man, beast and zombie

edinburgh international science festival, 16 April 2001

Reason, Descartes believed, 'is the noblest thing we can have because it makes us in a certain manner equal to God and exempts us from being his subjects.' For much of the past 500 years, scientists and philosophers have taken it for granted that human beings are exceptional creatures because of our possession of reason and consciousness, language and morality.

This was the philosophy of humanism - a desire to place human beings at the centre of philosophical debate, to glorify human abilities and to view human reason as a tool through which to understand nature; a belief that human beings, while an inherent part of nature and subject to its laws, nevertheless had an exception status in nature because of their ability to reason. This was the philosophy at the heart of both the scientific revolution and the Enlightenment.

But no longer do we think this way. Today, the idea of humans as exceptional beings is regarded as both scientifically false and politically dangerous. For most scientists, exceptionalism smacks of mysticism. Their Holy Grail is to understand humans in the same language as the rest of physical nature. 'Everything can be explained as neurophysiology and deep genetic history', as EO Wilson has put it. Or, in the words of John Tooby and Leda Cosmides, two of the founders of evolutionary psychology 'Human minds, human behaviour, human artefacts and human culture are all biological phenomena'. Recent advances in evolutionary biology, neuroscience, genetics, and AI certainly seem to make possible the understanding of humans not as exceptional beings but as simply sophisticated animals or sophisticated machines, as beasts or zombies.

And politically, there is an increasing tendency to see human hubris as the root of most of the ills of the world, from global warming and species depletion to ethnic cleansing. 'We need protection from ourselves', as the biologist Lynn Margulis has put it.

I want to argue that the retreat from human exceptionalism makes for both bad science and bad politics. It might seem perverse for someone like me – a rationalist, a materialist, an atheist – to argue against a naturalistic view. After all, naturalism has been the key means of expunging mysticism from our understanding of humanity, of allowing us to talk about humanness in the absence of God. The trouble is, though, the attempt to understand humans in the same language as the rest of nature ignores an essential quality of being human – our subjectivity. Humans simply are not like other animals, and to assume that we are is irrational. Moreover, the retreat from exceptionalism makes for bad politics because once we accept that human reason is a force for destruction rather than advancement, we dispose of the only means we possess for our betterment, whether moral, social or technological.

A paradox of science is that its success in understanding nature has created problems for its understanding of human nature. The success of science derives from the way that it has 'disenchanted' the natural world. Whereas the prescientific world viewed the universe as full of purpose and desire, the scientific revolution transformed nature into an inert, mindless entity.

At the heart of the scientific methodology is its view of nature, and of natural organisms, as machines; not because ants or apes work like computers or TVs, but because, like all machines, they lack agency and will. Animals are objects of natural forces, not potential subjects of their own destiny. They act out a drama, not create one.

Humans, however, are not disenchanted creatures. We possess purpose and agency, consciousness and will, qualities that science has expunged from the rest of nature. Uniquely among organisms, human beings are both objects of nature and subjects that can shape our own fate. We are biological beings, and under the purview of biological and physical laws. But we are also conscious beings with purpose and agency, traits the possession of which allow us to design ways of breaking the constraints of biological and physical laws. We are, in other words, both inside nature and outside of it.

The very development of the scientific method has exacerbated this paradox of being human. To study nature scientifically requires us to make a distinction between a humanity that is a thinking subject and a nature that presents itself to thought but is itself incapable of thought. When studying 'external' nature the distinction between the thinking subject and the object of study is easy to make. But with the study of humans, such a neat division becomes impossible: human beings are simultaneously the subject that thinks and the object of that thought. We can understand humans as beings within nature that can be studied by science. But the very act of studying humans in this fashion takes them outside of nature because of the distinction we must make between inert, mechanical nature and active, thinking humanity. This is, in philosopher Kate Soper's words, 'the paradox of humanity's simultaneous immanence and transcendence'. Nature, she points out, 'is that which Humanity finds itself within, and to which in some sense it belongs, and also that from which it seems excluded in the very moment it reflects upon either its otherness or its belongingness.'

