Even though some genes have been shown to influence longevity in worms, fruit flies, and mice..
...scientists do not believe that our life spans are actually programmed into us. After all, for most of our hundred-thousand-year existence—all but the past couple of hundred years—the average life span of human beings has been thirty years or less...Today, the average life span in developed countries is almost eighty years. If human life spans depend on our genetics, then medicine has got the upper hand. We are, in a way, freaks living well beyond our appointed time. So when we study aging what we are trying to understand is not so much a natural process as an unnatural one...Gawande proceeds to a discussion of social and medical consequences of people over 65 becoming 20% of the population.
...complex systems—power plants, say—have to survive and function despite having thousands of critical components. Engineers therefore design these machines with multiple layers of redundancy: with backup systems, and backup systems for the backup systems. The backups may not be as efficient as the first-line components, but they allow the machine to keep going even as damage accumulates...within the parameters established by our genes, that’s exactly how human beings appear to work. We have an extra kidney, an extra lung, an extra gonad, extra teeth. The DNA in our cells is frequently damaged under routine conditions, but our cells have a number of DNA repair systems. If a key gene is permanently damaged, there are usually extra copies of the gene nearby. And, if the entire cell dies, other cells can fill in.
Nonetheless, as the defects in a complex system increase, the time comes when just one more defect is enough to impair the whole, resulting in the condition known as frailty. It happens to power plants, cars, and large organizations. And it happens to us: eventually, one too many joints are damaged, one too many arteries calcify. There are no more backups. We wear down until we can’t wear down anymore.
Improvements in the treatment and prevention of heart disease, respiratory illness, stroke, cancer, and the like mean that the average sixty-five-year-old can expect to live another nineteen years—almost four years longer than was the case in 1970. (By contrast, from the nineteenth century to 1970, sixty-five-year-olds gained just three years of life expectancy.)
The result has been called the “rectangularization” of survival. Throughout most of human history, a society’s population formed a sort of pyramid: young children represented the largest portion—the base—and each successively older cohort represented a smaller and smaller group. In 1950, children under the age of five were eleven per cent of the U.S. population, adults aged forty-five to forty-nine were six per cent, and those over eighty were one per cent. Today, we have as many fifty-year-olds as five-year-olds. In thirty years, there will be as many people over eighty as there are under five.
Americans haven’t come to grips with the new demography. We cling to the notion of retirement at sixty-five—a reasonable notion when those over sixty-five were a tiny percentage of the population, but completely untenable as they approach twenty per cent. People are putting aside less in savings for old age now than they have in any decade since the Great Depression. More than half of the very old now live without a spouse, and we have fewer children than ever before—yet we give virtually no thought to how we will live out our later years alone.
...medicine has been slow to confront the very changes that it has been responsible for—or to apply the knowledge we already have about how to make old age better. Despite a rapidly growing elderly population, the number of certified geriatricians fell by a third between 1998 and 2004.