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Review: "Evolution — A Theory in Crisis"
Evolutionary biology is in robust health. The current flurry of debates is an early sign of a new burst of growth. Some observers, apparently deceived by the hyperbole that has accompanied these debates, have mistaken growth pains for terminal illness. Michael Denton is one such observer. Evolution: A Theory in Crisis is an anti-evolution treatise. Its theme, exemplified by the title and stated explicitly in the preface, is that there is a crisis in evolutionary biology of fatal proportions. Its parting conclusion is the fallacious assertion that the achievements of evolutionary biology amount to nothing more than "the great cosmogenic myth of the twentieth century" and provide no new insight to the origin of living beings on earth.
The book belongs to the "creation science" genre. Denton's presentation differs from the usual creation science works in only one respect: he does not actively espouse the creation science claim for a scientific basis in Genesis. The book, therefore, has the appearance of being strictly a book on biology. Intelligent laypersons reading Denton's book may think that they have encountered a scientific refutation of evolutionary biology. As a serious piece of biology, however, the book could not pass the most sympathetic peer review. In its approach, methods, and style it is straight out of the creation science mold. Abuses typical of creation science literature abound: evolutionary theory is misrepresented and distorted; spurious arguments are advanced as disproof of topics to which the arguments are, at best, tangentially relevant; evolutionary biologists are quoted out of context; large portions of relevant scientific literature are ignored; dubious or inaccurate statements appear as bald assertions accompanied, more often than not, with scorn.
Deciding how to deal with such a book is not a trivial problem. The book purports to be a biological treatise. Its scope ranges from paleontology to molecular biology, with excursions into the history and philosophy of biology. No area escapes misrepresentation and distortion. Point by point rebuttals would require a treatise of comparable proportions, which is certainly beyond the limits of any one review. Besides, detailed exposes of creation science literature already exist, including Philip Kitcher's Abusing Science: The Case Against Creationism (Cambridge: MIT Press, 1982) and the collection of essays, Scientists Confront Creationism, edited by Laurie Godfrey (New York: Norton, 1983). Many of Denton's misconceptions and distortions are addressed by these two works.
If this were simply a book written for scientists it could be ignored. However, it is not; it is clearly intended for laypersons, whose interest is most likely motivated by philosophical and theological issues. Such an audience cannot be expected to have the necessary expertise to avoid being deceived by the book's manifold abuses of evolutionary biology. A detailed critique being out of the question, the strategy adopted here is to focus upon two themes that are characteristic of the book's treatment of evolutionary biology: chance and typology.
The first theme, which occurs repeatedly as a leitmotif, is that familiar old war horse, "Mere Chance." It first appears in the preface with the statement that since Charles Darwin's time "... chance ruled supreme. God's will was replaced by the capriciousness of a roulette wheel." In a later passage is found the assertion: "The driving force behind the whole of evolution was the purely random process of natural selection" (p. 60). Equating natural selection and the origin of adaptations with "problem solving by trial and error" and "gigantic random searches" is a repeated theme (e.g., pp. 61 and 308).
Pejorative appeal to naive notions of "chance" is typical of creation science literature and is a clear sign that Denton's book is not to be taken as a serious book on biology. Describing natural selection as a purely random process distorts basic population genetic theory. Such statements demonstrate lack of understanding of Darwin's ideas and fail to acknowledge a vast amount of contemporary literature, especially the relevant writings of Ernst Mayr (who is, nevertheless, referenced sixteen times in Denton's index with respect to other topics). Nonbiologists can find a good discussion of the way in which random processes interact with deterministic processes in the theory of organic evolution through natural selection in Mayr's article "Evolution," The Scientific American 239 (September 1978):46-55.
Furthermore, the word chance, in its every day usage, is filled with ambiguity and imprecision. Kitcher (chap. 4) provides a good discussion of different meanings subsumed by the term, several of which commonly occur in discussions of evolution. The different usages imply very different contexts and carry very different connotations. Because stochastic processes occur in virtually every branch of science, including evolutionary biology, and because lay-persons, especially those who are less than comfortable with mathematics, often have difficulties with the concept of random events and with processes governed by probabilistic laws, any writer attempting a serious discussion of phenomena that involve random processes has an obligation to exercise reasonable precision in the way that the role of random events is presented. Uncritical imputation of "mere chance" is not appropriate.
