For centuries, scholars and scientists have wondered precisely what causes human beings to age. Today, researchers who are investigating aging in lower organisms (and its similarities with human aging) predict that this enigmatic process could be fully understood in the twenty-first century.

Some scientists argue that human longevity can be pushed far beyond current limits, primarily by controlling the genetic mechanisms which inevitably halt cell division and cause cells to die. In the words of evolutionary biologist Michael Rose, “I don’t think there is any predefined limit to life span in flies or humans. Aging can be changed, since it is something that we can manipulate, analyze, and understand.” Geneticist Michael West adds, “For the first time in history, we have the power to manipulate aging on a very profound level.”

Others, however, are...