Scientists are beginning to understand that ageing is not a simply linear process. Instead, recent research appears to show that we age in three accelerated bursts; at about 40, 60 and 80 years old. To find out what might be going on, Ian Sample hears from Prof Michael Snyder, the director of the Center for Genomics and Personalised Medicine at Stanford University School of Medicine, who explains what the drivers of these bursts of ageing could be, and how they might be counteracted