Archaeological and genetic evidence suggests that modern humans originated in Africa during the Stone Age, between 30,000 and 280,000 years ago. The latest excavations in southern Africa have shown that technological innovations took place abruptly, and an international team of researchers has linked these pulses to the climate that prevailed in sub-Saharan Africa in that period.
     The researchers describe how rainfall patterns varied in southern Africa over the last 100,000 years - analysing river delta deposits at the edge of the continent, where 1 millimetre corresponds to 25 years of sedimentation. In each layer the ratio of iron (dissolved from rocks by rain water) to potassium (present in arid soils) records the sediment carried by rivers, and therefore the relative amount of rainfall.
     Their reconstruction shows a series of spikes that occurred between 40,000 and 80,000 years ago, showing rainfall levels rising sharply over just a few decades and falling off again soon afterwards, in a matter of centuries. Wetter periods coincided with increases in population and technology, as seen in the archaeological records. In turn, the end of certain stone tool industries coincides with the onset of drier climate.
     The findings confirm one of the principal models of Palaeolithic cultural evolution, which correlates technological innovation with the adoption of new refuges, and a resulting increase in population and social networks.
     Climate changes in southern Africa were probably key factors in the origin of modern humans' behaviour in Africa, and in the dispersal of Homo sapiens from its ancestral home.

Edited from EurekAlert! (18 June 2013)