Paper short abstract:

In many ways it is unsurprising that human evolution occurred in East Africa because of the huge changes that have occurred in the local environment. On the long-term these include major tectonics event and global climate changes. On the short time scale wet-dry cycles are driven by orbital forcing.

Paper long abstract:

In many ways it is unsurprising that human evolution occurred in East Africa because of the huge changes that have occurred in the local environment. Long-term changes in the African environment have been influenced by the birth of the Sahara desert, re-evolution of C4 plants, Messinian Salinity Crisis, uplift and rifting of East Africa, start of Northern Hemisphere glaciation, Development of the Walker circulation and Mid-Pleistocene transition. On shorter time scales African climate is profoundly altered by orbital forcing. Every 400,000 years there are distinct periods when the climate of East Africa cycles between extremely wetness when the whole of the Rift valley was full of deep freshwater lakes to hyper-arid conditions when huge amounts of dust were blown into the surrounding oceans. This extreme climate variability varies on a 20,000 years frequency and suggests that precession is forcing the local climate to switch between extremely wet and dry phases. These periods of highly variable climate seem to only last 100,000 years. In between there are long periods of time when there seems to very little change in East Africa climate and no lakes apart from the large permanent ones such as Lake Turkana. These short periods of extreme climate variability seem to correlate to key periods of hominin evolution; such as the appearance of A. ramidus, the first appearance of Homo and Paranthropus genus, the first appearance of P. robustus H. erectus and H. ergaster, the first appearance of H. heidelbergensis and the first appearance of H. sapiens.