The second theme, which is the major theme of the book, is a typological view of organisms. Six chapters are devoted to a resurrection of this view of biological organization. Under a typological view, different kinds of organisms are regarded as constituting distinct, independe[n]t types between which any concept of genealogical relatedness is meaningless. Under a typological view, variation is without significance: variations within a type are distractions, inconsequential deviations from the essence of the type; similarities (and differences) between types are mere coincidents, the by-products of each type's being what it is. Subscription to a typological view of organisms was the norm among early nineteenth-century biologists. (It is still a central tenet of current creationism. Denton's focus on typology is right in step with the creationists' agenda.) Abandonment of a typological view of organisms and recognition of the significance that individual variability has had in the history of life on earth is precisely what the Darwinian revolution was all about. In The Genetic Basis of Evolutionary Change (New York: Columbia Univ. Press, 1974), Richard Lewontin emphasized this point with a touch of elegance: "He [Darwin] called attention to the actual variation among actual organisms as the most essential and illuminating fact of nature. Rather than regarding the variation among members of the same species as an annoying distraction, as a shimmering of the air that distorts our view of the essential object, he made that variation the cornerstone of his theory."
When stripped of its cloak of respectable terminology, Denton's case for a typological view of organisms is seen to be nothing more than the old arguments of "missing links" and "gaps in the fossil record-arguments that long ago ceased to have biological support. Current debates among biologists on the topic of gradualism versus punctuationalism might appear to involve new evidence, but these debates are, in fact, a red herring for advocates of a typological view of organisms. The key issue for typological thinkers is an absence of genealogical relations between types. The questioning of gradualism by contemporary biologists is a debate, first, about the tempo of morphological change and, second, about processes responsible for large-scale patterns of variation among organisms. Nowhere in the debates is the issue of genealogical relatedness brought into question.
Denton attempts to build a broad case for his typological perspective. I shall confine attention to his treatment of molecular data, which his editors specifically tout in the blurbs on the dust jacket. (Readers interested in problems with Denton's treatment of other areas should see the chapters by Joel Cracraft, Laurie Godfrey, and C. Loring Brace in Scientists Confront Creationism.) Advances in molecular biology during the past thirty years opened a new window for viewing genealogical relations among organisms. The results are close to spectacular. Embedded in the structures of common proteins are telltale clues of genealogical relationships that provide overwhelming, independent, corroboration of the principle of biological evolution. Typological thinking in biology died long ago; molecular data have sealed the coffin. Denton, however, contends that molecular biology provides new evidence for a typological view of organisms. Inspection of Denton's arguments in Chapter 12-A Biochemical Echo of Typology"-reveal that his conclusions are based upon an artifact produced by faulty interpretation of the data. Since Denton's professional training is said to be in molecular biology, a detailed look at the situation is in order.
Biochemists have elucidated detailed structures of a variety of proteins obtained from a diverse array of organisms. (Anyone unfamiliar with rudimentary molecular genetics can read, with confidence, Denton's Chapter 11.) Some of the proteins studied are found only in certain kinds of organisms; others occur in virtually all organisms. In the latter case, the molecular structure of a specific protein-cytochrome C is a classic example and the one used by Denton-can be determined in each of many different organisms. It turns out that the structures of the same protein in two different organisms are rarely identical and in some cases quite dissimilar. The amount of difference can be quantified.
Denton provides representative data in Table 12.1. The data are extracted from the leading biochemical reference on the subject and are good; Denton's analysis and conclusions are not. Denton builds his arguments upon a phenomenon that he calls "molecular equidistance." He uses this phrase to refer to empirical results such as the observation that cytochrome C in bacteria, for example, differs by approximately the same amount (roughly 65-70 percent) from the cytochrome C's found in each one of the other organisms listed in the table (vertebrates, insects, plants, and yeasts). Denton uses such observations to infer (erroneously) distinct typological classes. Discussing the data, he makes statements such as: "The bacterial kingdom has no neighbour in any of the fantastically diverse eucaryotic types. The 'missing links' are well and truely missing" (p. 281); and "There is not a trace at a molecular level of the traditional evolutionary series: cyclostome --> fish --> amphibian --> reptile --> mammal. Incredibly, man is as close to lamprey as are fish!" (p. 284).
These conclusions are erroneous: in his interpretation of 'molecular equidistance," Denton has confused ancestor-descendant relationships with cousin relationships. The telltale clues of molecular data are not, directly, concerned with parents and offspring, intermediate forms, and "missing links." They are, instead, reflections of relative relatedness between contemporary cousins. Twentieth-century bacteria are not ancestors of twentieth-century turtles and dogs: they are very distant cousins, and, as the data in Denton's presentation show, the bacteria are roughly equally distant cousins of both turtles and dogs (and all the other organisms that Denton included in Table 12.1).
