Abstract
Current evidence suggests that all of the major events in hominin evolution have occurred in East Africa. Over the last two decades, there has been intensive work undertaken to understand African palaeoclimate and tectonics in order to put together a coherent picture of how the environment of East Africa has varied in the past. The landscape of East Africa has altered dramatically over the last 10 million years. It has changed from a relatively flat, homogenous region covered with mixed tropical forest, to a varied and heterogeneous environment, with mountains over 4 km high and vegetation ranging from desert to cloud forest. The progressive rifting of East Africa has also generated numerous lake basins, which are highly sensitive to changes in the local precipitation-evaporation regime. There is now evidence that the presence of precession-driven, ephemeral deep-water lakes in East Africa were concurrent with major events in hominin evolution. It seems the unusual geology and climate of East Africa created periods of highly variable local climate, which, it has been suggested could have driven hominin speciation, encephalisation and dispersal out of Africa. One example is the significant hominin speciation and brain expansion event at ∼1.8 Ma that seems to have been coeval with the occurrence of highly variable, extensive, deep-water lakes. This complex, climatically very variable setting inspired first the variability selection hypothesis, which was then the basis for the pulsed climate variability hypothesis. The newer of the two suggests that the long-term drying trend in East Africa was punctuated by episodes of short, alternating periods of extreme humidity and aridity. Both hypotheses, together with other key theories of climate-evolution linkages, are discussed in this paper. Though useful the actual evolution mechanisms, which led to early hominins are still unclear and continue to be debated. However, it is clear that an understanding of East African lakes and their palaeoclimate history is required to understand the context within which humans evolved and eventually left East Africa.
Highlights
Human evolution is characterised by speciation, extinction and dispersal events that have been linked to both global and/or regional palaeoclimate records
In East Africa, long-term climatic change is controlled by tectonics, with the progressive formation of the East African Rift Valley leading to increased aridity and the development of fault graben basins as catchments for lakes (Fig. 2)
There is evidence, presented above, of periods of extreme environmental variability during the Plio-Pleistocene (Trauth et al, 2005, 2007, 2010; Deino et al, 2006; Kingston et al, 2007; Maslin and Trauth, 2009; Magill et al, 2013; Potts, 2013; Ashley et al, 2014). These periods of extreme climate variability would have had a profound effect on the climate and vegetation of East Africa and, we suggest, human evolution
Summary
Human evolution is characterised by speciation, extinction and dispersal events that have been linked to both global and/or regional palaeoclimate records (deMenocal, 1995; Trauth et al, 2005; Carto et al, 2009; Castan~eda et al, 2009; Armitage et al, 2011; Donges et al, 2011; Shultz et al, 2012) None of these records fully explain the timing or the causes of these human evolution events (Maslin and Christensen, 2007; Trauth et al, 2009; Potts, 2013). A direct development of the variability selection hypothesis is the pulsed climate variability hypothesis, which highlights the role of short periods of extreme climate variability specific to East Africa in driving hominin evolution (Maslin and Trauth, 2009) It is the palaeoclimate evidence for this later framework, the pulsed climate variability hypothesis, which is discussed in this review along with how the other evolutionary theories may be applied given the new context (see Fig. 1)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
