I’ve never been one to judge somebody’s arguments by their scholarly credentials. After all, two major contributors to my own field of evolutionary genetics, Gregor Mendel and Charles Darwin, were amateur naturalists and autodidacts trained more thoroughly in theology than in biology.
So when well-known Yale professor and computer scientist David Gelernter rejected Darwinian evolution in his recent essay, ‘Giving Up Darwin,’ we can’t dismiss him simply because he’s not a biologist. Nor can we ignore his arguments because the piece appeared in a conservative journal, the Claremont Review of Books. No, we must attack his arguments head on, especially because they’ve been widely parroted by the media, as well as by conservative, religious, and intelligent-design (ID) websites.
Sadly, his arguments are neither new nor correct. Gelernter’s claim—that evolution as envisioned by Darwin (and expanded into “neo-Darwinism” since the 1930s) cannot explain features of organisms and of the fossil record—depends heavily on the arguments of ID creationists. And every one of those arguments has been soundly rebutted over the past few decades. While Gelernter doesn’t fully embrace all the tenets of ID, like the existence of an Intelligent Designer, he’s bought into virtually all its criticisms of Darwinism.
And he’s culpable for this, as he seems to have gotten his education in evolution solely from books written by ID advocates like Stephen Meyer, David Berlinski, and William Dembski, ignoring the many critiques that have demolished their claims. You simply can’t do good science by spouting only one side of an argument and ignoring the claims of the other.
I’m not sure why Gelernter so thoroughly accepts the nonsense that is ID. But given his own religiosity, the religious tone of several bits of his essay, and his teleological view on how life might have changed over time, I suspect he, like all ID advocates, is susceptible to religious blandishments, immunizing him against the scientific truths that rebut faith. And so he asks us, “How cleanly and quickly can the field get over Darwin, and move on?” The answer, I suggest, is “We don’t need to.”
Rebutting such arguments is a perpetual and tiresome battle, useful only for those sporting open minds rather than religious blinkers. Nevertheless, I’ll try to show why Gelernter’s anti-Darwinian assertions hold no water.
One of his major claims is a staple of many brands of creationism: the view that all major groups of animals, the “phyla,” appeared suddenly in the “Cambrian explosion,” the appearance of diverse animals about 540 million years ago (Mya). This “sudden appearance,” said to defy the slow, gradual evolution inherent in Darwinism, is taken by IDers to reflect the intervention of an intelligent agent, jibing nicely with Biblical accounts of creation.
Unfortunately, Gelernter, like his mentor Stephen Meyer, severely distorts the fossil record to arrive at this claim.
Initially, the Cambrian “explosion” was seen as occupying a roughly 20-million-year period from about 541 Mya, when the Cambrian period began, to about 520 Mya. Even this is an “explosion” only in geological terms, and comfortably allows for a lot of biological evolution to take place (after all, modern whales evolved from small terrestrial deerlike organisms in just 12 million years). But as we have built up an increasingly detailed picture of early life by unearthing more fossils from the Precambrian, even the concept of an explosion is disappearing, with paleontologists increasingly speaking of a “Cambrian diversification.”
Contra Gelernter, who pretends that the animal groups appearing during the “explosion” had no likely ancestors, the more fossils we find, the clearer it becomes that there was a long story preceding the “explosion.” For instance, in the period before the Cambrian—the Ediacaran—we see animals that appear to be arthropods, muscle-clad cnidarians (the group that includes modern jellyfish and anemones), echinoderms, mollusks, and probable sponges, with the simplest animals dating back 20 million years before the Cambrian even began. And evidence for the advent of predators in the form of burrowing traces and formation of shells—an innovation that might have driven the Cambrian diversification—is seen beginning about 545 Mya. (For an overview of the antecedents to the “explosion,” see this new paper by Rachel Wood et al. )
In short, the “explosion” was hardly explosive, and Gelernter is wrong when he says “those predecessors of the Cambrian creatures are missing.” Even a brief survey of the paleontological literature would (or should) give the lie to this assertion.
