A team of researchers from the Spanish National Cancer Research Centre (CNIO), headed by CNIO Director María Blasco, has demonstrated in a pioneering study on mammals that longevity is defined at a molecular level by the length of telomeres. The work—which is published today in the online edition of the journal Cell Reports—opens the door to further study of these cellular components in order to calculate the rate at which cells age and thus be able to determine life expectancy for a particular organism.