This video segment adapted from NOVA scienceNOW examines how a gene called FOXO affects life span. Researcher Cynthia Kenyon at the University of California, San Francisco, increased the activity of a single FOXO gene in the microscopic worm C. elegans and doubled the worm's life span. FOXO regulates about 100 other genes that protect an organism's cells and tissues. Researchers Bradley Willcox and Timothy Donlon found that FOXO performs a similar role in humans. People who possess a single copy of the protective version of the gene are twice as likely to live to the age of 100, while those with two copies have triple the chance.