Gelernter displays further ignorance of biology when making the common but false claim that there may be Darwinian “microevolution” (small changes within species) but that we lack evidence that neo-Darwinian processes can produce the big changes seen as “macroevolution.” In his case, macroevolution means not just the emergence of drastically different forms of organisms, but “the emergence of new species”:
There’s no reason to doubt that Darwin successfully explained the small adjustments by which an organism adapts to local circumstances: changes to fur density or wing style or beak shape. Yet there are many reasons to doubt whether he can answer the hard questions and explain the big picture—not the fine-tuning of existing species but the emergence of new ones. The origin of species is exactly what Darwin cannot explain.
This claim is doubly wrong. First, we have ample evidence from the fossil record for gradual but really substantial macroevolution, however you define the term. We have transitional forms between fish and amphibians, between amphibians and reptiles, and between reptiles and mammals on one hand, and reptiles and birds on the other. In fact, there are forms so intermediate between mammals and reptiles that we can’t slot them in one group or another: they’re called “mammal-like reptiles.” Likewise, we have bird-like dinosaurs—or dinosaur-like birds. The evolution of whales I mentioned above involved a gradual change from land organisms to amphibious organisms to fully-fledged whales, with almost every step of the process documented with fossils.
Further, we have the bête noire of creationists: the transitional series between early australopithecines with brains smaller than chimps to modern Homo sapiens. Yes, some of the details of our ancestry are unclear, but one thing is clear: modern humans didn’t spring into existence in a short time, but emerged over at least four million years from small-brained ancestors that lived in trees.
Second, Gelernter confuses true speciation—the branching of an ancestral species into two or more reproductively isolated descendants, a process called “cladogenesis”—with gradual changes in a single lineage, a process called “anagenesis.” He claims we have no evidence for either process. But I gave the evidence for anagenesis in the last two paragraphs, and it also rests in hundreds of big changes within lineages that I didn’t mention. As for splitting, I describe the evidence for that in my book Speciation with Allen Orr. It includes the observation of new lineages arising within human lifetimes, as well as of intermediate stages of groups splitting in nature, including some populations with reproductive barriers so intermediate that they can’t be classified as either members of the same species or of different species.
Now it is ironically true that despite the title of his great book, On the Origin of Species, Darwin failed to explain the origin of species in the cladogenetic sense, for he had no notion of species as populations that evolve reproductive independence from each other. But we’ve come a long way since then—the study of speciation really began in the 1930s—and now have a good understanding of how lineages split and produced the branching tree of life.
Gelernter then tells us not only that macroevolution wasn’t seen to happen, but is also theoretically impossible. These claims have also been discredited.
First, he argues that the chance that useful proteins could evolve is close to zero, asserting that “random mutation plus natural selection” are insufficient to create new protein shapes. That’s equivalent to the claim that these processes aren’t sufficient to explain new protein sequences.
The fallacy here is obvious. Gelernter assumes there is a useful, pre-specified target protein that must be reached from a “nonsense” sequence of amino acids. Then he multiplies together the small probabilities needed to convert each amino acid in the starting “gibberish protein” into the ones in the final target. The resulting probability is so minuscule that, he concludes, the Darwinian evolution of useful proteins is impossible.
This argument rests on several big errors. First, evolution doesn’t start with “gibberish proteins”; it continues with what it had before: useful proteins that evolved via natural selection from earlier sequences, but can still improve further. Second, evolution doesn’t drive proteins toward pre-specified target sequences. All that’s required for evolution to work is a mutation changing a gene (and its protein product) in such a way that the new gene leaves more copies than its antecedent. It’s an incremental form of improvement, not a narrowing-in on a specified target.
In fact, we have plenty of examples, in our species and others, in which a small change in an existing protein leads to a better protein. This has occurred, for instance, in proteins adapting human cultures to diving in water, enzymes for making fatty acids in populations that are largely vegetarian, in genes controlling armor plating that reduces predation on marine stickleback fish, and in proteins conferring an attraction to human odor in mosquitoes that invaded urban areas.
There are many similar examples, all showing that a small change in an already useful protein sequence can make it extra useful in new environments. This is the way evolution has worked from the very first Ur-protein.
