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In the Light of Evolution Volume IV: The Human Condition
began his search for the evolutionary link between apes and modern humans. He found a piece of hominin lower jaw at Kedung Brubus, Java, in November 1890, and in 1891 Dubois began excavating along the banks of the Solo River near the village of Trinil. In September of that year a hominin molar was discovered, and in October Dubois’ team of excavators found the hominin skullcap that was to become the type specimen of Pithecanthropus erectus, later designated as Homo erectus.
The first important hominin fossil discoveries in Africa, the cranium found at Broken Hill (now Kabwe) in 1921 and the Taung child’s skull recovered in 1924, were both chance discoveries, and it took more than 50 years for the search for hominin sites in Africa to become more systematic. In the late 1980s the Paleoanthropological Inventory of Ethiopia (Asfaw et al., 1990) successfully located potential hominin fossil sites on a regional scale. Led by Berhane Asfaw, the inventory used Landsat thematic mapping (TM) and large-format camera high-resolution images. The former measures the intensity of reflected sunlight in seven wave-bands, and the resulting color images were used to identify the distinctive ash layers, or tephra, that are typically found in the types of strata that contain Plio-Pleistocene fossils. The two sets of data were used to identify promising sedimentary basins, which were explored by vehicle and on foot to verify the presence of potential sites. At least two sources of hominin fossils in the Ethiopian Rift Valley, the site complex within the Kesem-Kebena basin in the north and the site of Fejej in the south, were located this way.
This grade includes hominin fossil evidence that is indistinguishable from the morphology found in at least one regional population of modern humans. Modern humans belong to the species Homo sapiens Linnaeus 1758, and the earliest H. sapiens fossils are dated to just less than 200 ka. Since the initial discovery of a fossil modern human in 1822–1823 in Goat’s Hole Cave in Wales, fossil evidence of H. sapiens has been recovered from sites on all continents except Antarctica. Many H. sapiens fossils are burials, so the fossil evidence is abundant and generally in good condition. The earliest evidence of anatomically modern human morphology in the fossil record comes from Omo Kibish in Ethiopia (McDougall et al., 2005), and it is also in Africa that we find evidence of crania that are generally more robust and archaic-looking than those of anatomically modern humans, yet they are not archaic or derived enough to justify being allocated to Homo heidelbergensis or to Homo neanderthalensis (see below). Specimens in this category include Jebel Irhoud from North Africa, Laetoli 18 from East Africa, and Florisbad and the