Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [66]
The East Side Story became a popular theory among palaeoanthropologists until 1995, when members of a new expedition exploring the Djurab Desert—the Mission Paléoanthropologique Franco-Tchadienne (MPFT)—found the lower jaw of an australopithecine aged between 3 and 3.5 million years near Koro Toro—the first discovery of a hominid fossil west of the Rift Valley.
The expedition was led by a fifty-four-year-old French palaeontologist, Michel Brunet, who had previously hunted for fossils in the rain forests of Cameroon without success before turning to Chad. Brunet named the hominid Australopithecus bahrelghazali, describing it as a western cousin of Lucy. The cradle of humankind, he told a press conference in Paris, clearly covered a far wider area than had hitherto been thought.
The discovery of bahrelghazali—river of the gazelles—prompted further exploration of the Djurab Desert. In 2001, at a site named Toros-Ménalla, a young Chadian researcher, Ahounta Djimdoumalbaye, found a well-preserved and nearly complete cranium of an unknown hominid. Two lower-jaw fragments and three isolated teeth added to the find. From animal fossils found alongside the skull—ancient elephants and extinct pigs—it was dated at nearly 7 million years old—twice as old as Lucy. It displayed a combination of primitive and derived characteristics clearly showing it was not related to the ancestors of chimpanzees or gorillas, but living close in time to the last common ancestor between chimpanzees and humans. The skull had an elongated shape with a short, vertical face and with a massive brow ridge; the eyes were set far apart from each other; the front teeth were relatively small. The brain was estimated to be 360 cubic centimetres, below the average for all three living great apes but well within their range of variation. The positioning of the foramen magnum—the opening at the base of the skull through which the spinal cord passes—suggested that it could have walked upright on two legs, but no limb, hand or foot remains were discovered to help ascertain this.
Brunet and his colleagues concluded that the skull represented a new kind of hominid deserving a genus of its own. They called it Sahelanthropus —‘man from the Sahel’—the name of the region bordering the southern Sahara Desert; and added the species name tchadensis.
Critics argued that Sahelanthropus was more likely to be related to chimpanzees than hominids. Martin Pickford and Brigitte Senut, the discoverers of Orrorin tugenensis, suggested that its features were consistent with a knuckle-walking proto-gorilla.
Nevertheless, Sahelanthropus became a new landmark on the frontiers of human evolution. It became commonly known as Toumaï, a word in the local Goran language meaning ‘hope of life’. It was a name given to children born in the desert before the hot, dry season began when the chances of survival diminished.
The flurry of new hominid discoveries required some rethinking about the origins of bipedalism. Ever since Darwin’s time, it had been more a matter of inspired speculation than scientific evidence. Darwin averred that hominids had assumed a bipedal posture to free their hands for fashioning tools and performing other activities that in turn provided further stimulus to intelligence; the apes, meanwhile, had been trapped by the continued use of their hands as a means of locomotion among trees.
Dart, on the basis of his observations about Australopithecus africanus, developed the theory that upright walking had evolved in open savannah country, ‘where competition was keener between swiftness and stealth, and where adroitness of thinking and movement played a preponderating role in the preservation of the species’. Essentially, Dart argued, australopithecines