between microevolution and macroevolution, and thus use the evidence for micro to prove macro. By failing to make this critical distinction, Darwinists can dupe the general public into thinking that any observable change in any organism proves that all life has evolved from the first one-celled creature. (Geisler and Turek 140-41)

Turek and Geisler use the term ‘macroevolution’ here, but other incarnations phrase it differently, as ‘evolution between kinds’ or even simply ‘evolution from one species to another.’ In any case the argument is the same: that the bodies of evidence in favor of evolutionary biology are not showing what the overwhelming majority of modern biologists purport them to be showing. The evidences are valid, say such responders, but are only showcasing little changes that occur within one species or (if the responder is particularly generous) within one closely related group of species.

While the logical structure of this microevolution vs. macroevolution response shall require some attention hereafter, the motivation for the response is entirely clear: if it can be shown that the sum of all evolutionary data available today does not account for the existence of highly differentiated types of creatures, then there is a role retained in that process for any given apologist’s preferred creative force.

A Statement of the Scientific Macroevolution Argument:

Here is the logical form of the argument for evolution by natural selection as an explanation of speciation:

(1) The genetic structure of organisms largely determines the phenotypical (physical) structure of organisms.

(2) The genetic structure of organisms naturally changes across generations—primarily due to mutation and recombination.

(3) While the majority of such changes have no effect on an individual organism’s survival, some small amount of such changes have either a net positive or net negative effect on an individual organism’s chances of surviving within its environment.

(4) Positive changes that increase the likelihood of any given organism’s survival thereby increase the likelihood of that organism surviving long enough to pass on its genes—and thus the positive change(s) in question—to the next generation (whereas negative changes have the opposite effect).

(5) By (2), (3), and (4), changes would amass over time.

(6) The survival-efficacy of any given change in an organism’s structure is wholely dependent on the organism’s environment, which may itself be changing (whether because of the changes to other organisms, or climate fluctuations, or migration of the species, or another reason).

(7) By (5) and (6) and the different climate and landscape conditions present across the planet, differently located populations of organisms would be amassing different genetic changes.

(8) Therefore, by (1) and (7), over a long enough timescale such changes would result in a wide array of phenotypical variations, which humans categorize as species.

So that’s my quick run-down of the scientific stance. You could lay out the premises in a different order or with different divisions (like, for example, establishing the heritability of traits in its own premise with reference to scientific data on sexual and asexual reproduction), but the general form of the argument would be the same.

Photo by Clint Loveness

Now what is the method of doubt utilized by the macroevolution vs. microevolution dichotomy? In the case of the argument as I have just laid it out, the method would be to object to premise (5), or at least to its phrasing. ‘Yes,’ a proponent of macroevolution denial might say, ‘such changes would amass over time, as follows logically from the premises you have listed. But you have not mentioned that there are limitations to such amassment. As a result, your use of (5) in justifying (7) is null, which makes (7) ineligible for justifying your conclusion, (8).’ Thus microevolution alone would come about.

Why is this person under the impression that such limitations exist? Such a person may be under that impression due to one or more of a number of mistaken notions, from reference to irreducible complexity[2] to a perceived lack of viable transitional animals[3] to suggestions of molecular or genetic limitations[4]. Indeed, Turek and Geisler, the writers quoted above, make use of all three of those notions in their efforts to deny evolution. But for the purposes of this article, all that you need to notice is that such people have provided no mechanism whereby such limits operate. They posit the existence of limits, erroneously claim that no observations have passed those limits, and yet provide no (even theoretical) specific limit or limiting mechanism.

The Logical Error in the Creationist Macroevolution Objection:

Consider, for instance, the following quotation from that same chapter of Turek and Geisler’s book, in the subsection on proposed genetic limits:

Unfortunately for Darwinists, genetic limits seem to be built into the basic types. For example, dog breeders always encounter genetic limits when they intelligently attempt to create new breeds of dogs. Dogs may range in size from the Chihuahua to the Great Dane, but despite the best attempts of intelligent breeders, dogs always remain dogs. Likewise, despite the best efforts of intelligent scientists to manipulate fruit flies, their experiments have never turned out anything but more fruit flies (and usually crippled ones at that). (Geisler and Turek 142)

The writers refer to genetic limits, but they do not present (here or later in the section) any actual scientific data suggesting such limits. Instead they launch into strings of anecdotes like those seen above regarding dogs and flies. Domesticated dogs—which are, ironically, a great example of a new species that arose within the past 50,000 years from a common ancestor with wolves—should not be expected to produce a non-dog offspring; nor should flies be expected to produce a non-fly; nor should bacteria be expected to produce a non-bacterium. At least, not this millennium. The failure here on the part of those writers is one of scope.

Chart from the Wikipedia article on the origin of the domestic dog

After all, if there is no proposed mechanism of limitation (regardless of any given interlocutor’s concept of choice to express the idea), then there is no reason that changes would not amass as described in the above argument. So I can call it a failure of scope because expecting a dog to give birth to a non-dog is expecting a few years of targeted action to do what naturally takes tens of thousands of years. And for a change from one family of animals into two or more distinct families, that calendar grows by multiple orders of magnitude.

Along the same lines, although humans and chimpanzees differ in genome by less than 5%, the most recent common ancestor between the two species is thought to have existed over four million years ago. For reference, four million years is over 600 times longer than all of recorded history. But humans are not used to thinking on such timescales—nor are they naturally any good at it—so such a mistake is perfectly understandable.

