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Evolution: The Pleasures of Pluralism

Charles Darwin began the last paragraph of The Origin of Species (1859) with a famous metaphor about life’s diversity and ecological complexity:

It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us.

He then begins the final sentence of the book with an equally famous statement: “There is grandeur in this view of life….”

For Darwin, as for any scientist, a kind of ultimate satisfaction (Darwin’s “grandeur”) must reside in the prospect that so much variety and complexity might be generated from natural regularities—the “laws acting around us”—accessible to our intellect and empirical probing. But what is the proper relationship between underlying laws and explicit results? The “fundamentalists” among evolutionary theorists revel in the belief that one overarching law—Darwin’s central principle of natural selection—can render the full complexity of outcomes (by working in conjunction with auxiliary principles, like sexual reproduction, that enhance its rate and power).

The “pluralists,” on the other hand—a long line of thinkers including Darwin himself, however ironic this may seem since the fundamentalists use the cloak of his name for their distortion of his position—accept natural selection as a paramount principle (truly primus inter pares), but then argue that a set of additional laws, as well as a large role for history’s unpredictable contingencies, must also be invoked to explain the basic patterns and regularities of the evolutionary pathways of life. Both sides locate the “grandeur” of “this view of life” in the explanation of complex and particular outcomes by general principles, but ultra-Darwinian fundamentalists pursue one true way, while pluralists seek to identify a set of interacting explanatory modes, all fully intelligible, although not reducible to a single grand principle like natural selection.

The first part of this article outlined the general fallacies of ultra-Darwinian fundamentalism, especially in the light of new theories and discoveries in the core disciplines of developmental biology, paleontology, and population genetics.1 In this second and concluding part, I shall analyze a prominent philosopher’s influential but misguided ultra-Darwinian manifesto—Darwin’s Dangerous Idea, by Daniel Dennett. I shall also take upthe meth-odology of so-called “evolutionary psychology”—a field now in vogue as a marketplace for ultra-Darwinian explanatory doctrine. Evolutionary psychology could, in my view, become a fruitful science by replacing its current penchant for narrow, and often barren, speculation with respect for the pluralistic range of available alternatives that are just as evolutionary in status, more probable in actual occurrence, and not limited to the blinkered view that evolutionary explanations must identify adaptations produced by natural selection.

1.

Daniel Dennett devotes the longest chapter in Darwin’s Dangerous Idea to an excoriating caricature of my ideas, all in order to bolster his defense of Darwinian fundamentalism. If an argued case can be discerned at all amid the slurs and sneers, it would have to be described as an effort to claim that I have, thanks to some literary skill, tried to raise a few piddling, insignificant, and basically conventional ideas to “revolutionary” status, challenging what he takes to be the true Darwinian scripture. Dennett claims that I have promulgated three “false alarms” as supposed revolutions against the version of Darwinism that he and his fellow defenders of evolutionary orthodoxycontinue to espouse.

Dennett first attacks my view that punctuated equilibrium is the dominant pattern of evolutionary change in the history of living organisms. This theory, formulated by Niles Eldredge and me in 1972, proposes that the two most general observations made by palentologists form a genuine and primary pattern of evolution, and do not arise as artifacts of an imperfect fossil record. The first observation notes that mostnew species originate in ageological “moment.” The second holds that species generally do not change in any substantial or directional way during their geological lifetimes—usually a long period averaging five to ten million years for fossil invertebrate species. Punctuated equilibrium does not challenge accepted genetic ideas about the rates at which species emerge (for the geological “moment” of a single rock layer may represent many thousand years of accumulation). But the theory does contravene conventional Darwinian expectations for gradual change over geological periods, and does suggest a substantial revision of standard views about the causes of long-term evolutionary trends. For such trends must now be explained by the higher rates at which some species branch off from others, and the greater durations of some stable species as distinguished from others, and not as the slow and continuous transformation of single populations.

In his second attack, Dennett denigrates the importance of nonadaptive side consequences (“spandrels” in my terminology) as sources for later and fruitful reuse. In principle, spandrels define the major category of important evolutionary features that do not arise as adaptations. Since organisms are complex and highly integrated entities, any adaptive change must automatically “throw off” a series of structural byproducts—like the mold marks on an old bottle or, in the case of an architectural spandrel itself, the triangular space “left over” between a rounded arch and the rectangular frame of wall and ceiling. Such byproducts may later be co-opted for useful purposes, but they didn’t arise as adaptations. Reading and writing are now highly adaptive for humans, but the mental machinery for these crucial capacities must have originated as spandrels that were co-opted later, for the brain reached its current size and conformation tens of thousands of years before any human invented reading or writing.

