Evolution: A Theory In Crisis [Paperback]

As Sir Peter Ustinov said, "If you are not confused about the world then you are not thinking clearly".

The "pro" rhetoric of most of the reviews here reveals the problem. Phillip Johnson and Michael Denton share a lot of common ideas about the orthodox neo-Darwinist synthesis and its ostensible weaknesses. Neither really rejects "evolution" outright. Denton even has an excellent discussion of the evidence for natural selection in speciation, "microevolution" that even most Creationists no longer seem to doubt. The problem is that they, and Johnson in particular, have no interest in enhancing science from this discussion, they are interested in retaining someplace for God to intervene in natural processes.

The association with Johnson and the ID movement unfortunately makes Denton's really excellent discussion here moot scientifically by making it sound as if Denton is a Creationist and that "evolution" ostensibly being "a theory in crisis" means that antievolution texts and disclaimers should be foisted on schools.

Denton is not a creationist, particularly not in this book (although in later work he seems to be a theistic evolutionist of sorts), and he makes some fascinating points here. Some of his points have been invalidated, but many of them are still valid.

Denton accepts natural selection as the primary mechanism of evolution and the only scientifically valid one, and accepts what Mayr calls "evolution as such" as pretty much a given here. He notes that speciation has been clearly observed in various ways and that the fossil record is completely inconsistent with anything even vaguely resembling the literal Biblical view of Creation. However, he has lots of issues with the assumption that all form and function in nature arises from a process of gradual incremental change.

The alignment of Denton with Johnson and the ID movement is mostly in Denton's primary focus on the puzzling conceptual break in the evolutionary view of nature, something ignored by most evolutionary theory and harped on endlessly by Creationists. The break is between so-called "micro" and "macro" evolution, or what Denton exaggerates somewhat as Darwin's "special" and "general" theories of evolution.

The basic point is reasonable. We do get a surprisingly different perspective from observing evolution closely at a "micro" level, where changes in gene frequencies give rise to new species-typical features, and then looking at the pattern of phenotypes of higher orders in nature. But what general conclusion about evolution does this lead us to ? There's the rub.

Darwin's point was that the whole thing was part of a single set of natural mechanisms, and this point is driven home for recent general audiences by Richard Dawkins (whose radical anti-religionism makes him a good foil for the religious opponents of evolution as well). Denton *correctly* points out that the patterns of nature are different from what a truly uniformitarian gradual branching of biological diversity would produce. At least in theory. So he points out that gradual change is essential to Darwinian theory (which is probably true) and then concludes that gradual change is not really the rule in nature, and so evolution needs a major overhaul. His argument is nuanced and well made and it requires some sophistication in biological systematics to appreciate where it veers off track at some points.

Denton points out first that even given the scarcity of the fossil record, we still find fewer forms that are transitional between than we would expect from a random sampling, and the transitional forms that we do find are "less transitional" than we should expect from a gradual view of phenotypic change. We see animals that have some organ systems of one taxon and some from another, we never find fossils or species that have organ systems that really seem in some intermediate stage between the higher taxa.

The truly uniformitarian gradualist view emphasized by Darwin and underscored by Dawkins doesn't seem consistent with the actual organization of the main branches of biological life.

The discovery of speciational evolution explained much of this, and evolutionary developmental biology seems to explain the rest, at least potentially. Features that support each other are often carried along together during evolutionary change. Small populations can change very rapidly and are very unlikely to leave transitional fossils, giving the impression of sudden jumps in the fossil record.

Second, the Darwin-Dawkins strict uniform gradual view predicts that there should be an adaptive radiation of diversity that increases in distance over time. On the contrary, what we find is that there were several major body plans that arose fairly early, and that we seem to have had no new ones over time.

Third, we don't find a continuum of genetic change between species, we see sharp discontinuities in mechanisms.

These points are not unique to Denton, of course. Stephen Jay Gould made a career of pointing out the diversity of mechanisms that seemed to be at work in macroevolution and the need for a new evolutionary synthesis. Wallace Arthur provides what may be the early basis for such a new synthesis in his writings on evolutionary developmental biology. The problem of "macromutations" is no longer really relevant when you consider how developmental systems evolve. We no longer need to rely on the assumption that new phenotypic features result from the mutation of individual genes. A tiny genetic change can be corrected by existing genetic mechanisms, or even cause meaningful and significant change in a developmental system without disrupting its existing function.

With the emergence of evo-devo and complexity theory to begin to help explain some of the patterns of form that were previously so puzzling, many of the issues raised in this book could be adopted for an introduction to the issues in evo-devo just as they have been adopted unfortunately to the arguments of Creationists. In addition, this book serves as a nice bridge to help advanced biology students understand the anti-evolutionary arguments, stripped of religious elements.

Taking an example, M. Denton writes a chapter about palaeontology and "missing links". There is a wonderful drawing supposedly showing that there are no transitional fossils between, for example, terrestrial mammals and whales or bats, or between reptiles and birds. But it is false ! Each time, there are many transitional species between extreme individuals which are presented. But Denton writes that such intermediary forms do not exist ! In the whale evolution case, his drawing show only Pakicetus and a modern whale, without Protocetus, Rhodocetus, Ambulocetus, etc. which are evidently intermediates between these two species.

In another case, he asserts that homologous structures are not built by homologous genes - of course, he wants to show that homology between species or other taxonomic levels is a false idea. But he presents in each case a few pleiotropic genes which do not play a major role in embryogenesis - because all main "architects" proteins, such homeotic genes, support evidently the homology concept.

In fine, this book is scientifically uninteresting. For a biologist, it is very funny - but it is its only one advantage.