An international team led by a researcher at Cardiff University believe that the movement of our ancestors across East Africa was shaped by the locations of groundwater springs.
In a new study, the team argue that the springs acted as pit stops to allow early humans to survive as they moved across the African landscape.
The team believe that populations were able to mix with each other at these junctions, influencing genetic diversity and, ultimately, the evolution of the human population.
The results of the study have been published today, 30 May, in the journal Nature Communications.
Humans are thought to have first evolved in Africa, and evidence currently suggests that early humans first migrated out of the continent probably between 2 million and 1.8 million years ago.
During this time, rainfall was affected by the African monsoon which strengthened and weakened on a 23,000 year cycle driven by the precession of the equinoxes. During intense periods of aridity, monsoon rains would have been light and drinking water in short supply.
By mapping persistent springs across the African landscape, the researchers have been able to model how our ancestors may have moved between water sources at different times and how this impacted their ability to traverse the landscape as the climate changed.
Lead author of the study Dr Mark Cuthbert, from Cardiff University's School of Earth and Ocean Sciences, said: "We found that the geology is really important in controlling how much rainfall gets stored in the ground during wet periods. Modelling the springs showed that many could still flow during long dry periods because this groundwater store acts like a buffer against climate change.
"As such, we begin to see that the geology, and not just the climate, control the availability of water - the landscape was a catalyst for change in Africa."
Co-author of the study Professor Matthew Bennett, from Bournemouth University, said: "What we are seeing is the movement of people across vast areas of land. You can think of springs as the service stations or rest stops along the way, where people would be drawn to get their vital water sources.
"Through our mapping we have found the routes on the current landscape by which our ancestors may have walked, like motorways, taking people from one water source to the next. This is another vital clue in understanding how these people migrated across the African continent, from water source to source, and how this may have impacted on gene flow and mixing."
Isabelle Durance, Director of the Cardiff University Water Research Institute, said: "Groundwater currently provides nearly a third of the world's population with drinking water. It is also used to produce the largest share of the world's food supply and is a vital component of our natural capital, but this research shows that it may have also shaped our evolutionary history".
The research was conducted by a collaborative team of academics from Cardiff University, University of Birmingham, University College London, UNSW Australia, Bournemouth University, Rutgers University (USA) and the University of Victoria (Canada).
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