The Illogic of Creationism An Essay Review by Michael T. Ghiselin, based on +quot;Evolutio

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The Illogic of Creationism An Essay Review by Michael T. Ghiselin, based on "Evolution: A Theory In Crisis" by Michael Denton Adler & Adler, Bethesda, MD 1986,$19.95 William Harvey's book entitled "De Motu Cordis et Sanguinis in Animalibus" was published in 1628. It established beyond reasonable doubt that the blood circulates, and it overthrew the ancient physiology of Galen. So compelling were Harvey's arguments that his conclusions became the consensus among the learned community within his own lifetime, even though the passage of the blood through the capillaries had yet to be seen. Charles Darwin's book entitled "On The Origin of Species by Means of Natural Selection" was published in 1859. It established beyond reasonable doubt that organisms of different species are united by common descent, and overthrew the traditional view that they had come into being through supernatural acts. So compelling were Darwin's arguments that the evolutionary conception of the living world became the consensus among the learned community within ten years, even though the sort of fossil record that would have been all the more convincing was not yet available. Harvey's idea that the heart is a pump and provides the main driving force behind the circulation remains a fundamental principle in cardiac physiology. So too with Darwin's principle of selection, without which so much of biology would be utterly unintelligible. Indeed, we owe much of our present understanding of the heart and blood to the fact that anatomists and physiologists know that such things evolve. All this is common knowledge, or at least it ought to be. No properly educated person would entrust his own life, or that of his child, to a physician who did not know that the blood circulates and why it does. If a medical practitioner claimed that the blood does not circulate his intellectual credentials and professional integrity would be questioned. So we would look very carefully at his claims, admitting perhaps that all sorts of things are possible and we would not pre-judge the issues. If we found that his premise were false and his logic formally invalid, we would consider him discredited; and if we found him marketing such notions to a gullible public we would denounce him as a quack. The same applies to scientific matters in general, including those from which modern cardiac physiology derives its legitimacy. If somebody said that the circulation of the blood is "just a theory, not a fact," we would take it as an insult to our intelligence. That the blood circulates is a fact, in the sense that the blood does in truth circulate. The theory presented in Harvey's book makes the structure of the blood intelligible in the light of the fact that the blood circulates. By the same token there is no contradiction in speaking of evolutionary theory on the one hand, and the fact that evolution has occurred on the other. One does not have to be a professional logician, or to know the technical term for it in formal logic to recognize such a flagrant instance of the fallacy of false disjunction. But the general public, having little acquaintance with theories anyway, is apt to be misled if such matters are not clearly explained in terms they can understand. And fallacious reasoning can be subtle. Logical fallacy becomes all the more pernicious when coupled with false premises of the sort that only an expert can identify as such. A book by an author who is obviously incompetent, dishonest, or both -- and it may be very hard to decide which is the case -- ordinarily is not worth the attention of a professional scholar. If, however, the deficiencies are not apt to be recognized by the audience to whom a work is addressed, warning potential readers might be a valuable service. And discussing some examples of fallacious and false premises can sometimes be a useful exercise. Michael Denton attempts to convince his readers that something is wrong with evolutionary biology. This he does primarily by attempting to resurrect one of the positions that revolutionary biology rendered untenable in the first place, namely the typological interpretation of biological classification systems (or taxonomy). A typologist would have us believe that organisms exist in nature as members of discrete classes, in the sense that everything clearly falls under one head or another. Hence each and every group can be rigidly defined, and there can be no overlap or intermediates between them. If this be so, then it would appear that either the groups in question have not evolved, or that if they have evolved, they have done so by large and discontinuous steps -- by "saltation." Because the current version of evolutionary theory rejects genuine saltations, there would seem to be something problematic about it. Contemporary philosophy of taxonomy has a ready answer to Denton's argument. The groups, or taxa as they are called, are not classes in Denton's sense at all. They are lineages, or branches of genealogical trees. Therefore we should not expect to "define" them at all, in the sense that an organism simply must have a given property to occupy some position on a tree. The mischief comes from efforts to translate the branching diagram into a heirarchical arrangements of groups within groups. Denton claims that organisms always possess the diagnostic features that purportedly "define" each group. If he understands why this is so, he does not tell his readers. Of course, if you go out in the wild, and find an animal with hair, you can be reasonably sure that it is a mammal -- though perhaps you might have trouble, say, with the "hair" on a tarantula. Why should this be? For the simple reason that whenever taxonomists find a group, they