In other words, our very capacity to reflect upon nature takes us in some sense outside of nature, for if we could not view nature from the outside we could not reflect upon it objectively. It's a phenomenon familiar from everyday life. You are more likely to have a objective view of something - a relationship, a job opportunity, a moral dilemma - if you are able to view it from the outside than if you are intimately involved and hence can only view it from the inside. An objective view requires us to transcend that which we wish to investigate.

To talk of humans as 'transcendent' is not to ascribe to them spiritual properties. It is, rather, to recognise that as subjects we have the ability to transform our selves, our natures, our world, an ability denied to any other physical being. In the six million years since the evolutionary paths of humans and chimpanzees first diverged on either side of Africa's Great Rift Valley, chimpanzees have evolved, but their behaviour and lifestyles have barely changed. Human behaviour and lifestyles clearly have. Humans have learnt to learn from previous generations, to improve upon their work, and to establish a momentum to human life and culture that has taken us from cave art to quantum physics and the conquest of space.

It is this capacity for constant innovation that distinguishes humans from all other animals. All animals have an evolutionary past. Only humans make history.

This transformative quality of being human is why the so-called nature-nurture debate, while creating considerable heat, has thrown little light on what it means to be human. Over the past half century there has been a fierce dispute as to whether human behaviour is determined by our genes or by our environment. In the decades following the Second World War, the experience of racial science, eugenics and the Holocaust led many scholars to denounce genetic theories of human behaviour and to insist on the importance of nurture in shaping who we are. More recently, disillusionment with social explanations, and advances in genetics and evolutionary biology, have helped swing the pendulum back towards theories that stress the importance of nature in the human make-up.

This question of whether we are determined by our genes or our environment is, however, misleading. We are, as many have observed in recent years, shaped by both. But we are also defined by our ability to transcend both. Unlike any other creature, humans have developed the capacity to overcome the constraints imposed both by our genetic and our cultural heritage. It is not that human beings have floated free of the laws of causation. It is rather that humans are not simply the passive end result of a chain of causes, whether natural or environmental. We have developed the capacity actively to intervene in both nature and culture, to shape both to our will.

All non-human animals are constrained by the tools that nature has bequeathed them through natural selection. They are incapable of striving towards truth; they simply absorb information, and behave in ways useful for their survival. The kinds of knowledge they require of the world have been largely pre-selected by evolution. No animal is capable of asking questions or generating problems that are irrelevant to its immediate circumstances or its evolutionarily-designed needs. When a beaver builds a dam, it doesn't ask itself why it does so, or whether there is a better way of doing it. When a swallow flies south, it doesn't wonder why it is hotter in Africa or what would happen if it flew still further south.

Humans do ask themselves these and many other kinds of questions, questions that have no relevance, indeed make little sense, in the context of evolved needs and goals. What marks out humans is our capacity to go beyond our naturally-defined goals – such as the need to find food, shelter or a mate – and to establish human-created goals.

Some contemporary thinkers believe that there are indeed certain questions that humans are incapable of answering because of our evolved nature. Steven Pinker, for instance, has argued that,Our minds evolved by natural selection to solve problems that were life-and-death matters to our ancestors, not to commune with correctness or to answer any question we are capable of asking. We cannot hold ten thousand words in our short-term memory. We cannot see ultra-violet light. We cannot mentally rotate an object in the fourth dimension. And perhaps we cannot solve conundrums like free will and sentience. Whether or not this is true remains to be seen - and I will return to the question of free will later. What we do know, however, is that most scientific problems - from the structure of DNA, to the physical composition of the sun, to the mechanism of evolution - are problems that would not have been 'life-and-death matters to our ancestors'. We have solved them despite our evolutionary legacy, not just because of it. The development of science requires mental skills, many of which are evolved adaptations. But it also requires us to transcend those adaptations. Our evolutionary heritage certainly shapes the way that humans approach the world. But it does not limit it absolutely, as it does for all other animals.

