IF THERE WERE FOUR MILLION AFRICANS TWO THOUSAND YEARS ago, there were probably as many as 150 million by the eve of the colonial period. They had settled in all but the most arid parts of the continent; even in the deserts they travelled and sometimes lived. When considering how they developed to this remarkable extent one needs to look first of all, even if briefly, at the ecological problems of their environment. These were neither small nor few.

One is helped towards understanding these ecological problems by the fact that Africa's climate seems to have changed little in historical times. Back in the 540s, Julian the missionary to the Nubians used to say that ‘from nine o'clock until four in the afternoon he was obliged to take refuge in caves where there was water, and where he sat undressed except for a linen garment such as the people of the country wear’. Anyone travelling in Nubia today will understand why.

It was, as it is now, a continent of startling natural extravagance. Nothing here is done by halves. The dimensions are always big; often they are extreme. There are deserts large enough to swallow half the lands of Europe, where intense heat by day gives place to bitter cold by night, and along whose stony boundaries the grasslands run out and disappear through skylines trembling in a distance eternally flat. There are great forests and woodlands where the sheer abundance of nature is continually overwhelming in tall crops of grass that cut like knives, in thorns which catch and hold like hooks of steel, in a myriad mardhing ants and flies and creeping beasts that bite and itch and nag, in burning heat which sucks and clogs or rains that fall by slow gigantic torrents out of endless skies, and often in the stumbling miles which he between your feet and where you need to be. There are fine and temperate uplands, tall mountains, rugged hills, but even these are filled with an extravagance of nature.

If you tramp through the African bush you will soon wonder how anyone could ever impose human settlement on this land, much less keep a footing here and steadily enlarge it.