Evolution Book

This is an unusual book. First, it is unusual because it is a book about evolution that manages to avoid the theological polemics (on both sides!) so common whenever the topic of evolution arises. Second, it is unusual because it is a 30 year old book about the science of evolution that is still relevant today. It is the book about evolution that I wish I had read 30 years ago. My background is computer software design so my understanding of biology has not come easily to me. I started studying the subject about two years ago and the details still challenge me. And so I appreciated that the author kept the discussion at the level of basic science with few forays into the minutia of molecular biology. When he did need to present technical material, he explained it with analogy and sufficient definition, so that the lay reader could understand his points.

The book is still relevant today because the core contradiction in evolution has not been solved. That is why Denton calls it a crisis. He does not mean that evolution is wrong. He means that there are "inconvenient facts" that do not fit cleanly into the theory. His first point in the book is that experts know about these facts, but most take the conservative view that ultimately the inconsistencies will be fully explained by the core theory. But Denton is writing the book for the minority who think the core of the theory needs to be revised. He is calling for a "paradigm shift" in the popular terminology introduced by Thomas Kuhn in The Structure of Scientific Revolution (1962).

So what is the core paradigm of evolution theory? First of all, the core paradigm applies mainly to what is called "macroevolution." Macroevolution refers to the large scale changes in living species that accrue over long periods of time and to the creation of new species. In contrast, microevolution is the evolution that can be observed over short periods of time, in the laboratory and in the field. Microevolution is subject to experimental verification and nobody doubts that it exists and is an accurate representation of the changes that all living populations undergo.

The problems arise when microevolution is extrapolated to macroevolution. The issues are traceable to Darwin and his insistence that "nature does not make a leap" ("Natura non facit saltum"). This expression was the common wisdom of Darwin's time. Darwin might have first encountered the expression in Linneaus' Philosophia Botanica (1778) or perhaps in his gatherings with the Linnean Society. But even if he didn't encounter it there, the idea was common in the science of his times. Leibniz (1646'1716) used it as did Newton (1642'1727) in their co-invention of the calculus.

Math was not Darwin's strong suit, but he was very knowledgeable about the Principles of Geology (1830--1833) written by Charles Lyell, the first volume of which accompanied him when he set sail on the HMS Beagle in late 1831. But it was Lyell's second volume, which arrived in the fall of 1832 when Darwin was in South America that raised the question that would preoccupy Darwin after his return to England. Lyell raised the question of whether plants and animals changed along with the Earth's geology. Lyell's answer was "no," but he had planted a seed. And Lyell's insistence on gradualism must have made an impression on Darwin: it was key to Lyell's theory that "causes now in operation," in the terminology of his subtitle, can be used to explain the past.

Science applied to past events is very different from research into current phenomenon. One cannot observe the past or run repeated experiments on past phenomenon. But if the forces of nature are gradual, continuous, and uniform, then current forces of nature can be reasonably applied to past events. In other words, nature does not make jumps. And Natural Selection was a current force of nature. Darwin had seen it in action in the breeding of sheep'one of his uncles was a leading sheep breeder ' although in that case the selection was intentional.

Some historians say that Darwin insisted on the principle of gradualism for theological reasons. The creationists of Darwin's day invoked catastrophe theories to explain creation and the social movements in the 19th century were moving against the power of the church. Catastrophism relied on supernatural forces and Darwin certainly wanted to avoid any taint of supernaturalism. But, whatever the origin of the idea of gradualism, the science of evolution took a path that Darwin could not have anticipated.

In the late 19th century the mystery about how traits were inherited was partially clarified by the discovery of genetics. And in the 20th century the molecular basis of genetics was discovered in the structure and function of DNA. This meant that the science of evolution could be very rigorous about microevolution; it could be studied in detail at the molecular level. With these advances, macroevolution had to be extrapolated anew from the detailed understanding of microevolution. The answer was that genetic mutations were gradual. They had to be otherwise the reasoning about current forces could not be applied to past events! This translated into random mutations generally thought to be the result of copying errors as DNA is replicated.

