I’m rather proud of myself at the moment. This week I accomplished a major undertaking: I finished reading The Structure of Evolutionary Theory by the late Stephen Jay Gould. I had been reading this 1300+ page tome for quite some time (I refuse to say precisely how long because I like to think of myself as being a fast reader, but the speed at which I read this book was anything but fast) and now I’m finally done. I’ll present a short summary for those people who, unlike me, are not interested enough—or not insane enough—to spend countless hours reading dense discussions of obscure evolutionary topics.
At its most basic, The Structure of Evolutionary Theory is an epic summation of the ideas and concepts that Gould spent most of his well-celebrated career researching and discussing. In particular, he presents three central features of Darwinian theory that he feels are in need of revision:
1. The individual organism as the sole unit of natural selection—in other words, the idea that natural selection focuses only upon the differential reproductive success of individual organisms in shaping the history of evolutionary change. Gould contends that natural selection works at a hierarchy of levels—from the gene to the clade (groups of species)—and that the various levels of this hierarchy must all be recognized as “Darwinian individuals” (a concept that he differentiates from individual organisms). He especially focuses on natural selection working at the level of the species where he feels that differential levels of birth (speciation) and death (extinction) hold strong sway over long-term evolutionary trends. He bolsters this concept with evidence from the theory of punctuated equilibrium—a controversial and contentiously debated paleontological concept developed by Gould and Niles Eldridge in the 1970’s which states that, based upon the evidence of the fossil record, the fate of most lineages throughout geological time is primarily that of stasis (ie. little evolutionary change). It is their belief that most long-term evolutionary change takes place through comparatively quick (in geological terms) events of speciation. To Gould, since most species seem to primarily exhibit stasis throughout their “lifetimes” and speciation events are therefore responsible for most lasting evolutionary change, natural selection working at the species level becomes a topic of paramount importance.
2. The supremacy of natural selection over internal constraint. Gould presents a long-standing argument between two competing camps of evolutionary biology: the structuralists, those who believe that internal are responsible for most evolutionary change, and the functionalists (also known as adapationists) who believe that natural selection is the main force responsible for evolutionary change. It is Gould’s belief that the modern Darwinian consensus is too focused upon natural selection as an all-powerful force. He uses evidence collected from recent discoveries in the field of Evolutionary Developmental Biology (lovingly known as “Evo-Devo”) to show that internal forces of development are important for both setting limits to evolutionary change and also for channeling change in particular directions. With this in mind, he cautions researchers against assuming a priori that all well-functioning organismal characteristics are adaptive features shaped soley by the power of natural selection.
3. The extrapolation of small changes over enormous amounts of time to explain all long-term trends. Gould states that it has been all too common for both biologists and geologists to succumb to the temptation to explain long-running trends simply using small, presently observable changes. It is Gould’s belief that not all trends of macroevolution (change above the level of the species) can be adequately explained simply by microevolutionary change (change at or below the level of the species) extrapolated over tens or hundreds of millions of years. He also states that the same principle applies to geologists who attempt to explain all geological trends using small, gradual changes. Gould particularly focuses on the extinction of the dinosaurs which was formerly thought to have happend gradually, but is now considered by most paleontologists to have happened relatively quickly due to the catastrophic impact of a giant meteor hitting the earth. Gould uses this highly relevant example—without the demise of the dinosaurs, mammals (including humans) would most likely never have come to dominate the world—as evidence that sometimes macroevolution and large-scale geological change are best explained by forces other than extrapolated short-term changes. He especially hightlights what sees as the potentially important roles that catastrophes and unpredicatable contingencies have had to play in shaping the history of life on earth.
I must admit that I, with my complete lack of formal evolutionary training, often got bogged down by and had a difficult time completely comprehending the minute details that Gould uses to support his arguments, but I do believe that I was able to grasp the major points he attempted to make. While I certainly think that the book was at times overly self-indulgent and could definitely have benefited by a less lenient editor, I certainly don’t begrudge Gould the opportunity to present us with his magnum opus just as he wants it. By all accounts, Gould had a exemplary career and if he, as the most public voice for evolutionary biology for the past thirty years, wants to be a little self-indulgent with his final work, who am I to gainsay him?
Time and again, I was amazed at Gould's ability to thoroughly examine the logic of an idea. He has the enviable ability to truly understand the implications of the concepts with which he works. He seems to be able to take an idea, examine it with a fine-toothed deductive comb, and then bring forth a treasure of interesting and important ramifications. Interestingly, this is something that he often praised Darwin for, and I can’t help but feel that he deserves no less praise. Apart from Gould’s ability to think, he is simply a brilliant writer. While much of the book is written in a fairly technical (and verbose!) style, every now and then one of his characteristic flourishes of beautifully striking prose shines through. The final pages, in which—after spending hundreds of pages explaining why he feels that some of Darwin’s ideas are fundamentally deficient—he rejoices that the field of evolutionary biology has as its primary (or at least most important) founder a man as fascinating in character and powerful in mind as Charles Darwin, are especially evocative.
Its astounding how much you can learn about the inner workings of a person’s mind after reading 1300 pages of their thoughts and ideas. After I finished the book, I was struck by a sense of sadness and finality. Because The Structure of Evolutionary Theory was Stephen Jay Gould’s last major work before his death, when I reached the end, I felt almost as if I was saying goodbye to a friend. But what a way to go! Goodbye, Dr. Gould. Your writing has has been (and continues to be) an inspiration to millions and I fear that we will not see your equal for many years to come. You are missed.