In “Humans originated alongside rivers, evidence suggests” ( MSNBC, December 20, 2011), Charles Choi reports, “Sediment studies dispel woodland, grassland theories at 4.4 million-year-old site in Ethiopia”:
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.
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.
Knowing the context in which our distant relatives dwelt when key traits such as walking upright evolved can shed light as to why such characteristics developed in the first place. For instance, as savannas began dominating what were once primarily forests, it might have made more sense to start walking on two feet to conserve energy when moving through tall grasses.
Hmmm. If walking upright makes so much sense, why didn’t various wildlife start doing it? Just wondering.
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