SAN FRANCISCO - Fancy living another 100 years or more? Some experts said recently that scientific advances will one day enable humans to last decades beyond what is now seen as the natural limit of the human life span.

　　"I think we are knocking at the door of immortality," said Michael Zey, a Montclair State University business professor and author of two books on the future. "I think by 2075 we will see it and that's a conservative estimate."

　　Zey spoke on the sidelines of the annual conference of the World Future Society, a group that ponders how the future will look across many different aspects of society.

　　In a presentation at the meeting in San Francisco, Donald Louria, a professor at New Jersey Medical School in Newark said advances in manipulating cells and genes as well as nanotechnology make it likely humans will live in the future beyond what has been possible in the past.

　　"What was science fiction a decade ago is no longer science fiction," he said.

　　500 years?

　　"There is a dramatic and intensive push so that people can live from 120 to 180 years," he said. "Some have suggested that there is no limit and that people could live to 200 or 300 or 500 years."

　　Outside the conference, many scientists who specialize in ageing are skeptical of such claims and say the human body is just not designed to last past about 120 years. Even with healthier lifestyles and less disease, they say failure of the brain and other organs will eventually condemn all humans.

　　"These people spout off as though a large part of the population is going to be able to do something like this. It's just way beyond reality," said Thomas Perls, who leads the New England Centenarian Study, the largest such analysis of the oldest of the old. "It's just pure science fiction."

　　"We are fast approaching what our bodies are capable of achieving," he said in a telephone interview. "To get even the average person to be 100 or to get them to 180 is like trying to get a space shuttle to Pluto."

　　Stamping out disabilities

　　Any dramatic extension of the human life span would depend on altering the onset of disabilities that accompany the ageing process by changing one's genetic make up, said Harvey Cohen, director of the Centre for the Study of Ageing and Human Development at Duke University Medical Centre.

　　"It's certainly unlikely any time in the near future," he said in an interview. "Sure there is a possibility but there is no data currently available to suggest ways that would happen."

　　Scientists also differ on what kind of life the super aged might live.

　　"It remains to be seen if you pass the threshold of say 120, you know; could you be healthy enough to have good quality of life?" said Leonard Poon, director of the University of Georgia Gerontology Centre. "Currently people who could get to that point are not in good health at all."

　　Poon, who leads a study of more than 150 centenarians in Georgia, cited the case of Jeanne Louise Calment of France, the oldest person on record who died at age 122 in 1997.

　　"At 122 she was fairly debilitated. I visited her when she was 119 in France and at that time she was pretty much blind and having very much difficulty hearing," he said.