Thomas Nagel, Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False
Oxford University Press, $24.95 (cloth)
Thomas Nagel, a distinguished philosopher at NYU, is well known for his critique of materialistic reductionism as an account of the mind-body relationship. In his new and far-reaching book Mind and Cosmos, Nagel extends his attack on materialistic reductionismwhich he describes as the thesis that physics provides a complete explanation of everythingwell beyond the mind-body problem. He argues that evolutionary biology is fundamentally flawed and that physics also needs to be rethoughtthat we need a new way to do science.
Nagels new way is teleologicalscientific explanations need to invoke goals, not just mechanistic causes. The conventional story of the emergence of modern science maintains that Galileo and Newton forever banished Aristotles teleology. So Mind and Cosmos is an audacious book, bucking the tide. Nagel acknowledges that he has no teleological theory of his own to offer. His job, as he sees it, is to point to a need; creative scientists, he hopes, will do the heavy lifting.
Nagels rejection of materialistic reductionism does not stem from religious conviction. He says that he doesnt have a religious bone in his body. The new, teleological science he wants is naturalistic, not supernaturalistic. This point needs to be remembered, given that the book begins with kind words for proponents of intelligent design. Nagel applauds them for identifying problems in evolutionary theory, but he does not endorse their solution.
Nagels main goal in this book is not to argue against materialistic reductionism, but to explore the consequences of its being false. He has argued against the -ism elsewhere, and those who know their Nagel will be able to fill in the details. But new readers may be puzzled, so a little backstory may help.
In his famous 1974 article What is it like to be a bat? Nagel argues that current science lacks the concepts that would allow us to understand how subjective experience is possible. Present-day science can give us information about the bats brain, but it cannot answer the titular question of Nagels articlewhat is it like, how does it feel from the inside, to be a bat? Nagel chooses bats as his example because they have a sensory system (echolocation) that we lack. This choice makes the problem vivid, but Nagel thinks the difficulty arises at home: each of us knows what sugar tastes like, yet current science lacks the vocabulary to understand and explain what that peculiar subjective experience is like. Nagel is cautious in the bat article; he hopes that a future materialistic science might be able to do better.
In Mind and Cosmos, Nagel holds that materialism cant deliver the goods. Drawing on his bolder and more recent paper The Psychophysical Nexus, he now says that materialistic reductionism is false, not that we currently dont understand how it could be true. For Nagel, perception and other psychological processes involve irreducibly subjective facts; important aspects of the mind are, therefore, forever beyond the reach of physical explanation.
This position is compatible with many doctrines that are associated with materialism. For example, Nagel doesnt gainsay the slogan no difference without a physical differenceif you and I have different psychological properties, then we must be physically different. Indeed, Nagels position is even compatible with the idea that every mental property is identical with some physical propertyfor example, it may be that being in pain and being in some neurophysiological state X are identical in the same way that being made of water and being made of H2O are identical properties. The problem, Nagel thinks, is that this identity claim, if true, cannot in principle be explained by physics. Mind and Cosmos begins with the thesis that materialistic reductionism hits a roadblock with the mind-body problem, but there are others ahead. Although Nagel has more to say about the mind-body problem than I have just outlined, the most novel part of his book, and my focus, lies elsewhere.
Nagel believes that evolutionary biology is in trouble, but what sort of trouble is it in? There are two possibilities. Evolutionary theory could be in trouble just because it is committed to materialistic reductionism; if so, the theory would be perfectly okay if it dropped that commitment. Understood in this way, its the philosophy that has gone wrong, not the biology. But much of what Nagel says is not in this vein. He thinks that the biology itself is flawed. Even without a commitment to materialistic reductionism, the theory would be in bad shape. For Nagel, the combination of evolutionary theory and materialistic reductionism is false, while evolutionary theory taken on its own (without the philosophical add-on) is incomplete. Incompleteness means that the theory cannot fully explain important biological events.
For Nagel, important aspects of the mind are forever beyond the reach of physical explanation.
Here I want to consider two criticisms that Nagel makes of evolutionary theory. The first concerns probability, the second, ethics. Neither criticism depends on the idea that evolutionary theory is committed to materialistic reductionism.
