Classic Paper: Climate Change the Motor of Africa's Evolution

In this post I will explore a classic paper by Kuper and Kröpelin published in Science (2006). Entitled ‘Climate-Controlled Holocene Occupation in the Sahara: Motor of Africa’s Evolution’, the research article exains the linkages between climatic variation and prehistyoric occupation of the Sahara over the last 12,000 years.

With contemporary climate reconstruction approaches permitting the increasingly presice exhibition of environmental fluctuations, it is now clear that the Holocene represents an era of marked environmental changes. The addition of archaelogical, anecdotal and geological evidence can provide a remarkably fine resolution of environmental change.

Kuper and Kröpelin state that because of the hyperaridity and lack of natural oases and wells, the Eastern Sahara has been absent of human occupation in recent millennia.  As such, they describe it as ‘a unique natural laboratory for the reconstruction of the links between changing climate and environments, and human occupation and adaptation, with prehistoric humans as sensitive indicators of past climate and living conditions’. Evidence of previous occupation through archaeological remains and settlement sites provides a powerful argument for shifting climatic zones and innovative adaptive strategies.

During the Alleröd interstadial the Eastern Sahara was about as dry as it was during the LGM 20,000 B.C.E. However, carbonate lake formations in Sudan, radiocarbon dated to roughly 8,500 B.C.E., provide evidence of a changing climate and pluvial conditions between latitudes 16⁰N and 24⁰N. This indicates a northward shift of tropical rain belts over as much as 800km, largely attributed to migration of the palaeomonsoon system. A semi humid climate was prevalent over larger portions of the Sahara. Radiocarbon dates from occupation sites through the Eastern Sahara reveals the cesation of settlement at about 5,300 B.C.E. (bar favourable refugia).

Phases of human occupation can be mapped through time to illustrate the major stages of early and mid-Holocen occupation.

The early Holocene reoccupation is depicted by the blossoming rainfall across previously hyperarid regions. Savannah-like environments saw the migration of already adapted societies to this ecology in a northwards direction. Archaeozoological evidence suggests these settlers may have been hunter-gatherers. Sparseness of settlement along the Nile valley reflects conditions far too hazardous for dwelling. By 7,000 B.C.E, settlement was firmly founded and populations were maturing in turn with the development of the first farming communities and domestic livestock.

An abrupt end in occupation is described at 5,300 B.C.E. Monsoonal rainfall became irregular an infrequent. Settlement became more sporadic and fragmented . By 3,500 B.C.E., rainfall ceased even in ecological refugia such as Gilf Kebir. The return of hyperarid conditions to much of the Sahara tested the adaptive capabilities of prehistoric civilisation to the limit. Only the most advanced communites could survive and adapt and aclimatise to the changing environement. The expansion and contraction of the Sahara desert is described as ‘the motor of Africa’s evolution up to modern times’.