Steven Jay Gould, was one of our deepest, most creative and most careful evolutionary thinkers, here delivered his magnum opus, and it inevitably rates five stars for importance. And, yes, those essays from Natural History have given you a lot of pleasure over the years. But, good Lord, look at the heft of the thing! Would you perhaps be better advised to give it a pass?
The answer is no, not if you really care about where evolutionary theory is going during the next forty years. It's true that it's longer than it had to be, and many of its luxuriating sentences are more like a bush than a tree. A good editor could have helped Gould bring it down to 1000 pages or so, and improved it thereby. But the main reason it's such a doorstop is because it's busy opening so many doors. There's far too much to respond to and critique in a review of Amazon length. So what I'm going to do is provide cheats and spoilers: I'll say what you can skip or skim without missing gist or cream, and then give a *very* brief precis of that gist.
THE QUICK TOUR.
Chiefly a summary of what's to come, a summary so dense and abstract that it's likely to convince many readers, falsely, that the book is going to be unreadable. (In the paperback edition, please add a brief glossary!) Scoop up the material on Scilla's coral (pp. 12-24) and save the rest for later.
The next 6 chapters survey the history of evolutionary thought, with a focus on old controversies Gould believes need re-opening, albeit at a higher level. As influential as Gould's been as a scientist, his real genius is for history of ideas, and these chapters are a richly rewarding read, very reminiscent of his Natural History essays in tone. But all that's needed to follow the main thread of the book's arguments are chapter 2 (an illuminating tour of Darwin's "Origin"), some talk about how Darwin dealt with the generation of diversity (pp. 224-229), the metaphor of Galton's polyhedron (pp. 342-351), and, to show what Gould is contrasting himself with, the exposition of how the "Modern Synthesis" of the 40s and 50s froze Darwinism into a rigid form (all of chapter 7).
Little is skippable. The last 50 pages of chapter seven, the punk eek centerpiece, discuss the abuses poured on punk eek by nefarious parties like Dawkins and creationists. It's juicy, but peripheral. The passages on D'Arcy Thompson (pp. 1182-1208) and on mass extinctions (all of chapter 12) are necessary to the organizational scheme, but not necessary to the logic or substance of Gould's "one long argument."
WHAT IT HAS TO SAY...
Darwin gave us a slam-dunk proof of the fact of common descent, which no scientist but the aging Aggasiz has seriously disputed since. But initially his causal theory of how it happened drew a great deal of fire. For the first 60 years after the Origin, the woods were crawling with evolutionists, some of them naturalists at the top of their game, who wanted to replace natural selection with some other mechanism. Darwin triumphed, Gould tells us, because his basic idea was right. But now the time has come for major upheaval and revision, because several of his major secondary commitments were mistaken.
What Gould says Darwin got right: Selection acting on ordinary variation, which is in some sense random, is what produces almost all evolutionary change.
Mistaken secondary commitment 1: Selection acts only on individual organisms. Gould argues that selection acts up and down the hierarchy - on genes, cells, organisms, demes, species, and clades, but (other than organisms) especially on species, because species have the sort of cohesion that makes for good selective "individuals."
Mistaken secondary commitment 2: The environment shapes almost all change, by selective pressures which mold adaptations. Gould points out that Darwin's argument for this thesis rests on the assumption that variation is "isotopic" - equally likely in all directions - and "imperceptible." He argues that recent genetic discoveries prove the contrary: deep homologies across phyla make certain major inventions such as optical lenses more likely than others, and small genetic changes in homeobox and other regulatory genes can lead to very perceptible variations, in preferred directions. And consequently, the direction of change is shaped as much by internal availabilities - creating "exaptations" - as by external selective pressures creating adaptations.
Mistaken secondary commitment 3: Selective pressure is always producing small changes, and these are always accumulating in the direction of greater fitness; simple extrapolation from them can account for the whole panoply of living things. Gould argues that (1) selective pressures fail to produce change most of the time, the phenomenon of stasis first highlighted as part of punctuated equilibrium, and (2) the changes don't accumulate. Rather, among organisms within a species, they mostly fluctuate back and forth, unless a change gets locked in by being isolated in a new species. And any trends across species are the result of selection at the species or clade levels, a kind of selection with its own emergent mechanisms not extrapolatable from Darwinian natural selection among organisms.
Is all this really all that revolutionary? Gould clearly documents how vehemently each item in the programme he outlines was denied and resisted by the old guard of the Modern Synthesis; if he seems to be making a mountain out of a molehill, it's mostly because we've grown so used to offenses against pure Darwinism in the last twenty-five years. Certainly the positions he takes open myriad fruitful lines of future inquiry. And that's really what he's after. In his "segue" between parts one and two, he notes that the time is not now ripe for still another New Synthesis; we don't know enough yet. He says that he intends this book as an antithesis to the Modern Synthesis, undoubtedly overstated and overreaching, but likely to spur the birth of the next synthesis in its own good Hegelian time. Despite (and perhaps even because) of the numerous criticisms and counter-arguments that I found myself penciling into the margins of Gould's "Structure", I think his tome will admirably serve that prodding purpose.