Third, and finally, Dennett denies theoretical importance to the roles of contingency and chance in the history of life, a history that hasfew predictable particulars and no inherent directionality, especially given the persistence of bacteria as the most common and dominant form of life on Earth ever since their origin as the first fossilized creatures some 3.5 billion years ago.2 Bacteria are biochemically more diverse, and live in a wider range of environments (including near-boiling waters, and pore spaces in rocks up to two miles beneath the earth’s surface), than all other living things combined. The number of E. coli cells in the gut of each human being exceeds the total number of human beings that have ever lived. Moreover, if recent reports of Martian fossil bacteria are true, then bacterial domination may be interplanetary or universal, and not merely earthly.

These three concepts work as pluralistic correctives to both the poverty and limited explanatory power of the ultra-Darwinian research program. Punctuated equilibrium requires that substantial evolutionary trends over geological time, the primary phenomenon of macroevolution, be explained by the greater long-term success of some species versus others within a group of species descended from a common ancestor. Such trends cannot be explained, as Darwinian fundamentalists would prefer, as the adaptive success of individual organisms in conventional competition, extrapolated through geological time as the slow and steady transformation of populations by natural selection. The principle of spandrels, discussed at greater length later in this article, stresses the role that nonadaptive side consequencesplay in structuring the directions and potentials of future evolutionary change. Taken together, punctuated equilibrium and spandrels invoke the operation of several important principles in addition (and sometimes even opposed) to conventional natural selection working in the engineering mode that Dennett sees as the only valid mechanism of evolution.

My third pluralistic corrective to traditional theory does not invoke other principles in addition to natural selection, but rather stresses the limits faced by any set of general principles in our quest to explain the actual patterns of life’s history. Crank your algorithm of natural selection to your heart’s content, and you cannot grind out the contingent patterns built during the earth’s geological history. You will get predictable pieces here and there (convergent evolution of wings in flying creatures), but you will also encounter too much randomness from a plethora of sources, too many additional principles from within biological theory, and too many unpredictable impacts from environmental histories beyond biology (including those occasional meteors)—all showing that the theory of natural selection must work in concert with several other principles of change to explain the observed pattern of evolution.

Since Dennett shows so little understanding of evolutionary theory beyond natural selection, his critique of my work amounts to little more than sniping at false targets of his own construction. He never deals with my ideas as such, but proceeds by hint, innuendo, false attribution, and error. I will cite concrete examples in four categories:

  1. False assimilation to statements made by other authors. Since Dennett can’t nail me on his desired charges (for I never said the things he wishes to lay upon me), he often invents a ridiculous interpretation, which he attributes to others and not to me, and then hopes out loud that I never meant such a thing. For example, Dennett invents and attributes to “some” writers an absurd mischaracterization of my views on the Cambrian explosion, the short episode (535-530 million years ago) when nearly all the major groups of animals make their first appearance in the fossil record, including the creatures preserved in the Burgess Shale:

Some say this misses Gould’s point: “What is special about the spectacular diversity of the Burgess Shale fauna is that these weren’t just new species, but whole new phyla! These were radically novel designs!” I trust this was never Gould’s point, because if it was, it was an embarrassing fallacy of retrospective coronation.

It would be—but since I have never even hinted at such a silly view, why bother to point out how stupid I would be if I ever had?

In an even more unfair example, Dennett conjectures about what I might believe (but I don’t, and he cites nothing to support his supposition), and then seems to pretend that I hold such a view by attacking someone else who truly does:

Is it likely that Gould could be so confused about the nature of algorithms? As we shall see in chapter 15, Roger Penrose, one of the world’s most distinguished mathematicians, wrote a major book (1989) on Turing machines, algorithms, and the impossibility of Artificial Intelligence, and his whole book is based on that confusion. This is not really such an implausible error, on either thinker’s part [I have now become an explicit supporter of the idea—]. A person who really doesn’t like Darwin’s dangerous idea often finds it hard to get the idea in focus.

  1. False characterization.Dennett depicts me as constantly and explicitly claiming to invent one scientific “revolution” after another. No characterization appears more frequently throughout the chapter, and none could be so false. “Gould,” he states, “has gone from revolution to revolution. So far, his declarations of revolution have all been false alarms.” We then learn that “the spandrel revolution (against panadaptationism) and the exaptation revolution (against preadaptationism) evaporate on closer inspection,” and that “Gould’s attempted revolution against gradualism was actually his first.” In a final summary, we learn that “Gould’s self-styled revolutions …all evaporate.”

  1. 1

    Darwinian Fundamentalism,” The New York Review, June 12, 1997, pp. 34-37.

  2. 2

    See my recent book Full House (Crown, 1996) for an account of this.

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