The study investigates the relationship between thermotolerance and longevity in *Caenorhabditis elegans*. Three longevity mutants—*age-1*, *spe-26*, and *daf-2*—are found to exhibit increased intrinsic thermotolerance (Itt) as young adults. The *age-1* mutation, which increases life expectancy by 65%, also confers Itt. Other long-lived mutants, such as *spe-26* and *daf-2*, show similar phenotypes. The researchers found that pretreatment with sublethal temperatures can induce significant increases in thermotolerance and, to a lesser extent, in life expectancy, suggesting a causal link between stress resistance and longevity. This finding is consistent with the hypothesis that enhanced stress resistance limits the life expectancy of *C. elegans* and may have broader implications in other metazoans. The study also explores the genetic basis of these phenotypes and suggests that the same mutational event may underlie both increased thermotolerance and longevity.The study investigates the relationship between thermotolerance and longevity in *Caenorhabditis elegans*. Three longevity mutants—*age-1*, *spe-26*, and *daf-2*—are found to exhibit increased intrinsic thermotolerance (Itt) as young adults. The *age-1* mutation, which increases life expectancy by 65%, also confers Itt. Other long-lived mutants, such as *spe-26* and *daf-2*, show similar phenotypes. The researchers found that pretreatment with sublethal temperatures can induce significant increases in thermotolerance and, to a lesser extent, in life expectancy, suggesting a causal link between stress resistance and longevity. This finding is consistent with the hypothesis that enhanced stress resistance limits the life expectancy of *C. elegans* and may have broader implications in other metazoans. The study also explores the genetic basis of these phenotypes and suggests that the same mutational event may underlie both increased thermotolerance and longevity.