THE possibilities are mind-boggling. Just think what it would mean if we could genetically programme future generations of human beings to be better, more balanced people.

We could ensure, for example, that everyone had a genetically-enhanced dress sense. No more silver-haired council leaders parading around York in 'funky' leather jackets 20 years too young for them.

We could programme kids to be obedient so they don't run teachers ragged - and parents, too, so they don't keep complaining when education officials tell them little Johnny can't go to the same school as big sister Sally, because under the new admissions policy it's far too close.

We could even screen out of future generations our innate dislike of the French - so those of us who want to could enjoy the odd continental market in York without feeling like traitors. Breakthrough indeed.

Seriously, though, the success of scientists in cracking the human genetic code will quite possibly turn out to have been the single most important development of the 21st century.

It holds out the promise of a revolution in medicine: of medical treatments tailored to suit individual patients; of more precise preventive medicines to forestall heart attacks and cancers; of the elimination of inherited diseases such as muscular dystrophy, cystic fibrosis and diabetes; of a greatly extended human lifespan.

There are, though, dangers as well.

We won't need to start tampering with people's genes to feel the medical benefits of the new knowledge. Our understanding of our own genetic structure will make it possible to target treatments precisely, without the need to alter the genetic make-up of patients. But the potential for human genetic engineering is now there and, once learned, that knowledge can never be unlearned.

It is a dangerous knowledge: just as the discovery of nuclear fission was a dangerous discovery. No one knows quite where it may lead. We are like little children who have just learned how to make fire. Unfortunately - though the religious may disagree - there is no one standing by ready to hold our hand and show us how best to use it.

It is often said that scientific knowledge proceeds faster than our ability to decide, ethically and morally, what to do with it. Human beings have a great capacity for kindness and compassion - but as a race we also have a great capacity for fear, mistrust, hostility and greed. Our discovery of nuclear fission led not to cheap, clean power for all, but the nuclear bomb. If the marvellous breakthrough in our understanding of the human genetic code is to become a thing of good, rather than of evil, we need to start thinking now about the uses we should make of it - and where we should draw the line.

If we start tampering with human DNA to remove the risk of cystic fibrosis from future generations, why not do the same to increase intelligence, or beauty, or longevity? And if we do begin to do these things, do we make the 'benefits' available to all, or simply those who can afford them? The chilling prospect looms of a population divided not just by wealth, but by the quality of their genetic makeup, too - of a genetic 'super-race' lording it over the rest.

York University's own professor Norman Maitland has suggested the new science may well require a new breed of scientist to police it - the 'genetic ethicist'. It's a sobering thought.

Worrying, too, is the potential for exploitation of the new knowledge for commercial gain. It would be a tragedy if 'patenting' of stretches of the human DNA sequence for sale to industry were allowed. It must be stopped.

Perhaps there's one area, at least, where we should consider genetic engineering of future generations.

Wouldn't it be great if we could screen out of humanity the insane desire for ever greater profit for profit's sake?