The long goodbye: Growing old is inevitable and across the world average life expectancy is increasing. With the prevalence of age-related diseases following suit and a limited pot of resources, where should scientists be targeting research? In this Nature Video, superstar statistician Hans Rosling sets the record straight about the cause of the world’s ageing population and Nobel laureate Oliver Smithies, now 89, gives his opinion on medical research priorities. But when Lorna talks to young researchers, they disagree with the laureates on where scientists should be focusing their efforts.