"The ageing of the world's population is one of the most important issues facing humanity in the 21st century. Sometime before 2020, the number of people over 65 worldwide will, for the first time, be greater than the number of 0-4 year olds, and this will keep on rising. The strain this is causing on society are already evident as health and social services everywhere struggle to cope with the care needs of the elderly. But why do we age, and how?...