The Emergence of Earliest Homo

The first member of our own lineage occurs in East Africa and is called Homo habilis (meaning "handy man"). First specimens of this species were discovered by the Leakeys at Olduvai Gorge in the mid-1960s and date to 1.8 Ma (L.S.B. Leakey et al., 1964). Other probable specimens have turned up in Koobi Fora at 1.89 Ma (see B.A. Wood, 1991) (Figure 4.7). At Olduvai, the species survived to 1.6 Ma (Tobias, 1991). And there is a maxilla indistinguishable from Homo habilis from Hadar, dating to 2.3 Ma (Kimbel et al., 1997). From South Africa, specimens from Swartkrans and from the upper levels at Sterkfontein (later than the Australopithecus levels) have tentatively been allocated to this species, though they are different in some aspects and may represent a new species of Homo (Tattersall & Schwartz, 2000).

This early representative of our own genus still retained a number of australopithecine-like features; clearly it had not yet developed the more complex physical and behavioral repertoire of its descendant Homo ergaster (see later). In its daily rate of molar dentine formation, H. habilis is closer to the proto-australopithecine and extant ape condition, with almost three times the amount of deposition per day, compared to the reduced amounts observed in later hominins (M.C. Dean, 2000). Homo habilis also had body proportions that are reminiscent of Australopithecus: Its legs were relatively short; its arms were relatively long. Its arm and hand bones suggest to some that it had the apelike ability of arboreal locomotion (Johanson et al., 1987). If so, it was adapted to tree climbing while also being able to walk bipedally, just as has been proposed for Australopithecus. Indeed, Hartwig-Scherer and Martin (1991) suggested that if the postcranial specimens allocated to H. habilis (OH 62) really belong to this species, then H. habilis was even more primitive than

Figure 4.7 ► Koobi Fora Homo habilis specimen KNM-ER 1813.

Pr. afarensis in its postcranial morphology (see also B.A. Wood & Richmond, 2000). In other features, it is distinct from its australopithecine ancestors, and in the phylogenetic analyses discussed in the next chapter, it clearly belongs to the Homo clade. It has a larger cranial capacity, between 510 and 680 cc, and it appears to have been a regular toolmaker and user; fossil specimens are regularly found associated with primitive stone tools, hence its name. Even the earliest specimen, the Hadar maxilla, is associated with stone tools (see Tobias, 1991; B.A. Wood, 1991; Kimbel et al., 1997; Tattersall & Schwartz, 2000; Dunsworth & Walker, 2002).

With the removal of the "rudolfensis group" from the genus Homo, there is now only one species left that is a likely representative of the next stage of human evolution. This species is Homo ergaster (Groves & Mazak, 1975), which probably evolved from H. habilis, although the earliest H. ergaster remains at Koobi Fora overlap in time with the latest H. habilis (see B.A. Wood, 1991). Until recently, many of the specimens allocated to this species had been placed within the species Homo erectus; many researchers today, however, believe that the African specimens previously allocated to H. erectus are quite distinct from the Asian fossils, which constitute the "true" H. erectus (see Andrews, 1984; Stringer, 1984; B.A. Wood, 1984; see partly

Groves, 1989a; B.A. Wood, 1991; B.A. Wood & Richmond, 2000). Recently, three skulls and a jaw from Dmanisi, in the Republic of Georgia, have been ascribed to H. ergaster (Gabunia et al., 2000a; Vekua et al., 2002; see also partly Bräuer & Schultz, 1996). If this allocation is correct, then H. erectus may not, strictly speaking, have been the first to leave Africa, but it was still almost certainly the first to come out and stay out.

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