
© Nahid GaniAfar people, living in the adjoining floodplain of the Jara River. Early humans lived in a similar river-margin environment at Aramis, Ethiopia, 4.4 million years ago.
Just as great civilizations once emerged along the banks of major rivers such as the Tigris, Euphrates, Ganges and Nile, the ancestors of humans might have originated on riversides too, scientists find.
This discovery could help us better understand the environmental forces that shaped the
origin of the human lineage, such as factors of the landscape that prompted our ancestors to start walking upright on two legs, researchers said.
What may be the earliest known ancestor of the human lineage, the 4.4-million-year-old
Ardipithecus ramidus, or "
Ardi," was discovered in Aramis in Ethiopia. The precise nature of its habitat has been
hotly debated - its discoverers claim it was a woodland creature far removed from rivers, while others argue it lived in grassy, tree-dotted savannas.
To learn more about what the area was like back then, scientists investigated sediments from the site where Ardi was excavated. They noticed layers of sandstone that were likely created by ancient streams regularly depositing sand over time. These rivers may have reached up to 26 feet (8 meters) deep and 1,280 feet (390 m) wide.