Michael Denton's "Evolution: A Theory in Crisis" is a classic for a reason. After a period of openness towards skepticism of Darwin in the 1960s, there was a revival of Darwinist orthodoxy in the 70s and 80s. Other than those involved with young-earth creationist organizations, there was very little in terms of an attempt at a scientific critique of the Neo-Darwinian synthesis. Michael Denton's book changed that, and it provided the foundation upon which later proponents of intelligent design would build. Most notably, Michael Behe, author of the famous (or infamous) "Darwin's Black Box" traces the beginning of his evolutionary skepticism to this book. In my estimation, Denton's book absolutely deserves its classic status.
The book aims at a comprehensive critique of Darwinian evolution. The essence of Darwinism, suggests Denton, is continuity. Darwinism suggests that life is fundamentally continuous, and that in principle, the gaps between living organisms can all be bridged, and were all bridged at some point in the past. By contrast, Denton holds to the discontinuous, typologist view of biology propounded in the 19th century by Richard Owen. Denton marshals a great deal of evidence, both theoretical and empirical, to buttress his case. He points out that for many organisms, even conceptualizing an intermediate is impossible. For example, the structure of a bird feather is such that its particular features are all required for it to fulfill its function at facilitating flight. The wing itself is a similar feature- anything which was adapted for faster running or gliding would look very different from a wing adapted for bird flight. Birds have a host of other anatomical adaptations allowing them to function as they do- their lungs are different, their bones are hollow, and so on. What possible intermediates could there be?
The gap in conceptual possibility is correlated with a gap in empirical data, which is a significant point, and demonstrates that the conceptual gap is not simply due to lack of ingenuity on the part of evolutionary theorists. The fact is that the relative few morphological intermediates suggested by paleontologists are at best mosaics of traits. The distinction between a mosaic and an intermediate is subtle, but crucial. The question facing evolutionary theory is how to build a new complex organ or anatomical trait. In order to answer this question empirically, we should be able to detect a series of intermediate fossils which show a trait or set of traits in development. But this is not actually what we find. What we find are sets of anatomically mature traits mixed together. The avian features of Archaeopteryx are perfectly avian, even as it possesses other reptilian features. What we ought to be looking for is a specific trait that is intermediate.
The discontinuities on the anatomical level are paralleled by a remarkable pattern of discontinuities on the molecular level. This is what Denton describes as an equidistant pattern of similarity and difference. Human and fish hemoglobin is separated by an identical degree of difference to fish and amphibian hemoglobin, which suggests that these organisms do not cluster in the expected pattern. Instead, we find groups of organisms which are irreducibly different from one another, and the degree of difference (23-24% in the case of hemoglobin) among these organisms is nearly mathematically perfect. The explanation for this stunning fact, Denton suggests, is little more than a tautology. Evolutionary biologists have posited a "molecular clock" which is the constant rate of mutational change over time. Yet, the only evidence for such a clock is the pattern of equidistant differences in organisms. Such a molecular clock is also hard to reconcile with the different rates of generational turnover among different organisms. The hitjob review by the "National Center for Science Education" appeals to a constant rate of mutation among the germ cells, which do not depend on generational turnover. This misses the obvious point that natural selection and genetic drift operate at the level of the population, not individual organisms, and that especially selection depends on the whole creature and not individual germ cells. Furthermore, it is nearly inconceivable that a rough molecular clock would generate such a mathematically precise distribution of protein similarity across so many different groups.
The chapters on homology are worth the price of the book. Darwin rested a substantial portion of his case on homology, suggesting that it was impossible to explain why so many "unnecessary" features like the pentadactyl limb were distributed across so many organisms unless it was the result of descent from a common ancestor. Denton points out that Darwin's critique depended on functionalism, where the only purpose of an organ or anatomical feature is better fitness. Denton is a structuralist, so that the living world is pervasive with nonadaptive order. But the critical point Denton makes is that this kind of homology is not really what is predicted by Darwinism. If the pentadactyl limb is really unimportant in terms of fitness, then why is it so highly conserved? One would expect local variations in branches of the evolutionary tree. If evolution can transform the pentadactyl foot of a mouse into the pentadactyl wing of bat, why not vary the pentadactyl structure itself? On Darwinism, one would expect such variations, requiring only that they cluster in a nested hierarchy.
The other problem with using homology as evidence for Darwinian evolution is that anatomical homology is often not correlated with genetic or developmental homology. If the similarities among organisms were mostly the result of descent from a common ancestor, then one would expect the same genes to regulate the same features, and one would expect homologous features to take homologous developmental pathways. This prediction has been falsified by the data: different genes often regulate the same features, and homologous features often take different developmental pathways. Furthermore, there is plenty of homology which cannot be explained by common descent. For example, echolocation (and the genes that regulate it) allegedly developed multiple times on the evolutionary tree: at least twice in bats and at least once in cetaceans. This is merely called "convergent evolution" without specifying a mechanism for such specific and sophisticated convergence. Essentially, homology is evidence for common descent except when it isn't. Homology was perhaps the most critical evidence marshaled by Darwin in support of his theory: its breakdown is a massively significant event.
There are a few problems with the book: I think Denton is too dismissive of some intermediate sequences, such as the whale sequence. I don't think he treats notions of Lamarckian inheritance fairly, and some of the biology is outdated. Denton wrote before the revolution in epigenetics, and he views the genome as a complete prescription for the whole structure of an organism. The influx of genetic data in the modern day has given rise to the "missing heritability problem" where much biological inheritance is unaccounted for, even in whole-genome sequencing. Some of what Denton says about protein folds has also been falsified: since some identical polymers fold differently to produce different proteins, the folds cannot be specified by the codons: it requires an additional layer of specified information, presently of unknown origin. Yet these developments do nothing to detract from Denton's central point. On the contrary, they buttress it. Life, as Denton predicted in this book, has been found to be more complex the more it is studied, not less. And standard Neo-Darwinism is as empty-handed as it was when Denton wrote.
I commend this book to anyone interested in a genuine and rigorous scientific critique of Darwinian orthodoxy.
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