Nagel thinks that adequate explanations of the origins of life, intelligence, and consciousness must show that those events had a significant likelihood of occurring: these origins must be shown to be unsurprising if not inevitable. A complete account of consciousness must show that consciousness was something to be expected. Nagel thinks that evolutionary theory as we now have it fails in this regard, so it needs to be supplemented.
Nagel doesnt impose this condition of adequate explanation on all the events that science might address. He is prepared to live with the fact that some events are just flukes or accidents or improbable coincidences. For example, it may just be an improbable coincidence that in the mid-1980s Evelyn Marie Adams won the New Jersey lottery twice in the span of four months. But the existence of life, intelligence, and consciousness are not in the same category. Why do Nagels standards go up when he contemplates facts that he deems remarkable? Maybe the answer falls under what Nagel refers to, in a different context, as his ungrounded intellectual preference. It isnt theistic conviction that is doing the work here, but rather Nagels faith that the remarkable facts he mentions must be intelligible, where intelligibility requires that these facts had a significant probability of being true.
My philosophical feelings diverge from Nagels. I think that Beethovens existence is remarkable, but I regard it as a fluke. He could easily have failed to exist. Indeed, my jaded complacency about Beethoven scales up. I dont think that life, intelligence, and consciousness had to be in the cards from the universes beginning. I am happy to leave this question to the scientists. If they tell me that these events were improbable, I do not shake my head and insist that the scientists must be missing something. There is no such must. Something can be both remarkable and improbable.
Moreover, if an improbable state of affairs comes to pass, this does not mean that the state of affairs is unintelligible. Consider: mom and dad have two daughters. Why are both children female? A simple Mendelian answer is that all of moms eggs had an X chromosome while half of dads sperm had an X and half had a Y. The process of fertilization randomly combines an egg from mom with a sperm from dad. This means that the chance of a daughter is 1/2, so the chance of two daughters is 1/4. We explain the two-daughter outcome not by showing that it was to be expected, but by elucidating the process that produced the outcome with a certain probability. Before you insist that the Mendelian story doesnt really explain the outcome, reflect on whether you think that the Mendelian story sheds no light at all on why the parents had two daughters. Surely it does not leave us totally in the dark.
In thinking about Nagels probability argument, we need to be careful about which facts we are considering. The fact that life on earth started some 3.8 billion years ago, and that intelligence and consciousness made their terrestrial appearances more recentlythis is a local fact about our planet, and maybe it was very improbable, given how the universe got started. But consider the more global fact that the universe contains life and intelligence and consciousness at some time in its total history. Whats the probability of that, given the universes initial state? Science doesnt really have much of a clue (yet), but this gap in our present knowledge does not show that fundamental presuppositions of the sciences need rethinking. After all, conventional science does tell us that the universe is a very big place with lots of planets that are about as close to their stars as our planet is to the sun. Maybe life and intelligence and consciousness had a high probability of arising (someplace and sometime, not necessarily on earth in the last 3.8 billion years). If this global fact is the remarkable fact that Nagel has in mind, he should not conclude that biology needs to be supplied with new organizing principles. Do not confuse the proposition that Evelyn Marie Adams won the New Jersey lottery twice in four months with the proposition that someone won some state lottery or other twice, at some time or other. The first was very improbable, the second much less so.
Before leaving the topic of probability, I want to highlight what is involved in Nagels requirement that the facts he says are remarkable must be shown to be unsurprising. For the sake of concreteness, lets take this to mean that the probability must be greater than 1/2. Suppose that to get from the universes first moment to the origin of consciousness, 200 stages must be traversed. The universe starts at stage S1, then it needs to pass to S2, then to S3, and so on, until it reaches S200, at which time consciousness makes its first appearance. Suppose further that we have a theory that says that the probability of going from each of these stages to the next is 99/100: this means that each individual step is very likely. Still, the probability of going from S1 all the way to S200 is (99/100)199, or about 1/10. The demand that the origin of consciousness must have had a probability greater than 1/2 entails that the theory I just described must be wrong or seriously incomplete.
