Human embryos, too, contain stem cells, but as these are obtained from the extras made after test-tube fertilisation, their use has caused controversy. They could be useful in making skin for burn victims, replacing the damaged nerve cells of those with Parkinson's disease, or even to generate whole organs, either for transplants, or to replace old tissue with new. Most illnesses nowadays are those of old age; and with the promise of such cells in fighting heart disease, cancer and so on as much as half the population might benefit from their use.

Nerve cells from foetuses inserted into the brains of patients with Parkinson's disease can relieve their symptoms of slow movement and rigidity: such juvenile cells can, it seems, change their personalities to adapt to the adult brain in which they find themselves. Even adults have stem cells in parts of the body that, like blood, muscle or liver, often regenerate. Such cells can be retrained to take up new and quite different jobs. Stem cells from the brain or from muscles will, with some urging, make blood cells, while the bone marrow is even more flexible as its stem cells can change into brain, liver and muscle. To inject adult stem cells from the marrow of a healthy patient can strengthen the bones of children with inherited damage to the skeleton and the same approach may reduce the severity of symptoms in people who suffer from Huntington's disease. Perhaps other damaged tissues such as those involved in Alzheimer's disease or diabetes might be helped. In mice, those from a normal embryo injected into a mutant animal lacking part of the sheath of insulation around certain nerves (a structure damaged in multiple sclerosis) make the missing material. Such cells injected into paralyzed rats restore movement. Stem cells are rare  - about one in ten billion in the marrow — and not all the news is good; in mice, such cells injected into adults can grow into tumours and it may be necessary to add a suicide gene to kill them off if they turn nasty. Their very malleability may cause problems — who, after all, wants teeth to grow in their brain?

If stem cells pay off, a new era of medicine will begin. Perhaps everyone will keep a store of frozen cells taken at birth in the expectation that they will be needed later to repair an organ that fails with age or disease. On a more modest scale, it should be possible for every hospital to fill a freezer with such things taken from thousands of different people in the hope of having one ready for a match with some future patient who has not stored his own. Even if the hope of new organs is not fulfilled, they might be engineered to make them resistant to anti-cancer drugs so that anyone unfortunate enough to get the disease later in life can be treated with larger doses and his blood-making capacity maintained with material kept in frozen adolescence.

Chimaeras made with the help of stem cells sometimes use them to make not liver or brain but sperm or eggs. Then, all its offspring resemble the stem-cell parent, and, if that individual has been engineered, will carry the inserted gene. That played a crucial part in the tale of Dolly. Remarkable animal as she is, Dolly is, in the end, just a sheep. By adding DNA a small proportion of the millions of cells in a culture dish can be persuaded to rake up the alien gene and, with luck, force it to do its job. To insert such transformed stem cells into another animal does to mammals what was once possible only with bacteria. Dolly's successor, Polly, was cloned from cells that contained a human gene for the blood protein missing in one form of haemophilia attached to an on-off switch for sheep milk proteins. Sheep cells can be transformed in this way and, from one engineered beast, a whole herd can grow. Not many may be needed: a thousand animals could satisfy the world demand for the enzyme used to help patients with emphysema, but each may be valued at many thousands of dollars.

The public has an impressive capacity for boredom; and many of the methods used to manipulate genes and produce animals without sex are becoming commonplace. In 1998, Switzerland, where the gothic tale of Frankenstein begins, held a referendum on whether to ban gene technology, electrical fusion included, altogether. The motion was defeated and the research has gone on. Perhaps cloning itself will, in a few years, be a standard medical technology.

A passage written in 1818 on the first Swiss genetic engineering experiment: 'With an anxiety that almost amounted to agony, I collected the instruments of life around me, that I might infuse a spark of being into the lifeless thing that lay at my feet. It was already one in the morning, the rain pattered dismally against the panes, and my candle was nearly burnt out, when, by the glimmer of the half-extinguished light, I saw the dull yellow eye of the creature open; it breathed hard, and a convulsive motion agitated its limbs.' That reads better than its modern equivalent: The birth of lambs from differentiated fetal and adult cells reinforces previous speculation that by inducing donor cells to become quiescent it will be possible to obtain normal development from a wide variety of differentiated cells'. The report of Dolly's genesis does not have quite the ring of Mary Shelley; but marks the beginning of an era that will tax the most Gothic of imaginations. And what would Dolly's spiritual ancestor, that failed Scottish clone, the Bride of Frankenstein, have thought?

One reason why science fiction is so boring is that it is nearly all the same. The monsters may differ, but the plots do not. The same is true for most imaginary Utopias. From The War of the Worlds to Planet of the Apes an alien life form appears, masters the human race, and meets its doom because of its own weakness. Most novels of the future ignore one of the few predictable things about evolution, which is its unpredictability. No dinosaur could have guessed that descendants of the shrew-like beasts that played at its feet would soon replace it, and rhe chimpanzees who outnumbered humans a hundred thousand years ago would be depressed to see that their relatives arc now abundant while their descendants are an endangered species.

Evolution always builds on its weaknesses, rather than making a fresh start. The lack of a grand plan is what makes life so adaptable and humans — the greatest opportunists of all — such a success. That utilitarian approach means that speculations about the future of evolution are risky. As Hegel put it, the greatest lesson of history is that no one ever learns the lesson of history.

In the earliest Utopian novels, from Thomas More onwards, societies of the future were quite different from those of the writer's day. They might have golden chamberpots; but there imagination ended. The people who urinated into them were much like those who preferred to hoard the metal. After Darwin, Utopia evolved: society stayed the same bur people changed instead. Many of the best-known Utopian novels trace their visions of the future to Darwin. Samuel Butler, author of Erewhon (called in its first version Darwin Among the Machines), shared an education — Shrewsbury School and Cambridge — with the great man and was himself a keen evolutionist (albeit an anti-Darwinian). Aldous Huxley's Brave New World owes much of its plot to his biological brother Julian and to their grandfather Thomas Henry Huxley, Darwin's bulldog. H. G. Wells — whose Utopia, in The Time Machine, was based on the evolutionary theme of the human race splitting into two species — himself wrote a biological textbook with Julian Huxley; and, as we have seen, George Bernard Shaw, author of Back to Methuselah, was a follower of Galton and appeared on public platforms with him.