Still, it can be shown in this way that the objection is null. It is not pointing out a mistake in premise (5), but simply stopping the argument at (5) and baselessly ignoring the further implications of that and the preceding premises. It is too late for this responder as soon as they have understood the truth of microevolution. Microevolution and macroevolution describe the exact same process, merely at different scales. When Geisler and Turek, in the first quotation above, grant that microevolution has occurred in the bacteria, they are also granting that macroevolution has occurred (only less so).

You could almost say that this is the opposite of the more well-known ‘slippery slope’ fallacy. Where a slippery slope involves reaching an unjustified conclusion by extensively extrapolating from the facts of a case, the microevolution fallacy involves not reaching a logical conclusion by stopping in the middle of a well-justified line of thought.

My first article in this series, now over a year in the past, was titled “The Macroevolution of Morals.” It was so-named because it dealt not with the natural selection of individuals by their environment, but with the large-scale natural selection of a community of moral individuals by their ongoing communal existence.

I chose the word in that earlier title just because—in addition to succinctly referencing the idea of organically selective phenomena on a larger scale—its alliterative capacity with ‘morality’ struck me as relatively pithy. In actuality, separating ‘microevolution’ from ‘macroevolution’ is a vestige of an earlier scientific moment when big-picture details of evolutionary processes were still being enmeshed with small-picture details, and among today’s biologists it is only a useful or meaningful distinction when clarifying between changes in allele frequency and changes at or above the species level; they are interrelated and both operate via the very same low-level processes.

Conclusion:

In closing, I would like to point out once again that this mischaracterization of the distinction between microevolution and macroevolution is just one tactic among the many ways that creationist thinkers deny modern evolutionary biology. Evolution denial rests on a network of interrelated beliefs and arguments (if you will pardon the phrase, it is a macrobelief . . .) and also gains emotional credence by lending support to other beliefs which may be central to a person’s constructed or imparted self-identity.

Indeed, there are numerous other logical and factual errors which bely those other methods of denial—including everything from citing irrelevancies (such as alluding to the fact that the theory of evolution contains no account of abiogenesis[5]) to reformulating disproven notions (such as the apparent revival of the erroneous notion that no ‘intermediate fossils’ or ‘missing links’ have been found[3]) to plain misinformation (if anyone ever tells you that evolution breaks the second law of thermodynamics because the earth is a closed system, you respond, “So then you deny the existence of the sun?”).

But I don’t personally find those other denial tactics as interesting as this one, because those others often boil down to a straightforward lack or unjustified rejection of education or research on the relevant topic. This microevolution fallacy, however, is a more nuanced mistake, for a few reasons.

First, it can only be formulated by someone who has already accepted a great deal of biology’s practices and data; this indicates to me that those who sincerely hold to this response are not beyond help. Second, while the refutation of this response makes use of scientific data, the mistake itself can be illustrated as here using purely logical processes; this indicates to me that this article could have conversational utility. And third—unlike something in the vein of the comical, self-defeating thermodynamics or transitional fossil claims—distinguishing between microevolution and macroevolution is a more complex maneuver, whose errors may require some investigation into both the underlying science and the underlying philosophy to recognize.

Notes:

[1] That is, in response to everything from DNA evidence to the fossil record to mutually conclusive dating methods to evolution having been observed in a laboratory setting. Evolution having been observed in-action in a laboratory setting has occurred a number of times. One prominent case is the E. coli long-term evolution experiment. For a brief tour through the various types of evidence for evolution, the Wikipedia article on common descent provides a surprisingly thorough tour.

[2] Citing irreducible complexity as an objection to evolution involves a rhetorical trick. The rhetorical trick is this: the responder says that a system is irreducibly complex and therefore could not have developed from smaller systems, and leaves it at that. They hope you will simply not notice the possibility of a system being a reduction of a larger, non-irreducibly-complex system; or a system being a change from a similar-but-not-irreducibly-complex system; or a system being wrongly categorized as being irreducibly complex. For more on the problems with this denial strategy, see the list on this page.

[3] Even taking into account the rarity of useful fossilization, there is nevertheless a remarkably full chronological record of mutually consistent organisms transitioning among all strata of biological classification. There is a cited list of some such changes on this page.

[4] This is the most direct concept concerning the idea of limitations, and yet even within this concept no mechanism of limitation has been proposed. Turek and Geisler mention this concept twice, first as genetic limits supported only by vague anecdotes about dog breeders and experimental flies, and then as “molecular isolation,” supported by reference to a perceived lack of ‘transitional proteins.’ It’s not clear why the writers in question expect scientists to have access to the DNA of common ancestors among orders, families, or even genera when those ancestors have been dead for hundreds of thousands of years—but this is possibly nothing more malicious than a simple misunderstanding on their part. For a cited, technical discussion of this talk of barriers, see this page.

[5] It is of course true that evolutionary theory contains no account of abiogenesis. Evolution and abiogenesis are separate phenomena, which are largely studied separately. Abiogenesis concerns the origin of life from non-life. Evolution concerns what happens over time in any system wherein there are finite varied resources and imperfect replication (e.g. biological reproduction in any given ecosystem).

Work Cited:

Geisler, Norman L., and Frank Turek. “New Life Forms: From the Goo to You via the Zoo?” I Don’t Have Enough Faith to Be an Atheist. Wheaton, IL: Crossway, 2007. 137-67. Print.