[On January 21st, Steven Pinker and Steven Rose debated each other in an event chaired by Susan Blackmore and held at London University's Institute of Education under the sponsorship of Dillon's and The London Times. Part I of "The Two Steves," was published on EDGE 36 (March 10th) and is available on the EDGE site. In Part II Pinker and Rose answer questions from the audience.]

QUESTION for STEVEN PINKER: What do you believe consciousness is?

STEVEN PINKER: There is an extensive discussion of consciousness in the book. Consciousness is a word that refers to a number of different concepts. There's Freud's distinction between the conscious and unconscious mind, which I relate, following a number of other cognitive scientists, to the fact that no computational system can make all its information available to all of its processes. Thus there is a division in the human brain between the kind of information that we can verbally report on and that can affect our day-to-day decision making, and the kind that goes on "beneath the level of consciousness," such as the control of individual muscles in arms and legs or the rules of syntax that govern how we put sentences together. That's, I think, a tractable definition of consciousness, and it can be readily explained by the fact that the particular sequence of muscle movements is not relevant to my global course of planned action, and so therefore should be sealed off and not allowed to interfere with that planning process.

There are other definitions of consciousness, such as the philosophical concept of "qualia," or pure subjective experience: why red looks red to me, or whether my red is the same as your red. I don't have an evolutionary, or neural, or any kind of explanation as to the origin of that sense of consciousness.

ROSE: I don't regard consciousness as a property locked inside the brain of an individual. I regard it as a process which emerges in interaction between individuals, particularly humans, during their development, and the society and culture in which they're embedded. Therefore consciousness, in a very interesting sort of way, is not a brain property alone; it involves many many other features as well, and we reduce it excessively-and I don't think Steve is as guilty of this as many of my neuro-scientific colleagues are, in trying to argue that it's simply the reverse of being asleep, or unconscious. Or make the Freudian distinction. I think there are richer meanings; it's a process, not a thing.

QUESTION for Pinker and Rose: The parts of the brain which distinguish us from the animals are the least modular, and that's the frontal lobes, which take up 30% of the brain. The frontal lobes have the capacity to modulate and even change the physical structure of the brain. Posterior structures, for instance, are extremely flexible; you can cut out quite large chunks of them and they can reorganize. Similarly, the growing evidence for plasticity generally in the cortex, for instance, the use of apparently visual areas ... in blind people who are not using them gives a very different picture of, if you like, culture and society shaping, the brain-particularly, for instance, the growth of intelligence as society has developed over the last 50 or 60 years. It is quite a different picture of determinance of behavior and brain function than the picture of these rather crude and easily overridable systems of ancient structures of evolutionary adapted brain.

STEVEN PINKER: It is certainly true that the brain has a great deal of plasticity. I think of each one of these subsystems or faculties as systems that are designed to learn, that are designed to shape themselves in interaction with the environment. But it's not true that these faculties are infinitely plastic, and that the brain can do whatever it wants with itself. One example is the difference between spoken language and written language. All children learn to speak without lessons, spontaneously, by exposure to a community of other people, whereas to learn to read requires extensive practice, artificial curricula, and has a high failure rate. If the brain were completely plastic there should be no difference between reading and speech. There is a huge difference, and that is likely to characterize other mental faculties as well. But it certainly is true that they all are designed to learn and interact with the environment.

ROSE: I think the dialogue between specificity and plasticity in the development of the brain is much the most important and interesting thing that we need to understand. Of course the brain cannot be infinitely plastic; our eyes as we develop need to wire up to the visual cortex in the brain in a fairly ordered and systematic sort of way, or we couldn't preserve binocularity, we couldn't have a visual analyzing system of the sort that we've got. At the same time we have to have brains that are modified by experience. That's plasticity, and the capacity for both specificity and plasticity is there genetically to start with, so I entirely agree with you, and I think it's a mistake to have to think in terms of modularity, to an excessive degree, when one's concern is much more complex functions than simply visual analyzing functions.

QUESTION for Pinker and Rose: As our environment is changing by the decade, and our interactions with the environment impact who we are, how can our genetics keep up? Surely we're way out of date genetically, so how are we surviving?

