Thomas Nagel, a professor of philosophy and of law at New York University, has made his reputation over the last fifty years as a leading contributor to moral and political philosophy, with occasional forays into the philosophy of mind. Most famously, and most relevant to his new book, Mind and Cosmos, he wrote an influential paper in the 1970s with the memorable title “What Is It Like to Be a Bat?” Nagel tried to demonstrate the implausibility of the notion that, even if one knew all the relevant physical facts about the brains of bats, one could have any idea what it felt like to be a bat. How could the subjective feeling of this experience be captured by a set of cold, objective biological and chemical facts about neurons? Nagel’s new book revisits some of these ideas and aims to “develop the rival alternative conceptions” to what he calls the “materialism and Darwinism” of our age.
Nagel’s is the latest in what has become a small cottage industry involving a handful of prominent senior philosophers expressing skepticism about aspects of Darwin’s theory of evolution by natural selection. Some, like the overtly Christian philosopher Alvin Plantinga, have made a career of dialectical ingenuity in support of the rationality of religious faith. Others, such as Jerry Fodor, are avowed atheists like Nagel, and have only tried to raise challenges to discrete aspects of evolutionary explanations for biological phenomena. Plantinga’s influence has largely been limited to other religious believers, while Fodor’s challenge was exposed rather quickly by philosophers as trading on confusions (even Nagel disowns it in a footnote). Nagel now enters the fray with a far-reaching broadside against Darwin and materialism worthy of the true-believing Plantinga (whom Nagel cites favorably). We suspect that philosophers—even philosophers sympathetic to some of Nagel’s concerns—will be disappointed by the actual quality of the argument.
Nagel opposes two main components of the “materialist” view inspired by Darwin’s theory of evolution by natural selection. The first is what we will call theoretical reductionism, the view that there is an order of priority among the sciences, with all theories ultimately derivable from physics and all phenomena ultimately explicable in physical terms. We believe, along with most philosophers, that Nagel is right to reject theoretical reductionism, because the sciences have not progressed in a way consistent with it. We have not witnessed the reduction of psychology to biology, biology to chemistry, and chemistry to physics, but rather the proliferation of fields like neuroscience and evolutionary biology that explain psychological and biological phenomena in terms unrecognizable by physics. As the philosopher of biology Philip Kitcher pointed out some thirty years ago, even classical genetics has not been fully reduced to molecular genetics, and that reduction would have been wholly within one field. We simply do not see any serious attempts to reduce all the “higher” sciences to the laws of physics.
Yet Nagel argues in his book as if this kind of reductive materialism really were driving the scientific community. The only named target is the Nobel Prize–winning physicist Steven Weinberg, famous for his defense of the primacy of physics in such popular works as Dreams of a Final Theory (1992). Here is what Nagel writes in describing Weinberg’s view:
My target is a comprehensive, speculative world picture that is reached by extrapolation from some of the discoveries of biology, chemistry, and physics—a particular naturalistic Weltanschauung that postulates a hierarchical relation among the subjects of those sciences, and the completeness in principle of an explanation of everything in the universe through their unification. Such a world view is not a necessary condition of the practice of any of those sciences, and its acceptance or nonacceptance would have no effect on most scientific research.
Nagel here aligns himself, as best we can tell, with the majority view among both philosophers and practicing scientists. Just to take one obvious example, very little of the actual work in biology inspired by Darwin depends on reductive materialism of this sort; evolutionary explanations do not typically appeal to Newton’s laws or general relativity. Given this general consensus (the rhetoric of some popular science writing by Weinberg and others aside), it is puzzling that Nagel thinks he needs to bother attacking theoretical reductionism.
The second component of the thesis Nagel opposes is what we will call naturalism, the view that features of our world—including “consciousness, intentionality, meaning, purpose, thought, and value”—can ultimately be accounted for in terms of the natural processes described by the various sciences (whether or not they are ever “reduced” to physics). Nagel’s arguments here are aimed at a more substantial target, although he gives us few specifics about the kind of naturalism he opposes. He does characterize it as the attempt to explain everything “at the most basic level by the physical sciences, extended to include biology,” and the one named proponent of this view is the philosopher Daniel Dennett. Although Dennett would not characterize his project as trying to explain everything at the “most basic level,” he does aim to show that phenomena such as consciousness, purpose and thought find a natural home in a picture of human beings inspired by Darwin. In the absence of any clearer statement of the argument, we will assume that this is the so-called “neo-Darwinian” picture that Nagel opposes.
