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Dr. Stephen C. Meyer

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Dr. Stephen C. Meyer

from  https://stephencmeyer.org/2001/05/16/the-meanings-of-evolution/

Metcalf’s statement suggested, as many modern biologists have noted, that the term evolution can mean different things.

occurred - but how?

His comment also suggested that not all senses of evolution have the same epistemological standing. We can assert confidently that evolution “has occurred,” Metcalf explained, but we may be more uncertain about how it occurred.

Metcalf made this distinction to show the court that critique of evolution in one sense did not necessarily count as critique of evolution in other senses. To assume otherwise would be to commit the logical fallacy of equivocation.

the fact of evolution and the theory of evolution are two different things

He feared that confusion between the fact of evolution and the theory of evolution would justify excluding all teaching about evolution simply because some aspects of evolutionary theory did not have the same degree of confirmation as others...

Good science teachers must define terms carefully and use them consistently to avoid conflating different ideas. Good biology teachers must tease apart the distinct ideas associated with evolution to help students to evaluate each idea separately and to distinguish evidence and observations, on the one hand, from inferences and theories, on the other.

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 Yale biologist Keith Stewart Thomson has identified at least three distinct meanings associated with evolution.

Six principle meanings of evolution in biology textbooks:

1. Change over time; history of nature; any sequence of events in nature.

2. Changes in the frequencies of alleles in the gene pool of a population.

3. Limited common descent: the idea that particular groups of organisms have descended from a common ancestor.

4. The mechanisms responsible for the change required to produce limited descent with modification, chiefly natural selection acting on random variations or mutations.

5. Universal common descent: the idea that all organisms have descended from a single common ancestor.

6. “Blind watchmaker” thesis: the idea that all organisms have descended from common ancestors solely through an unguided, unintelligent, purposeless, material processes such as natural selection acting on random variations or mutations; that the mechanisms of natural selection, random variation and mutation, and perhaps other similarly naturalistic mechanisms, are completely sufficient to account for the appearance of design in living organisms.

“The Fact of Evolution”: Conflating Meanings #1–3 with Meaning #5

A recent booklet, Science and Creationism: A View from the National Academy of Sciences (1999), defends teaching the subject of biological origins from an exclusively evolutionary perspective.23 According to Science and Creationism, not only do alternative theories (such as intelligent design) fail to qualify as science, but evolution has been established beyond any reasonable doubt. The booklet’s introduction argues that the “theory of evolution” is a scientific explanation “so thoroughly tested and confirmed” that it is “held with great confidence” and is “one of the strongest and most useful scientific theories we have.” It even claims that evolution is so well established that it can legitimately be described as a fact. As the booklet explains, “Scientists most often use the word ‘fact’ to describe an observation. But scientists can also use fact to mean something that has been tested or observed so many times that there is no longer a compelling reason to keep testing or looking for examples. The occurrence of evolution in this sense is a fact. Scientists no longer question whether descent with modification occurred because the evidence supporting the idea is so strong.”²⁴

Those statements aptly illustrate the ambiguity associated with the term evolution and the confusion that its unqualified use creates. Precisely which sense of evolution has been “so thoroughly tested and confirmed” that it “is held with great confidence” and can even be regarded as “a fact”? Mere evolution, or evolution #5 and/or #6? The NAS statement never specifies, though presumably it means to affirm the theory of universal common descent, evolution #5.

Indeed, the booklet often employs ambiguous (or shifting) definitions from one sentence to the next. The second-to-last sentence in the quotation asserts that “the occurrence of evolution” is a fact. And, of course, it may well be, depending upon which sense of evolution is meant. The phrase, “the occurrence of evolution,” seems to imply evolution in the sense of change over time (evolution #1) or perhaps change in the frequency of expression of alleles (evolution #2). Certainly, evolution in these senses has occurred. Yet the next sentence affirms that “descent with modification” is so well established as to be an unquestioned fact. Throughout the booklet, “descent with modification” is equated with the theory of universal common descent (evolution #5), though technically it could refer either to limited or universal common descent (evolution #3 or #5). In any case, given the booklet’s conventions, the last sentence of the quotation seems to affirm a stronger meaning of evolution (evolution #5) than that affirmed in the previous sentence (evolution #1, #2, or possibly #3). Yet the booklet provides no additional justification for affirming this stronger meaning. As such, the passage commits the fallacy of equivocation.

The writers of the NAS booklet do, of course, seem aware that the term evolution can refer to different concepts. In particular, they make a distinction between whether evolution occurred (that is, the fact of evolution) and how (that is, the mechanism by which it occurred). Yet their attempt to clarify definitional matters on such grounds only confuses the issue further, as the following passage illustrates:

The scientific consensus around evolution is overwhelming. Those opposed to the teaching of evolution sometimes use quotations from prominent scientists out of context to claim that scientists do not support evolution. However, an examination of the quotations reveals that the scientists are actually disputing some aspect of how evolution occurs, not whether evolution occurs. For example, the biologist Stephen Jay Gould once wrote that “the extreme rarity of transitional forms in the fossil record persists as the trade secret of paleontology.” But Gould, an accomplished paleontologist and educator about evolution, was arguing about how evolution takes place. He was discussing whether the rate of change of species is slow or gradual or whether it takes place in bursts after long periods when little change takes place—an idea known as punctuated equilibrium.²⁵

This passage betrays confusion on several counts. First, scientists can affirm that evolution (in several different senses, #1–4) has occurred without necessarily affirming the theory of universal common descent. To say that evolution has occurred does not necessarily imply that enough morphological change has occurred to ensure that all organisms are connected by common ancestry. Thus, a scientist could affirm that evolution (#1–4) has occurred and yet doubt the universal common ancestry thesis. In fact, as noted above, many scientists do now take precisely that position. The simple twofold distinction (between “the” fact and the mechanism of evolution) in the NAS booklet obscures this possibility. There are many alleged “facts” of evolution, and the booklet does not distinguish among them.

