One of the greatest areas of public unease about the rapid pace of gene research is that people will alter the human germ line for non-medical or cosmetic reasons - to make their descendants more beautiful or intelligent or athletic.

This is a very distant threat, a leading US geneticist told the World Economic Forum on Thursday, while a much more imminent prospect is genetic engineering of people who are alive now.

George Church, professor of genetics at Harvard University, said what was known as somatic genetic enhancement could "spread like wildfire" as soon as it became technically possible and available at a reasonable price.

This would be a non- medical application of gene therapy, which is just beginning to show benefits in clinical trials for diseases such as haemophilia after several years of disappointment.

It involves adding new genes to cells or tissues in particular parts of the body, such as the blood or brain, which would not be passed on to future generations.

"In certain cases it would be easier to engineer a [living] child or adult than the next generation," Prof Church said, "and the effects would be felt much more quickly."

The traits concerned might range from physical appearance to intelligence.

"Some people say intelligence is too complex to influence in this way, but I have not seen any evidence for that," said Prof Church, who directs Harvard's Lipper Centre for Computational Genetics and is a leading figure in the international human genome project.

For many characteristics, it would be more effective to adapt a child, whose basic characteristics were already evident, than to estimate the likely effect of genetic changes on a new embryo, he said.

This possibility has been largely overlooked by geneticists and people commenting on their work, Prof Church said.

"We may think of this as less of a threat because it is not inherited and therefore does not capture emotion in the same way as germ line changes, but it would have an effect far more quickly than genetic engineering that relies on procreation," he said, adding that genomics was going to increase the gap between rich and poor people - and developed and developing nations.