Can We Learn To Beat The Reaper?

Give the human body half a chance and before you know it, it tries to die. If it's not cancer, it's heart disease; if it's not heart disease, it's stroke. With all the ways the body can do itself in, you would almost think it wanted to end it all. The fact is, it does.

Before earthly organisms even got a chance to live, they had to agree to some pretty punishing terms: you're born, you grow up, you produce some young, then you get out of the way and leave room for the generation coming along. Animals and plants have no trouble honoring the deal; humans, however, keep trying to change it, hoping to hang around longer than nature envisioned--or our bodies can manage. For scientists and physicians, there has been no goal more seductive than extending human life, and none that has been harder to achieve. Only now are we learning that it is a goal that may forever be out of our reach.

For a long time, many scientists believed that the human life-span was infinitely extendible. The average life-span early in the evolution of Homo sapiens is thought to have been just 20 years. By the beginning of the 20th century, that figure more than doubled--to a still brief 47. Since then, however, life expectancy has been exploding, with people in the developed world now able to live deep into their 70s and often beyond.

But life expectancy (the number of years you can expect to live before being claimed by illness or accident) is not life-span (the maximum age to which the perfectly maintained, disease-free body could remain alive before it simply wore out and broke down). All the gains in length of life have been achieved by treating diseases that used to kill us in youth or, at best, in what we now consider our middle years--and are thus gains in life expectancy. Meanwhile, life-span has remained fixed at a hard ceiling of about 125 years.

"If science cured every known disease of the elderly, you'd add only 15 years to current life expectancy," says Dr. Leonard Hayflick, professor of anatomy at the University of California, San Francisco, and author of How and Why We Age. Accidents and age-related loss of organ function would then start claiming the old--though some, at least in theory, would reach the 125-year mark.

But many people continue to believe that life-spans can be pushed further still. If the aged body breaks down, it must be because something in the cells directs it to do that, and if that thing could be found and shut off, couldn't we live indefinitely? The short answer is yes. The long answer is that the short answer is way too simple.

Even before the human genome was mapped, scientists found genes that appeared to play a role in how cells age. More significantly, they discovered a cufflike structure--dubbed a telomere--at the end of chromosomes that shortens each time a cell divides. When the telomere all but disappears, the cell stops dividing, and the cell line dies out. A naturally occurring enzyme, called telomerase, can maintain telomere length in some cells.

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