The New Yorker looks at medicine and aging; folk on the Gerontology Research Group list have been disputing some of the presented information, but it's a decent article overall: "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. ... Hair grows gray, for instance, simply because we run out of the pigment cells that give hair its color. ... We rely on stem cells under the surface to migrate in and replace them. Gradually, however, the stem-cell reservoir is used up. ... Inside skin cells, the mechanisms that clear out waste products slowly break down and the muck coalesces into a clot of gooey yellow-brown pigment known as lipofuscin. ... The eyes go for different reasons. ... Even without cataracts [the] amount of light reaching the retina of a healthy sixty-year-old is one-third that of a twenty-year-old. ... There is [no] single, common cellular mechanism to the aging process. Our bodies accumulate lipofuscin and oxygen free-radical damage and random DNA mutations and numerous other microcellular problems. The process is gradual and unrelenting. ... We just fall apart."