It is very commonly believed that the causes of ageing are unknown. For an inaugural professorial lecture, P. B. Medawar (1952) chose the topic ‘An unsolved problem in biology’, and this wide-ranging discussion of ageing has been influential and frequently cited. Since that time much has been learned about ageing, but most in and outside the field of gerontology would believe that the mechanism or mechanisms involved remain elusive.

My own interests in ageing began in the mid-1960s, and in the following two decades I had the same viewpoint, because it seemed that progress in research worldwide was extremely slow, so the unsolved problem remained. More recently, I have become more optimistic and have come to believe that the biological basis of ageing is now well understood. This is in part due to a consideration of the biological reasons for ageing, from an evolutionary standpoint. Also, the evolved physiological and anatomical design of mammals is well understood. The changes that occur during human ageing are documented by an enormous range of studies on age-related pathologies. A great deal is known about the many homeostatic, repair or maintenance mechanisms, which preserve the adult in a functional state for a given length of time and allow it to propagate itself. All this comprises a substantial part of biology. I believe that to understand ageing one need only look at and appreciate this vast body of existing knowledge.