Kenya’s Great Rift Valley -Discovery Sowed Doubt on Origins of the Human Species

Final_Volcanic_uplift_image_L (1) Using satellites provides us with stunning new InSAR images of two Kenyan volcanoes in the Great Rift Valley in Africa. 

The Great Rift Valley was the site of a discovery by Meave Leakey, a member of a famous Kenya-based family of paleontologists, that revealed that our human ancestry is still uncertain. Leakey’s research poked a very big hole in the most commonly accepted theory of man's early evolution and is causing the experts to redefine our family tree.

The traditional theory is that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became human Homo sapiens. But Leakey's findings shows that those two earlier species actually lived side-by-side about 1.5 million years ago in parts of Kenya for at least half a million years, making it highly improbable that Homo erectus evolved from Homo habilis, the researchers said.

Keynanskull_200 This discovery also debunks the iconic depiction of human evolution that begins with a knuckle-dragging ape and ends with a briefcase-carrying man. The fossilized bones of Homo erectus were discovered within walking distance of bones from Homo habilis, and both dated from the same time period. It's the equivalent of finding that your grandmother and great-grandmother were sisters rather than mother-daughter, said study co-author Fred Spoor, a professor of evolutionary anatomy at the University College in London.

Great_rift_valley  The two species lived near each other, but probably didn't interact, each having its own "ecological niche," Spoor said. Homo habilis was likely more vegetarian while Homo erectus ate some meat, he said. Like chimps and apes, "they'd just avoid each other, they don't feel comfortable in each other's company," he said.

There remains some still-undiscovered common ancestor, often referred to as the “missing link” that probably lived 2 million to 3 million years ago, a time that has not left much fossil record, Spoor said.

Overall what it paints for human evolution is a "chaotic kind of looking evolutionary tree rather than this heroic march that you see with the cartoons of an early ancestor evolving into some intermediate and eventually unto us," Spoor said.

That old evolutionary cartoon, while popular with the general public, is inaccurate and keeps getting revised, said Bill Kimbel, director of the Institute of Human Origins at Arizona State University.

"The more we know, the more complex the story gets," he said. Scientists used to think Homo sapiens evolved from Neanderthals, he said. But now we know that both species lived during the same time period and that we did not come from Neanderthals.

Posted by Casey Kazan with Rebecca Sato

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