Humans are special beings, inside and outside nature. Scientists who cannot acknowledge this will never be able to fathom us, says Kenan Malik.

It may not be too much to say that sociology and other social sciences, as well as the humanities, are the last branches of biology," E. O. Wilson wrote 25 years ago in his book Sociobiology . Then, his claim drew a howl of protest. Today, many believe the idea that all human activity can be explained by the natural sciences is self-evidently true. The neuroscientist Susan Greenfield opened her recent acclaimed television series, Brain Story , with the suggestion that "we can explain everything about ourselves by looking inside the brain". According to 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."

For such thinkers, the question of what it means to be human will eventually be solved, like any other question about nature. The evolutionary biologist Rob Foley suggests that science "turns every large philosophical and metaphysical question into what are often straightforward and even boring technical ones". Recent dramatic advances in genetics, evolutionary biology, psychology and neuroscience seem to be proving such arguments right. Yet, however much we learn about our brain, our genes or our evolutionary history, we will not learn fully what it is to be human. Why? Because humans are not like other natural creatures and cannot be understood in the same terms. Humans are special, and we require special tools to understand ourselves.

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 scientific methodology is its view of nature, and of natural organisms, as machines; not because ants or apes work like watches or televisions, but because, like all machines, they lack consciousness, foresight and will. Animals are objects of natural forces, not potential subjects of their own destiny. They act out a drama rather than create it. Humans, however, do possess purpose and agency. Uniquely among organisms, human beings are both objects of nature and subjects able to shape their own fate. We are biological beings. But we are also conscious beings with purpose and agency, traits that allow us to design ways of breaking the constraints of biological and physical laws. We are, in other words, both inside and outside nature.

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The relationship between humans as physically determined beings, and humans as social beings and moral agents, is a problem for scientists and philosophers. But denying one or other aspect of our humanness, as many scientists in effect do, is not a way of solving the problem. By insisting that humans can be understood in purely naturalistic terms, scientists give up on the attempt to understand them as subjective beings - as both natural and social - and are compelled to view them simply as objects. Understanding human beings requires not just the tools of natural science, but also those of other disciplines: the social sciences, history and philosophy. None of these is any less valuable or less rational than physics, biology or chemistry. They are simply more, or less, useful in different circumstances.

Why are so many scientists so reluctant to see humans as special beings? Largely because of the terror they have of falling into the Cartesian pit. Descartes divided the world into two substances: the physical and the mental. Physical stuff was something it was possible to 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 impossible to grasp. It occupied no space, possessed no smell, taste or feel and had no physical presence. Hence scientists could not begin to understand it.

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They responded to Descartes by trying to reduce everything to the physical. For most scientists, the only material entities in the world are physical entities, the only material forces are physical forces. Reality consists of atoms and molecules, gravity and electricity.

Natural scientists investigating human nature are particularly keen on this insistence that the only reality is physical. No teetering at the edge of the Cartesian pit for them, no juggling with angel dust or mind stuff; simply an insistence that all aspects of the human - including the human mind and human society - must be understood in a purely naturalistic way.

As a result, they have become sociophobes, possessing a morbid fear of all social explanations. As the anthropologists Randy Thornhill and Craig Palmer have put it, to say that society causes something is to make a "metaphysical assertion" because it is to "attribute cause to a non-corporeal reified entity". Sociophobes do not deny the social. They simply insist that social phenomena can only be understood as natural or physica l phenomena. Cosmides and Tooby, for instance, believe that social process is like natural process - a society is like a zebra herd - and that social systems should be studied as ecosystems.

Yet every day of our lives we are reminded that not everything can be reduced to the physical. The world contains myriad things that are not physical entities: racism, Nato, the debate between rationalism and empiricism, a sense of duty, the number of offsides in a football match, reasons to be sceptical of evolutionary psychology and so on. Are these physical things? No - but most also have a physical manifestation. Nato has a headquarters in Brussels, but it would be hard to argue that the organisation consists solely of the building, its contents or its occupants. If they are not physical things, do they exist? Clearly they do. And we know they do because they have effects on the world, including physical ones. Racism led to the murder of Stephen Lawrence. Nato bombed Yugoslavia.

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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. 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. There are no social atoms or molecules of mind. Social entities exist not as "stuff" but as relationships. Interactions between certain physical entities give rise to non-physical entities that can affect the physical world. Human beings are the only physical entities that can do this. And they can do this not because they possess magic powers or live in a spiritual realm but because, uniquely, they are not just physical but social beings, too. The social world is unique to humans; we cannot investigate it using the same tools we use to investigate non-human animals. Imagine going to the dentist with a broken tooth, and instead of his usual array of drills, he produces a chest-cutter. You just might get worried. We should similarly be worried by people who tell us that we can understand human societies using tools developed to open ecosystems or poke inside zebra herds.

None of this should give scientists palpitations. Accepting the irreducibly social character of social entities is neither giving into barbarians besieging the gates of science nor falling into the Cartesian pit. It is simply accepting that human reason can be applied not just to the physical or natural realm but also to the social realm.

There is an old joke about two men sitting on a park bench. One has a paper bag over his head. "Why are you sitting with a paper bag on your head," the other asks him. "To keep the elephants away," comes the reply. "What elephants?" asks the first man, looking about greatly puzzled. "I can't see any elephants." "Exactly," says the paper bag man. "It's working brilliantly." If you invent a non-existent problem, you can always invent an unnecessary solution. So it is with sociophobes. There is nothing mystical or unscientific about social explanations of human behaviour, or in the belief that there exist non-physical entities able to cause changes in the physical world. One does not have to posit purely biological answers to questions about human behaviour. Sociophobes can remove the paper bags from their heads. There are no elephants (Cartesian or otherwise) in the park.

Kenan Malik is a writer and lecturer. His book Man, Beast and Zombie is published next week by Weidenfeld and Nicolson, £20.00.

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