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 …