Average life expectancy today is 77 years. The oldest recorded human, Frenchwoman Jeanne Calment, died in 1997 at 122. Can this maximum life span be extended?

The Optimist's View: Aubrey de Grey, a British biogerontologist, is "bullish on the prospects for indefinite life span." De Grey believes it's only fatalism about aging that stands in the way of progress. Most optimists, such as Cynthia Kenyon, PhD, a professor of biochemistry and biophysics at the University of California, San Francisco, are more measured. Kenyon's lab found that altering a small number of genes and cells in the worm species C. elegans lengthened the worm's typical 20-day life span up to sixfold. In human terms, that would be like living a healthy, active 500 years.

Even though some 70 percent of our genes are also in C. elegans, Kenyon is very clear that there are big obstacles in converting genetic discoveries in lab animals into longer life spans for human beings. "We don't know for sure whether these genes that affect aging in small animals will turn out to affect aging in humans. Even if they do, it's not clear how long it would take scientists to make any drug."

Yet, over the next 100 to 200 years, says Kenyon, she's "wildly optimistic" that humans can achieve perhaps as much as a doubling of life span. "If you think about it, the precursor of worms and humans in evolution probably had a life span of about two weeks, so changes in genes have already extended life about a thousandfold," she says. "If life span is determined by the balance of forces that damage cells against forces that protect them, then it should be possible to strengthen the repair and maintenance forces of cells, and tip the balance, so we would never get old, or at least stay young longer."

The Realist's View: "People are bombarded with misinformation about our ability to extend life," says S. Jay Olshansky, PhD, a biodemographer and professor in the School of Public Health at the University of Illinois in Chicago, who believes that "a seven-year delay in the aging process" is more possible. Earlier gains in average life expectancy (for U.S. females, it's gone from 48.3 in 1900 to 79.8 in 2001) were largely achieved by saving the lives of the young, through improved sanitation, vaccines, and the discovery of antibiotics. To increase life expectancy today requires saving the lives of older people, who have accumulated random damage to their cells -- a much more difficult proposition.

Where the Two Shall Meet: "Health span" is a new term which sums up the common ground between the optimists and realists -- it's shorthand for all the measures necessary to live longer, healthier, and more active lives. As Kenyon puts it: "Nobody wants to check into the nursing home and just hang on forever." We'll have to clean up our lifestyle, make sure more people get treated for existing disease, and develop new drugs that will tackle the underlying process of aging. It's the last two points that have researchers racing to find solutions -- hopefully before the majority of baby boomers enter their retirement years.