ROSE: I think it's a great mistake to argue about our genetics being way out of date. The point is that it is precisely, if you like, the human capacity given to us by our genome, given to us by environmental and cultural history, that enables us go on creating this changing society all the way along the line. And that is that it's our genetics that enable us to make these transformations. I think it's really a mistake to believe that somehow genes got left behind somewhere in the Stone Age, or somewhere in the evolutionary process and they're running to keep up with the things that we are doing as a result of it. It's that way of thinking that we need to transform if we're to understand the complexity of the processes. Some people get round it by talking about gene environment, co- evolution. I think that's a step in the right direction, but it really doesn't begin to address the complexity of the interactions which you're hinting at there, and which are for the biology of the future, once we've got rid of the sterile dichotomies of gene and environment and understand the richness to try to come to terms with it.

PINKER: Let me answer that in a slightly different way. I don't think that our man-made environment is necessarily running away from us and it's going to be a matter of how the genes are going to keep up. I do think there are some aspects of human nature that are stuck in the Stone Age, and it's BECAUSE our minds are adapted to that period that we change our technology and our environment to make ourselves feel at home. An example is the design of computers-I assume that's one of the things you were referring to as "rapid environmental change." Computers work on ones and zeros. Our minds have not been able to grasp that way of interacting with machines, on their own terms, but there hasn't been a problem of how are we going to cope with all these ones and zeros. Indeed, the brain is not plastic enough to get itself to think that way. Instead we've designed computers so that THEY mesh with OUR way of thinking. We have designed elaborate graphic interfaces that translate quite abstract information into representations of physical objects, in a particular location in space, that can be moved in a particular way, because that's how human intuition works. So I think the answer is: our minds are going to shape the environment in ways that we can cognitively deal with.

QUESTION: It seems to me that the only constant in societies over the last four thousand years has been the presence of some sort of religious suasion forming a moral and ethical framework. Where is the God module in the brain?

PINKER: As I mentioned, I don't think that religion is an adaptation, so I don't think there is a God module. I do discuss at some length in the book how it arises as an interaction of other parts of the minds. One part is an intuitive psychology. Once you have an ability to interpret other people's behavior in terms of unobservable beliefs and desires, that is, a mind. We impute minds to one another; we don't treat one another as wind-up dolls. That faculty can, then, in a sense, run amok, and imagine minds that exist independently of bodies, namely spirits, souls, ghosts, and so on. That's an example of how a part of the mind that evolved for one purpose can give rise to something quite different. I don't think that's the totality of religious belief, and I discuss some of the other components that collectively give rise to it, but that's an example of how a kind of belief can be a major part of human experience, but not necessarily specifically selected by evolution.

ROSE: I'm not sure that I have a mind that deals either in god or in modules, so I'm not sure I can answer the question. I do think it's extremely important to understand the function religion has played through humanity's history and the moral vacuum which is the result perhaps in the loss of the faith and the creation either of a religious society or of a more socially just society, which we're facing at the moment. I would not like to see ultra-Darwinism become the religion of the future.

QUESTION: If history plays such an important part in our development, how come human beings keep making the same mistakes time and time again? How do you predict the future? You've got all that history-can you not see the future with that information?

ROSE: The whole point is the future is radically unpredictable. It's unpredictable because we can only track change. We can't predict futures. Humans can do a little better than other species in predicting futures, but because of the rate of change of technology in human society, constantly throwing out new problems because of the complexity of the social changes that are occurring, then predicting the future becomes extremely hard. That is why I say in many respects it's radically unpredictable. What I do insist is that we have the freedom to make choices about it, which is a different argument. But we don't have infinite flexibility in making those choices. Steve Pinker and I would both agree that we are constrained by our evolutionary past, by our biological givens-none of us can walk on water, any more than we can grow wings. What we can do is find technology that can solve those problems. Those constraints are there. We see and understand the world through spectacles that are given us by our biology-the fact that we are somewhere between one and a half and two and a half meters high, most of us, rather than a couple of centimeters high radically transforms the way that we understand the world. If we were those small creatures we'd see the world-we'd have quite different biological problems and social problems to resolve. So our past is indeed in many ways the key to the present.

PINKER: I have nothing to add to that; I agree with it.