Cousin relationships between contemporary individuals are governed by the number of generations since there last was an ancestor in common to the individuals. Different members of a group of close relatives always have the same relationship to a more distantly related individual who stands outside the group. Two sisters are equally related to a mutual first cousin. Members of a group of siblings and first cousins are all equally related to a mutual fifth cousin. Lampreys are equally distant cousins of both fish and humans because the last ancestor that lampreys had in common with humans was the same ancestor lampreys had in common with fish. The "molecular equidistance" argument that Denton invokes is invalid, resulting from making comparisons between a single distantly related organism and various members of a more closely related group.
There is an irony in Denton's presentation to anyone familiar with the data of molecular evolution. Reflections of genealogical relationships are so strong in molecular data that Denton, in spite of his arguments to the contrary, is unable to hide them. The missing "trace" of which he speaks is not a trace; it is a shout. Simple inspection of the data in Table 12.1 will reveal that cytochrome C found in horses, for example, is quite similar in its molecular structure to that found in turtles, slightly less similar to that in fish, still less similar to that in insects, and very much less similar to that in bacteria. The traditional evolutionary series is very much in evidence.
Denton provides a series of diagrams (pp. 282-87) in which nested e[l]lipses, arranged on the basis of molecular data, are used to illustrate his spurious "molecular equidistance" thesis. In these delightful figures organisms are seen to cluster fully in accord with the genealogical relationships that evolutionary biologists deduced from comparative anatomy and paleontological evidence long before molecular data were available. In the final figure, humans and chimps are seen side by side as each other's closest cousin. Anyone who wants to argue that these nested groups of organisms constitute separate, distinct, and unbridg[e]able groups has to contend with obvious hierarchical patterns of relatedness among the various groups. Notions of relatedness are, of course, antithetical to a typological view of organisms.
Denton claims that a crisis exists within evolutionary biology. His claim is off base: to the extent that evolutionary biology is at all involved with a crisis, the crisis lies outside of biology. For creationists, with a strictly literal interpretation of the Bible, the biological facts of human history create a theological crisis. Their assault upon sound science has elevated the American penchant for anti-intellectualism to a crisis stage with which everyone, including biologists, should be concerned. British evangelicals wrote in the 1830s that "If sound science appears to contradict the Bible, we may be sure that it is our interpretation of the Bible that is at fault" (Christian Observer , p. 437; quoted by Stephen Neill, Anglicanism [Baltimore: Penguin Books, 1960], p. 240). Nevertheless, not only creationists but also many contemporary evangelical Christians are genuinely uncomfortable with evolutionary biology and what they perceive as a threat to the scriptural basis of their faith.
In other theological circles, evolutionary biology created little, if any, crisis. In 1930 William Temple, the Archbishop of York, wrote: "When my Father [Frederick Temple, Archbishop of Canterbury] announced and defended his acceptance of evolution in his Brough Lectures in 1884 it provoked no serious amount of criticism . . . The particular battle over evolution was already won by 1884" (F. A. Iremonger, William Temple, Archbishop of Canterbury, His Life and Letters [London: Oxford Univ. Press, 1948], p. 491). To a large extent it would seem that evolution has been tacitly accepted and essentially ignored within such circles, although there has been a significant number of serious attempts to integrate evolutionary understanding into theology. Pierre Teilhard de Chardin provides a famous example, as does biologist Theodosius Dobzhansky. For more than twenty years the pages of Zygon, to cite an obvious example, have carried notable contributions from scientists and theologians. I suggest, however, that such efforts have been predominantly academic and philosophical. For the typical cleric and the average person in a pew on Sunday mornings, evolutionary biology, if not considered outright hostile to religious convictions, tends to be kept in a separate mental compartment.
Biology and theology each have important things to say about the human condition. Sound science without theology leaves us stranded with subjective values, no basis for morality, and no conception of purpose. Sound theology, if it ignores biology, can give at most incomplete-and at times faulty- understanding of human nature. Creationists use an objectionable piece of theology to justify inexcusably bad science. Books like Evolution: A Theory in Crisis are, at the very least, hindrances. We need good science and good theology. The two have operated too long in isolation. The time is ripe for a grand synthesis that will bring into register the complementary insights into human nature provided by modern biology and biblical theology.
[Zygon, vol. 22, no. 2 (June 1987)]
© 1987 by the Joint Publication Board of Zygon. ISSN 0591-2385