From Ouroboros: "The observation that long-lived and relatively healthy animals can be obtained by simple genetic manipulation prompts the search for chemical compounds that have similar effects. Since aging is the most important risk factor for many socially and economically important diseases, the discovery of a wide range of chemical modulators of aging in model organisms could prompt new strategies for attacking age-related disease such as diabetes, cancer and neurodegenerative disorders ... Long-lived organisms tend to be resistant to many types of stress, whereas short-lived organisms tend to be stress sensitive. This happy coincidence allows us to screen for longevity mutants by looking for stress resistance rather than long life ... it's quite impressive that so many different antioxidants of so many different types can confer thermotolerance and increased longevity [in nematode worms], and suggests that perhaps the association between antioxidants and longevity may have never had much to do with oxidation as such, but rather with some as-yet-uncovered connection between antioxidants and the activation of stress response pathways."

Link: http://ouroboros.wordpress.com/2008/10/27/discovering-lifespan-extension-drugs-by-screening-for-stress-resistance/