The Origin of Humankind by Richard Leakey Read Free Book Online Page B

ground.” This description, which I support, clearly fits closely with the Susman camp and not the Love joy camp.
    Even stronger support for this view comes from the innovative use of computerized axial tomography (CAT scanning) to discern the details of the inner ear anatomy of these early humans. Part of the anatomy of the inner ear are three C-shaped tubes, the semicircular canals. Arranged mutually perpendicular to each other, with two of the canals oriented vertically, the structure plays a key role in the maintenance of body balance. At a meeting of anthropologists in April 1994, Fred Spoor, of the University of Liverpool, described the semicircular canals in humans and apes. The two vertical canals are significantly enlarged in humans compared with those in apes, a difference Spoor interprets as an adaptation to the extra demands of upright balance in a bipedal species. What of early human species?
    Spoor’s observations are truly startling. In all species of the genus Homo , the inner ear structure is indistinguishable from that of modern humans. Similarly, in all species of Australopithecus , the semicircular canals look like those of apes. Does this mean that the australopithecines moved about as apes do—that is, quadrupedally? The structure of the pelvis and lower limbs speaks against this conclusion. So does a remarkable discovery my mother made in 1976: a trail of very humanlike footprints made in a layer of volcanic ash some 3.75 million years ago. Nevertheless, if the structure of the inner ear is at all indicative of habitual posture and mode of locomotion, it suggests that the australopithecines were not just like you and me, as Love joy suggested and continues to suggest.
    In promoting his interpretation, Lovejoy seems to want to make hominids fully human from the beginning, a tendency among anthropologists that I discussed earlier in this chapter. But I see no problem with imagining that an ancestor of ours exhibited apelike behavior and that trees were important in their lives. We are bipedal apes, and it should not be surprising to see that fact reflected in the way our ancestors lived.
    At this point, I will switch from bones to stones, the most tangible evidence of our ancestors’ behavior. Chimpanzees are adept tool users, and use sticks to harvest termites, leaves as sponges, and stones to crack nuts. But—so far, at any rate—no chimpanzee in the wild has ever been seen to manufacture a stone tool. Humans began producing sharp-edged tools 2.5 million years ago by hitting two stones together, thus beginning a trail of technological activity that highlights human prehistory.
    The earliest tools were small flakes, made by striking one stone—usually a lava cobble—with another. The flakes measured about an inch long and were surprisingly sharp. Although simple in appearance, they were put to a variety of uses. We know this because Lawrence Keeley, of the University of Illinois, and Nicholas Toth, of Indiana University, microscopically analyzed a dozen such flakes from a 1.5-million-year-old campsite east of Lake Turkana, looking for signs of use. They found different kinds of abrasions on the flakes—marks indicating that some had been used to cut meat, some to cut wood, and others to cut soft plant material, like grass. When we find a scattering of stone flakes at such an archeological site, we have to be inventive to imagine the complexity of life that took place there, because the relics themselves are sparse: gone is the meat, the wood, and the grass. We can imagine a simple riverbank campsite, where a human family group butchered meat in the shade of a structure made from saplings and thatched with reeds, even though all we see today are the stone flakes.
    The earliest stone-tool assemblages that have been found are 2.5 million years old; they include, besides flakes, larger implements, such as choppers, scrapers, and various polyhedrons. In most cases, these items, too, were produced by