With copious evidence ranging from Plato’s haughtiness to Beethoven’s tirades, we may conclude that the most brilliant people of history tend to be a prickly lot. But Charles Darwin must have been the most genial of geniuses. He was kind to a fault, even to the undeserving, and he never uttered a harsh word—or hardly ever, as his countryman Captain Corcoran once said. Darwin’s disciple, George Romanes, expressed surprise at the only sharply critical Darwinian statement he had ever encountered: “In the whole range of Darwin’s writings there cannot be found a passage so strongly worded as this: it presents the only note of bitterness in all the thousands of pages which he has published.” Darwin directed this passage that Romanes found so striking against people who would simplify and caricature his theory as claiming that natural selection, and only natural selection, caused all evolutionary changes. He wrote in the last (1872) edition of The Origin of Species:
As my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position—namely at the close of the Introduction—the following words: “I am convinced that natural selection has been the main but not the exclusive means of modification.” This has been of no avail. Great is the power of steady misrepresentation.
Darwin clearly loved his distinctive theory of natural selection—the powerful idea that he often identified in letters as his dear “child.” But, like any good parent, he understood limits and imposed discipline. He knew that the complex and comprehensive phenomena of evolution could not be fully rendered by any single cause, even one so ubiquitous and powerful as his own brainchild.
In this light, especially given history’s tendency to recycle great issues, I am amused by an irony that has recently ensnared evolutionary theory. A movement of strict constructionism, a self-styled form of Darwinian fundamentalism, has risen to some prominence in a variety of fields, from the English biological heartland of John Maynard Smith to the uncompromising ideology (albeit in graceful prose) of his compatriot Richard Dawkins, to the equally narrow and more ponderous writing of the American philosopher Daniel Dennett (who entitled his latest book Darwin’s Dangerous Idea).1 Moreover, a larger group of strict constructionists are now engaged in an almost mordantly self-conscious effort to “revolutionize” the study of human behavior along a Darwinian straight and narrow under the name of “evolutionary psychology.”
Some of these ideas have filtered into the general press, but the uniting theme of Darwinian fundamentalism has not been adequately stressed or identified. Professionals, on the other hand, are well aware of the connections. My colleague Niles Eldredge, for example, speaks of this coordinated movement as Ultra-Darwinism in his recent book, Reinventing Darwin.2 Amid the variety of their subject matter, the ultra-Darwinists share a conviction that natural selection regulates everything of any importance in evolution, and that adaptation emerges as a universal result and ultimate test of selection’s ubiquity.
The irony of this situation is twofold. First, as illustrated by the quotation above, Darwin himself strongly opposed the ultras of his own day. (In one sense, this nicety of history should not be relevant to modern concerns; maybe Darwin was overcautious, and modern ultras therefore out-Darwin Darwin for good reason. But since the modern ultras push their line with an almost theological fervor, and since the views of founding fathers do matter in religion, though supposedly not in science, Darwin’s own fierce opposition does become a factor in judgment.) Second, the invigoration of modern evolutionary biology with exciting nonselectionist and nonadaptationist data from the three central disciplines of population genetics, developmental biology, and paleontology (see examples below) makes our pre-millennial decade an especially unpropitious time for Darwinian fundamentalism—and seems only to reconfirm Darwin’s own eminently sensible pluralism.
Charles Darwin often remarked that his revolutionary work had two distinct aims: first, to demonstrate the fact of evolution (the genealogical connection of all organisms and a history of life regulated by “descent with modification”); second, to advance the theory of natural selection as the most important mechanism of evolution. Darwin triumphed in his first aim (American creationism of the Christian far right notwithstanding). Virtually all thinking people accept the factuality of evolution, and no conclusion in science enjoys better documentation. Darwin also succeeded substantially in his second aim. Natural selection, an immensely powerful idea with radical philosophical implications, is surely a major cause of evolution, as validated in theory and demonstrated by countless experiments. But is natural selection as ubiquitous and effectively exclusive as the ultras propose?
The radicalism of natural selection lies in its power to dethrone some of the deepest and most traditional comforts of Western thought, particularly the notion that nature’s benevolence, order, and good design, with humans at a sensible summit of power and excellence, proves the existence of an omnipotent and benevolent creator who loves us most of all (the old-style theological version), or at least that nature has meaningful directions, and that humans fit into a sensible and predictable pattern regulating the totality (the modern and more secular version).
To these beliefs Darwinian natural selection presents the most contrary position imaginable. Only one causal force produces evolutionary change in Darwin’s world: the unconscious struggle among individual organisms to promote their own personal reproductive success—nothing else, and nothing higher (no force, for example, works explicitly for the good of species or the harmony of ecosystems). Richard Dawkins would narrow the focus of explanation even one step further—to genes struggling for reproductive success within passive bodies (organisms) under the control of genes—a hyper-Darwinian idea that I regard as a logically flawed and basically foolish caricature of Darwin’s genuinely radical intent.
