The history of science is partly the history of an idea that is by now so familiar that it no longer astounds: the universe, including our own existence, can be explained by the interactions of little bits of matter. We scientists are in the business of discovering the laws that characterize this matter. We do so, to some extent at least, by a kind of reduction. The stuff of biology, for instance, can be reduced to chemistry and the stuff of chemistry can be reduced to physics.
Thomas Nagel has never been at ease with this view. Nagel, University Professor of Philosophy and Law at New York University, is one of our most distinguished philosophers. He is perhaps best known for his 1974 paper, “What Is It Like to Be a Bat?,” a modern classic in the philosophy of mind. In that paper, Nagel argued that reductionist, materialist accounts of the mind leave some things unexplained. And one of those things is what it would actually feel like to be, say, a bat, a creature that navigates its environment via the odd (to us) sense of echolocation. To Nagel, then, reductionist attempts to ground everything in matter fail partly for a reason that couldn’t be any nearer to us: subjective experience. While not denying that our conscious experiences have everything to do with brains, neurons, and matter, Nagel finds it hard to see how these experiences can be fully reduced with the conceptual tools of physical science.
In Mind and Cosmos, Nagel continues his attacks on reductionism. Though the book is brief its claims are big. Nagel insists that the mind-body problem “is not just a local problem” but “invades our understanding of the entire cosmos and its history.” If what he calls “materialist naturalism” or just “materialism” can’t explain consciousness, then it can’t fully account for life since consciousness is a feature of life. And if it can’t explain life, then it can’t fully account for the chemical and physical universe since life is a feature of that universe. Subjective experience is not, to Nagel, some detail that materialist science can hand-wave away. It’s a deal breaker. Nagel believes that any future science that grapples seriously with the mind-body problem will be one that is radically reconceived.
As Nagel makes clear in the subtitle of Mind and Cosmos, part of what he thinks must be reconceived is our reigning theory of evolutionary biology, neo-Darwinism. Neo-Darwinism maintains, or at least implies, that the origin and history of life can be explained by materialist means. Once the first life arose on earth, the fate of the resulting evolutionary lineage was, neo-Darwinists argued, shaped by a combination of random mutation and natural selection. Biological types that survive or reproduce better than others will ultimately replace those others. While natural selection ensures that species constantly adapt to the changing environments around them, the process has no foresight: natural selection responds only to the present environment and evolution cannot, therefore, be aiming for any goal. This view, Nagel tells us, is “almost certainly false.”
Before creationists grow too excited, it’s important to see what Nagel is not claiming. He is not claiming that life is six thousand years old, that it did not evolve, or that natural selection played no part in this evolution. He believes that life has a long evolutionary history and that natural selection had a part in it. And while he does believe that intelligent design creationists have asked some incisive questions, Nagel rejects their answers. Indeed he is an atheist. Instead Nagel’s view is that neo-Darwinism, and in fact the whole materialist view elaborated by science since the seventeenth century, is radically incomplete. The materialist laws of nature must, he says, be supplemented by something else if we are to fold ourselves and our minds fully into our science.
His leading contender for this something else is teleology, a tendency of the universe to aim for certain goals as it unfolds through time. Nagel believes that (currently unknown) teleological laws of nature might mean that life and consciousness arise with greater probability than would result from the known laws of physics, chemistry, and biology.
Scientists shouldn’t be shocked by Nagel’s claim that present science might not be up to cracking the mind-brain problem or that a profoundly different science might lie on the horizon. The history of science is filled with such surprising transformations. Nor should we dismiss Nagel’s claims merely because they originate from outside science, from a philosopher. Much the same thing happened when natural theology—the scientific attempt to discern God’s attributes from His biological handiwork—gave way to Darwinism.
It was the philosopher David Hume who began to dismantle important aspects of natural theology. In a devastating set of arguments, Hume identified grievous problems with the argument from design (which claims, roughly, that a designer must exist because organisms show intricate design). Hume was not, however, able to offer an alternative account for the apparent design in organisms. Darwin worked in Hume’s wake and finally provided the required missing theory, natural selection. Nagel, consciously or not, now aspires to play the part of Hume in the demise of neo-Darwinism. He has, he believes, identified serious shortcomings in neo-Darwinism. And while he suspects that teleological laws of nature may exist, he recognizes that he hasn’t provided anything like a full theory. He awaits his Darwin.
Mind and Cosmos is certainly provocative and it reflects the efforts of a fiercely independent mind. In important places, however, I believe that it is wrong. Because Nagel’s book sits at the intersection of philosophy and science it will surely attract the attention of both communities.1 As a biologist, I will perhaps inevitably focus on Nagel’s more scientific claims. But these are, it appears, the claims that are most responsible for the excitement over the book.
I begin by considering the reasons Nagel believes that materialist science, including neo-Darwinism, is false. I then turn to his alternative theory, teleology.
Nagel believes that materialism confronts two classes of problems. One, which is new to Nagel’s thought, concerns purported empirical problems with neo-Darwinism. The other, which is more familiar to philosophers, is the alleged failure of materialism to explain consciousness and allied mental phenomena.
