Mutations that affect aging, known as "longevity-associated mutations," are actually quite rare, occurring at a much lower frequency than previously believed. While studying aging-related mutations in the model organism Caenorhabditis elegans, researchers found that only a small fraction of mutations had a significant impact on lifespan. Out of over 200,000 mutations screened, only a handful were identified as longevity-associated. This suggests that the effects of mutations on aging are highly specific and that the vast majority of mutations do not play a significant role in determining lifespan.