I agree that it might be wrong or incomplete, but this is not because it violates Nagels demand that we must show remarkable facts to be likely. In addition, I think that a theory of this sort could shed considerable light on why consciousness arose. It doesnt show that the event was to be expected, given the universes initial state. Instead, if true, it elucidates the step-wise process that produced the outcome we observe. When a theory says that X was improbable, this does not mean that the theory says that X is unintelligible: the final result could be improbable even though each step in the process was highly likely.
The words belief and desire do not occur in theories in physics, yet you and I have beliefs and desires.
What makes more sense than Nagels probability requirement is one about possibilitythat an adequate theory must allow that the origin of life, mind, and consciousness all were possible, given the initial state of the universe. If this were all that Nagel meant by his claim that the propensity for the development of organisms with a subjective point of view must have been there from the beginning, I would have no quarrel. But then there would be no objection to the sciences we now have.
Not only does Nagel require that remarkable facts be fairly probable; he also insists that they cant be byproducts (a.k.a. side effects). He applies this requirement to the appearance of minds, consciousness, and reasoning. Nagel doesnt reject all byproduct explanations. For example, he is comfortable with the standard evolutionary account of why vertebrate blood is red. This didnt happen because there was an adaptive advantage in having red blood. Rather, the hemoglobin molecule was selected because it transports oxygen to tissues, and hemoglobin just happens to make our blood red. And it isnt only useless traits such as the color of blood that evolutionary biology says are byproducts. Sea turtles use their limbs to dig nests in the sand when they come out of the water to lay their eggs, but the tetrapod arrangement evolved long before turtles developed this behavior. Being able to build nests in sand is a side effect. Evolution often recruits old structures to new uses.
Evolutionary biology leaves open the possibility that even Nagels remarkable facts are byproducts. For instance, the co-discoverers of the theory of evolution by natural selection, Darwin and Alfred Russel Wallace, disagreed about how the human capacity for abstract theoretical reasoning should be explained. Darwin saw it as a byproduct. There was selection for reasoning well in situations that made a difference for survival and reproduction, and our capacity to reason about mathematics and natural science and philosophy is a happy byproduct. Wallace, on the other hand, thought that a spiritualistic explanation was needed. Nagel finds Darwins side effect account very far-fetched, but he does not say why.
I now turn to Nagels second reason for thinking that something is seriously amiss with current evolutionary theory. Nagel is what philosophers call a moral realist. This doesnt mean he has the cynicism of a Humphrey Bogart character. It means he thinks that some statements about right and wrong are true and that what makes them true isnt anyones say-so. Nor are they made true by the fact that we would come to believe them if we engaged in a certain type of deliberation. For Nagel, the statement that causing suffering is bad is like the statement that the Rocky Mountains are more than 10,000 feet tallboth are true independently of whether anyone thinks they are true. Nagel thinks moral realism is incompatible with a Darwinian account of the evolutionary influence on our faculties of moral and evaluative judgment. He resolves the conflict as follows: since moral realism is true, a Darwinian account of the motives underlying moral judgment must be false.
Why does Nagel think that evolutionary theory conflicts with moral realism? His reasoning is based on Occams razor, the principle of parsimony. It seems pretty clear that some of our psychological capacities evolved because they provided our ancestors with reliable information about the world they inhabited. Perceptual beliefs are the clearest example. Our ability to use our sensory systems to form beliefs about our immediate surroundings evolved because the beliefs they generated were largely true. Nagel thinks that no such explanation can be offered for why we have the moral beliefs we have. Indeed, biologists dont often make such offers. For example, Darwin argued that moral norms enjoining altruistic behavior are now widespread in human societies because groups that internalized and complied with these norms outcompeted groups that did not. Whether it is true that we ought to act altruistically isnt something that Darwin or more recent biologists need to take a stand on to explain why people accept such norms.
Okay, you may be thinking, why is the evolutionary explanation of our moral beliefs an argument against moral realism? Here you need to reach for your razor. Nagels idea is that if you dont need to postulate the existence of moral facts to explain why we have the moral beliefs we have, then you should slice those alleged facts away. This doesnt just mean that you should decline to believe that there are moral facts of the sort that moral realism postulates. It means that you should believe that there are no such things. The razor doesnt tell you to suspend judgment; it tells you to deny. That is Nagels reason for thinking that there is a conflict between evolutionary theory and moral realism: evolutionary theory underwrites a parsimony argument against moral realism.
