Excerpted from Aging: A Natural History, by Robert E. Ricklefs and Caleb E. Finch. Copyright © 1995 by Robert E. Ricklefs and Caleb E. Finch. Reprinted by arrangement with Henry Holt and Co.

NONE OF US CAN LIVE FOREVER Even if we didn’t age, the many dangers in life – accidents at home and on the road, contagious disease, violent crime – would eventually cut our lives short. The safest age for human beings is around puberty; 10- to 15-year-olds have the lowest risk of dying, and about 1 in 2000 adolescents, or 0.05 percent, dies per year in North America and Europe. Then, throughout the world, and regardless of the adolescent risk of dying, the death rate begins to increase steadily soon after puberty as we begin to experience the slow physiological decline called aging. By the time we reach 100 years of age, our capacity to deal with disease and injury has diminished so much, and wear and tear has taken such a toll, that the risk of dying reaches 50 percent per year.
For the moment, consider a fantasy world without aging, in which individuals have a constant lifelong risk of death at the low adolescent rate of 0.05 percent per year. In such a world, we would have an immensely better outlook for attaining longevity. Indeed, we would be, potentially, immortal. Even so, just the roll of the dice each year, at an odds of 1 in 2000 of striking out, will lead to gradual attrition. Still, if not for aging, 95 percent of us would celebrate our centenaries and 50 percent of us would reach the seemingly astonishing age of 1200 years.
Returning now to the real world, it is clear that for most of us the age of death will be mainly determined by the processes of aging, rather than by any accident of fate. Most of us will not experience our centenaries, not because of bad luck, but because, even under the best of circumstances, we cannot avoid some consequences of living that cause our bodies to age. The same appears to be true for most other species of animals and plants.
Next to the miracle of life itself, aging and death are perhaps the greatest mysteries. We may wonder whether death is an inevitable consequence of life. Does the body deteriorate in the same way as the machines we build, or do living systems have special attributes that make them vulnerable to time? Why does the collection of cells that is the body age, while the lines of germ cells leading from parent to child to grandchild persist indefinitely? Do different individuals among us age faster or slower? Do other species? Can aging be modified, and, most importantly, can life be extended?
… Although many aspects of aging remain enigmatic, biological research has provided tentative answers to the questions most often asked about aging….
How do we know that most or all plants and animals must inevitably “age” with the passing of time? Certainly all species seem to have a maximum life span beyond which no individual lives. Humans as a species, for example, appear to live longer than any other mammal. The Guinness Book of World Records recognizes Shigechiyo Izumi, a Japanese man, as having lived a record 120 years. While there are doubts about the authenticity of his birthdate, there are none for Madame Jeanne Calment, who was born on February 21, 1875. At the time this book is published she will have just celebrated her 120th birthday. [Calment died on August 4, 1997, at age 122.]
The mammals closest to humans in life span may be orangutans, whales, and elephants, which live to at least 70 years. Many other large mammals survive to 20 to 30 years, whereas smaller mammals tend to have shorter life spans. Ten to 15 years is a normal life span for a dog, and the Virginia opossum is as short-lived as a laboratory rat or mouse, animals that under the best circumstances may survive five years. Birds show the same range of life span as mammals and, at the upper end, may rival humans in longevity, since there are reliable records of individual parrots living to 90 years. In contrast, flies have among the shortest life spans found in animals – typically two months in the genus Drosophila. The singled-celled yeasts, which we use to brew beer and leaven bread, are even shorter lived – they survive but a few days.…
These examples do not prove that all species must experience aging. Even if organisms were potentially immortal, none would live forever and the maximum recorded life span would fall short of infinity. To find out whether aging, as opposed to death, is truly universal, we need to examine more closely what aging is, then look for signs of its presence.

Photographed by Joe Pugliese

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