What is it? For the first time in history, humans may be able to suppress the action of harmful genes, remove damaged genes and replace them with more desirable ones, and amplify the action of genes that enhance health.

Evidence: While no one doubts that aging is in part genetically influenced, scientists were startled by discoveries 10 years ago that a single gene alteration in lab animals could significantly extend life. Now many such "longevity genes" have been identified in laboratory animals, and studied to see what happens when genetic "switches" are turned on or off.

Current and future use: Such studies will very likely lead to the identification of genes that influence longevity in humans. Genetic manipulations will focus on various pathways to reduce the risk of fatal diseases and possibly to slow aging: Some aim for efficient glucose metabolism, for example, and others for enhancing DNA maintenance and repair. Studies on long-lived humans are just now yielding results: The analysis of genetic material from family clusters of centenarians has found a specific gene that regulates blood lipids in a way that protects against cardiovascular disease -- even among those who eat a high-fat diet. Researchers hope to develop drugs based on that discovery.

What is it? We produce antioxidants that prevent and repair cell damage caused by free radicals -- but over time, our antioxidant production becomes less efficient and free radicals dominate. Will ingesting antioxidants keep cell-repair mechanisms high-functioning?

Evidence: Although epidemiological studies have shown that eating foods containing antioxidant vitamins E and C may reduce the risk of cancer, macular degeneration, and other disorders, no one has established that antioxidant supplements influence aging. There is no evidence that vitamin supplements containing antioxidants mount a significant defense against cellular damage, says Olshansky.

Current and future use: Researchers are studying antioxidant pills in older heart patients; Olshansky thinks supplements are unlikely to improve upon nature. "Instead, scientists are working on a way to enhance the body's ability to use its own free radical scavengers to protect itself -- that has great potential." When researchers insert a gene that overproduces antioxidants in fruit flies, for example, the flies live longer.