The hand made us more than just gifted chimps and put us on the road to becoming self-aware humans, argues Raymond Tallis.

Man's place in nature is writ upon the hand," the great anatomist Frederic Wood Jones once asserted. The same idea was pondered by ancient Greeks, while thinkers as diverse as Immanuel Kant, for whom the hand was "a window upon the mind", and Erasmus Darwin, Charles' polymathic grandfather, have echoed its sentiment. Many people, it seems, have sensed the key role of the hand in making us human beings the self-conscious and (comparatively) free creatures we are today.

In fact, it is in the grasp of the human hand that our remoteness from the natural world can be reconciled with our undoubted biological origins. And with its help, we can liberate ourselves from "biologism" - the fashionable belief that almost everything of importance about humans can be explained in biological, indeed evolutionary, terms.

Over the past century, Darwinian thought has colonised academic habitats remote from its origins. Evolutionary psychology and sociobiology - which together purport to account for most aspects of the human mind and society - are very much part of this trend and are in the ascendant.

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The fury that 25 years ago greeted E. O. Wilson's assertion that "behaviour and social structure" could be studied as "extensions of genes that exist because of their superior adaptive value" has given way to uncritical acceptance. Ethical principles, political structures, human knowledge and even the idea of truth seem to be disappearing into the voracious orifice of neo-Darwinian thought.

All of which is rather depressing because biologism overlooks most of what constitutes day-to-day life and is deeply misleading about what it is to be human. It should hardly be necessary to point out that there is a fundamental difference between the one species that argues over evolution and all the others that are merely its products. Humans are self-conscious agents whose comparatively free actions are shaped by complex, abstract frames of reference that have no counterpart in the experiences and drives of all other animals.

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Those who want to deny the huge gap between us and the other animals use two strategies: describing human behaviour in animalomorphic terms and describing animal behaviour in anthropomorphic terms. In this, they are assisted by terms such as "learning behaviour" that cross the great divide.

Daisy the cow bumps into an electrified fence and never strays there again.

Mrs Smith, deciding that she wants to improve her prospects after a messy divorce, signs up for an extramural university course to start in 2005 and in the meantime increases her availability for the babysitting circle to stockpile tokens to use for her own childcare needs while she studies.

Sociobiologists would describe both Daisy and Mrs Smith as exhibiting learning behaviour.

Determined exponents of biologism recognise no limits to the Disneyfication of animal behaviour; Matt Ridley in his recent, otherwise excellent, book Nature via Nurture speaks of the microscopic worm Caenorhabditis elegans - which has no brain and the princely total of 302 neurons - as showing "flexible learning", and discusses the difference between "social" worms that "go to school" (that is, are housed together in a Petri dish) and those that are "kept at home", and how they develop different adult "personalities".

Anyone who defends human exceptionalism risks being branded a closet creationist or a deluded sentimentalist running away from the implications of what the philosopher Daniel Dennett dubbed "Darwin's dangerous idea".

The challenge facing those of us who want to remind evolutionary psychologists of what is in front of their noses and reaffirm human difference is to avoid seeming anti-scientific or anti-Darwinian. Opponents of biologism must find a biological account of how we came to escape biology.

Given the relative triviality of the physical and genetic differences between ourselves and our closest primate cousins, this may seem a tall order. But the explanation is right before us. I would argue that it is through possession of a fully developed hand that man has been permitted progressive liberation from nature.

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The hand has the unique property of full opposability between the thumb and other fingers. The most obvious consequence of this is incomparable versatility. When opposability is added to the ability to move individual fingers independently, which was inherited from our primate ancestors, humankind gained a forelimb with unparalleled potential. As man assumed an upright posture, this potential became free to develop relatively unhindered while hand-eye coordination improved as the forelimb became much easier to see. As the physiologist Charles Sherrington pointed out, walking on two legs changed our forelimb from "a simple locomotor prop to a delicate explorer of space".

