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Back in the field at Aramis for another season, two months after the Nature report was published, the Middle Awash group made another remarkable ramidus discovery. Crawling up an embankment where recent rains had eroded the surface, an Ethiopian graduate student, Yohannes Haile-Selassie, spotted two pieces of bone from the palm of a hand. In the following weeks, the team uncovered the partial skeleton of a single individual—pieces of a pelvis; leg, ankle and foot bones; arm, wrist and hand bones; a lower jaw with teeth; and a crushed skull; in all, 125 bone fragments. Over the course of three subsequent field seasons, they found body parts of at least thirty-five other individuals.

Because of the marked differences between ramidus and the australopithecines, in 1995, White and his colleagues dropped the genus Australopithecus and substituted a new genus—Ardipithecus—drawing on the Afar word ardi, meaning ‘ground’. Critics, however, remained sceptical about the claims of Ardipithecus ramidus to bipedal status.

It took White’s team fifteen years of painstaking reconstruction and analysis before they could reach a definitive conclusion. Naming the skeleton ‘Ardi’, they announced in 2009 that it belonged to a female, standing four feet tall, weighing about 110 pounds and able to walk upright on flat feet in a primitive manner. Ardi’s long arms and fingers and opposable big toes meant that she was also adept at climbing trees and moving through the forest canopy, to reach food, to sleep in nests and to escape predators. ‘In Ardipithecus’, said White, ‘we have an unspecialised form that hasn’t evolved very far in the direction of Australopithecus’.

Analysis of the teeth of Ardipithecus pointed to a varied, omnivorous diet of fruit, roots, insects, eggs and perhaps small mammals. Of particular significance, both male and female Ardipithecus had small incisors and canines, suggesting that unlike chimpanzees, baboons and gorillas, the male did not bare its teeth in battles over females and was already part of a more cooperative social group. ‘In all the great apes—and that includes fossil and modern—the large, tusk-like, projecting, shearing canine teeth are used as weapons, and in most of them the main use is in males fighting with other males for access to estrus females’, said White. ‘The earliest hominids lack that adaptation, showing much smaller canines that are not at all chimpanzee-like’. He concluded: ‘Natural selection has led to the reduction of this male canine tooth very, very early in time, right at the base of our branch of the family tree’.

Another spectacular Ardipithecus find was made by Yohannes Haile-Selassie in 1997. Exploring the Alayla Basin on the remote western margin of the Middle Awash, he spotted a piece of jawbone lying among basalt cobbles. It came from sediments that were 5.8 million years old, making it 1.4 million years older than the Aramis skeleton. Over the next four years, Haile-Selassie and other members of the Middle Awash team collected a total of eleven hominid fossils from five individuals ranging in age from 5.8 million years to 5.2 million years, but they failed to find a skull or intact limb bones. A 5.2-million-year-old toe bone at a site near Aramis, however, provided some evidence that Ardipithecus at that stage might have walked upright. Six teeth uncovered in 2002 added further vital clues, indicating that although Ardipithecus was closely related to chimpanzee ancestors, it had started to evolve towards the human lineage. Originally considered to be a subspecies of ramidus, in 2004 this collection of fossils was considered to be sufficiently distinctive to be accorded its own species title: Ardipithecus kadabba. ‘Ardipithecus kadabba’, said Haile-Selassie, ‘may represent the first species on the human branch of the family tree just after the evolutionary split between lines leading to modern chimpanzees and humans’.

Alongside the Ethiopian discoveries, researchers in Kenya were also making headway. A new phase of exploration