The man-like creatures who roamed Britain and Europe 100,000 years ago are not the ancestors of present-day Europeans - who came from somewhere else entirely. So far away, in fact, that the average white Briton is closer genetically to the average black African than to a pre-Stone Age Briton.

For a long time scientists have been digging into the ground hoping to find fossils and so trace human ancestry back millions of years. But it now seems that they ought to dig into the human body, because all individuals carry around a library of information in their cells, and recent advances in medical science make it possible to decode this, with startling results. "Horizon" looks at some of the latest discoveries about just where modern man came from, and when.

(shown again next Saturday)