I dont buy this argument. I agree that you dont need to postulate moral truths to have an evolutionary explanation for why we have the moral beliefs we do. But that doesnt mean that evolutionary theory justifies denying that there are such truths. Nagel is assuming that if moral realism is true, then the truth of moral propositions must be part of the explanation for why we believe those propositions. I disagree; the point of ethics is to guide our behavior, not to explain it, a thesis that Nagel defended in The View from Nowhere (1989) but has now apparently abandoned.
Nagel demands that we show remarkable facts to be likely, but Beethoven is remarkable, and he could easily have failed to exist.
I said before that Nagel thinks evolutionary theory, shorn of its commitment to materialistic reductionism, is incomplete, not false. Nagels probability argument conforms to this pattern, but his argument about ethics does not, at least not when it involves a claim of incompatibility. If evolutionary theory and moral realism are incompatible and moral realism is true, then what follows is that evolutionary theory is false, not that it is incomplete. This suggests that we should set this talk of incompatibility to one side. Nagels considered position is that evolutionary theory, construed as proposing a complete explanation of why we have the moral convictions we have, would conflict with moral realism. The upshot is that something needs to be added to the evolutionary explanation.
So Nagel thinks that an adequate scientific account of the existence of life, mind, and consciousness must show that those events had significant probabilities. He holds that current science does not do that and therefore needs to be supplemented. But with what? Nagels answer is that science should go teleological: concepts of goal and purpose need to be used in new scientific theories. This suggestion conflicts with the dominant scientific tradition of Galileo, Newton, and their successors. Teleology is the most radical idea in Nagels book.
Nagel says that teleology means that things happen because they are on a path that leads to certain outcomes. Suppose that X caused Y and that Y then caused Z. A teleological explanation of Y will say that it occurred because it was on the path from X to Z. This explanation of Y cites Z, which occurs later than Y. However, the teleological explanation does not say that the later event caused the earlier one; for Nagel, teleological explanations are non-causal. In addition, Nagel wants a naturalistic and non-intentional teleology, one that does not involve God or any other intelligent designer directing the universe toward a goal.
According to Nagel a teleological theory says that things tend to change in the direction of certain types of outcome. This is right, but, as Nagel realizes, it isnt sufficient for a theory to be teleological. The second law of thermodynamics says that closed chambers of gas tend to evolve in the direction of increasing entropy, but that doesnt mean that they are goal-directed systems. Nagel also says that conventional (non-teleological) physics describes how each state of the universe evolved from its immediate predecessor, but a teleological science will be different: teleology requires that [some] successor states . . . have a significantly higher probability than is entailed by the laws of physics alone. Whether or not this is a necessary condition for teleology, it too is insufficient. Suppose I buy a lottery ticket on Monday, win the lottery on Tuesday, and splurge on luxury goods and big charitable donations on Wednesday. The probability of my winning on Tuesday, given that I bought the ticket on Monday, is low, but the probability that I win on Tuesday, given that I bought the ticket on Monday and was a big spender on Wednesday, is much higher. This isnt teleological, however, since it isnt true that my spending on Wednesday explains why I won the day before.
I do not reject teleology wholesale. I do not reject claims such as flowers have bright petals because they attract pollinators and Sally went to the park at 8:30 because there were fireworks at 9 oclock. These statements do not say that a later event caused an earlier one, but they are true because certain causal facts are in place. The statement about flowers is true because there was selection for bright colors among plants that gained from the services of pollinators that used color vision. The statement about fireworks is true because Sally knew there would be fireworks at 9 oclock, and she wanted to arrive in time to get a good seat. Maybe there are true teleological statements about life, mind, or consciousness. But if there are causal underpinnings for those teleological statements, as there are for the teleological statements about flowers and fireworks, the materialist need not object.
Nagels thesis is not just that there are true teleological statements about the emergence of life, mind, and consciousness, but that these statements cannot be explained by a purely causal/materialistic science. Only then does his teleology go beyond what materialistic reductionism allows. I see no reason to think that there are true teleological statements of this sort. If readers are to take seriously the possibility of teleological explanations that are both true and causally inexplicable, it would help if Nagel identified some modest phenomenon that clearly has that sort of explanation. He never does. That raises the worry that the kind of explanation for which Nagel hankers is a pipe dream.
