Anthropologists call all the species and sub-species of our ancient ancestors hominids, to distinguish them from the ape lineage, which includes chimpanzees. The two branchesapes and hominidsare believed to have separated and evolved from one common ancestor between 6 million and 8 million years ago.
In a telephone interview from Adis Abeba (Addis Ababa), where he is analyzing the fossils, Haile-Selassie said he is being extremely conservative, and the fragments he and WoldeGabriel plucked from the sun-baked ground may represent an entirely new species of pre-human creature.
"It could be the earliest hominid, or it could be a common ancestor, or it gave rise only to the chimpanzee lineage, or it went extinct around 6 million years ago without giving rise to any species," he said.
A major mystery in the story of human evolution is how climate affected the environment where creatures that regularly walked uprightthe hominidsfirst emerged. Now, both sets of recent findsin Ethiopia and Kenyacould help resolve the puzzle.
One widely accepted theory holds that after the ape and hominid lineages split, the earliest human ancestors were forced into the expanding tropical grasslands of the African savanna after the continent's thick forests dwindled as a result of climate change.
But geochemical analysis of the ancient sedimentary soils where Haile-Selassie's Ardipithecus creatures lived shows that the region between 5 million and 6 million years ago was well forested, well watered, and rich in woody plants, according to anthropologist Stanley Ambrose of the University of Illinois, who is also a chemist and a co-author of WoldeGabriel's report in Nature.
The clear inference, according to Haile-Selassie and WoldeGabriel, is that those early human ancestors of the Miocene epoch were already thriving in the forests of a land that was then being shattered by volcanic eruptions, and millions of years later was to become the stony scrubland it is today.
Copyright 2001 The San Francisco Chronicle
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