EAST AFRICA - THE CRADLE OF HUMANKIND

In this post I will discuss the influence of climate change on our origins. The first question we might ask ourselves here is: when and where did it all happen? And then, naturally, a more complicated question occurs: why did it happen? The answers are quite complex - scientists have spent decades exploring them – but here I will summarise the most important findings.
 

When and where?

Existing evidence suggests that the majority of hominin species originated in East Africa, and that’s why we will look closely at the climatic variations in that particular region (Maslin et al.: 2014). (In this place it’s worth noting that by hominin I mean all bipedal apes, as opposed to hominid which refers to all great apes). The question of the timing of our beginning is a bit trickier – I will treat the emergence of be the first Australopithecus species, Australopithecus afarensis, as the starting point. The figure below explains why.

Anatomical comparisons of apes, early hominins, Australopithecus, Homo erectus, and humans. Nature Education: 2012 (www.nature.com/scitable/knowledge/library/overview-of-hominin-evolution-89010983)

Early hominin evolution coincided with both global cooling and extensive tectonic changes in East Africa (Behrensmeyer:  2006). In very simple words, marine-core records (as well as long cores from deep African lakes, but we’re looking at a global picture now) indicate that a colder, drier and – very importantly – more variable climate begun 4-3.5 million years ago, triggering the climatic shift towards northern continental glacial-interglacial cycles (Trauth et al.: 2007). But, although the fossils tell us a lot about what happened and when; they can’t tell us why – it’s all down to our interpretation of the records.

Why?

There are a few factors that lead to said climatic shift and, consequently, environmental and evolutionary changes. There is no real consensus on the reasons behind the late Cenozoic intensification of Northern Hemisphere Glaciation. Some attribute it to tectonic changes, such as the uplift and erosion of the Tibetan-Himalayan plateau, the restriction of the Indonesia seaway or the emergence of the Panama Isthmus. Others relate it to the long-term decrease in atmospheric CO2. However, whatever the reasons behind it, the intensification of Northen Hemisphere Glaciation resulted in increased aridity in East Africa (Hetherington: 2012).

What’s more, such unfolding of events in high latitudes lead to the compression of the Intertropical Convergence Zone, which consequently rendered East Africa locally sensitive to orbital (precessional) forcing. In other words, it brought about extreme climate variability and the East African overall long-term drying trend was punctuated with periods of wetness.

Rapidly changing condition and dramatic variations in climate obviously had a huge influence on the environment, and as I said at the very beginning of this blog, our environment is what shapes us. No wonder many scientists believe that extreme climate variability in East Africa might have been a catalyst for evolutionary change and hominin speciation.

In the next posts I will go into detail of environmental effects of climatic changes I talked about, and I will explain their possible influence on the development of hominin traits.

For more details check:

• Behrensmeyer, A.K. (2006) ‘Climate Change and Human Evolution’, Science, 311, 5760, 476-478
• Hetherington, R. (2012) Living in a dangerous climate: climate change and human evolution, Cambridge: Cambridge University Press
• Maslin, M. A., C. M. Brierley, A. M. Milner, S. Shultz, M. H. Trauth and K. E. Wilson (2014) ‘East African climate pulses and early human evolution’, Quaternary Science Review, 101, 1-17
• Trauth, M. H., M. A. Maslin, A. L. Deino, M. R. Strecker, A. G. N. Bergner and A. Duhnforth (2007) ‘High- and low-latitude forcing of Plio-Pleistocene East African climate and human evolution’, Journal of Human Evolution, 53, 475-486