Chapter 8: Early Hominins

Bipedalism (two-footed; upright locomotion), rather than a big brain, is the key attribute that helps distinguish early hominins from the apes. Other fundamental human attributes include a long period of childhood dependency and tool making. Small teeth, big brains, and language, other key human attributes, developed later in hominin evolution. Skeletal material from the fossil Danuvius guggenmosi (11.6 m.y.a., southern Germany) show that it combined adaptive features of bipeds and of suspensory apes. Danuvius provides some of the earliest evidence yet for bipedalism among proto-apes—and possible hominin ancestors.

A skull found in 2001 in northern Chad, dated at 7–6 million years ago, officially named Sahelanthropus tchadensis, more commonly called “Toumai,” may or may not be the earliest hominin yet known, as may the somewhat less ancient Orrorin tugenensis, found in Kenya, also in 2001.

Hominins have lived during the late Miocene, Pliocene (5.0–2.6 m.y.a.), and Pleistocene (2.6 m.y.a–11,700 b.p.) epochs. The earliest definite hominin remains, from Ethiopia, are classified as Ardipithecus kadabba (6.3–5.2 m.y.a.) and ramidus (4.8–4.4 m.y.a.). Next comes Au. anamensis, then a group of fossils from Hadar, Ethiopia, and Laetoli, Tanzania, classified as Au. afarensis. The australopiths had appeared by 4.2 m.y.a. (as Au. anamensis). The australopiths include two genera: Australopithecus and Paranthropus. The known species of Australopithecus are as follows: Au. anamensis (4.2–3.8 m.y.a.), Au. afarensis (3.9–3.0 m.y.a.), Au. africanus (3.7–2.3 m.y.a.), Au. garhi (2.6–2.5 m.y.a.), and Au. sediba (1.98–1.78 m.y.a.). The species of Paranthropus are as follows: Paranthropus robustus (2.3–0.8 m.y.a.), Paranthropus boisei (2.5–1.4 m.y.a.), and Paranthropus aethiopicus (2.8–2.1 m.y.a.).

The earliest definite hominins (Ardipithecus, Au. anamensis, and Au. afarensis) shared many primitive (apelike) features, including upper bodies adapted for climbing; elongated premolars; a small, apelike skull; and marked sexual dimorphism. Still, Au. afarensis and its predecessors were definite hominins. In Au. afarensis this is confirmed by abundant skeletal evidence for upright bipedalism.

Remains of two later groups, Au. africanus (graciles) and Paranthropus robustus (robusts), have been found in South Africa. Both groups show the australopith trend toward a powerful chewing apparatus. They had large molars and premolars and large and robust faces, skulls, and muscle markings. All these features are more pronounced in the robusts than they are in the graciles.

Paranthropus boisei, the hyperrobust australopiths, became extinct around 1.4 m.y.a., while Paranthropus robustus survived longer–until perhaps as recently as 800,000 years ago. Paranthropus became increasingly specialized, dependent on a diet with heavy chewing demands associated with its mostly vegetarian diet.

Oldowan tools (flakes and choppers) dated to 1.8 m.y.a. were first found at Olduvai Gorge in Tanzania, hence, their name. Earlier Oldowan tools (some older than 3 m.y.a.) have been found subsequently at other African sites, including one in Algeria. Even earlier stone tools (3.3 m.y.a.) come from a recent discovery at the Lomekwi 3 site in Kenya. A regular diet of red meat was a key factor allowing the growth of the hominin body and brain and the spread of hominins within and beyond Africa. Among the likely social changes associated with the new diet were a gender-based division of labor, pair bonding, and increased parental (especially male) investment in children.