QUESTION for Pinker: I wanted to ask Professor Pinker again about Cartesian dualism. Although your book does argue that you want to approach understanding consciousness in physical terms, in a materialist way, in the book at one point you talk about your materialist work being the project you do during the day, and in the evening when you're talking with your friends and so on you acknowledge that human beings are sentient and have free will and so on. You acknowledge that it's a non- trivial problem to bridge that gap. You say it might not be possible to do that, whereas elsewhere in the book you talk about the computational theory of mind, I assume as a way to bridge that gap. But I wasn't convinced by that, because it seemed to me that it was just relocating the problem. Social categories like desires and beliefs were just being relocated in the heads of individuals. So when your Bill gets on the bus, his belief that the bus is going to his granny's can just be re-represented as a physical symbol in the brain, and that fills that gap. There seems to be some flip-flopping between being a physicalist on the one hand, and on the other saying that you can approach the same subject in two completely different ways. PINKER: There's no flip-flop in my discussion of mental states such as beliefs and desires, which doesn't call for any kind of substance dualism-the idea that there is some kind of stuff different from neural interactions that accounts for how we behave and how we perceive the world. As a nonreductionist I think there are different levels of analysis, and that the information-processing level of analysis gives rise to psychological regularities and generalizations that can't easily be captured directly in terms of the neurophysiology. Take the simple example that our short-term memory can hold only five or so items. We have no neurophysiological explanation of that, but we can characterize it in computational terms. Eventually it will be tied to the neurophysiology because they're two different levels of analysis of the same phenomenon. In terms of morality, I believe that there is a role in our discourse for moral judgments and for a concept of free will that is not dualistic but that simply is part of a different system of reasoning, in the same way that mathematics is a system of reasoning that differs from science. We don't actually believe that there are perfect circles or infinite straight lines or Euclidean planes, but we can still perfectly well reason within mathematics. Like many moral philosophers I believe that there's a sphere of moral reasoning we can engage in that makes use of idealizations like free will but without making any commitments that there's actually a different kind of stuff in the physical world. It's an assumption that makes that system of reasoning possible. We can't have ethics unless we hold someone responsible for their behavior; we can't hold them responsible for their behavior unless we believe that the behavior is not directly caused. That's how we make moral judgments, but it doesn't obligate us when we shift to a scientific mode of explanation to believing that there's a ghost in the machine.

ROSE: Very briefly, there's a book which has just been published called The Number Sense by Stanislas Dehaene. It makes a very interesting point about this question about whether you can hold more than five things in your mind at the same time, which is a classical piece of data which appears in every student psychology textbook. Dehaene points out that it is entirely culture-bound. Chinese culture, for example, which has a different way of counting and representing numbers, can hold many more than five items in their mind at the same time. So it's got again this beautiful interaction between culture, society, biology and history, which I think we have to again take into account whenever we try to say these are universals about the way the mind works.

PINKER: The Dehaene finding is part of a set of phenomena that's been known for as long as the five-item constraint has been known, namely that a particular item in memory can point to a much larger data structure, a phenomenon called chunking. The difference between the Chinese memory span and the American one is simply a difference in chunking; the underlying constraint in memory, according to my memory of Dehaene's work, is the same as it is in American children.

QUESTION to Pinker and Rose: What experimental scientific procedures would you do to determine which of your theories is correct?

PINKER: For approaches of this magnitude there isn't going to be one experiment that's decisive. The proof is going to come from the entire body of research that's inspired by the general idea: the hypotheses that flow out of the theory and the ability of the theory to make correct predictions in a wide variety of domains that mutually cohere and that wouldn't have been made otherwise. One of the main points in How the Mind Works is that there has been an enormous body of experimental literature that has been generated by the hypotheses that I present and that hang together well. Any one of them could turn out to be false and require reinterpretation, but it's our general understanding of the emotions and memory and visual perception and so on over a long period that will determine whether we hang onto that approach as basically sound.

ROSE: I don't think that theories are ever overthrown by decisive experiments. Their protagonists merely fade away, despite what Karl Popper said. However there are two sorts of experiments or pieces of biological information I would like. One is very specific: I would like to know why it is that although we share 98% of our genome with chimpanzees no one can mistake the phenotype of a chimpanzee with the phenotype of a human. And the second, and it's a much more easy question to answer in some ways, is the information-the understanding that's coming-on mapping mental processes that come out of the windows into the brain which are provided by positron emission tomography, magnetoencephalography, and all the other technologies that there are around at the moment, that are bound to give us a richer understanding than the rather crude mechanistic models that we all share of the way minds and brains work at the moment.

QUESTION to Pinker and Rose: Both speakers espouse the idea that we have active control over what we do and what we don't do. I've got a bit of a problem with that. For myself and what I see in other people, we operate within very strictly controlled parameters. So I just wonder why in both your investigative researches, there hasn't been more emphasis on what we might call simple preference, such as why you've both got different hairstyles and wear different suits.

PINKER: I'm not sure I understand the question.