All humans view the world from a specific perspective: from the perspective of our individual senses, of our particular species, of our particular culture, of the historical period we inhabit. But we are also able to proceed beyond the particularities of our individual lives, to take a more inclusive, objective view of the world. To acquire such an understanding, we need, in the words of the American philosopher Thomas Nagel, 'to step back from our initial view of it and form a new conception which has that view and its relation to the world as its object.'

To go beyond a purely personal view of the world, we need to climb out of our individual minds, as it were, and view the world from a more external viewpoint. To go beyond the view afforded by a particular culture, we need to climb out of that culture and view it from the outside. To go beyond the view afforded by our species, we need metaphorically to climb out of our natures and view human beings from beyond ourselves. And so on. This process of climbing out of our immediate circumstances to achieve a more inclusive view is precisely the process of transcendence. Without such a process neither history nor science would be possible.

To understand how we are human, therefore, we need to understand not so much whether we are creatures of nature or nurture, but, more, how we are simultaneously object and subject, how we are at the self-same time a physically determined being and a social being and moral agent. Many animals, of course, from ants to zebras, are also social creatures. Such animals live as part of a group, within which there is considerable interaction and often a division of labour. Human sociability, however, is of a different order. For humans, unlike for animals, a society is not simply an aggregation of individual actions and interactions. The dynamics of an animal group or society can be understood by analysing the actions of the individuals who make up that group or society. Human societies cannot be so understood. When we talk about humans as social we are describing a different kind of being, individuals who have acquired new capacities and possibilities that they would not, and could not, have possessed simply as individuals. The social acts as a mediating bridge between humans as objects and humans as subjects.

In humans, sociability is intimately linked to our capacity for language and for self-awareness. The importance of language is not just that it is a unique form of communication that helps create the possibilities of social intercourse beyond simply the kinds of individual interactions that animals experience. It is also an expression of the human capacity for symbolic thought, a capacity that enables humans to think about the world and ourselves in a way denied to other animals. Only because humans are capable of creating in our minds symbolic representations of the world are we able to think about, as opposed merely to experience, the world.

Three elements are necessary for me to be able to think about the world: me, the self that does the thinking; the world about which I think; and my representation of the world, the means by which I think. Through creating a representation that is separate from both me and the world, I am able to make a distinction between the world as it is and the world as it seems to me.

If I could not do this, I would be unable to think about the world. If I did not recognise a distinction between myself and my picture of the world, I would not be able to reflect upon my thoughts as a distinct entity. If I did not recognise the distinction between the world and my picture of it, then I could only apprehend the world in its immediacy, without applying any thought to it.

Animals can, and clearly do, represent the world in their heads, and act upon such representations. But what animals cannot do, because they lack the capacity for symbolic thought, is to distinguish between themselves, their thoughts and the world. They can, therefore, experience the world, and react to it, but they cannot be aware of themselves as doing so. Humans, on the other hand, do not simply have experiences, desires and needs, and react to them. We are also aware we have them, that there is an 'I' which is the subject of these experiences, and which is a possessor of experiences, desires and needs. In other words, humans are aware of themselves as agents, and of the world towards which their agency is directed.

But if symbolic thought is a necessary condition for being able to think about the world, and for developing a sense of agency, it is not a sufficient one. To understand this we need to understand what is wrong with the conventional view of the mind, which derives largely from the ideas of Descartes. The mind, in the Cartesian world, is the private possession of the individual, an essentially 'inner' phenomenon, revealed only to itself. No one else has access to my mind, just as I can never have access to yours. It's a view that appears not just conventional, but commonsense.

