THE DESERTS OF AFRICA The African deserts have from time immemorial represented a huge challenge to populations and their societies. The lack of water, the insufficient supply of other natural resources, frequent periods of drought - often lasting for several years - and the vulnerability of the ecosystem when exposed to excessive exploitation, have imposed radical limits on human activity and cast doubt on the ability of populations to survive in arid zones. Mobility, flexibility and solidarity are strategies providing protection against often hostile conditions. The handing down of personal experience, knowledge of local conditions and oral traditions is of paramount importance. The same is true of information about the environment, the caravan routes, markets and peoples in far flung regions. This knowledge,