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This is all rather standard biological thinking and would explain only why humans might have become gifted chimps. To understand the immeasurable impact of possessing a hand, you have to appreciate the transformation it brought about in the hominid's relationship to its own body. Two properties of the human hand are crucial. The first is the way digits touch and interact with each other in the course of some manual task such as tying a shoelace. The second is choice, as reflected in the great range of different grips that can be used to achieve a goal, as when carrying three pints of beer through a crowded pub.

These two aspects combine to give the human a higher level of physical self-awareness. They make the hand a "proto-tool", a part of the body that we consciously use as an instrument. This tool-like status of our hands is unmatched in the animal kingdom. It makes the human organism as a whole an instrument to solve problems and ignites the sense that an individual can bring about change in its environment. The hand awakens the first-person sense that "I am this (body)". This lies at the root not only of the agency that sets humans apart from other animals but also the sense of self.

It may seem implausible to claim that something as contingent and as slight as a difference in the functional anatomy of the hand should have such momentous consequences. We may, however, assume that other primates were close to the threshold that humans crossed. There is, for example, evidence of fleeting self-consciousness in chimpanzees. In other words, the hand did not have to deliver much to start the process by which humans became ever more self-aware and distant from their status as organisms.

Once the threshold was crossed, a virtuous circle of self-consciousness and agency began. This would soon be driven largely by secondary consequences of the possession of a proto-tool. It inspired the sense that the environment around us was filled with an array of potentially useful instruments. Although it has been noted that non-human animals also seem to use tools, their comparatively unimpressive efforts - for example, it takes a chimp five years to learn to break a nut with a stone - are clearly not rooted in an instrumentalised awareness of their own bodies. It is doubtful, therefore, that this is truly analogous to human tool use. The latter extends not only the power of the human organism but also an awareness of both the environment and interaction with it. Furthermore, it raises the constant possibility of finding new ways to do things.

A tool, moreover, has many important spin-off properties. It displays a generalised human intention, showing both the needs of the individual and the way in which they will be met. So the bearer of a hand axe clearly wants to cut wood or some other material. This enhances human self-consciousness and also opens the way to collective awareness as others take in the message bound up in the publicly displayed tool. The sharing of experiences between individuals distinguishes the socialised knowledge that only humans enjoy from the solitary sentience to which other animals are confined. It lies at the origin of the pooling of animal needs in the explicit scarcities that human collectives address. It is the difference between a hunger-crazed wolf attacking its siblings and the starving humans rationing food between them.

The central role of tools inspired by the hand in promoting distinctively human forms of socialisation has been attested to by many palaeoanthroplogists. Furthermore, it is arguable that the use of tools is the precursor of language. After all, they are abstract and general representations of intentions and needs whose use involves skills and areas of the brain that overlap with those ultimately involved in speech.

All of these developments - instrumentalisation of the hominid body, use of tools, collectivisation of consciousness and language - would subsequently both drive and be driven by the increased complexity of the human brain.

This collective awakening of humanity out of the state of an organism would be gradual, with a slow start (more than a million years separates the pebble chopper from the hand axe) and then accelerating to its present dizzying rate.

There are many objections to this reconstruction of how (as the German philosopher Friedrich Schelling put it) in man, "nature opened its eyes and noticed that it exists". But none, I believe, is insuperable. The hand and its consequences provide us with a means of understanding the unique nature of human beings without denying what evolutionary science has to say about our biological roots. One can be a good Darwinian without reducing our cultural leaves to their biological roots.

Minimising human difference is not Darwinism but Darwinitis. Evolutionary psychology, sociobiology and their fundamentalist kin, far from being up to date, cannot get past the point several million years ago at which hominids started to wave farewell to the animal kingdom.

Raymond Tallis is professor of geriatric medicine at the University of Manchester. His book The Hand: A Philosophical Inquiry into Human Being is published by Edinburgh University Press this week (?17.99).

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