There is no spot on earth more fascinating and more deeply significant for all of us than Olduvai Gorge. It has, to begin with, extraordinary scenic beauty. In one direction stretches the great, open Serengeti Plain, broken here and there by hills that are massifs of old, weathered rock piercing the younger sediments. In the opposite direction is the rifted Balbal depression and, beyond it, the towering slopes of the Ngorongoro Caldera. Other volcanoes, extinct and living, crenellate the long horizon. The varicoloured gorge itself displays high vertical cliffs, steep, sweeping slopes, and fantastic eroded forms. For those of us who enjoy occasional escape from our own teeming species, the gorge has an added charm: few places in the world are so free from recent works of man. It has been thousands of years since any human maintained a permanent dwelling there. The occasional visitors are all sporadic nomads: wandering tribesmen and palaeontologists.

The desert grandeur of the scene is, however, only an unexpected bonus at Olduvai. The true significance lies literally deeper, in the successive strata exposed in the walls of the gorge. The stunning dimension of the gorge is not in space but in time, not in the seemingly ageless and unchanging face of pristine Africa but in a dated sequence of major events with repercussions everywhere on earth. Here, one after another, are chapters in history ranging from sometime in the early Pleistocene to the present day.