But skeptics say that extending life span through genetic manipulation is not inevitable. The distinguished gerontologist Leonard Hayflick, a pioneer in the study of aging cells, says he doubts that lives can be significantly prolonged by genetic tinkering and has famously stated that eradicating cancer, heart disease, diabetes and other principal causes of death would add, at most, about 15 years to average life expectancy. S. Jay Olshansky, a biodemographer at the University of Illinois at Chicago, applauds the work on nematode aging but questions its relevance to people. Human life span, he suggested at a recent scientific meeting, is not a simple matter of genetics: “There are no death or aging genes—period.” He bases his assertion on evolutionary reasoning, arguing that natural selection operates primarily on traits that affect an organism’s ability to reproduce; accordingly, one would not expect evolution to favor genes that extend an organism’s life much beyond its reproductive years. In fact, Olshansky has warned that trying to extend human life by manipulating genes could have “unintended and unwanted consequences,” such as an extremely old person who is physically fit but cognitively impaired.
Every month, however, it seems a new research report adds credence to the notion that the fundamental ravages of aging might at least be blunted by exploiting the biochemical pathways discovered by Kenyon and Guarente. This past August, HarvardMedicalSchool researcher David Sinclair and colleagues reported that several common organic molecules— including resveratrol, an ingredient in red wine—activate sir-like proteins in human cells and extend the life span of laboratory yeast. Those findings have bolstered the observation that people who drink moderate amounts of alcohol, including wine, appear to live longer than those who abstain. Sinclair, a former post-doctoral fellow in Guarente’s MIT lab, has said he plans to set up his own company to develop a drug that acts like resveratrol. Says Kenyon: “It’s kind of romantic that red wine contains something that could extend your longevity, don’t you think?”
Given the mere hint of such possibilities, she is struggling to balance the unforgiving demands of science against the expectations of a public understandably eager to live longer. Some scientists have gone so far as to talk of “practical immortality,” the idea that human life span can be extended perhaps hundreds of years. Kenyon recoils from the notion, but does not entirely retreat from its contemplation. “These worms aren’t immortal. They live twice as long. Or they live four times as long. In fact, we can now get ’em to live six times as long.” She pauses, then allows that it’s not theoretically impossible to make nematodes practically immortal, though, she says, “we haven’t.”
And therein may lie the difference between molecular biologists and philosophers: the latter often inflect their pronouncements with a palpable, if unspoken, “but.” The unspoken phrase for biologists is always “not yet.”