History

New Study Shows That Our Ancient East African Ancestor Migrations Were Determined by Groundwater Spring Locations

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A researcher at Cardiff University recently led an international team that believes that the movement of our East African ancestors was determined by groundwater spring locations.

In the study, the team proposes that the groundwater springs were used as rest stops, allowing early humans to survive while moving across the African landscape. The team believes that populations mixed with each other at these junctions and that this influenced genetic diversity and ultimately, the human population’s evolution.

It is thought that humans first evolved in Africa and current evidence suggests that early humans migrated out of the continent for the first time approximately between 1.8 and 2 million years ago.

Rainfall during this time was affected by the African monsoon. This monsoon weakens and strengthens in a 23,000 year cycle that is driven by the precession of the equinoxes. During intense periods of drought, monsoon rains would have been light, causing drinking water to be in short supply.

The researchers mapped persistent springs across the African landscape and were thus able to model how our ancestors may have moved between water sources at different times. The team also looked at how this influenced their ability to navigate the landscape as the climate changed.

Dr Mark Cuthbert from Cardiff University’s School of Earth and Ocean Sciences and lead author of the study noted that the team found that geology is critically important in determining how much water gets stored in the ground during wet periods. By modelling the springs, the researchers could determine that many would still flow, even during long dry periods, as the groundwater store acts like a buffer against climate change.

Cuthbert added that this shows that the geology, and not just the climate, determines the availability of water, and that the landscape was a catalyst for change in Africa.

Professor Matthew Bennett, from Bournemouth University and co-author of the study explained that people moved across huge areas of land. The springs can be thought of as rest stops or service stations along the way, and people would be drawn there to get to vital water sources.

By mapping the ancient landscape, the team has identified the routes on the current landscape that our ancestors may have taken from one water source to the next. This is an important clue in understanding how people migrated across the African continent from water source to source and the impact this may have had on gene flow and mixing.

Isabelle Durance is the Director of the Cardiff University Water Research Institute. She noted that groundwater provides drinking water to nearly a third of the world’s population at the moment. It is also used to produce the biggest share of the world’s food supply and is a critical component of the world’s natural capital. This research does however show that it may also have had a big influence on our evolutionary history.

The results of the study are described in an article published in the Nature Communications journal.