An astonishing fact about Charles Darwin’s theory of evolution is that it was conceived in the absence of two major kinds of support that would have been helpful to it—evidence from the then meager fossil record and knowledge of the mechanism of inheritance. The endurance of a theory so conceived—almost from first principles—has excited the admiration of generations of biologists. It has also given them the opportunity, as discoveries in genetics and paleontology have been made, to determine if this new evidence merits a revision of Darwinism, as the theory is now known.
The Structure of Evolutionary Theory is the latest—and perhaps the grandest—of such attempts. In effect it is a summation of Stephen Jay Gould’s life work, building on Darwinism to provide a novel synthesis of how evolution has shaped the living world. Explaining his motivation in writing it, Gould, who was trained as a paleontologist, says it
does fire my very best shot in the service of…general theory. I am a child of the streets of New York City; and although I reveled in a million details of molding on the spandrel panels of Manhattan skyscrapers…I guess I always thrilled more to the power of coordination than to the delight of a strange moment—or I would not have devoted 20 years and the longest project of my life to macroevolutionary theory rather than palaeontological pageant.
Gould employs two metaphors to assist the reader in understanding the complex theory that the book develops: the Duomo of Milan and a fossil coral. The Duomo, Gould says, is similar to Darwin’s evolutionary theory in that it has been built on in ways that add significantly to it but nonetheless leave the original form and intent recognizable. The fossil coral (see illustration on page 54), which was discovered near Messina and figured in Agostina Scilla’s La vana speculazione disingannata dal senso, published in 1670, has special significance for Gould because its branches mimic Gould’s theoretical structure.
Gould envisages the trunk and each branch of the coral as representing a hierarchy within Darwinism. The trunk is Darwin’s theory of evolution by natural selection itself. The first three branchings represent the three fundamental principles of Darwinian logic, which Gould characterizes as “agency [the central branch], efficacy [the left branch] and scope [the right branch].” The three fundamental principles so characterized arise from Darwin’s thesis that evolution produces new species by natural selection (efficacy) acting on individuals (agency), resulting in small changes that accumulate over very long periods of time (scope).
The potentially confusing structure of The Structure of Evolutionary Theory itself can only be understood in these terms. Gould says of his book that it “cycles through the three central themes of Darwinian logic at three scales—by brief mention of a framework in [the introduction], by full exegesis of Darwin’s presentation in Chapter 2, and by lengthy analysis of the major differences and effects in historical (part 1) and modern critiques (part 2) of these three themes in the rest of the volume.” To many readers, the arguments that Gould mounts in support of his evolutionary synthesis will not be new. Most have appeared in articles and exchanges over the past quarter-century.1 Here, they are brought together for the first time.
The historical overview presented in Part One consists of a reflective commentary on thought relating to evolution as it has developed over the past three hundred years. Gould provides an admirably comprehensive review of the literature, dealing with great scientists such as Richard Owen, Georges Cuvier, and Étienne Geoffroy St. Hilaire, as well as many lesser-known but interesting and worthy contributors. This section includes many fresh insights into how thinking about evolution slowly changed, and who built on whose prior work. Central to the discussion is an exegesis of Darwin’s work, where considerable emphasis is given to the idea that Darwin was a gradualist; that is, that he saw evolution resulting from the aggregation of countless small changes over a vast period of time. This is followed by a discussion of the ideas of Darwin’s “brilliant and eccentric cousin” Francis Galton, who challenged Darwin’s concept of gradualism by suggesting that species come into existence almost instantaneously. Galton illustrated his idea with the metaphor of the polyhedron; a shape that rests stably on any of its facets, but that when disturbed switches rapidly from one resting position (facet) to another. Species, Galton argued, are likewise stable, not changing or evolving until something happens; then they are rapidly transformed into new (stable) species. Here Gould finds an intellectual predecessor, for his theory of punctuated equilibrium (of which more presently) is more akin to Galton’s polyhedron than to Darwin’s gradualism.
One fascinating aspect of evolutionary thought to which Gould gives prominence is the idea that Darwin’s concept of natural selection owes much to Adam Smith’s economic arguments as presented in The Wealth of Nations. It is known that Darwin devoted much time in the late 1830s to studying Smith. Gould goes so far as to say that “the theory of natural selection is, in essence, Adam Smith’s economics transferred to nature,” adding that while “Adam Smith’s economics doesn’t work in economics,” it does admirably well in “amoral nature.”
Part Two of The Structure of Evolutionary Theory returns to the three principles of Darwinian logic in the context of contemporary evolutionary debate. Here the author and his collaborators take center stage as the reformulators of two of these three principles. The theory of punctuated equilibrium, conceived by Niles Eldredge and Gould, is seen as having revised the principle of agency, because Gould believes that it lays the theoretical groundwork for natural selection to act upon species as well as individuals. Gould and E.S. Vrba’s ideas on internal constraint are said to have performed the same service for efficacy, because they challenge the omnipotence of natural selection in shaping species. Of the remaining principle, that of scope, Gould says that although his contribution to the understanding of mass extinction and catastrophic events which challenge Darwin’s concept of gradualism “cannot claim much novelty…. I do explicate [their significance] perhaps more fully than before.”