It was the philosopher Ludwig Wittgenstein who pointed out why the Cartesian view is muddle-headed. If my mental world was truly private, he observed, then I would be unable to communicate my thoughts and my feelings to anyone else. For language is a public activity; words get their sense by being attached to publicly accessible conditions that warrant their application. If I say 'I'm feeling happy', or 'Paris is a beautiful city' such statements could only make sense to other people if there is a common agreement as to what constitutes 'I', 'feelings', 'happiness', 'Paris', 'beauty', and so on. You would have to know which of your neural events corresponded to the neural events that I define as 'I' or 'happiness' or 'beauty'. Hence, if everyone knew only their own minds, then no word in our language could refer to our mental events, and I could not communicate my thoughts or feelings to anyone else.

Not only could no one else know what I am thinking or feeling, but I could not know myself. Feelings and thoughts may be internal, but meanings are external. Meanings arise through social intercourse; they are public labels we put on private feelings and they make sense only insofar as we agree by convention which labels fit which feelings. Hence if we are unable make public our private mental events, then we cannot attach meaning to them. In other words, we could not know our own minds. We could possess sensations and experiences, but we could never interpret those sensations or experiences, or make them meaningful. We could only react to the world in the way that every other animal does.

If my mind was truly private, then, I could neither know my own mind nor communicate its contents to anyone else. But clearly I do and I can. This can only be if my inner feelings are not truly private, if I become conscious of my inner world in the same way as you do - in other words, through a public process. The contents of my inner world mean something to me, in part at least, insofar as I live in, and relate to, a community of thinking, feeling, talking beings. I can make sense of my mind, in other words, to the extent that I can make sense of yours. Paradoxically, humans become aware of themselves as individual selves only insofar as they are social beings.

This intimate interplay of sociability, language and self-awareness allows humans to break out of the prison of our heads, to go beyond a purely personal, solipsistic view of the world. It allows us to understand other peoples' perspectives and experiences - as well as understanding our own perspectives and experiences in a way no animal can. It enables us to think of the future and the past, about the present and the absent, about the has-beens and the might-have-beens. It emancipates thinking from the here and now, the here and now both of our senses and of our culture, and causes it to range freely over the actual, the probable, the possible and even the impossible. It permits debate and criticism, hopes and aspirations, fears and longings. And it permits us to act upon those hopes, aspirations, fears and longings, and hence to transform ourselves and our world.

The interplay between sociability, language, and self-awareness, in other words, helps turn humans into conscious agents: into individuals with distinct personalities and abilities who only realise themselves through their interaction with each other, and with the social and natural world.

The relationship between humans as individuals and humans as social beings is a complex, organic one. On the one hand, social institutions, forces and entities are created by the conscious activities of human individuals. On the other hand, those same social institutions, forces and entities have a life beyond the individuals that create them. Capitalism, racism, democracy - each can be analysed and understood in its own terms, independently of the individuals who may be capitalists, racists or democrats. Moreover, while individual humans help create social institutions and entities, they are also, in a certain sense, created by them.

Consider, for instance, why modern Western societies, unlike those of a few centuries ago, believe in equality and democracy, and oppose slavery and torture, in principle at least if not in practice. This is not because inhabitants of modern liberal democracies are more noble than their forebears. Rather it is because economic, political and social developments over the past three centuries have made it possible both to imagine and to establish freedoms that were previously unthinkable. The intellectual ferment of the Enlightenment helped establish ideas of equality and universality. Economic development paved the way for social progress. Social changes opened the way to political struggles for the emancipation of slaves, of colonial subjects, of women, and so on. Social change engenders change in human consciousness, and changes in human consciousness further social change.

The capacity of human beings for conscious activity helps create history - the narrative of change that is one of the defining characteristic of the human species. But the very process of historical change transforms the ways in which we think about ourselves and the world around us. Humans make history, but in the process history helps remake the kind of humans that we are. If human beings could not act as conscious agents, there could be no social or historical development. Individual agency, however, cannot exist in the abstract but is only constituted in specific historical and social contexts. This is why human beings are, uniquely, both individual and social, at the same time and in a true sense. It is this dual aspect of being human that lies at the heart of our transformative capacities.

