While Nagel’s worries about neo-Darwinism are misplaced, he’s on somewhat firmer (or at least more familiar) ground when he turns to mental phenomena like consciousness. These are, after all, separate problems. A science might explain the evolution of life but leave consciousness—the subjective experience of the saltiness of popcorn, the shock of cold water, or the sting of pain—unaccounted for. Consciousness is Nagel’s big problem:
Consciousness is the most conspicuous obstacle to a comprehensive naturalism that relies only on the resources of physical science. The existence of consciousness seems to imply that the physical description of the universe, in spite of its richness and explanatory power, is only part of the truth, and that the natural order is far less austere than it would be if physics and chemistry accounted for everything.
Nagel’s story here starts, as it must, with Descartes. As Nagel writes, Descartes posited that matter and mind are “both fully real and irreducibly distinct, though they interact.” Given this, science was, from the outset, concerned solely with matter; mind belonged to a different domain. While scientists happily toiled under Cartesian dualism, giving rise to a recognizably modern science, philosophers often demurred. Instead, thinkers like Berkeley favored various forms of idealism, which maintains that nature is at bottom mind. Under idealism, then, any reductionist program would be in the business of collapsing matter to mind.
Nagel argues that as a result of a rapid shift whose causes are unclear, these idealist philosophies were “largely displaced in later twentieth-century analytic philosophy by attempts at unification in the opposite direction, starting from the physical.” This approach likely seems natural to most of us. But we live with a tension. Though the materialist program of reducing mind to matter would appear the properly “scientific” approach, we haven’t the slightest idea how it would work. And it’s not for lack of trying. Philosophers have, Nagel reminds us, attempted many ways of tying mind to matter: conceptual behaviorism, physical identity theory, causal behaviorism, and functionalism, to name a few. To Nagel all these approaches have failed “for the same old reason”:
Even with the brain added to the picture, they clearly leave out something essential, without which there would be no mind. And what they leave out is just what was deliberately left out of the physical world by Descartes and Galileo in order to form the modern concept of the physical, namely, subjective appearances.
Nagel is deeply skeptical that any species of materialist reductionism can work. Instead, he concludes, progress on consciousness will require an intellectual revolution at least as radical as Einstein’s theory of relativity.
Nagel’s chapter on consciousness is a concise and critical survey of a literature that is both vast and fascinating. He further extends his survey to other mental phenomena, including reason and value, that he also finds recalcitrant to materialism. (Nagel concludes that the existence of objective moral truths is incompatible with materialist evolutionary theory; because he is sure that moral truths exist, he again concludes that evolutionary theory is incomplete.)
Nagel concedes that many philosophers do not share his skepticism about the plausibility of reducing mind to matter. And I can assure readers that most scientists don’t. I, however, share Nagel’s sense of mystery here. Brains and neurons obviously have everything to do with consciousness but how such mere objects can give rise to the eerily different phenomenon of subjective experience seems utterly incomprehensible.
Despite this, I can’t go so far as to conclude that mind poses some insurmountable barrier to materialism. There are two reasons. The first is, frankly, more a sociological observation than an actual argument. Science has, since the seventeenth century, proved remarkably adept at incorporating initially alien ideas (like electromagnetic fields) into its thinking. Yet most people, apparently including Nagel, find the resulting science sufficiently materialist. The unusual way in which physicists understand the weirdness of quantum mechanics might be especially instructive as a crude template for how the consciousness story could play out. Physicists describe quantum mechanics by writing equations. The fact that no one, including them, can quite intuit the meaning of these equations is often deemed beside the point. The solution is the equation. One can imagine a similar course for consciousness research: the solution is X, whether you can intuit X or not. Indeed the fact that you can’t intuit X might say more about you than it does about consciousness.
And this brings me to the second reason. For there might be perfectly good reasons why you can’t imagine a solution to the problem of consciousness. As the philosopher Colin McGinn has emphasized, your very inability to imagine a solution might reflect your cognitive limitations as an evolved creature. The point is that we have no reason to believe that we, as organisms whose brains are evolved and finite, can fathom the answer to every question that we can ask. All other species have cognitive limitations, why not us? So even if matter does give rise to mind, we might not be able to understand how.
To McGinn, then, the mysteriousness of consciousness may not be so much a challenge to neo-Darwinism as a result of it. Nagel obviously draws the opposite conclusion. But the availability of both conclusions gives pause.
Given the problems that Nagel has with materialism, the obvious question is, What’s the alternative? In the most provocative part of Mind and Cosmos, he suggests one, teleology. While we often associate teleology with a God-like mind—events occur because an agent wills them as means to an end—Nagel finds theism unattractive. But he insists that materialism and theism do not exhaust the possibilities.
Instead he proposes a special species of teleology that he calls natural teleology. Natural teleology doesn’t depend on any agent’s intentions; it’s just the way the world is. There are teleological laws of nature that we don’t yet know about and they bias the unfolding of the universe in certain desirable directions, including the formation of complex organisms and consciousness. The existence of teleological laws means that certain physical outcomes “have a significantly higher probability than is entailed by the laws of physics alone—simply because they are on the path toward a certain outcome.”
Nagel intends natural teleology to be, among other things, a biological theory. It would explain not only the “appearance of physical organisms” but the “development of consciousness and ultimately of reason in those organisms.” Teleology would also provide an “account of the existence of the biological possibilities on which natural selection can operate.”
Nagel concedes that his new theory isn’t fully fleshed out. He hopes merely to sketch the outlines of a plausible alternative to materialism. It’s unfortunate, though, that Mind and Cosmos is too brief to allow consideration of problems that attend natural teleology. For it seems to me that there are some, especially where the view confronts biology.