ROSE: I'm not quite sure why Steve wants (as he was described in The Guardian a few days ago) his hair to look so beautifully like a bouffant rock star . On the other hand I do think you're right to speak about the constraints in which we operate. I've given the impression that we are free agents, but of course we're not free agents; we're bound socially, we're bound economically, we're bound culturally, we're bound historically, and we're bound biologically, so the constraints which all of those provide-and they're much much sharper, despite what Steve says, for unemployed workers than they are for company directors, and much sharper for black footballers than white racists on the terrace, again a point he seems to disapprove of, and a point I made in the book. I think those are the constraints in which we need to operate, and those are the constraints which I think a different sort of science than either Steve's or mine needs to try to understand.

PINKER: The point I made concerning people with different social backgrounds is not that they have equal choices in life, which they obviously don't. I was raising a specific point as whether that affects the scientific metaphors and analogies that they take seriously, and I think that there's no evidence that they do and some evidence that they don't.

QUESTION for Pinker: Steve Pinker talks about the 45% personality variation which is not under genetic control or family influence. I have a question about identical twins. In both of your books, you selected convergent examples of identical twin behavior and did not talk about the divergent behavior, which is so interesting, in identical twins. When one interviews identical twins that are divergent, what one is struck by is the thoughtful way in which they have thought about their differences and come to observe them compared to the extraordinarily boring way in which the identical twins converge. It's almost as bad as memes, as in the time when wearing your baseball hat backwards was a similar piece of behavior many people did. They're like that. Divergent twins seem to have fought their way along different pathlines, and if they end up with a different inner environment, which leaves them freer. Can you say a word about divergent twins?

PINKER: Yes, I talk not only about the extraordinary similarities in quirks of behavior, such as sneezing in elevators; that I mentioned just to illustrate that the mind has a great deal more genetic specificity than we would have naively predicted. But I also talk about more profound similarities and differences between identical twins. The similarities are not just in the quirks; they are in fundamental dimensions of personality, such as whether you're conscientious or sloppy, whether you're anxious or relaxed, and whether you're antagonistic or friendly. Those traits also show a high, though nowhere near perfect, correlation between identical twins.

I also discuss hypotheses about why identical twins, though highly similar, are not identical in personality. One possibility is sibling interaction, in which each twin strives to differentiate herself or himself from the other twin. I also talk about chance factors that occur in an individual's lifetime: perhaps there is some effect of being chased by a dog, or receiving an act of kindness. Also, there are surely many unpredictable factors in the growth of the brain, since the gene can't specify every connection. I think it's an exciting project for psychology to test these hypotheses, and many personality psychologists are engaged in it. We know that one putative factor, namely growing up with a given set of parents, has a surprisingly small effect on long-term personality. In general, this research focuses our attention on the factors other than the genes that make us what we are.

QUESTION for Pinker: I partly agree with Pinker that procreation is important for loving your partner. But I would argue that procreation actually can much better explain why partners cheat each other, trying to find a higher chance for procreation, but it doesn't necessarily explain why. So: why would a partner stay with their spouse, as opposed to cheating and trying to find higher chances for procreation. Also, you didn't comment on what Rose said about homosexual love.

PINKER: I actually do have an extensive discussion of love as opposed to lust and sexual desire. I think the long-term commitment that you see in a husband and a wife, or in two close friends, and in homosexual lovers-although I don't talk much about homosexuality in the book-comes from a different dynamic. It's analogous to symbiosis in the natural world. You start off with a commonality of interest, that is, what is good for me is good for someone else. In the case of heterosexual marriage that trigger can be the shared genetic interest in the children, but in the case of close friends it could be things like having common interests, having common enemies, having common tastes, and so on. Once what's good for you is good for someone else, that gives you a stake in their well-being, and so you're apt to value them. If you value them, that makes you more valuable to them, and they're likely to value you, and you can get a positive feedback loop where the coalition of two people with common interests can develop into a long-term attachment. We experience this as the emotion of long-term companionate love. I think that's what keeps married couples together, and what keeps close friends together. It's a different emotion than sexual desire, and it's a different emotion than the head-over-heels infatuation that often gets a couple together to begin with. So love is a set of emotions, and I discuss them separately in the book.

ROSE: Steve has provided a neat cost benefit analysis of the merits of love, and it's precisely the point that I was making before about metaphors which he was so uneasy about. Here's a metaphor and a mode of thinking that he's taken over lock stock and barrel from a particular set of economic theories, and applied with enormous energy and ingenuity by evolutionary psychology. I happen to think it's a very impoverished way of trying to describe much more complex phenomena.