Many scientists recoil from this dual view of humanness. There seems to be something unscientific, almost mystical, about the claim that humans are 'transcendent'. To talk of the 'dual aspect' of humanness appears to be diving straight into the Cartesian pit.

Descartes divided the world into two kinds of substances: the physical and the mental. Physical stuff was something we could touch, feel, see, poke, prod and measure. Hence it was something that scientists could investigate. Mental stuff, on the other hand, was like fairy dust: something we could never quite grasp in our sweaty palms. It occupied no space, possessed no smell, taste or feel, and had no physical presence. Hence scientists could not begin to understand it. Mind stuff did not exist within the empire of science.

Such dualism is clearly anathema to any modern scientist. Many have responded to Descartes by attempting to reduce everything to the physical. For most scientists, reality only exists as physical stuff; the only material entities in the world are physical entities, the only material forces are physical forces. Reality consists of such as atoms and molecules, gravity and electricity.

Natural scientists investigating human nature are particularly keen on this insistence that the only reality is a physical reality. As a result most have become sociophobes - they have developed a morbid fear of all explanations social. Human behaviour and human institutions, they insist, must be explained in biological - physical - terms. According to the anthropologists Randy Thornhill and Craig Palmer, to say that society causes something is to make a 'metaphysical assertion' because it is to 'attribute cause to a non-corporeal reified entity.' Or, as Leda Cosmides and John Tooby have put it, 'what mostly remains, once you have removed from the human world everything internal to individuals, is the air between them.'

It is not that sociophobes deny the social. It is simply that they insist that social phenomena can only be understood as natural or physical phenomena. Cosmides and Tooby, for instance, argue that human society is like 'an ecosystem…whose relationships are structured by feedback processes driven by the dynamic properties of its component parts.' A human society, in other words, is like a zebra herd. When sociophobes talk of the social what they are really talking of is the psychological, the ecological, the natural and the physical.

Yet everyday of our lives we are reminded that not everything can be reduced to the physical, and nor can the social be understood as natural. The world contains a myriad of things that are not physical entities: racism, Nato, the debate between rationalism and empiricism, a sense of duty, the number of off-sides in a particular football match, reasons to be skeptical of evolutionary psychology, and so on. Are these physical things? No - although most also exist in a physical manifestation. Nato has a headquarters in Brussels. But it would be hard to argue that the organisation consists simply of the building or of its contents, or of the individuals that are its employees.

But if they are not physical things, do they exist? Clearly they do. And we know they do because they have effects upon the world, including physical effects upon the world. Racism led to the murder of Stephen Lawrence. Nato bombed Yugoslavia. My reasons for being skeptical of evolutionary psychology have left you reading these words and not some others. And so on.

Any scientific view of the world must accept that things exist insofar as they cause other things to happen, or have themselves been caused by other things. Hence, unless we want to believe that fairy dust causes certain things to happen in the real world, we must acknowledge that non-physical entities exist. This is not to say that there exists 'mind stuff' or 'social stuff' in the same way that there exists physical stuff. The only stuff in the world is physical, built out of electrons and protons and atoms and molecules. There are no social atoms or molecules of mind. Social entities exist not as 'stuff', as things, but as relationships. Interactions between certain physical entities - human beings - give rise to non-physical entities that can impact with, and cause changes in, the physical world. Human beings are the only physical entities that can do this. And they can do this not because they possess some magic powers, or because they live in some spiritual realm, but because, uniquely, they are not just physical but social beings too.

The natural world is objective: were humans not present, it would still exist. The social world is subjective: it exists only because humans exist. But the social world is no less real for being subjective: its entities interact with the physical world, and cause changes in the physical world.

'There is a persistent confusion', the philosopher John Searle points out, 'between the claim that we should try as much as possible to eliminate personal subjective prejudices from the search for truth and the claim that the real world contains no elements that are irreducibly subjective.' Epistemologically, he writes, 'the ideal of objectivity states a worthwhile, even if unattainable goal.' Ontologically, however, the claim that all reality is objective is 'simply false.'