The very phenomena that traditional views cite as proof of benevolence and intentional order—the good design of organisms and the harmony of ecosystems—arise by Darwin’s process of natural selection only as side consequences of a singular causal principle of apparently opposite meaning: organisms struggling for themselves alone. (Good design becomes one pathway to reproductive success, while the harmony of ecosystems records a competitive balance among victors.) Darwin’s system should be viewed as morally liberating, not cosmically depressing. The answers to moral questions cannot be found in nature’s factuality in any case, so why not take the “cold bath” of recognizing nature as nonmoral, and not constructed to match our hopes? After all, life existed on earth for 3.5 billion years before we arrived; why should life’s causal ways match our prescriptions for human meaning or decency?
We now reach the technical and practical point that sets the ultra-Darwinian research agenda. Natural selection can be observed directly, but only in the unusual circumstances of controlled experiments in laboratories (on organisms with very short generations such as fruit flies) or within simplified and closely monitored systems in nature. Since evolution, in any substantial sense, takes so much time (more than the entire potential history of human observing!), we cannot, except in special circumstances, watch the process in action, and must therefore try to infer causes from results—the standard procedure in any historical science, by the way, and not a special impediment facing evolutionists.
The generally accepted result of natural selection is adaptation—the shaping of an organism’s form, function, and behavior to achieve the Darwinian summum bonum of enhanced reproductive success. We must therefore study natural selection primarily from its results—that is, by concentrating on the putative adaptations of organisms. If we can interpret all relevant attributes of organisms as adaptations for reproductive success, then we may infer that natural selection has been the cause of evolutionary change. This strategy of research—the so-called adaptationist program—is the heart of Darwinian biology, and the fervent, singular credo of the ultras.
Since the ultras are fundamentalists at heart, and since fundamentalists generally try to stigmatize their opponents by depicting them as apostates from the one true way, may I state for the record that I (along with all other Darwinian pluralists) do not deny either the existence and central importance of adaptation, or the production of adaptation by natural selection. Yes, eyes are for seeing and feet are for moving. And, yes again, I know of no scientific mechanism other than natural selection with the proven power to build structures of such eminently workable design.
But does all the rest of evolution—all the phenomena of organic diversity, embryological architecture, and genetic structure, for example—flow by simple extrapolation from selection’s power to create the good design of organisms? Does the force that makes a functional eye also explain why the world houses more than five hundred thousand species of beetles and fewer than fifty species of priapulid worms? Or why most nucleotides—the linked groups of molecules that build DNA and RNA—in multicellular creatures do not code for any enzyme or protein involved in the construction of an organism? Or why ruling dinosaurs died and subordinate mammals survived to flourish and, along one oddly contingent pathway, to evolve a creature capable of building cities and understanding natural selection?
I do not deny that natural selection has helped us to explain phenomena at scales very distant from individual organisms, from the behavior of an ant colony to the survival of a redwood forest. But selection cannot suffice as a full explanation for many aspects of evolution; for other types and styles of causes become relevant, or even prevalent, in domains both far above and far below the traditional Darwinian locus of the organism. These other causes are not, as the ultras often claim, the product of thinly veiled attempts to smuggle purpose back into biology. These additional principles are as directionless, nonteleological, and materialistic as natural selection itself—but they operate differently from Darwin’s central mechanism. In other words, I agree with Darwin that natural selection is “not the exclusive means of modification.”
What an odd time to be a fundamentalist about adaptation and natural selection—when each major subdiscipline of evolutionary biology has been discovering other mechanisms as adjuncts to selection’s centrality. Population genetics has worked out in theory, and validated in practice, an elegant, mathematical account of the large role that neutral, and therefore nonadaptive, changes play in the evolution of nucleotides, or individual units of DNA programs. Eyes may be adaptations, but most substitutions of one nucleotide for another within populations may not be adaptive.
In the most stunning evolutionary discoveries of our decade, developmental biologists have documented an astonishing “conservation,” or close similarity, of basic pathways of development among phyla that have been evolving independently for at least 500 million years, and that seem so different in basic anatomy (insects and vertebrates, for example). The famous homeotic genes of fruit flies—responsible for odd mutations that disturb the order of parts along the main body axis, placing legs, for example, where antennae or mouth parts should be—are also present (and repeated four times on four separate chromosomes) in vertebrates, where they function in effectively the same way. The major developmental pathway for eyes is conserved and mediated by the same gene in squids, flies, and vertebrates, though the end products differ substantially (our single-lens eye vs. the multiple facets of insects). The same genes regulate the formation of top and bottom surfaces in insects and vertebrates, though with inverted order—as our back, with the spinal cord running above the gut, is anatomically equivalent to an insect’s belly, where the main nerve cords run along the bottom surface, with the gut above.