A person’s biological age can be measured with a new type of ‘clock’ that is based on gene activity. Credit: Eduardo Parra/Europa Press via Getty A powerful molecular clock calibrated using data on gene activity from thousands of individuals can predict biological ageing in rodents, monkeys and humans — and time to death in people 1 . The clock, described today in Nature , is based on an analysis of gene activity in more than 25 tissues across four species: mice, rats, the monkeys called crab-eating macaques ( Macaca fascucularis ) and humans. Although it is not ready for medical applications, the clock could eventually be a boon to biologists keen to learn which drugs or lifestyle changes might mitigate ageing’s myriad effects on the body. “Even if you want to do an experiment in mice, to test the lifespan of mice takes a very long time,” says João Pedro de Magalhães, a biologist at the University of Birmingham, UK, who studies the genetics of ageing and was not involved in the work.…