go through a great deal of material, looking for characters that happen to be present in all specimens of the group. These they treat as diagnostic -- which means that they are useful in identification, like the symptoms in a doctor's diagnosis of an illness. If they later find a specimen that belongs to the group, but does not have the diagnostic feature, they decide that the feature is not diagnostic after all, and perhaps look for other ones. The whole argument is circular, as Darwin clearly explained in 1859. By the same token, Denton tells us that as a rule taxonomic groups are separated from one another by gaps, with few intermediates between them. Of course. One traditional practice among taxonomists has been to delimit groups at precisely those places where the gaps , for whatever reason, occur. They sometimes get filled in, as when expeditions are sent to previously unexplored areas, and the gaps get de-emphasized in the new systems of classification. Denton alleges that few if any intermediates have been found between taxonomic groups. But he gerrymanders the evidence so as to rule out the kind of intermediate that most of us would consider a decent example. Consider the following diagram, which represents a genealogy among objects denoted by letters: E D C \ \ / \ \ / \ B \ / \ / A | | According to one not unreasonable usage, the lineage BD is "intermediate" between AE and C. So D in a sense would fall between E and C. (Invertebrate chordates such as sea-squirts and Amphioxus, which have notochords but not vertebrae, would thus be intermediate between vertebrates and other invertebrates.) Of course, E, D, and C do not represent a direct, ancestor-descendant relationship. A, B, and C do, and this is the only sense of an intermediate that Denton will accept. When dealing with extant creatures, we would only expect a certain amount of change to have occurred between, say, B and D. Furthermore, if we found a fossil specimen of B, we might have trouble deciding whether it really was a specimen of B, in the sense of occupying the exact point of bifurcation, or whether it was located along AB or BC, or perhaps some minor branch not shown on the diagram. Furthermore, if we look at a fossil such as B, we find that it has some properties present in C and D, but not in A -- Archaepteryx, as close an intermediate as one could wish between birds and dinosaurs, is a good example. But all this is precisely what we would expect, given the fact that the objects are united by descent with modification. So these arguments turn out to be flagrant instances of the fallacy of irrelevant conclusion: they do not bear upon the question of whether we have been able to document intermediate conditions such as must have existed if evolution has in fact occurred. We have. The question that was asked in the first place gets begged as well. Darwin suggested that the fossil record was far less complete than people thought. If so, then further research should lead to an increasing number of items lying close to A or B, and it has. Therefore the argument from lack of intermediates can be turned on its head, and made to show that evolution has in fact occurred, merely by adducing a few of them. To refute the proposition that no intermediates occur, we need only show that *one* does occur: it is a formally valid test for universal negative proposition. (To refute "All men are immortal" it suffices to kill just one of them.) In the above example, B would suffice. But Denton accepts the creationists' version of logic, and insists that we fight not just B, but A, and every other object in the universe analogous to it. In other words, he insists that we verify a universal affirmative. What this means is clear if we let the letters in our diagram stand for languages. Let B stand for Latin, C for French, D for Portuguese, E for Russian. In B, we we do have a well documented common ancestor. But what about A? Unless I am mistaken, we have no documents of the common ancestor of the Slavic and Romance languages. And even if we did, the creationists would simply ask for the common ancestor of Nahuatl and Basque. Such is the logic, if we may dignify fallacious reasoning with such an epithet, upon which "creation science" rests. That logic is inseparable from its content, for the movement has presented us with one long series of excuses for evading the canons of scientific evidence, in order to suppress truths that some people find objectionable. Insofar as special creation has been treated as a scientific hypothesis, it was decisively refuted in 1859. The only way to get around that fact is to repudiate not just some particular findings of science, but its very foundations in logic itself. But if logic -- and that means everything from higher mathematics to common sense -- has to be repudiated, then rational judgment of every kind loses its validity. That is precisely what the creationists want. If they can degrade your child's intellect enough, perhaps he will become one of them. Denton's book may be read as an able piece of propaganda. As such it has many fine qualities. The rhetoric is by no means as bad as the logic. Except in a few places the author maintains a reasonable and earnest tone. The liberal use of end-notes suggests that a considerable amount of work has been done, and the reader unaware of what should have been cited but was not may have some difficulty distinguishing the reality of scholarship from mere appearances. The occasional use of creationist cliches tips off only the more perceptive reader to what motivates the author. The creationists need a book that is not overtly creationist at all, but purports to be motivated by purely scientific interests. So I do recommend the book, but only as an example of how reason is getting abused these days.

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