National Geographic : 1997 Nov
slow metabolism. It may be no coincidence that many other animals with slow metabolism also enjoy relatively long life spans, includ ing various species of snakes, fish, and frogs. No one knows, however, whether individual people with slightly slower metabolic rates live significantly longer than their fast-burning counterparts. And the rule is not perfect: Some birds with very high metabolic rates, for exam ple, live quite a long time. Ongoing studies may determine whether turtles' longevity is due primarily to their cells' genetic programming or to their cold blooded chemistry-or to some entirely dif ferent evolutionary adaptation. But if turtle studies are going to lead to life extension for people, Gibbons sees a certain irony in the situation. After all, people are the only serious threat to the survival of these otherwise long-lived rep tiles. People capture them for pets, kill them for their shells, and drain their wetlands to build homes for the aged. "If turtles know what's good for them," Gib bons says, "they won't give away their secret." NEVER THOUGHT I'd be looking for a foun tain of youth in a dish full of worms, but that's what I'm doing in Boulder, Colorado. The worms are nematodes only a millimeter long-a tiny squiggle of a species called Caenorhabditiselegans. Although they live in soil and feed on putrefying bacteria, they are surprisingly beautiful when viewed through a microscope, shimmering and translucent as they wriggle across my field of view in a shallow dish of nutrients. Most impressive, the ones I am looking at are almost 40 days old, or about twice the normal nematode life span. Their longevity is due to a single mutation in one of their 13,000 genes-a gene aptly named age-1. Tom Johnson, the University of Colorado researcher whose lab I am visiting, explains that age-1 is one of several recently isolated nematode genes that, when mutated, can greatly extend a worm's life span. The dis covery gave credence to the notion that aging may be controlled by a molecular program. It has been known for some time that genes can influence life span. A good way to predict how long a person will live is to find out how long his parents lived, evidence that longevity AGING-NEW ANSWERS TO OLD QUESTIONS Mutations good and bad could offer information leading to cures for many diseases of old age. Caterina Segala, 80, and some other residents of Limone, Italy, carry a gene that boosts the effects of beneficial cholesterol, lowering the risk of heart disease. In San Diego 12-year-old Courtney Arciaga shows off her basketball skills. A mysterious mutation at concep tion has given her symptoms of the very old, such as a wizened appearance. is at least partly inherited. Some genes affect life expectancy indirectly, by altering the odds of getting a deadly disease. But lately scientists have discovered a few genetic mutations that appear to affect aging specifically. Last year, for example, researchers identified a mutation that causes Werner's syndrome, a disease that mimics certain aspects of the human aging process. People with Werner's grow wrinkled and gray while they are still in their 20s, develop cataracts a few years later, get cancer and heart disease in their 30s and 40s, and usually die before their 50th birthday. Recent studies suggest that the Werner's mutation shortens life by interfering with the body's ability to repair the damage caused by metabolism, while the age-1 mutation length ens life by enhancing the ability to reduce, resist, or repair the damage done. Could the se cret of longevity lie in something as basic as the ability to counteract the ill effects of metab olism? And if so, is there a way to cool that met abolic furnace without changing our genes?