The dramatic development of humans from early prehistory began with mass migration into Eurasia and dealing with climate change, according to a University of Manchester academic.
In partnership with UCL, early human brain expansion and alterations in the lakes of the East African Rift Valley have been linked for the first time.
Dr Susanne Shultz, from the faculty of Life Sciences at the University of Manchester, and Professor of Geography at UCL Mark Maslin, have been carrying out the research in the area.
Looking into known occurrences of lakes from North Ethiopia to Tanzania over the last five million years, the academics compared the climatic development of the area with rates of human evolution.
From statistical models, it was discovered that species advancement and climate change are inextricably linked from this time.
Professor Maslin said: “It seems modern humans were born from climate change, as they had to deal with rapid switching from famine to feast – and back again – which drove the appearance of new species.
“The climate of East Africa seems to go through extreme oscillations from having huge deep freshwater lakes surrounded by rich lush vegetation to extremely arid conditions – like today – with sand dunes in the floor of the Rift Valley.
“These changes resulted in the evolution of a new species with bigger brains, and also forced humans to disperse out of East Africa.”
This theory, known as the Pulse Climate Variability hypothesis, was originally proposed in 2009.
It states that at 2.6, 1.8, and one million years ago, East Africa became particularly sensitive to the Earth’s orbit for periods of around 200,000 years. This susceptibility resulted in rapid climatic fluctuations, and it is now believed that these alterations immeasurably affected human populations in the area.
According to the report, when the Rift Valley was very wet early humans migrated as a result of reduced space. Following the Nile tributary north out of East Africa, an unstoppable colonisation of Eurasia that led to the spread of human life across the globe began.
Further, the remarkable increase in brain size means that early humans were not only forced to move from a hostile environment, but were also affected to the extent that the development of the entire species was precipitously forced to advance.
Dr Shultz said: “We have long recognised that many key events in human evolution, including the appearance of modern humans, occurred in East Africa. Our study highlights how important the Rift Valley climate was in driving the evolution of our species.
“We found that around 1.9million years ago a number of new species appeared, which we believe is directly related to new ecological condition in the East African Rift Valley, in particular the appearance of deep-freshwater lakes. Among these species was early Homo erectus with a brain 80% bigger than its predecessors.”
From the findings in this report, previous theories which advocated the long-term effect of desert expansion or environmental unpredictability must now take into consideration the clearly enormous impact of acute climate shifts on early human adaptation.
Nonetheless, the report acknowledges that it is only the beginning. Ensuing theories may consider intra-species competition and other social factors, but the discovery of such significant coincidences is sure to be just the starting point of what promises to be a very interesting and original vein of research.
Image courtesy of Jaroslav A. Polák via Flickr, with thanks.
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