Naturalists, including Dennett, defend their view by appealing to the extraordinary fruitfulness of past scientific work, including work growing out of Darwin’s theory of evolution by natural selection. So what should we make of the actual work in biology that supports the “materialist Neo-Darwinian conception of nature” that Nagel thinks “is almost certainly false”? Defending such a sweeping claim might seem to require a detailed engagement with the relevant science, yet in a striking admission early on, Nagel reveals that his book “is just the opinion of a layman who reads widely in the literature that explains contemporary science to the nonspecialist.” And a recurring objection to what he learned from his layman’s reading of popular science writing is that much science “flies in the face of common sense,” that it is inconsistent with “evident facts about ourselves, that it “require[s] us to deny the obvious,” and so on.
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This style of argument does not, alas, have a promising history. After all, what could be more common-sensical, obvious or evident than the notion that the earth is flat and the sun revolves around the earth? All ordinary evidence supports that verdict: we know from experience that people fall off things that are spherical, especially when trying to hang upside down from them, and we know that the sun rises in the sky in one direction and sets in the other as it revolves around the seemingly flat earth. Happily, Nagel does not attempt to repudiate the Copernican revolution in astronomy, despite its hostility to common sense. But he displays none of the same humility when it comes to his preferred claims of common sense—the kind of humility that nearly 400 years of nonevident yet true scientific discoveries should engender. Are we really supposed to abandon a massively successful scientific research program because Nagel finds some scientific claims hard to square with what he thinks is obvious and “undeniable,” such as his confidence that his “clearest moral…reasonings are objectively valid”?
In support of his skepticism, Nagel writes: “The world is an astonishing place, and the idea that we have in our possession the basic tools needed to understand it is no more credible now than it was in Aristotle’s day.” This seems to us perhaps the most startling sentence in all of Mind and Cosmos. Epistemic humility—the recognition that we could be wrong—is a virtue in science as it is in daily life, but surely we have some reason for thinking, some four centuries after the start of the scientific revolution, that Aristotle was on the wrong track and that we are not, or at least not yet. Our reasons for thinking this are obvious and uncontroversial: mechanistic explanations and an abandonment of supernatural causality proved enormously fruitful in expanding our ability to predict and control the world around us. The fruits of the scientific revolution, though at odds with common sense, allow us to send probes to Mars and to understand why washing our hands prevents the spread of disease. We may, of course, be wrong in having abandoned teleology and the supernatural as our primary tools for understanding and explaining the natural world, but the fact that “common sense” conflicts with a layman’s reading of popular science writing is not a good reason for thinking so.
Incompatibility with common sense is not Nagel’s only argument against naturalism. A second line of argument begins by appealing to what he takes to be an everyday opinion: that there are objective moral, logical and mathematical truths. He then argues that the existence of these kinds of objective truths is incompatible with naturalism. For the moral case, Nagel asks: If our moral faculties are simply the result of evolution, how can they be reliable measures of objective moral truth? Why should evolution prefer the perception of moral truth to whatever happens to be advantageous for reproduction? Thus, if some of our moral beliefs really are objectively true, then they cannot be the result of evolution. And because he is confident that we do know some objective moral truths, Nagel concludes that “a Darwinian account of the motives underlying moral judgment must be false, in spite of the scientific consensus in its favor.” Recognizing that readers will find this inference jarring, Nagel adds: “I, even more strangely, am relying on a philosophical claim to refute a scientific theory supported by empirical evidence.”
There is, indeed, much that is strange here. To begin, there is nothing remotely common-sensical about Nagel’s confidence in the objectivity of moral truth. While Nagel and his compatriots apparently take very seriously their moral opinions—so seriously that they find it incredible to suggest that their “confidence in the objective truth of [their] moral beliefs” might, in fact, be “completely illusory”—this can hardly claim the mantle of “the common sense view.” Ordinary opinion sometimes tends toward objectivism, to be sure—often by relying on religious assumptions that Nagel explicitly rejects—but it also often veers toward social or cultural relativism about morality. Whether morality is truly objective is a philosopher’s claim (and a controversial one even among philosophers) about which “common sense” is either agnostic or mixed.
