Letter to the Editor


More on Michael Denton

Walter Hearn

762 Arlington Ave
Berkeley, CA 94707

From: PSCF 42 (March 1990): 62-63.

My evaluation of Michael Denton's Evolution: A Theory in Crisis falls somewhere between "one of the most important (and controversial) works on evolution in this century" (T.E. Woodward's review, Perspectives, Dec 1988) and "a book whose claims to scholarship or integrity are woefully deficient" (M. Kuehn's letter, Dec 1989). One of Marvin Kuehn's examples of woeful deficiency sent me back to Denton's book and then to the library to look up the words of a leading biologist allegedly twisted by Denton. Kuehn wrote that in Denton's discussion on taxonomy, "he makes Halstead sound like a cladist!"

Despite a minor deficiency (no Halstead in the book's index) I found the sentence in question: "Whatever the future of cladism, the fact that a significant number of biologists in the 1980s are insisting, in the words of Beverly Halstead (no friend of cladism himself), that `no species can be considered ancestral to any other21 [emphasis added] marks without question a watershed in evolutionary thought" (Denton, p. 139). Clearly, Denton identified Halstead as not being a cladist. No woe there, except for convoluted sentence structure.

Before pronouncing woe on Kuehn's own scholarship or integrity, however, I thought I should check Denton's ref. 21 (of Ch. 6): B. Halstead (1981) "Halstead's Defence Against Irrelevancy," Nature, 292: 403-04. Sure enough, L. Beverly Halstead had used essentially those words in describing a booklet he detested from the British Museum (Natural History): "But the booklet includes the most amazing assertion of all, that no fossil species can be considered the direct ancestor of any other." References cited by Halstead enabled me to trace a fierce dispute over the cladistic approach of certain Museum exhibits. In those days Halstead, reader in geology and zoology at Reading University, evidently objected strongly to just about everything done by the South Kensington Museum, or at least by its Public Services Department.

My feeling is that Denton is technically in the clear because he identified Halstead as "no friend of cladism." Denton might better have quoted the booklet rather than Halstead's response to it. Yet Halstead was reacting to a claim made by enough biologists to cause a big fuss in the literature. My guess is that when Denton was writing, he had access to Nature but not to the Museum booklet itself. Or perhaps some editor (the one who left Halstead out of the index?) distorted what Denton actually wrote. At any rate, the deficiency hardly seemed woeful. 

Halstead also stated that the "current drive against the concept of gradualism is motivated primarily by Marxists"-just the kind of innuendo frequently considered typical of "creationist" writings. Halstead expressed dismay at "the distortion of scientific data for ideological purposes" by fellow paleontologist Stephen Jay Gould. As I see it, the question raised by Denton's book is whether the concept of gradualism itself is primarily an empirical conclusion or a prior ideological commitment.

I checked out another of Kuehn's objections, that of important evidence "ignored or dismissed by some sleight of hand-see Denton's treatment of Archaeopterix." Using the index more successfully this time, I re-read everything Denton said about Archaeopterix without finding the "serious errors of logic, synedoches, direct misquotes, gross factual mistakes and even spelling errors" Kuehn led me to expect. (I assume that the misspelling of synecdoches in Kuehn's published letter was an editorial goof, one of those things that can happen even to good guys, hardly evidence of woeful deficiency in scholarship or integrity.) I did find the statement (Denton, p. 176) that Archaeopterix is an archaic bird with hints of reptilian ancestry-along with a warning that hints aren't enough to establish continuity. Has Archaeopterix actually been established as an ancestor of anything living today? Would it be a "gross factual mistake" to call all such ancestral relationships inferences rather than facts?

Kuehn said that Denton's typological perception of nature was "legitimately abandoned due to its lack of explanatory power." My impression is that Denton ¨appreciates the great explanatory power of macroevolutionary theory. The problem is that the theory can explain imaginary relationships that might turn out to be false. U.C. Berkeley geneticist Philip T. Spieth (Zygon 22, No. 2, pp. 252-7, June 1987) began an earlier review by saying that Denton's book  "belongs to the `creation science' genre." When stripped of its "cloak of respectable terminology," Spieth wrote, Denton's case is nothing more than the old argument of gaps in the fossil record. Nowhere in all the current debates over gradualism, Spieth asserted, "is the issue of genealogical relatedness brought into question." Is that a way of saying that certain scientists are so sure they're right that they don't worry about an empirical basis for their theory building?

A more recent review by William M. Thwaites (NCSE Reports 9, No. 4, pp. 14- 17, Jul-Aug 1989) called Denton's book "just another typical anti-evolution tract." Thwaites wrote that Denton is motivated "not by a desire to understand the workings of nature" but by an apparent fear of the "materialistic" and "skeptical outlook of the twentieth century." Thwaites took Denton's drawing of a two-dimensional map of hemoglobin relationships and showed that "If one makes the simple assumption that the sequence differences represent the time since the two organisms last shared a common ancestor, one can construct a vertical dimension....Presto! we have a phylogenetic tree." No one doubts that phylogenetic trees can be constructed if one makes certain simple assumptions. What Denton (and other critics of macroevolutionary theory) point out is that such trees are constructs, and are accepted "without bringing the issue of genealogical relatedness into question" (Spieth). In other words, genealogical relatedness is an a priori assumption, not something empirically established.

I met Michael Denton in June 1988 at a conference on the information content of DNA sponsored by ASA's Committee for Integrity in Science Education. I saw no evidence that he was any kind of "creationist" or any less competent than his reviewers, particularly in his own field of molecular biology. Further, I got the impression that he considers macroevolution a reasonably plausible inference that might turn out to be true. His current interest seemed to center on the potential of genetic engineering techniques to produce new organisms that could at last put neo-Darwinian mechanisms to empirical tests. 

Scientists tend to admire, even revere, the explanatory power of theories-at least until some plausible theory readily explains something we know to be false. The authors of ASA's Teaching Science in a Climate of Controversy were amazed to read what negative reviewers of that 1986 booklet said about the motivations of its authors, and to see how easily one reviewer's unfounded inference could become another's established fact. Perhaps my experience as one of those authors has sensitized me to these issues.