In this book, Michael Denton focuses like a laser on this basic foundation of Darwinian Evolution: nature does not make jumps. He rigorously examines the gaps in nature and what they might mean for the theory. These gaps are well known. There are gaps in the taxonomy of species because species do not flow continuously from one to the other. Mammals have hair, birds have feathers, reptiles have scales, etc. The best representation for the different species is something called a "nested hierarchy." In other words, species can be rigorously categorized by their features. The discontinuous categorization of species is supported by DNA evidence.

Secondly, there are gaps in the fossil record. Some of the nodes in the nested hierarchy can be associated with actual fossils, but most cannot. The fossils are missing. These gaps in the fossil evidence led Stephen J. Gould (1941'2002) and one of his students to propose a theory of Punctuated Equilibrium. In this theory, evolution of new species happens quickly but then each species stays constant for long stretches of time. Punctuated Equilibrium, if it is true, is neither uniform nor gradual evolution.

Finally, the genetics implied by random mutation cannot reasonably be expected to act quickly enough to produce the adaptive variations that we actually find. With over 3 billion letters in human DNA, if each mutation has an equal chance of occurring at each letter then the chance of an adaptive mutation is vanishingly small. Even the smallest bacterial organism needs about one-half million DNA letters. Adaptive mutations are as rare as the proverbial needle in a haystack based on the assumption of random mutation.

While the treatment of possible non-random processes for mutation was beyond the scope of the book, let me quote from University of Chicago microbiologist James A. Shapiro in his book, Evolution: A View from the 21st Century (2011):

It is difficult (if not impossible) to find a genome change operator that is truly random in its action within the DNA of the cell where it works. All careful studies of mutagenesis find statistically significant nonrandom patterns of change, and genome sequence studies confirm distinct biases in location of different mobile genetic elements.

Author Lee M. Spetner has proposed a theory of non-random evolution whereby environmental factors influence genetic change. This idea is based on the growing research into epigenetics.

In conclusion, Denton summarizes that the foundational assumption about nature not making jumps is flawed. There is no known law of nature that makes this assumption true. In fact, beginnings are known to be discontinuous. The universe had a discontinuous beginning 13.7 billion years ago and life is thought to have a discontinuous beginning over 3.5 billion years ago on Earth. Quantum theory requires nature to make jumps, albeit at small intervals. Cataclysmic forces are thought to have created Earth's moon. There is no requirement for nature to be continuous, particularly nature applied to living organisms, all of which will ultimately cease to be alive.

However, until a new theory comes along, Darwinian Evolution is the best we've got. But in order for there to be a new theory, a paradigm shift has to occur. When this book was written in the 1980's, too many specialists believed in random mutation for that to change. Perhaps Denton is at his best in explaining how scientific paradigms turn into dogma:

As the years passed after the Darwinian revolution, and as evolution became more and more consolidated into dogma, the gestalt of continuity imposed itself on every facet of biology. The discontinuities of nature could no longer be perceived. Consequently, debate slackened and there was less need to justify the idea of evolution by reference to the facts.

Increasingly, its highly theoretical nature was forgotten, and gradually Darwinian concepts came to permeate every aspect of biological thought so that today all biological phenomenon are interpreted in Darwinian terms and every professional biologist is subject throughout his working life to continued affirmation of the truth of Darwinian theory.

The fact that every journal, academic debate and popular discussion assumes the truth of Darwinian theory tends to reinforce its credibility enormously. This is bound to be so because, as sociologists of knowledge are at pains to point out, it is by conversation in its broadest sense of the word that our views and conceptions of reality are maintained and therefore the plausibility of any theory or world view is largely dependent upon the social support it receives rather than its empirical content or rational consistency. Thus the all pervasive affirmation of the validity of Darwinian theory has had the inevitable effect of raising its status into an impregnable axiom which could not even conceivably be wrong.

30 years later perhaps we are beginning to see this change as more specialists like Dr. Shapiro begin to question the dogmatic underpinnings of traditional evolution theory. In view of the ongoing criticism of the traditional theory, perhaps Denton's book can even be called prophetic.