Tom Kirkwood, Professor of Medicine and head of the Department of Gerontology at the University of Newcastle presents his second of five Reith Lectures investigating new insights from the frontiers of science and the choices and decisions we face in the uncharted territories of a greying world.

In this lecture he looks at a revolution in the life sciences; a revolution that has unfolded with breathtaking speed over the last half century and which has accelerated greatly of late. It is this revolution, he argues, that will allow us to understand the role of DNA in the ageing process.

We sometimes say, in extremis, that a person's life hangs by a thread. In fact, all our lives hang by a thread all the time. The thread in question is DNA, the medium through which we inherit our genetic destiny. DNA directs our growth and all of the vital processes on which we depend for survival. DNA is the thread of life, but is it also the thread of death? Does DNA control our end as it controls our beginning?