Niles Eldredge and Gould first coined the term “punctuated equilibrium” in 1971 and published it the following year. The theory seeks to explain a persistent pattern in the fossil record whereby a species suddenly appears, then persists unchanged for a very long time before going extinct. This pattern is seen in a wide variety of contexts, from marine creatures such as shellfish and sea urchins to mammals and birds. Punctuated equilibrium posits that these species come into existence relatively rapidly (over tens of thousands of years), though just how (and indeed if) this happens is hotly debated. An opposing explanation is that these species have evolved much more slowly somewhere else, and their “sudden” appearance is the result of migration. While, as Galton’s polyhedron suggests, the concept of punctuated equilibrium was not entirely new to paleontology, Eldredge and Gould’s formulation of it was timely and coherent. Even among its supporters, however, argument has raged over its significance, with many questioning whether it really challenges Darwin’s concept of gradualism. (After all, tens of thousands of years is sufficient time for species to evolve “gradually.”) Most researchers, though, recognize that the concept has been invaluable in encouraging paleontologists to examine the fossil record with a rigor and attention to detail that previously was largely lacking.
Punctuated equilibrium has forced paleontologists to focus not only on the origin of species, but also on their often long, unchanged persistence in the fossil record. Before punctuated equilibrium, this phenomenon tended to be accepted as simply the way things were—yet it is an intriguing problem. One of the best examples given by Gould concerns the mammals (including rhino, pig, and camel relatives) of the White River Chronofauna of the American West, which endured almost unchanged through a period of astounding climatic upheaval. During this time the rain forests of Nebraska were transformed into forested grassland and the mean annual temperature dropped by 13 degrees Celsius. Revelations such as this remind us of how much we have to learn about our planet’s past.
What is particularly satisfying about reading Gould’s views of punctuated equilibrium is the sense he gives that a fundamental problem—that of how species originate and then persist over geological time—is not yet fully understood. If young biologists ever reach deep into his vast tome, they may find here materials with which to build careers.
Following a thorough treatment of the literature relating to punctuated equilibrium in nature, Gould brings his discussion into the social realm, debating how the concept might apply to changing human cultures and even to businesses in complex societies. He notes, not without some chagrin, that creationists have welcomed the theory because it has enabled them to argue that the fossil record does not show us “evolution in action” and that therefore evolution does not exist. The first part of this observation is indeed a corollary of the theory, which posits that the changes leading to new species usually happen so rapidly that they go undetected, but the second is clearly an unwarranted “leap of faith.”
Gould’s discussion of punctuated equilibrium concludes with an overview of nonscientific objections to the theory, including the accusation that he developed it as part of a Marxist political agenda. Gould resents “this absurd misreading,” writing that his politics are “a private matter that I do not choose to discuss in this forum.” Under the heading “THE MOST UNKINDEST CUT OF ALL” he discusses the dismissal of his theory as both “trivial and devoid of content,” a charge he intensely resents and feels is deeply unfair.
On the twenty-first anniversary of the publication of the theory of punctuated equilibrium, Gould and Eldredge wrote in Nature: “In developing punctuated equilibrium, we have either been toadies and panderers to fashion, and therefore destined for history’s ashheap, or we had a spark of insight about nature’s constitution.” In The Structure of Evolutionary Theory Gould appears to have revised this view, perhaps as a result of the criticism that the theory is extraordinarily difficult to test, because life is so diverse and so many differing interpretations of the fossil record are possible. He now believes that no one expects an either-or result, but only (eventually) a sense of what proportion of life’s diversity evolves gradually and steadily, and how much in leaps and bounds.
The emphasis on punctuated equilibrium opens the way for The Structure of Evolutionary Theory‘s most audacious proposal—the idea of species selection. Gould sees punctuated equilibrium as a prerequisite for species selection because it bestows on species some of the properties inherent in individuals. Thus Gould envisages a sort of life cycle of species: born via punctuated equilibrium, they live a life in mature (stable) form, and then die through extinction. Species selection is a central aspect of the book, and by it Gould means that species as a whole—not just individuals or populations—are being acted on by natural selection.
See, for example, the following: Stephen J. Gould, "The Confusion over Evolution," The New York Review, November 19, 1992; Daniel C. Dennett, John Maynard Smith, and Stephen Jay Gould, "'Confusion over Evolution': An Exchange," The New York Review, January 14, 1993; Stephen J. Gould, "Darwinian Fundamentalism," The New York Review, June 12, 1997; Stephen J. Gould, "Evolution: The Pleasures of Pluralism," The New York Review, June 26, 1997; Daniel C. Dennett and Stephen Jay Gould, "'Darwinian Fundamentalism': An Exchange," The New York Review, August 14, 1997.↩
See, for example, the following: Stephen J. Gould, “The Confusion over Evolution,” The New York Review, November 19, 1992; Daniel C. Dennett, John Maynard Smith, and Stephen Jay Gould, “‘Confusion over Evolution’: An Exchange,” The New York Review, January 14, 1993; Stephen J. Gould, “Darwinian Fundamentalism,” The New York Review, June 12, 1997; Stephen J. Gould, “Evolution: The Pleasures of Pluralism,” The New York Review, June 26, 1997; Daniel C. Dennett and Stephen Jay Gould, “‘Darwinian Fundamentalism’: An Exchange,” The New York Review, August 14, 1997.↩