Adam and Eve lost it, alchemists tried to brew it and, if you believe the legends, Spanish conquistador Juan Ponce de Leon was searching for it when he discovered Florida.

To live forever while preserving health and retaining the semblance and vigor of youth is one of humanity's oldest and most elusive goals.

Now, after countless false starts and disappointments, some scientists say we could finally be close to achieving lifetimes that are, if not endless, at least several decades longer.

This modern miracle, they say, will come not from drinking revitalizing waters or from transmuted substances, but from a scientific understanding of how aging affects our bodies at the cellular and molecular levels.

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Whether through genetic tinkering or technology that mimics the effects of caloric restriction — strategies that have successfully extended the lives of flies, worms and mice — a growing number of scientists now think that humans could one day routinely live to 140 years of age or more.

Extreme optimists such as University of Cambridge gerentology Aubrey de Gray think the maximum human lifespan could be extended indefinitely, but such visions of immortality are dismissed by most scientists as little more than science fiction.

While scientists go back and forth on the feasibility of slowing, halting or even reversing the aging process, ethicists and policymakers have quietly been engaged in a separate debate about whether it is wise to actually do so.

A doubled lifespan

If scientists could create a pill that let you live twice as long while remaining free of infirmities, would you take it?

If one considers only the personal benefits that longer life would bring, the answer might seem like a no-brainer: People could spend more quality time with loved ones; watch future generations grow up; learn new languages; master new musical instruments; try different careers or travel the world.

But what about society as a whole? Would it be better off if life spans were doubled? The question is one of growing relevance, and serious debate about it goes back at least a few years to the Kronos Conference on Longevity Health Sciences in Arizona.

Gregory Stock, director of the Program on Medicine, Technology, and Society at UCLA's School of Public Health, answered the question with an emphatic "Yes."

A doubled lifespan, Stock said, would "give us a chance to recover from our mistakes, lead us towards longer-term thinking and reduce healthcare costs by delaying the onset of expensive diseases of aging. It would also raise productivity by adding to our prime years."

Bioethicist Daniel Callahan, a cofounder of the Hastings Center in New York, didn't share Stock's enthusiasm. Callahan's objections were practical ones. For one thing, he said, doubling life spans won't solve any of our current social problems.

"We have war, poverty, all sorts of issues around, and I don't think any of them would be at all helped by having people live longer," Callahan said in a recent telephone interview. "The question is, 'What will we get as a society?' I suspect it won't be a better society."

Others point out that a doubling of the human lifespan will affect society at every level. Notions about marriage, family and work will change in fundamental ways, they say, as will attitudes toward the young and the old.

Marriage and family

Richard Kalish, a psychologist who considered the social effects of life extension technologies, thinks a longer lifespan will radically change how we view marriage.

In today's world, for example, a couple in their 60s who are stuck in a loveless but tolerable marriage might decide to stay together for the remaining 15 to 20 years of their lives out of inertia or familiarity.

But if that same couple knew they might have to suffer each other's company for another 60 or 80 years, their choice might be different.

Kalish predicted that as life spans increase, there will be a shift in emphasis from marriage as a lifelong union to marriage as a long-term commitment. Multiple, brief marriages could become common.

A doubled lifespan will reshape notions of family life in other ways, too, says Chris Hackler, head of the Division of Medical Humanities at the University of Arkansas.

If multiple marriages become the norm, as Kalish predicts, and each marriage produces children, then half-siblings will become more common, Hackler points out.

And if couples continue the current trend of having children beginning in their 20s and 30s, then eight or even 10 generations might be alive simultaneously, Hackler said.

Furthermore, if life extension also increases a woman's period of fertility, siblings could be born 40 or 50 years apart. Such a large age difference would radically change the way siblings or parents and their children interact with one other.

"If we were 100 years younger than our parents or 60 years apart from our siblings, that would certainly create a different set of social relationships," Hackler told LiveScience.

The workplace

For most people, living longer will inevitably mean more time spent working. Careers will necessarily become longer, and the retirement age will have to be pushed back, not only so individuals can support themselves, but to avoid overtaxing a nation's social security system.

Advocates of anti-aging research say that working longer might not be such a bad thing. With skilled workers remaining in the workforce longer, economic productivity would go up. And if people got bored with their jobs, they could switch careers.

But such changes would carry their own set of dangers, critics say.

Competition for jobs would become fiercer as "mid-life re-trainees" beginning new careers vie with young workers for a limited number of entry-level positions.

Especially worrisome is the problem of workplace mobility, Callahan said.

"If you have people staying in their jobs for 100 years, that is going to make it really tough for young people to move in and get ahead," Callahan explained. "If people like the idea of delayed gratification, this is going to be a wonderful chance to experience it."

Callahan also worries that corporations and universities could become dominated by a few individuals if executives, managers and tenured professors refuse to give up their posts. Without a constant infusion of youthful talent and ideas, these institutions could stagnate.

Hackler points out that the same problem could apply to politics. Many elected officials have term limits that prevent them from amassing too much power. But what about federal judges, who are appointed for life?

"Justices sitting on the bench for a hundred years would have a powerful influence on the shape of social institutions," Hackler writes.

Time to act

A 2003 staff working paper drawn up by the U.S. President's Council of Bioethics — then headed by Leon Kass, a longtime critic of attempts to significantly extend the human lifespan — stated that anti-aging advances would redefine social attitudes toward the young and the old, and not in good ways.

"The nation might commit less of its intellectual energy and social resources to the cause of initiating the young, and more to the cause of accommodating the old," the paper stated. Also, quality of life might suffer. "A world that truly belonged to the living would be very different, and perhaps a much diminished, world, focused too narrowly on maintaining life and not sufficiently broadly on building the good life."

While opinions differ wildly about what the ramifications for society will be if the human lifespan is extended, most ethicists agree that the issue should be discussed now, since it might be impossible to stop or control the technology once it's developed.

"If this could ever happen, then we'd better ask what kind of society we want to get," Callahan said. "We had better not go anywhere near it until we have figured those problems out."

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