What Searle means is this: In attempting to understand the world we should, as far as possible, be objective, leaving behind our personal prejudices and ideological views. But we should not confuse this with the idea that the world only contains objective entities; the world also contains subjective entities, entities that would not exist if humans did not exist - thoughts, feelings, capitalism, democracy.

We must accept, therefore, that many entities are irreducibly social or irreducibly mental, that they need to be understood in their own terms as social or metal entities. Just as animals or plants need to be understood not just as bags of chemicals but also as living beings, so humans need to understood not just as biological objects but also as social subjects. To accept the irreducibly social character of social entities, or the irreducibly mental character of mental entities, is not to fall into the Cartesian pit. It is simply to accept that human reason can be applied not just to the physical or natural realm but to the social and mental realms too. One doesn't have to be a sociophobe to believe in science and reason.

Many materialists find this argument troublesome because they hold steadfastly to the belief that there is only one way of understanding the world. Materialism, according to the mathematician Norman Levitt, 'refers to the view that there is essentially only one kind of reality, one kind of material existence, governed by its unique and invariable set of laws'.

There is, however, more than one way to understand 'materialism'. One definition is that the only stuff that exists is physical matter. A second is that one can explain all events and phenomena without recourse to the supernatural or the divine. Materialism can also refer to the belief that the explanations of natural science suffice to explain all phenomena, not simply the phenomena of nature; in other words that mental and social phenomena can be 'reduced' to physical phenomena. This is the sense in which naturalistically-inclined thinkers understand 'materialism'. To distinguish it from other visions of materialism, let us call this a 'mechanistic' view of the world.

It is quite possible to be a materialist - in the sense of rejecting divine explanations and accepting that the only stuff that exists is physical - without believing that mental and social phenomena can be explained in purely physical or mechanistic terms. A materialist view, in this sense, understands humans beings without resort to mystical explanations. But it also sees humans as exceptional because humans, unlike any other beings, possess consciousness and agency. And understanding human consciousness and agency requires us to understand humans as not just natural, but also historical and social beings.

A mechanistic view, on the other hand, sees human beings largely as objects through which nature acts. Few scientists, even those with a mechanistic worldview,would dispute that human beings possess consciousness or free will. Yet their desire for a purely naturalistic explanation of the world denies them the resources that allow them to understand humans as subjects. The peculiar place that humans occupy in the natural order means that we require special intellectual tools to understand ourselves. The tools of natural science have been developed for the understanding of inert objects (animals included), entities without consciousness or subjectivity. They are insufficient to understand what it is to be a human subject.

This is another way of saying that underlying human actions are causes distinct from that which underlie the rest of nature. All events have causes, but only humans act by reason. To understand this distinction, consider the following. Suppose one morning I rush out of the house and murder the first person I meet on the street. At my subsequent trial I put up one of two defences. The first is that I suffer from a brain tumour that has altered my personality and caused me to act in an irrationally violent fashion. The second is that I had spent the previous evening debating with a brilliant but evil existential philosopher who persuaded me that the only way to express my free will was by murdering the first person I met on the street. Most people would probably accept that in the first case I was not responsible for murder, but that I was in the second. Why? Because in one case I am caused to act as an object, in the other I act by virtue of reasoning as a subject. If a brain tumour causes me to act in certain fashion, I am acting like an object: I have no choice over my actions. I act in the same way as two stags may fight, or a cat may pounce on a bird. In neither case do they 'choose' to so act; they simply follow their impulses. But if I am persuaded by philosophical argument, I am acting as a subject, one who has a choice of actions, and has decided upon one of them. Being persuaded by a philosopher, therefore, is not simply a cause of my behaviour, it is also a reason for it. Causes happen to objects. Only subjects are motivated by reason. A reason is a special kind of cause, one that is only applicable to subjects; an act determined by reason we generally treat as an act of free will.

