What will be the big scientific breakthroughs of the 21st century? Leading scientists peek into the future...

"The genetic engineering of children," says Lee Silver, professor of genetics at Princeton University. "The breakthrough I have in mind will definitely happen, even though today there are still many scientists who refuse to believe it. We will not only identify every gene in the human genome, but we will find out the role that each gene plays in human development and how all the genes interact with each other, both normally and in cases of disease.

"This breakthrough will have an unprecedented impact on the practice of medicine, but its impact on the way people have children will be even greater as prospective parents (who have enough money) are given the opportunity to choose the precise genetic makeup of their children.

"Ultimately the ability to control the genetic makeup of children will change the nature of the human species."

"The discovery of a 'Theoryof Everything'..."

says Richard Peto, professor of medical statistics and epidemiology at Oxford University. "Particle physics and the astronomy of the early universe have the possibilities of producing qualitative changes in our knowledge of the universe, allowing us to understand why the universe and the laws of physics are as they are. There's the possibility of moving towards a theory of everything. It would be absolutely extraordinary - it could be the most beautiful thing ever created.

... and nearly everyone living to 70.

In medical science we have seen the most amazing transformation in life expectancy this century. I would hope we can get to a situation where 80 or 90 per cent (of the world's population) can expect to live to 70, though I don't think we will make much difference to the absolute proportion living above 100."

"Clean fuel," says Charles Baker, head of fusion research in the University of California San Diego's school of engineering. "The need to develop carbon-free forms of energy is a very important issue, related to global warming and carbon dioxide in the atmosphere. Fusion energy offers huge possibilities."

"The full understanding of humanconsciousness," says Richard Dawkins, Oxford University's professor of the public understanding of science.

"Searching for extra-terrestrial life," says Roger Angel, professor of astronomyat the University of Arizona. "On our earth, there was no oxygen until there was life. Oxygen is a pretty good indication of life. Within the next century, I think it's very likely that we will find planets whose temperature and size are similar to earth's and which probably have atmosphere and water. The question of whether life has begun elsewhere is the biggie. The technology to find out is there. In the next century we will get a look."

"The engagement of the public inscience and the expression ofscientific ideas in a way they can understand and contribute to," says Susan Greenfield, the first female head of the Royal Institution and a professor at Oxford University leading a multidisciplinary group on the brain.

"A fuller understanding of genetics," says Sir Robert May, Britain's chief scientist. "The understanding of the relationship between genetic codes and their functions, I suspect, is going to be vastly more difficult than people think. Just having the code is far short of telling you what this code is for."

"Comprehending the workings of thehuman brain," says Sir Aaron Klug, president of the Royal Society, "and then understanding gene networks in other parts of the body, understanding how they interact."

"It will be totally unpredictable," says Britain's 1996 Nobel prizewinning chemist Sir Harry Kroto, who discovered a remarkable new form of carbon fibre structured like a football. "If you can predict a discovery, it can't be that important. Major advances should be totally unpredictable."