And mutations don’t have to be changes in single proteins, either. There are many kinds of mutations, including the duplication of existing genes and their later divergence into multiple useful forms, the cobbling together of bits of different genes into new genes, and the co-option of DNA from invading microbes to make useful genes. This helped contribute to the evolution of the mammalian placenta.) The diversity of mutations that have produced adaptive changes in DNA are summarized in an influential paper by my colleague Manyuan Long and his collaborators.
Another reason Gelernter gives for the impossibility of big changes in animal evolution is that we have supposedly never seen useful mutations in genes involved in early development—changes he sees as required for the evolution of new body plans. In fact, he argues that “there are a total of no examples of mutations that affect early development and the body plan as a whole and are not fatal.” This assertion is based on a survey of genes affecting fly development in the fruit fly Drosophila. But that survey, which garnered a Nobel Prize for Eric Weischaus and Christine Nüsslein-Volhard, was designed to detect only mutations that were fatal, so Gelernter’s conclusion is trivial and misleading. Those experiments say nothing about whether genes involved in early development can be viable and can change by natural selection.
In fact, there’s plenty of evidence that they were and they did. First, there are tons of mutations affecting early development that are not lethal, refuting Gelernter’s claim for the inevitable fatality of such mutations. If you want examples of nonfatal mutations, go to the FlyBase site and look up the Drosophila mutations gt1, h2, enspt , kniri-1 (there are many others).
Further, there are examples of this kind of mutation that exist in multiple forms in fly populations in nature—forms that all produce not only viable adults, but fertile ones. (I dwell on flies because that’s the organism I work on, and hence know the literature.) This is the case, for example, for mutations affecting a gene involved in early-acting body segmentation.
We also know that there have not only been evolutionary changes between species in genes affecting early development, but also that those evolutionary changes were driven by natural selection. This can be demonstrated by either statistical analysis of DNA sequences of early-acting genes, or by actually making ancestral DNA, inserting it into organisms, and measuring its effect on fitness.
Although Gelernter says that “intelligent design might well be the ultimate answer,” he admits that ID has its own problems, like explaining frequent extinctions or why a Designer would intervene repeatedly over the course of evolution. Although he has no real alternative to either ID or the evolution he abhors, he does suggest that a teleological force drives evolution:
I’d expect complex biochemistry to be consistently biased in the direction that leads closer to consciousness, as gravitation biases motion towards massive objects. I have no evidence for this idea. It’s just the way biology seems to work.
Well, no, Dr. Gelernter, biology doesn’t seem to work that way. There’s nothing inherent in “complex biochemistry” or the nature of mutations to suggest such a bias, nor any evidence in the fossil record that evolution inexorably drives animals towards more and higher consciousness. Yes, that did happen in the hominin lineage and perhaps in some others like dolphins and octopuses. But remember that every living species has ancestors dating back as far as our own, yet hardly any of them are conscious in the way we are. Like us, jellyfish, sea anemones, sponges, and corals have lineages going back over a billion years, but they don’t even have brains—surely a prerequisite for consciousness. Indeed, the ancestors of echinoderms (the group that includes starfish and sea cucumbers) may have had brains but then lost them during evolution—a trend opposite to what Gelernter’s hypothesis predicts.
Ultimately, every criticism that Gelernter levels at neo-Darwinian evolution is wrong. I have pondered at length why a smart and accomplished computer scientist could engage in such a wrongheaded attempt to discredit evolutionary biology. Did he simply not bother to peruse the scientific literature? Was he credulous enough to accept the claims of ID advocates without checking them? Or does he really know better but was trying to serve a higher cause?
Although the falsity of Gelernter’s argument doesn’t depend on his motivations, there are several clues in his text. First, he derives from scripture the “factual” claim that “God created the universe, and put man there for a reason.” He notes that in arguments about evolution, “Biblical religion…forces its way into the discussion.” Well, that’s true only if you’re religious to begin with. If Gelernter’s views do indeed derive from his faith, then his god created in a very odd way.
The last lesson of Gelernter’s piece is that while we shouldn’t judge someone’s arguments by their credentials alone, neither should we give unwarranted credence to those who have impressive credentials, particularly when they pronounce on a field in which they lack expertise. Though he’s accomplished in his own area, in the end, Gelernter proves that he’s simply a garden-variety ID creationist.
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