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interrelatedness of species. This area of anthropology, known as taxonomy and systematics, is one of the most contentious. I will avoid the details of the many debates and concentrate instead on describing the overall shape of the tree.
    Knowledge of the human fossil record in Africa developed slowly, beginning in 1924 when Raymond Dart announced the discovery of the famous Taung child. Comprising the incomplete skull of a child—part of the cranium, face, lower jaw, and brain case—the specimen was so named because it was recovered from the Taung limestone quarry, in South Africa. Although no precise dating of the quarry sediments was possible, scientific estimates suggest that the child lived about 2 million years ago.
    While the Taung child’s head had many apelike features, such as a small brain and a protruding jaw, Dart recognized human aspects too: the jaw protruded less than it does in apes, the cheek teeth were flat, and the canine teeth were small. A key piece of evidence was the position of the foramen magnum—the opening at the base of the skull through which the spinal cord passes into the spinal column. In apes, the opening is relatively far back in the base of the cranium, while in humans it is much closer to the center; the difference reflects the bipedal posture of humans, in which the head is balanced atop the spine, in contrast to ape posture, in which the head leans forward. The Taung child’s foramen magnum was in the center, indicating that the child was a bipedal ape.
    Although Dart was convinced of the hominid status of the Taung child, almost a quarter of a century was to pass before professional anthropologists accepted the fossil individual as a human ancestor and not just an ancient ape. The prejudice against Africa as the site of human evolution and a general revulsion at the idea that anything so apelike might be a part of human ancestry combined to consign Dart and his discovery to anthropological oblivion for a long time. By the time anthropologists recognized their error—in the late 1940s—Dart had been joined by the Scotsman Robert Broom, and the two men had found scores of early human fossils from four cave sites in South Africa: Sterkfontein, Swartkrans, Kromdraai, and Maka-pansgat. Following the anthropological custom of the time, Dart and Broom applied a new species name to virtually every fossil they discovered, so that very soon it appeared that there had been a veritable zoo of human species living in South Africa between 3 million and 1 million years ago.
    By the 1950s, anthropologists decided to rationalize the plethora of proposed hominid species and recognized just two. Both were bipedal apes, of course, and both were apelike in the way that the Taung child was. The principal difference between the two species was in their jaws and teeth: in both, these were large, but one of the creatures was a more massive version of the other. The more gracile species was given the name Australopithecus africanus , which was the appellation Dart had given to the Taung child in 1924; the term means “southern ape from Africa.” The more robust species was called, appropriately, Australopithecus robustus (see figure 2.1 ).
    From the structure of their teeth, it was obvious that both africanus and robustus had lived mostly on plant foods. Their cheek teeth were not those of apes—which have pointed cusps, suited to a diet of relatively soft fruit and other vegetation—but were flattened into grinding surfaces. If, as I suspect, the first human species had lived on apelike diets, they would have had apelike teeth. Clearly, by 2 million to 3 million years ago the human diet had changed to one of tougher foods, such as hard fruits and nuts. Almost certainly this indicated that the australopithecines lived in a drier environment than that of apes. The huge size of the robust species’ molars suggests that the food it ate was especially tough and needed extensive grinding; not for nothing