In our third look into the 21st century, James Watson predicts that parents will still need to decide whether to abort genetically impaired foetuses.

Science fiction writers have long speculated that the advance of science will one day usher in an age of "superpersons", genetically modified humans with talents and characteristics far superior to those of 20th-century denizens. In my view this vision will remain just that - a dream - until far, far into the future. This is not to say that scientists will not attempt some genetic modification of human beings. I anticipate that sometime in the next century, they will. But the first steps will not be in frivolous pursuit of the creation of some super-race but to seek to alleviate the horrors and unfairness of existing human suffering.

Every day children are born crippled by "bad" genes - genes that, because of altered DNA messages, do not function normally. Huntington's disease, a ravaging illness that progressively destroys nerve cells, is caused by one such "bad" gene. Another "bad" gene has been linked to cystic fibrosis, an illness that often confers a life expectancy of less than 30 years. Yet another leads to the progressive awful wasting disease Duchennes muscular dystrophy.

These findings are the beginning tools with which in the next century scientists will strive to banish genetic disease. Prenatal diagnosis is the first step: doctors can now test for predisposition to illnesses like cystic fibrosis in the womb and mothers can then decide whether or not to continue with the pregnancy. But beyond diagnosis comes gene therapy, whereby good genes are introduced into cells to compensate for bad ones. Within the next ten to 20 years, I anticipate that there will be doctors and scientists who will correct faulty genes in living patients through the introduction of DNA into somatic cells, like those of our blood or muscular system.

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Although I am optimistic about the long-term outcome of such experiments there will inevitably be setbacks. In some cases science will not yet be up to the job. I fear that it will prove particularly difficult to compensate for genes that malfunction during foetal development - which would require intricate surgery in the womb. The sad truth is likely to be that, in some cases, parents will still have to make a decision about whether or not to terminate the existence of a genetically impaired foetus. This will always be a distasteful decision. But, in my view, doing so is incomparably more compassionate than allowing an infant to come into the world tragically impaired. It is crucial that such decisions be reserved to parents, and, in particular, mothers. The history of eugenics has taught us that governments should never be given authority in such cases.

Like many past genetic breakthroughs, many future scientific advances will be accompanied by controversy. Ever since 1973, when scientists at Stanford University first reinserted the novel test-tube rearranged DNA segments back into living cells, there has been criticism of "recombinant" DNA procedures. Doom-mongers then predicted that some of these test-tube made molecules would unleash disastrous plagues on human civilisation. They called for legislation to control such research, and ostensibly, protect humankind. Their calls came to nothing and most recombinant DNA research has proceeded effectively unrestricted by governmental regulations throughout the 1980s. And as most scientists predicted, these new procedures have led to virtually no human harm. At the same time, many important benefits to humankind have been made possible. For example, recombinant DNA procedures now let us understand the essential molecular features of cancer cells.

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But one potential goal has since remained off-limits. So-called "germ-line" manipulations - the insertion of functional genetic material into human germ cells, sperm and eggs, is a technique forbidden to most of the world's scientists. The fear is that any changes would not be confined to a single generation but would be passed on to descendants.

No government has been willing to sanction research that might redirect the course of human evolution. Yet germ-line manipulations will be attempted in the 21st century and for the same reasons that somatic gene therapy will earlier have been explored. In the face of human tragedy no avenue of hope should be left unexplored. Confronted, for example, with a deadly virus that we see no way of controlling, scientists will be given the green light to insert antiviral DNA segments into sperm and eggs in a bid to create protected children. Though mistakes will naturally be made in such attempts, we must not lack the courage to use science to challenge the all too often grossly unfair courses of human evolution.

James D. Watson, president of the Cold Spring Harbor laboratory in New York, won the Nobel prize for medicine for his part in unravelling the structure of DNA. This is an extract from Predictions: Thirty Great Minds on the Future (Oxford University Press/The THES), which is published on November 4. Reserve your copy for Pounds 12.99 (including postage and packaging) from The THES Bookshop, Freepost (SWB7 12) Patchway, Bristol BS32 022, or telephone 01454 7417.