We take no stance on Nagel’s hypothesis that if our moral faculties are simply the result of evolution, they cannot be reliable measures of objective moral truth. But we should note that Nagel’s colleague, philosopher Sharon Street, accepts it and draws the opposite conclusion. She argues that because this hypothesis is true, and because we are obviously the products of evolution, we should give up the idea that there are objective moral truths in Nagel’s sense. Given the philosophical plausibility of Street’s alternative response—not to mention the simplistic evolutionary reasoning the whole debate is predicated on—it is hard to see why any biologist should be given pause by Nagel’s argument.
A more interesting challenge—really, the only interesting philosophical point raised in the book—concerns logical and mathematical truths. Is it possible, Nagel asks, to reconcile a naturalistic and biological picture of the evolution of our cognitive capacities with the confidence we have in our ability to do logic and mathematics? Nagel’s argument invokes a contrast with our perceptual capabilities, because our ability to reliably perceive many of the features of our physical environment seems likely to have an evolutionary explanation. (After all, if we could not reliably spot sudden cliffs or saber-toothed tigers, our reproductive fitness would be seriously compromised!) But logical truths are not like that, Nagel argues. It is self-evident that something cannot be both red and not-red at the same time (the “law of non-contradiction”). So, too, it is self-evident that if all men are mortal, and Socrates is a man, then Socates is necessarily mortal. Even if evolution endowed us with the capacity to recognize the law of non-contradiction and to draw valid deductive inferences, how does it explain the obvious truth of these logical claims? Nagel’s response to this question is that evolution cannot—and the problem is even worse than that:
Any evolutionary account of the place of reason presupposes reason’s validity and cannot confirm it without circularity.
Eventually the attempt to understand oneself in evolutionary, naturalistic terms must bottom out in something that is grasped as valid in itself—something without which the evolutionary understanding would not be possible.
In other words, even if one thinks there is an evolutionary explanation for why we recognize the obviousness of logical, mathematical and scientific truths, there would still be the question of why we think evolutionary theory itself is justified. An evolutionary explanation of that latter fact would have to presuppose the correctness of the theory whose justification we are questioning, making the argument circular: we would have to assume that evolutionary theory is true in order to investigate whether it is true!
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There is a response to this kind of challenge, one that is widely embraced by philosophical naturalists (though, again, not mentioned by Nagel). This response starts by noting that we determine what is “rational” or “justified” simply by appealing to the most successful forms of inquiry into the world that human beings have developed. Paradigmatic examples of those successful forms of inquiry are, of course, physics, chemistry and biology. They are successful precisely in the way that Aristotelian science was not: they enable us to navigate the world around us, to predict its happenings and control some of them. To confuse one’s intuitive confidence in the logical and epistemic norms that make these sciences possible with some kind of a priori access to the “rational order of the world,” as Nagel puts it, is to forget whence that confidence derives—namely, the very success of these sciences. For philosophical naturalists, the charge of circularity is empty, akin to suggesting that the need for a usable table to have legs requires some justification beyond the fact that the legs actually do a necessary job.
Philosophical naturalists often appeal to the metaphor of “Neurath’s Boat,” named after the philosopher who developed it. Our situation as inquirers trying to understand the world around us, according to Neurath, is like that of sailors who must rebuild their ship while at sea. These sailors do not have the option of abandoning the ship and rebuilding a new one from scratch. They must, instead, try to rebuild it piecemeal, all the time staying afloat on other parts of the ship on which they continue to depend. In epistemological terms, we are also “at sea”: we cannot abandon all the knowledge about the world we have acquired from the sciences and then ask what we really know or what is really rational. The sciences that have worked so well for us are precisely our benchmark for what we know and what is rational; they’re the things that are keeping us “afloat.” Extending this metaphor, we can say that Nagel is the sailor who says, “I know the ideal form a ship should take—it is intuitively obvious, I am confident in it—so let us jump into the ocean and start building it from scratch.”
