Word: sahelanthropus
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...chromosomes in the different species. To their surprise, they deduced that chimps and humans split from a common ancestor no more than 6.3 million years ago and probably less than 5.4 million years ago. If they're correct, several hominid species now considered to be among our earliest ancestors--Sahelanthropus tchadensis (7 million years old), Orrorin tugenensis (about 6 million years old) and Ardipithecus kadabba (5.2 to 5.7 million years old)--may have to be re-evaluated...
...others may not be our direct ancestors at all but instead dead-end side branches of the family tree, like the Neanderthals. That would make them not our great-great-great-grandparents but rather ancient uncles and aunts whose lineages have long since gone extinct. One possibility is that Sahelanthropus gave rise to intermediate descendant species that have not yet been discovered. These descendants would have led to Homo habilis or Homo rudolfensis, both of which are contenders for the first member of our genus, which arose about 2 million years...
According to many anthropologists, Brunet's discovery supports the idea that evolutionary diversity was true for hominids as well. "My guess," Wood offers, "is that Sahelanthropus is the first of what will turn out to be a whole handful of apes and apelike creatures living throughout Africa 6 or 7 million years ago." In this bushy model of evolution, even a remarkably modern face might not guarantee that Brunet's new hominid was a direct ancestor of modern humans. Maybe it was just one of several modern-looking hominids that arose at about the same time...
...hominid does eventually upend the conventional wisdom, however, it will raise all sorts of questions. For example, if Sahelanthropus had descendant species that gave rise to H. habilis, asks Harvard's Lieberman, where are they? Nobody knows, moreover, what triggered the emergence of the earliest hominids in the first place. Virtually everyone now agrees that walking upright was the key physical adaptation that set the hominid line in motion. But that adaptation had to have some evolutionary advantage for it to persist. What, exactly, was so great about walking on two legs...
That all made sense until field scientists, including White, began finding early hominids who lived in partly wooded places, not pure savanna. As deduced from the sorts of animals Brunet found at Toros-Menalla, that seems to be the kind of environment Sahelanthropus inhabited as well. With the simple climate theory already on the way out, paleontologists have come up with other ideas. They now believe that woods survived in the changed climate but were probably interspersed with patches of savanna--precisely the setting in which Brunet found Toumai...