Darwin himself wrestled with attempts to reconcile his theory with teleology and concluded, reluctantly, that it seemed implausible. While Darwin published almost nothing on such philosophical matters they loom large in his correspondence, particularly with Asa Gray, an American champion of evolution and a Christian. Gray, like Nagel, wanted to believe that, while Darwin had identified an important force in the history of life, nature also features teleology. In particular, Gray suggested that the variation provided by nature to natural selection biases the process in desirable directions.
Darwin, though sometimes vacillating, argued that Gray’s reconciliation was implausible. Exercising his uncanny ability to discern deep truths in prosaic facts—in this case the artificial selection of a pigeon breed by a few fanciers—Darwin wrote Gray:
But I grieve to say that I cannot honestly go as far as you do about Design…. You lead me to infer that you believe “that variation has been led along certain beneficial lines”.—I cannot believe this; & I think you would have to believe, that the tail of the Fan-tail was led to vary in the number & direction of its feathers in order to gratify the caprice of a few men.5
Here’s another problem. Nagel’s teleological biology is heavily human-centric or at least animal-centric. Organisms, it seems, are in the business of secreting sentience, reason, and values. Real biology looks little like this and, from the outset, must face the staggering facts of organismal diversity. There are millions of species of fungi and bacteria and nearly 300,000 species of flowering plants. None of these groups is sentient and each is spectacularly successful. Indeed mindless species outnumber we sentient ones by any sensible measure (biomass, number of individuals, or number of species; there are only about 5,500 species of mammals). More fundamentally, each of these species is every bit as much the end product of evolution as we are. The point is that, if nature has goals, it certainly seems to have many and consciousness would appear to be fairly far down on the list.
Similarly, Nagel’s teleological biology is run through with talk about the “higher forms of organization toward which nature tends” and progress toward “more complex systems.” Again, real biology looks little like this. The history of evolutionary lineages is replete with reversals, which often move from greater complexity to less. A lineage will evolve a complex feature (an eye, for example) that later gets dismantled, evolutionarily deconstructed after the species moves into a new environment (dark caves, say). Parasites often begin as “normal” complicated organisms and then lose evolutionarily many of their complex traits after taking up their new parasitic way of life. Such reversals are easily explained under Darwinism but less so under teleology. If nature is trying to get somewhere, why does it keep changing its mind about the destination?6
I’ll be the first to admit that these problems may not be fatal. But they represent the sorts of awkward facts that occur immediately to any biologist. Minimally, they pose serious challenges to teleology, challenges that deserve, but do not receive, consideration in Mind and Cosmos.
I will also be the first to admit that we cannot rule out the formal possibility of teleology in nature. It could turn out that teleological laws affect how the universe unfolds through time. While I suspect some might regard such heterodoxy as a crime against science, Nagel is right that there’s nothing intrinsically unscientific about teleology. If that’s the way nature is, that’s the way it is, and we scientists would need to get on with the business of characterizing these surprising laws. Teleological science is, in fact, more than imaginable. It’s actual, at least historically. Aristotelian science, with its concern for final cause, was thoroughly teleological. And the biological tradition that Darwinism displaced, natural theology, also featured a good deal of teleological thinking.
The question, then, is not whether teleology is formally compatible with the practice of science. The question is whether the practice of science leads to taking teleology seriously. Nagel may find this question unfair. He is, he says, engaging in a “philosophical task,” not the “internal pursuit of science.” But it seems clear that he is doing more than this. He’s emphasizing purported “empirical reasons” for finding neo-Darwinism “almost certainly false” and he’s suggesting the existence of new scientific laws. These represent moves, however halting, into science proper. But science, finally, isn’t about defining the space of all formally possible explanations of nature. It’s about inference to the most likely hypothesis. And on these grounds there’s simply no comparison between neo-Darwinism (for which there is overwhelming evidence) and natural teleology (for which there is none). While one might complain that it’s unfair to stack up the empirical successes of neo-Darwinism with those of a new theory, this, again, gets the history wrong. Teleology is the traditional view; neo-Darwinism is the new kid on the block.
None of this is to suggest that evolutionary biology will not, someday, change radically. Of course it might; any science might. Nor is it to suggest that materialism represents some final unassailable view and that teleology or, for that matter, theism will inevitably be spoken of in the past tense by many scientists. It is to say that the way to any such alternative view will have to acknowledge the full powers of present science. I cannot conclude that Mind and Cosmos does this.
5 November 26, 1860; see www.darwinp roject.ac.uk/entry-2998. Historians of science do not all agree that Darwin wholly banished teleology from his thinking; see the exchange between James G. Lennox (1993, 1994) and Michael T. Ghiselin (1994) in Biology and Philosophy. ↩
6 It’s true that organisms are on average more complex now than they were three billion years ago. But as biologists have long recognized, this doesn’t require any inexorable bias toward complexity. If life starts from a floor of zero complexity, it can on average only get more complicated. ↩
November 26, 1860; see www.darwinp roject.ac.uk/entry-2998. Historians of science do not all agree that Darwin wholly banished teleology from his thinking; see the exchange between James G. Lennox (1993, 1994) and Michael T. Ghiselin (1994) in Biology and Philosophy. ↩
It’s true that organisms are on average more complex now than they were three billion years ago. But as biologists have long recognized, this doesn’t require any inexorable bias toward complexity. If life starts from a floor of zero complexity, it can on average only get more complicated. ↩