Today, what causes ageing, and why some animals age faster than others. Joao Pedro Magalhaes discusses ageing biochemistry; Noah Snyder-Mackler links "jumping genes" to shorter lifespans in big dogs; Stephen Clark introduces Jonathan, the 194-year-old tortoise; and Andrew Steele explains Peto's Paradox, showing why large animals get less cancer than expected. Like this podcast? Please help us by supporting the Naked Scientists