Holy Grail or poisoned chalice?: Science is revealing the blueprint for a human being. But humanity means more than genetics, warns Tom Wilkie

AS THE century of science draws to a close, the seemingly disparate paths of molecular biology, chemistry, biology and genetics have converged to produce a branch of inquiry that promises to touch all our lives in the most intimate way: the unravelling of the message of human inheritance.

Scientists are now confident that within little more than a decade they will have located all human genes and picked through the double helix of human DNA so that they can load into computer databases the entire set of genetic instructions that specifies a human being.

This is the Human Genome Project. It has been called the Holy Grail of modern biology. Costing more than pounds 2bn, it is the most ambitious scientific project since the Apollo programme to land a man on the moon. The project will reveal a new human anatomy - not the bones, muscles and sinews, but the complete genetic blueprint for a human bring.

The genetic inheritance a baby receives from its parents at the moment of conception fixes much of its later development, determining characteristics as varied as whether it will have blue eyes or suffer from a life-threatening illness such as cystic fibrosis. The human genome is the compendium of all these inherited instructions. Written out along the spiral of DNA is a sequence of chemicals that form the letters of the genetic text. It is an extremely long text, containing more than three billion letters.

Considering the length of the human genome, nature is an excellent proofreader. But sometimes there are mistakes. An error in a single gene can give rise to crippling disease, such as cystic fibrosis or thalassaemia. More than 4,000 such single-gene defects are known to afflict humanity. The majority of them are fatal; the majority of the victims children. The suffering caused by genetic disease embraces not just those with the disorder but also their parents, who must live with the knowledge that they have passed on the defect.

Rapid progress in genetic research since the mid Eighties has enabled scientists to identify the defects underlying common genetic diseases, and thus to screen parents who might be at risk of transmitting single-gene defects to their children. And in September 1991 a four-year-old girl became the first patient to receive a successful gene transplant in the treatment of a fatal genetic disorder. Intact copies of a gene were inserted into cells of her body to compensate for the defective copies she had inherited. The transplanted genes provided a new set of instructions for the affected cells which rectified her inborn defect.

With the success of such techniques, it was not long before momentum built up behind the grander project of finding out how to spell 'human' by 'sequencing' the entire genome - writing out all the letters in their correct order. The Human Genome Project is the boldest endeavour ever undertaken in biology; it will transform human life more profoundly than all the hi-tech inventions of the space age.

For example, there is clear evidence that diseases such as diabetes, heart disease, cancer and some psychiatric illnesses, although not inherited in a straightforward manner like sickle- cell anaemia, none the less have a strong genetic component. These are 'polygenic' traits which result from the co-ordinated action of many genes together rather than from a single defective gene. These diseases, too, will be amenable to the genetic approach.

Yet the ramifications of the project now under way in laboratories around the world go far beyond a narrow focus on disease. Some of its proponents have made claims of great extravagance - that the Human Genome Project will bring us to understand, at the most fundamental level, what it is to be human.

Such sweeping claims arise from a fatal temptation to import into biology some of the concepts and habits of thought peculiar to theoretical physics. The physicist searches for an inner simplicity and fundamental structure to the world of forces and matter. This search has led to the concept of the 'fundamental forces' that govern the material world and to the idea that material objects are composed of elementary constituent particles. Once the particles and the forces that govern their interaction have been specified, then the subsequent development of the universe has also been worked out, at least in principle - only a shortage of the necessary computational capacity prevents us from doing so in practice.

The temptation is to regard genes in a similar vein, as fundamental entities in biology, and to think that by specifying an individual's genes, one has somehow set out that person's life's course. It is a common misperception to think that the genes somehow encapsulate the inner 'essence' of an individual. This is clearly not true. The DNA of a chimpanzee and that of a human being differ by only about 1.6 per cent: it seems incoherent to assert that that 1.6 per cent is the part containing the essence of humanity.

Genes are important, but they are not all-important. People are more than their physical or genetic anatomy. Our anatomy rules out certain futures, but it does not dictate which of the many possible futures that could be mine will be mine.

Nor is our anatomy indispensable to our personal identity. If as a child I had lost both legs in an accident, then it would have severely changed my personal anatomy and would have ruled out many otherwise attainable futures. But even though my life history would have been different it would still recognisably be the same 'I'. Similarly, I could have a heart and lungs transplant, liver and kidneys, bone marrow - and still be me.

If the new genetics knowledge is not used wisely, it holds the threat of creating new forms of discrimination and new methods of oppression. No one will be untouched, for we have all been formed by the genetic inheritance we have received from our parents. Many characteristics, such as height and intelligence, result not from the action of genes alone, but from subtle interactions between genes and the environment. What would be the implications if humanity were to understand with precision the genetic constitution which, given the same environment, will predispose one person towards a higher intelligence than another individual whose genes were differently shuffled? The Human Genome Project holds the promise that ultimately we may be able to alter our genetic inheritance if we so choose. And there is the central moral problem: how can we ensure that when we choose, we choose correctly? That such a potential is a promise and not a threat?

One medical researcher who has been forced to confront the moral choices opened up by a earlier technology which he helped to create is Professor Robert Edwards, one of the pioneers of the in vitro fertilisation technique that led to the world's first 'test tube' baby. In a speech to the Centre for Social Ethics and Policy at Manchester University in 1987, Professor Edwards warned against looking to scientists for moral guidance about the consequences of their work:

'Scientists are notoriously shy of 'ethics' in relation to the general public. Many of them do not care to enter such debates even in their own field of work unless the social circumstances literally compel them . . . Most scientists have never been trained in ethics and they face considerable difficulties when faced with the formulation of their own ethical principles in relation to their subject.'

There is an undeniable arrogance on the part of some researchers, a sort of patrician disdain for the mass of the plebs. Our research, they seem to be saying, whether the masses know it or not, whether they like it or not, is going to change their lives, and if they want to comment on it or try to influence how it will affect their lives, then they must adopt our vocabulary and master our technical argot. Only discourse couched in our terms will be deemed legitimate.

But we, the laity, and not the professionals, must master the new knowledge and its technological application, so that we can place its insights into the human condition in a broader context.

At the end of the Human Genome Project, its most important lesson will be to remind us that genes and genetics are not the fundamental basis of human life. The project will have been successful if it teaches us to abandon the habits of thinking which we have inherited from physics, where the elementary particles are both fundamental essence and ultimate cause. The physicist's universe is in stasis, whereas life is a process - like a flickering candle flame which has a form and consumes energy. But although life leaves a trace of itself in the form of genetic inheritance when at last the candle has been used up, there is no essence to be found.

This, then, may be the final challenge posed by the Human Genome Project: to redefine our sense of our own moral worth and to find a way of asserting, in the face of all the technical details of genetics, that human life is greater than the DNA from which it sprang; and that human beings retain a moral value which is irreducible and which transcends the sequence of three billion base pairs within the human genome.

'Perilous knowledge: the human genome project and its implications', by Tom Wilkie, is published by Faber & Faber at pounds 14.99.