Now, suppose it has been established that I committed murder because I was persuaded by philosophical argument. But a philosophical argument by itself cannot cause anything. In order for me to murder someone, certain neurons in my brain must fire which lead me to seize a kitchen knife, run out of the house, and stick it into a passer-by. So even if we accept that I acted freely, that act has to have biological antecedents. But were I to say at my trial, 'I committed murder because certain neurons fired in by brain', I doubt if the judge (or the jury) would accept that as a proper defence. This is not because what I claimed was false (certain neurons did fire in my brain, and had they not done so I would not have acted as I did), but because it is the wrong kind of explanation. To understand human behaviour, we need to understand not simply the kinds of causes that afflict all objects, but also the kinds of reasons that affect only beings that possess rational selves. Animals are motivated by causes; human behaviours have both causes and reasons. We can talk of causes as being right or wrong. But only reasons can be good or bad. Causes belong to a physical world; reasons to a moral one. The problem with mechanistic explanations is that they conflate reasons and causes in trying to understand the human world purely through the tools of natural science, a science developed for the understanding of physical causes, not moral reasons.

Let me say here a few words about free will, an issue that for many people lies at the heart of the question of what it is to be human. For most people free will is expressed in opposition to the idea of determinism. We can either be free or we can be determined. The consequence has been an arid debate about human freedom. One side of this debate insists that genetic determinism, biological determinism, or any form of determinism must be wrong. The other side claims equally strongly that since nothing can happen without a cause, so free will must be an illusion. I want to argue that both sides in this debate are wrong. Free will only makes sense if we think of ourselves as both determined and free.

An undetermined world – a world in which events happen without cause – is not a free world but an arbitrary one. If human behaviour took place without cause, then we could not possibly possess anything called free will. For if there is no cause to my behaviour, then I could not be in control of it, and hence I could possess no autonomy. As John Locke pointed out more than three centuries ago, if free will is the freedom to act without cause, then only madmen would be free.

The implausibility of thinking of events in the world as uncaused has led many to adopt the opposite viewpoint: that since everything is determined, so free will must be an illusion. As the neuroscientist Colin Blakemore has put it: To choose a spouse, a job, a religious creed - or even to choose to rob a bank - is the peak of a causal chain that runs back to the origin of life and down to the nature of atoms and molecules. According to Blakemore, when 'we feel ourselves to be in control of an action, that feeling itself is the product of our brain, whose machinery has been designed, on the basis of its functional utility, by means of natural selection.' We think we are in charge, but in reality there is no self which can take charge. There is simply the machinery of the brain churning away, thanks to a chain of causal links that goes back to the Big Bang itself.

The proposition that free will is an illusion is as untenable as the belief that we live in an undetermined universe. For, as I have already suggested, humans are distinct from other animals because we are subjects as well as objects, agents of transformation, as well as the end product of a causal chain, the makers of history, not simply the products of evolution.

Suppose it were true that our belief in free will is an illusion foisted upon us by natural selection. But if our belief in free will is an illusion, how are we to view any knowledge as objectively true? How do we know, for instance, that our belief that there exists objective knowledge, and that science can help reveal it, is not itself a false belief inculcated in us by natural selection?

A Darwinian process is not driven by a search for objective truth. It is driven by considerations of utility. A belief or type of knowledge will be selected for not because it is true but because it increases relative fitness – the capacity to survive and reproduce. That is why, as I have argued, truth has no meaning to non-human animals. They simply act in ways useful to their survival.

Truth can have no meaning in a world composed simply of objects. It can only have meaning in a world that contains subjects. If we accept, as I do, that there are objective truths, and science can lead us to them, then we have also to accept that we are more than simply sophisticated animals. And we have to accept that the question of what it is to be human cannot be understood simply in the language of natural science. To accept the veracity of natural science is also to accept its limitations.

Many critics have responded to the inadequacies of mechanistic views of human nature by suggesting that the problem lies in scientific arrogance. Scientists, they suggest, place too great a faith in science and reason, and are insufficiently humble about the human capacity to understand ourselves and our world.

