Stephen Jay Gould wrote:Daniel Dennett's 1995 book, Darwin's Dangerous Idea, presents itself as the ultra[-Darwinists] philosophical manifesto of pure adaptationism. Dennett explains the strict adaptationist view well enough, but he defends a miserly and blinkered picture of evolution in assuming that all important phenomena can be explained thereby. His limited and superficial book reads like a caricature of a caricature—for if Richard Dawkins has trivialized Darwin's richness by adhering to the strictest form of adaptationist argument in a maximally reductionist mode, then Dennett, as Dawkins's publicist, manages to convert an already vitiated and improbable account into an even more simplistic and uncompromising doctrine. If history, as often noted, replays grandeurs as farces, and if T.H. Huxley truly acted as "Darwin's bulldog," then it is hard to resist thinking of Dennett, in this book, as "Dawkins's lapdog."
Dennett bases his argument on three images or metaphors, all sharing the common error of assuming that conventional natural selection, working in the adaptationist mode, can account for all evolution by extension—so that the entire history of life becomes one grand solution to problems in design. "Biology is engineering," Dennett tells us again and again. In a devastating review, published in the leading professional journal Evolution, and titled "Dennett's Dangerous Idea," H. Allen Orr notes:
His review of attempts by biologists to circumscribe the role of natural selection borders on a zealous defense of panselectionism. It is also absurdly unfair…. Dennett fundamentally misunderstands biologists' worries about adaptationism. Evolutionists are essentially unanimous that—where there is "intelligent Design"—it is caused by natural selection…. Our problem is that, in many adaptive stories, the protagonist does not show dead-obvious signs of Design.
In his first metaphor, Dennett describes Darwin's dangerous idea of natural selection as a "universal acid"—to honor both its ubiquity and its power to corrode traditional Western beliefs. Speaking of adaptation, natural selection's main consequence, Dennett writes: "It plays a crucial role in the analysis of every biological event at every scale from the creation of the first self-replicating macromolecule on up." I certainly accept the acidic designation—for the power and influence of the idea of natural selection does lie in its radical philosophical content—but few biologists would defend the blithe claim for ubiquity. If Dennett chooses to restrict his personal interest to the engineering side of biology—the part that natural selection does construct—then he is welcome to do so. But he may not impose this limitation upon others, who know that the record of life contains many more evolutionary things than are dreamt of in Dennett's philosophy.
Natural selection does not explain why many evolutionary transitions from one nucleotide to another are neutral, and therefore nonadaptive. Natural selection does not explain why a meteor crashed into the earth 65 million years ago, setting in motion the extinction of half the world's species. As Orr points out, Dennett's disabling parochialism lies most clearly exposed in his failure to discuss the neutral theory of molecular evolution, or even to mention the name of its founder, the great Japanese geneticist Motoo Kimura—for few evolutionary biologists would deny that this theory ranks among the most interesting and powerful adjuncts to evolutionary explanation since Darwin's formulation of natural selection. You don't have to like the idea, but how can you possibly leave it out?
In a second metaphor, Dennett continually invokes an image of cranes and skyhooks. In his reductionist account of evolution, cranes build the good design of organisms upward from nature's physicochemical substrate. Cranes are good. Natural selection is evolution's basic crane; all other cranes (sexual reproduction, for example) act as mere auxiliaries to boost the speed or power of natural selection in constructing organisms of good design. Skyhooks, on the other hand, are spurious forms of special pleading that reach down from the numinous heavens and try to build organic complexity with ad hoc fallacies and speculations unlinked to other proven causes. Skyhooks, of course, are bad. Everything that isn't natural selection, or an aid to the operation of natural selection, is a skyhook.
If you think that I am being simplistic or unfair to Dennett in this characterization, read his book and see if you can detect anything more substantial in this metaphor. I could only find a rhetorical stick for beating pluralists into line. Can't Dennett see that a third (and correct) option exists to his oddly dichotomous Hobson's choice: either accept the idea of one basic crane with auxiliaries, or believe in skyhooks. May I suggest that the platform of evolutionary explanation houses an assortment of basic cranes, all helping to build the edifice of life's history in its full grandeur (not only the architecture of well-engineered organisms). Natural selection may be the biggest crane with the largest set of auxiliaries, but Kimura's theory of neutralism is also a crane; so is punctuated equilibrium; so is the channelling of evolutionary change by developmental constraints. "In my father's house are many mansions"—and you need a lot of cranes to build something so splendid and variegated.
For his third metaphor—though he would demur and falsely label the claim as a fundamental statement about causes—Dennett describes evolution as an "algorithmic process." Algorithms are abstract rules of calculation, and fully general in making no reference to particular content. In Dennett's words: "An algorithm is a certain sort of formal process that can be counted on—logically—to yield a certain sort of result whenever it is 'run' or instantiated." If evolution truly works by an algorithm, then all else in Dennett's simplistic system follows: we need only one kind of crane to supply the universal acid.
I am perfectly happy to allow—indeed I do not see how anyone could deny—that natural selection, operating by its bare-bones mechanics, is algorithmic: variation proposes and selection disposes. So if natural selection builds all of evolution, without the interposition of auxiliary processes or intermediary complexities, then I suppose that evolution is algorithmic too. But—and here we encounter Dennett's disabling error once again—evolution includes so much more than natural selection that it cannot be algorithmic in Dennett's simple calculational sense.
Yet Dennett yearns to subsume all the phenomenology of nature under the limited aegis of adaptation as an algorithmic result of natural selection. He writes: "Here, then, is Darwin's dangerous idea: the algorithmic level is the level that best accounts for the speed of the antelope, the wing of the eagle, the shape of the orchid, the diversity of species, and all the other occasions for wonder in the world of nature" (Dennett's italics). I will grant the antelope's run, the eagle's wing, and much of the orchid's shape—for these are adaptations, produced by natural selection, and therefore legitimately in the algorithmic domain. But can Dennett really believe his own imperialistic extensions? Is the diversity of species no more than a calculational consequence of natural selection? Can anyone really believe, beyond the hype of rhetoric, that "all the other occasions for wonder in the world of nature" flow from adaptation?
Perhaps Dennett only gets excited when he can observe adaptive design, the legitimate algorithmic domain; but such an attitude surely represents a blinkered view of nature's potential interest. I regard the neutral substitution of nucleotides as an "occasion for wonder in the world of nature." And I marvel at the probability that the impact of a meteor wiped out dinosaurs and gave mammals a chance. If this contingent event had not occurred, and imparted a distinctive pattern to the evolution of life, we would not be here to wonder about anything at all!