Second, the “extreme rarity of transitional forms” does reflect negatively on evolution in the fifth sense—that is, it does seem to provide evidence against universal common descent. True, Stephen Gould does not question universal common descent, but he has reasons other than fossil data (molecular evidence, for example) for accepting the theory. The fossil evidence taken at face value, however, does suggest that, for example, the major taxonomic categories of animals did arise separately within a very narrow window of geologic history. The absence of transitional precursors between the representatives of the new animal phyla strongly supports that impression (see Stephen C. Meyer, Marcus Ross, Paul Nelson, and Paul Chien’s essay in this volume). Thus, Gould’s discussion of “the extreme rarity of transitional forms” does bear on the question of the truth of universal common descent (evolution #5), and critics of evolution in this sense quite legitimately cite him on this point.

Third, in the passage cited, Gould is not in fact discussing “whether the rate of change of species is slow or gradual”; he is discussing “the extreme rarity of transitional forms in the fossil record.” Because Gould accepts universal common descent and because he wants (as much as possible) to take the fossil evidence at face value, he assumes that a mechanism of morphological change exists that can produce change very rapidly. Gould’s belief that morphological change must occur very rapidly constitutes part of his interpretation of why the fossil evidence looks as it does. Others, of course, might choose to interpret that same evidence differently. They might view morphologically disparate groups of organisms (such as the representatives of the new animal phyla that appear in the Cambrian) as having originated separately—that is, without having descended from a common ancestor. Yet the NAS booklet treats critics of evolution (presumably in the fifth sense) as ignorant or confused for failing to recognize “the” distinction between the fact and the mechanism of evolution. In fact, it is the NAS booklet that fails to make important definitional distinctions (between evolution #1–3 and #5—that is, between different senses of evolution that may or may not constitute facts, or between the different senses of evolution that might or might not have occurred).

Interestingly, Gould (one of the fifteen members of the NAS steering committee for its 1999 edition of Science and Creationism) also fell into this same rhetorical imprecision by treating the distinction between the fact and theory of evolution as if it constituted a unitary distinction. For example, in “Darwinism Defined: The Difference between Fact and Theory,” Gould wrote:

The fact of evolution is as well established as anything in science (as secure as the revolution of the earth about the sun), though absolute certainty has no place in our lexicon. Theories, or statements about the causes of documented evolutionary change, are now in a period of intense debate—a good mark of science in its healthiest state. Facts don’t disappear while scientists debate theories. As I wrote in an early issue of this magazine (May 1981), “Einstein’s theory of gravitation replaced Newton’s, but apples did not suspend themselves in mid-air pending the outcome.”26

Here Gould argues that the occurrence of evolution is a fact and that scientists only theorize about how it happened. Yet clearly the sense of evolution that Gould means here to defend, namely, the theory of universal common descent, does not have the same epistemological status as observations of apples falling to the ground. No scientists can directly observe “evolution” (in this sense) occurring. No one can observe the history of life, or the pattern of a branching tree emerging, or the transitions between each of the major groups of organisms. In other places Gould himself speculates that evolution happened too fast for even the fossil record to preserve most of the transitional forms required by the theory of universal common descent.27 Instead, as noted above, the theory of universal common descent was (and is) inferred (abductively) from many classes of presently observable phenomena: biogeographical distribution, fossil succession, homology, and the like. These latter phenomena are arguably facts akin to apples falling, but the theory or theories inferred from them are not.

The leadership of the National Association of Biology Teachers (NABT) has also recently adopted this same way of defining the issue in a policy statement about how evolution should be taught. The NABT published its “tenets of science, evolution and biology education” with the following introductory remarks:

Modern biologists constantly study, ponder and deliberate the patterns, mechanisms and pace of evolution, but they do not debate evolution’s occurrence. The fossil record and the diversity of extant organisms, combined with modern techniques of molecular biology, taxonomy and geology, provide exhaustive examples and powerful evidence for genetic variation, natural selection, speciation, extinction and other well-established components of current evolutionary theory. Scientific deliberations and modifications of these components clearly demonstrate the vitality and scientific integrity of evolution and the theory that explains it.²⁸

The last phrase, “evolution and the theory that explains it,” and the earlier phrase, “biologists . . . do not debate evolution’s occurrence,” both employ the word evolution in an alleged “fact” mode. But precisely which sense of “evolution” is said to be factual rather than theoretical? Like Gould, the NABT statement excludes mechanism (evolution #4 and #6) from the category of fact but lumps most of the other senses of the term into one mold. Thus, like Gould and the NAS statement, the NABT statement conflates evolution #1–3 with evolution #5. Yes, evolution in the sense of change has occurred, but has enough morphological change occurred to ensure that all organisms are related by common ancestry? That question is never seriously addressed, nor can it be, given the equivocal definitions in play.