The social critic Bryan Appleyard, for instance, worries about the way that 'science has invaded the human realm'. Science, he insists, must be 'contained, humbled'. We must ensure that the human mind is protected from the glare of scientific investigation because we require a place 'beyond the reach of the so often disastrous tinkerings of human reason'.

In fact, mechanistic visions of humanness, far from being the product of overweening reason, are rooted in the same deep-seated pessimism that fogs much of contemporary culture and politics. A century of unparalleled bloodshed and destruction has created a widespread skepticism about human capacities. Every impression that Man makes upon his world, many feel, seems for the worse. The attempt to master nature has led to global warming and species depletion. The attempt to master society has led to Auschwitz and the gulags. We no longer believe, Michael Ignatieff recently observed, that 'material progress entails or enables moral progress'. We eat well, we drink well, we live well, Ignatieff observed, 'but we do not have good dreams'. The Holocaust 'remains a ghost at our feast'.

As we have become more pessimistic about the human condition, as the exceptional status of human beings has seemed at best mere self-delusion, at worst dangerously hubristic, so the idea that humans are just animals or machines has appeared both scientifically plausible and culturally acceptable.

The history of the twentieth century, the evolutionary biologist Rob Foley argues, has transformed scientists' vision of humanity, denting 'human self-esteem' and leading to 'a loss of confidence in the extent to which humans could be said to be on a pedestal above the swamp of animal brutishness'. The Victorians believed that humans were closer to the angels than to the apes. During the course of the twentieth century, however, Foley notes, 'apes have become more angelic' while humans have become 'more apish'.

Where it was originally thought that humans were the advanced and progressive form of life and other animals the more primitive, now it may be argued that the animal within us is our noble side, and humanity or civilisation the blacker side - a complete reversal of the original Victorian image.

The pessimism of contemporary culture has cleared a space for a more naturalistic vision of humanity, a vision that seeks to erase the distinctions between humanity and nature and to deny the special, exceptional qualities of being human. And, in turn, such a naturalistic vision of humanness reinforces the pessimism about what is to be human, undermining further faith in reason as a tool for human betterment.

Whatever calamities human beings have brought upon themselves and their world, it is not because they have tried to bring reason to bear on a problem, or tried to impose greater control upon the world. It is rather because they have acted irrationally, or ignorantly, or have had insufficient means of control. The barbarism of the past century, and the catastrophes of today, are the products not of the quest for progress, but of the lack of it. It is when we stop thinking of ourselves as political beings, with the capacity rationally to change the world, and begin to believe that the answers to human problems lie beyond the human sphere, in God or in Nature, that we unleash the monsters.

The key problem, then, is not as Bryan Appleyard believes that 'biology has invaded the human realm'. It is rather that humans have abandoned it, that we no longer think of ourselves as beings with the potential to shape our own futures. It is the political retreat from Enlightenment rationalism, from a belief in human agency, and from ideas of moral progress, that has opened up the space for a mechanistic view of Man.

Humans, Appleyard believes, need a 'refuge' from science, because we need to believe that life cannot be accounted for in purely scientific terms. Most people, he suggests, distrust reason because of the 'mess and indirection of human life'. For Appleyard, it is in such inadequacies that humanness expresses itself. In the past, Appleyard writes, God acted as a retreat from reason. 'God makes perfect sense to anybody who honestly faces the gulf between the human ability to conceive perfection, goodness, harmony and the facts of the world.' Since many people no longer believe in God, 'we must construct a place beyond the reach of the so often disastrous tinkerings of human reason.' That place, Appleyard believes, is 'the human mind'.

Such mysticism, however, offers no alternative to mechanist accounts of humanness. Revelling in mess and indirection as the essence of humanness is as profoundly antihuman as the attempt to squeeze subjectivity out of human life. To challenge mechanism we need not to retreat from reason, but to embrace it, for mysticism and mechanism are both irrational accounts of human nature. It would be inhuman to give up on the quest to understand humanness.