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Humans may have originated along banks of rivers

Washington, Sun, 25 Dec 2011 ANI

Washington, Dec 25 (ANI): Scientists have found new evidences that suggest humans may have originated on riversides.


According to the researchers, 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.


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, Live Science reported.


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.


The researchers also looked at isotopes within these sediments. All isotopes of an element have the same number of protons, but a different number of neutrons - for instance, carbon-12 has six neutrons, while the heavier carbon-13 has seven.


The grasses that dominate savannas engage in a kind of photosynthesis that involves both carbon-12 and carbon-13, while trees and shrubs rely on a kind of photosynthesis that prefers carbon-12.


All in all, carbon isotope ratios suggest the environment back then was mostly grassy savanna. However, the way in which those ratios fluctuate suggests riverside forests also cut through this area. Oxygen isotope ratios that are closely linked with climate also suggest the presence of streams, researchers added.


"Great rivers such as the Nile and Ganges have been very important in our history, and we now find that rivers might have also helped play a key role at the dawn of humanity," researcher Royhan Gani, a geologist at the University of New Orleans said.


The study has been published in the journal Nature Communications. (ANI)


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