Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [65]
Pickford and Senut provided more detail in two papers published in 2001. The 6-million-year-old hominid, they said, represented an entirely new genus and species. They named it Orrorin tugenensis, drawing on the Tugen name for ‘original man’, and claimed it was a direct ancestor to modern humans: Its thighbone was more humanlike than that of Lucy’s and other australopithecines; and its molar teeth were smaller than those of many subsequent hominids. In a simple phylogenetic diagram, they relegated Lucy and the other australopithecines to a dead-end branch, while Ardipithecus was moved out of the human family altogether into a line of apes. Given the age of Orrorin, they said, the divergence between apes and humans probably took place between 9 and 7 million years ago.
In a carefully worded comment in Nature, two palaeontologists from London’s University College, Leslie Aiello and Mark Collard, urged caution. ‘The age of Orrorin makes it a highly important addition to the debate about human origins. But we are a long way from a consensus on its role in human evolution’. Other palaeontologists were more critical, suggesting that the fossils belonged to a chimpanzee or one of its ancestors. To call Orrorin a hominid, said Bernard Wood of George Washington University, meant ‘you have to rewrite human evolutionary history’.
After an extensive examination of the fossils, two American palaeoanthropologists, Brian Richmond and William Jungers, concluded that there was ‘convincing evidence’ to show that Orrorin had stood and walked on its hind limbs, providing the earliest known example of bipedal locomotion. Their analysis of its hand and arm bones indicated that it also climbed trees, ‘presumably to forage, build nests and seek refuge’. But they disputed claims that Orrorin was a direct ancestor of the human line bypassing the australopithecines. They found instead a close similarity between the Orrorin thighbone and hip mechanics and those of the australopithecines.
What this meant, they said, was that the basic pattern of bipedal walking appeared very early on in human evolution and persisted with only minor variations over a period of 4 million years. The walking mechanism used by Orrorin had remained largely unchanged until the rise of Homo 2 million years ago.
Less than a year after Orrorin’s remains had been found, an even older fossil was uncovered in Chad in north-central Africa—more than 1,500 miles from the Rift Valley. Chad had interested French scientists since the 1960s. One of the first palaeontologists to search for fossils there was Yves Coppens. In 1960, he began exploring sandstone formations in the Djurab Desert that had turned to rock 7 million years ago; although the region is often swept by blinding sandstorms, for brief moments of time, ancient fossils there are exposed by wind stripping the surface. The following year, Coppens’s wife, Françoise, discovered part of a skull they called Tchadanthropus uxoris, thought to be a specimen of Homo erectus, about 1 million years old. But civil war in Chad meant that Coppens had to turn his attention elsewhere. In 1967, he joined the Omo expedition and later the Hadar expedition that found Lucy.
As director of the Musée de l’Homme in Paris during the early 1980s, Coppens developed the theory—known as the ‘East Side Story’—that the split between apes and hominids had occurred as a result of changing rainfall patterns some 8 million years ago caused by the formation of the Rift Valley, leaving apes to the west living in their natural habitat in dense equatorial forests while forcing apes to the east to adapt to more open terrain. ‘Our common ancestors, the apes, were