Nagel argues that there are purely “empirical reasons” to be skeptical about reductionism in biology and, in particular, about the plausibility of neo-Darwinism. Nagel’s claims here are so surprising that it’s best to quote them at length:
I would like to defend the untutored reaction of incredulity to the reductionist neo-Darwinian account of the origin and evolution of life. It is prima facie highly implausible that life as we know it is the result of a sequence of physical accidents together with the mechanism of natural selection. We are expected to abandon this naïve response, not in favor of a fully worked out physical/chemical explanation but in favor of an alternative that is really a schema for explanation, supported by some examples. What is lacking, to my knowledge, is a credible argument that the story has a nonnegligible probability of being true. There are two questions. First, given what is known about the chemical basis of biology and genetics, what is the likelihood that self-reproducing life forms should have come into existence spontaneously on the early earth, solely through the operation of the laws of physics and chemistry? The second question is about the sources of variation in the evolutionary process that was set in motion once life began: In the available geological time since the first life forms appeared on earth, what is the likelihood that, as a result of physical accident, a sequence of viable genetic mutations should have occurred that was sufficient to permit natural selection to produce the organisms that actually exist?
Nagel claims that both questions concern “highly specific events over a long historical period in the distant past, the available evidence is very indirect, and general assumptions have to play an important part.” He therefore concludes that “the available scientific evidence, in spite of the consensus of scientific opinion, does not in this matter rationally require us to subordinate the incredulity of common sense.”
This conclusion is remarkable in a couple ways. For one thing, there’s not much of an argument here. Instead Nagel’s conclusion rests largely on the strength of his intuition. His intuition recoils from the claimed plausibility of neo-Darwinism and that, it seems, is that. (Richard Dawkins has called this sort of move the argument from personal incredulity.) But plenty of scientific truths are counterintuitive (does anyone find it intuitive that we’re hurtling around the sun at 67,000 miles per hour?) and a scientific education is, to a considerable extent, an exercise in taming the authority of one’s intuition. Nagel never explains why his intuition should count for so much here.
As for his claim that evolutionary theory is somewhat schematic and that it concerns events that happened long ago, leaving indirect evidence, this is partly true of any historical science, including any alternative to neo-Darwinism, e.g., the one that Nagel himself suggests. In any case, a good part of the evidence for neo-Darwinism is not indirect but involves experiments in which evolutionary change is monitored in real time.2
More important, Nagel’s conclusions about evolution are almost certainly wrong. The origin of life is admittedly a hard problem and we don’t know exactly how the first self-replicating system arose. But big progress has been made. The discovery of so-called ribozymes in the 1980s plausibly cracked the main principled problem at the heart of the origin of life. Research on life’s origin had always faced a chicken and egg dilemma: DNA, our hereditary material, can’t replicate without the assistance of proteins, but one can’t get the required proteins unless they’re encoded by DNA. So how could the whole system get off the ground?
Answer: the first genetic material was probably RNA, not DNA. This might sound like a distinction without a difference but it isn’t. The point is that RNA molecules can both act as a hereditary material (as DNA does) and catalyze certain chemical reactions (as some proteins do), possibly including their own replication. (An RNA molecule that can catalyze a reaction is called a ribozyme.) Consequently, many researchers into the origins of life now believe in an “RNA world,” in which early life on earth was RNA-based. “Physical accidents” were likely still required to produce the first RNA molecules, but we can now begin to see how these molecules might then self-replicate.
Nagel’s astonishment that a “sequence of viable genetic mutations” has been available to evolution over billions of years is also unfounded.3 His concern appears to be that evolution requires an unbroken chain of viable genetic variants that connect the first living creature to, say, human beings. How could nature ensure that a viable mutation was always available to evolution? The answer is that it didn’t. That’s why species go extinct. Indeed that’s what extinction is. The world changes and a species can’t find a mutation fast enough to let it live. Extinction is the norm in evolution: the vast majority of all species have gone extinct. Nagel has, I think, been led astray by a big survivorship bias: the evolutionary lineage that led to us always found a viable mutation, ergo one must, it seems, always be available. Tyrannosaurus rex would presumably be less impressed by nature’s munificence.4
1 Nagel’s work has long attracted the attention of both philosophers and scientists. Indeed the careful reader will notice that I’m mentioned in his new book as a scientist-participant in a workshop that he organized on some of the topics covered in the book; many of the other participants were philosophers. ↩
2 The field of “experimental evolution” is concerned with watching evolution as it occurs. Because of their short generation time, microbes are the focus of much of this work. ↩
3 While I’ve heard this concern before, I must admit that I think I only now understand it. ↩
4 This is not to say that adaptation is rare or that natural selection doesn’t modify the DNA sequences of species. Even species that ultimately go extinct have experienced many previous bouts of successful adaptation. ↩
Nagel’s work has long attracted the attention of both philosophers and scientists. Indeed the careful reader will notice that I’m mentioned in his new book as a scientist-participant in a workshop that he organized on some of the topics covered in the book; many of the other participants were philosophers. ↩
The field of “experimental evolution” is concerned with watching evolution as it occurs. Because of their short generation time, microbes are the focus of much of this work. ↩
While I’ve heard this concern before, I must admit that I think I only now understand it. ↩
This is not to say that adaptation is rare or that natural selection doesn’t modify the DNA sequences of species. Even species that ultimately go extinct have experienced many previous bouts of successful adaptation. ↩