This piece arises from Future Tense, a collaboration among Arizona State University, the New America Foundation, and Slate. A Future Tense conference on life extension will be held at the New America Foundation on Tuesday, Nov. 16. (For more information and to sign up for the event, please visit the NAF Web site.) Read more of Slate's coverage on longevity.
We have grown accustomed to the wonders of clean water, indoor plumbing, laser surgery, genetic engineering, artificial joints, replacement body parts, and the much longer lives that accompany them. Yet we should remember that the vast majority of humans ever born died before the age of 10 from an infectious disease. Humanity responded to this high risk of early death with ingenious advances in public health and medical technology, the result of which was a dramatic 30-year boost in life expectancy in the 20th century. The longevity revolution that followed led to a trade-off for which the world was unprepared: the rise of an aged population suffering from multiple chronic degenerative diseases.
Older people may have always existed throughout history, but they were rare. Aging as we know it, and the diseases and disorders that accompany it, represent new phenomena—products of 20th century resourcefulness. When infectious diseases were largely vanquished in the developed world, few anticipated the extent to which chronic degenerative diseases would rise. We call them heart disease, cancer, stroke, arthritis, Alzheimer's disease, and many more, but we might as well collectively use one word to describe them all—aging.
Aging may be defined as the accumulation of random damage to the building blocks of life—especially to DNA, certain proteins, carbohydrates, and lipids (fats)—that begins early in life and eventually exceeds the body's self-repair capabilities. This damage gradually impairs the functioning of cells, tissues, organs, and organ systems, thereby increasing vulnerability to disease and giving rise to the characteristic manifestations of aging, such as loss of muscle and bone mass, decline in reaction time, compromised hearing and vision, and reduced elasticity of the skin.
This accretion of molecular damage comes from many sources, including, ironically, the life-sustaining processes involved in converting the food we eat into usable energy. Aging should most appropriately be thought of as an inadvertent byproduct of operating the machinery of life, which means that evolution could not have given rise to these processes directly. Because nature does not have a program for aging and death, this makes it possible to conceive of interventions that influence the length and quality of our lives, but more importantly, it means evolution has given humanity an entrée into manipulating the speed with which we age.
Aging bodies with chronic diseases are not the same as young bodies with independently acquired infectious diseases. Yet medicine continues to act as if the diseases of aging are separate from the consequences of aging itself. It's true that modern medicine has produced miracle treatments for some chronic diseases, such as dialysis for kidney failure, stents and bypass surgery for coronary artery disease, and new diagnostic procedures for detecting and successfully treating disease early. And we are learning how modifying behavioral risk factors can postpone the onset and progression of chronic diseases, such as keeping cholesterol in check to help prevent heart disease, losing weight to help prevent Type II diabetes, and quitting smoking to lower the risk of cancer.
However, while the risk of many infectious diseases can theoretically be reduced to zero through human interventions, even a complete control of behavioral risk factors for chronic degenerative diseases still leaves a population vulnerable to the destructive biological processes of aging. Humanity is paying a heavy price for the privilege of living extended lives—a new and much more complicated relationship with disease.