We agree with Nagel that if the sciences could not explain our capacity to have thoughts about the world around us, that would be a serious failing and a reason to call their findings into question. But they can and they do! It is here that Nagel’s lack of engagement with contemporary cognitive science and his idiosyncratic views about what a scientific explanation should look like make his argument especially perplexing. He writes, in what might seem a massive concession to his naturalistic opponents, “The appearance of animal consciousness is evidently the result of biological evolution, but this well-supported empirical fact is not yet an explanation—it does not provide understanding, or enable us to see why the result was to be expected or how it came about.” On Nagel’s view, consciousness arose from evolution, but despite knowing this fact, we have not explained the origin of consciousness. In a similar vein, Nagel writes:
It is not an explanation to say just that the physical process of evolution has resulted in creatures with eyes, ears, central nervous systems, and so forth, and that it is simply a brute fact of nature that such creatures are conscious in the familiar ways. Merely to identify a cause is not to provide a significant explanation, without some understanding of why the cause produces the effect.
Nagel endorses the idea that explanation and prediction are symmetrical: “An explanation must show why it was likely that an event of that type occurred.” In other words, to explain something is to be in a position to have predicted it if we could go back in time. He also writes, “To explain consciousness, a physical evolutionary history would have to show why it was likely that organisms of the kind that have consciousness would arise.” Indeed, he goes further, claiming that “the propensity for the development of organisms with a subjective point of view must have been there from the beginning.”
This idea, however, is inconsistent with the most plausible views about prediction and explanation, in both philosophy and science. Philosophers of science have long argued that explanation and prediction cannot be fully symmetrical, given the importance of probabilities in explaining natural phenomena. Moreover, we are often in a position to understand the causes of an event, but without knowing enough detail to have predicted it. For example, approximately 1 percent of children born to women over 40 have Down syndrome. This fact is a perfectly adequate explanation of why a particular child has Down syndrome, but it does not mean we could have predicted that this particular child would develop it. Causes alone are frequently deemed sufficient to explain events; knowing enough to predict those events in advance is an important scientific achievement, but not essential to explanation.
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Nagel doesn’t think so, and because of that, he advocates the reintroduction of teleological reasoning into science. (Teleology—the idea that natural phenomena have built-in purposes or ends—was central to Aristotelian science, and it remained very influential until the scientific revolution.) In his discussion of the origin of life, Nagel says that natural teleology would mean that, “in addition to physical law of the familiar kind, there are other laws of nature that are ‘biased toward the marvelous.’”
This is an astonishing though certainly evocative phrase (Nagel adapts it from another writer), yet Nagel offers no further explication of it. He does admit that this proposal “flies in the teeth of the authoritative form of explanation that has defined science since the revolution of the seventeenth century.” Unfortunately, he is also extremely unclear about what he means by “natural teleology,” other than assuring the reader that it is neither part of standard physical laws nor the introduction of theology. One might think that “principles of self-organization or of the development of complexity over time,” which Nagel gives as examples of natural teleology, are the sort of things studied by mainstream protein chemists, developmental biologists and condensed-matter physicists. But apparently these sciences, which study how complex order can be built up from simple physical processes, are not on the right track. Nagel never explains why.
We conclude with a comment about truth in advertising. Nagel’s arguments against reductionism are quixotic, and his arguments against naturalism are unconvincing. He aspires to develop “rival alternative conceptions” to what he calls the materialist neo-Darwinian worldview, yet he never clearly articulates this rival conception, nor does he give us any reason to think that “the present right-thinking consensus will come to seem laughable in a generation or two.” Mind and Cosmos is certainly an apt title for Nagel’s philosophical meditations, but his subtitle—”Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False”—is highly misleading. Nagel, by his own admission, relies only on popular science writing and brings to bear idiosyncratic and often outdated views about a whole host of issues, from the objectivity of moral truth to the nature of explanation. No one could possibly think he has shown that a massively successful scientific research program like the one inspired by Darwin’s theory of evolution by natural selection “is almost certainly false.” The subtitle seems intended to market the book to evolution deniers, intelligent-design acolytes, religious fanatics and others who are not really interested in the substantive scientific and philosophical issues. Even a philosopher sympathetic to Nagel’s worries about the naturalistic worldview would not claim this volume comes close to living up to that subtitle. Its only effect will be to make the book an instrument of mischief.
Why has natural selection always been the most contested part of evolutionary theory? asks Jeffrey A. Coyne in “The Improbability Pump ” (May 10, 2010), reviewing The Greatest Show on Earth, by Richard Dawkins, and Jerry Fodor and Massimo Piattelli-Palmarini’s What Darwin Got Wrong.