The first outline of The Ascent of Man was written in July 1969 and the last foot of film was shot in December 1972. An undertaking as large as this, though wonderfully exhilarating, is not entered lightly. It demands an unflagging intellectual and physical vigour, a total immersion, which I had to be sure that I could sustain with pleasure; for instance, I had to put off researches that I had already begun; and I ought to explain what moved me to do so. There has been a deep change in the temper of science in the last 20 years: the focus of attention has shifted from the physical to the life sciences. As a result, science is drawn more and more to the study of individuality. But the interested spectator is hardly aware yet how far reaching the effect is in changing the image of man that science moulds. As a mathematician trained in physics, I too would have been unaware, had not a series of lucky chances taken me into the life sciences in middle age. I owe a debt for the good fortune that carried me into two seminal fields of science in one lifetime; and though I do not know to whom the debt is due, I conceived The Ascent of Man in gratitude to repay it. The invitation to me from the British Broadcasting Corporation was to present the development of science in a series of television programmes to match those of Lord Clark on Civilisation. Television is an admirable medium for exposition in several ways: powerful and immediate to the eye, able to take the spectator bodily into the places and processes that are described, and conversational enough to make him conscious that what he witnesses are not events but the actions of people. The last of these merits is to my mind the most cogent, and it weighed most with me in agreeing to cast a personal biography of ideas in the form of television essays. The point is that knowledge in general and science in particular does not consist of abstract but of man-made ideas, all the way from its beginnings to its modem and idiosyncratic models. Therefore the underlying concepts that unlock nature must be shown to arise early and in the simplest cultures of man from his basic and specific faculties. And the development of science which joins them in more and more complex conjunctions must be seen to be equally human: discoveries are made by men, not merely by minds, so that they are alive and charged with individuality. If television is not used to make these thoughts concrete, it is wasted.