Nagel wants a teleological science partly because he is moved by probability considerations. If conventional science says that remarkable facts had low probabilities, given what came before, the probabilities of these facts can be boosted by adding information about what came after. In this respect, the emergence of life resembles my winning the lottery on Tuesday. Each event is quite probable, given what happened later. The problem is why we should regard that as an explanation.
Nagel is hardly unique in being an anti-reductionist. Most philosophers nowadays would probably say that they are against reductionism.
What sets Nagel apart is his idea that current biological and physical theories need to be fundamentally overhauled. Why do other anti-reductionists decline to take this radical step? It is not that they are faint of heart. Mostly they decline because they endorse the following picture. When an organism has a new visual experience, the physical state of the organism has changed. And when an economy goes into recession, the physical state of that social object also has changed. These examples obey the slogan I mentioned before: no difference without a physical difference.
That science should go teleologicalincorporate concepts of goal and purposeis a radical idea.
However, when it comes to understanding visual perception and economic change, the best explanations are not to be found in relativity theory or quantum mechanics. Sciences outside of physics can explain things that physics is not equipped to explain. But this doesnt mean that physics needs to be revised. The philosophers and scientists I am describing disagree with Nagels claim that evolution is more than a physical process, though they agree that physics is not the best tool to use in understanding evolution.
A true and well-confirmed causal statement such as smoking cigarettes causes lung cancer calls for explanation. We want to know how inhaling the smoke causes the tumor to grow. If someone said that this causal statement is just a brute factthat it is true but has no explanationwe would raise our eyebrows. When one event causes another, we expect there to be intervening events. We explain why C causes E by showing that C causes I1, that I1 causes I2, and so on, up to some further I that causes E.
But materialism should not assume that this must always be the case; maybe there are occasions where C causes E without there being an intervening event between C and E. Materialism should be open to the possibility that some causal relationships are brute facts. This is one reason to be suspicious of the view that Nagel calls materialistic reductionismthat physics provides a complete explanation of everything. Scientists already leave room for brute facts in another context. When they say that a law is fundamental, they mean that it cant be explained by anything deeper.
If there can be brute facts about purely physical causation, why cant there be brute facts about physical events having mental effects? Suppose event C is the hammer hitting your thumb and E is the pain you feel. Science explains why C caused E by interpolating causes. The chain of events that goes from C to E passes (perhaps gradually) from the physical to the mental. The idea that there cant be brute facts about physical-to-mental causation is just as misguided as the idea that there cant be brute facts about physical-to-physical causation.
Nagel writes, All explanations come to an end. This could point to a practical matter: when we run out of time or patience, we settle for what we have. But the limitation may also be forced on us by the world. Maybe there are brute causal facts. Maybe some scientific laws are fundamental. And maybe some crucial facts about the mind-body relation are brute as well. Not that we should be complacent. If smoking causes lung cancer, it makes sense to expect that there is an explanation as to why. But we should not over-generalize, turning a good heuristic into a metaphysical principle that brooks no exceptions. Whereas the materialistic reductionism that Nagel criticizes says that everything has a complete physical explanation, a more circumspect materialism would assert that everything that has an explanation has a complete physical explanation.
Mind and Cosmos is dominated by a set of very strong assumptions about explanation: remarkable facts must have explanations; those explanations must show that the remarkable facts have fairly high probabilities; and remarkable facts cannot be byproducts. Nagel does not take seriously the possibility that the world may not be so obliging.
Current science may suffer from fundamental flaws, but Nagel has not made a convincing case that this is so. And even if there are serious explanatory defects in our world picture, I dont see how Nagels causally inexplicable teleology can be a plausible remedy. In saying this, I realize that Nagel is trying to point the way to a scientific revolution and that my reactions may be mired in presuppositions that Nagel is trying to transcend. If Nagel is right, our descendants will look back on him as a propheta prophet whom naysayers such as me were unable to recognize.
Elliott Sober is Hans Reichenbach Professor of Philosophy at the University of Wisconsin, Madison and author of Did Darwin Write the Origin Backwards?