Window on Humanity Conrad Phillip Kottak Third Edition Chapter 5 The First Hominins © 2008 McGraw-Hill Higher Education. All right reserved.

Overview What makes us human? Early hominin evolution Australopithecines Gracile vs. robust Early Homo Oldowan tools © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Chronology of hominin evolution Pleistocene (2 m.y.a. to 10,000 B.P.) – epoch of human life Lower Pleistocene (2 to 1 m.y.a.) – late Australopithecus and early Homo Middle Pleistocene (1 m.y.a. to 130,000 B.P.) – Homo erectus Later Middle to Upper Pleistocene (130,000 to 10,000 B.P.) – Homo sapiens © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins What makes us human? Bipedalism Advantages provided in dry, savannah habitat Ability to see food and predators, and to carry materials More energy efficient Exposes less body surface area to solar radiation Brains, skulls, and childhood dependency Balance between structural demands of upright posture and tendency toward increased brain size Dependent offspring whose brains and skulls grow dramatically for several years after birth © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins What makes us human? Tools Early hominins likely shared ability to use and manufacture tools as a homology with the apes Upright bipedalism permitted use and carriage of tools Teeth Advantageous to have large back teeth and thick tooth enamel for fibrous, gritty vegetation Rotary motion of chewing this vegetation favored reduction of canines and first premolars (bicuspids) © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Earliest hominins Ardipithecus Earliest known hominin (although Toumai and Orrorin finds may represent even older hominins) Ardipithecus kadabba – 5.8 and 5.5 m.y.a. Ardipithecus ramidus – 4.4 m.y.a Ancestral to early Australopithecus and, ultimately, Homo © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Australopithecines At least six Australopithecus species: A. anamensis – 4.2 to 3.9 m.y.a. A. afarensis – 3.8? to 3.0 m.y.a. A. africanus – 3.0? to 2.0? m.y.a. A. garhi – 2.5 m.y.a. A. robustus – 2.0? to 1.0? m.y.a. A. boisei – 2.6? to 1.0 m.y.a. © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins A. anamensis Bipedal hominin from northern Kenya, first discovered by Maeve Leakey and Alan Walker in 1995 Fossils from two sites date to 4.2 m.y.a. (Kanapoi) and to 3.9 m.y.a. (Allia Bay) May be ancestral to A. afarensis, which is usually considered ancestral to later australopithecines and Homo © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins A. afarensis Fossils from Laetoli, Tanzania (3.8-3.6 m.y.a.), and Hadar, Ethiopia (3.3-3.0 m.y.a.) Apelike features of A. afarensis (as well as Ardipithecus and A. anamensis) suggest hominins’ common ancestry with the African apes (chimps and gorillas) is very recent – no more than 8 m.y.a. Certain features of dentition are similar to those of apes Evidence of powerful chewing – diet included tough vegetation © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins A. afarensis Cranial capacity smaller than that of later hominins, roughly comparable to modern chimpanzee Marked sexual dimorphism Probably long period of infant dependency – greater opportunity for observation, teaching, and learning Fossilized footprints at Laetoli (3.6 m.y.a.) and structure of postcranial features indicate that A. afarensis was bipedal © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Gracile and robust australopithecines Two australopithecine groups lived in South Africa between 3 and 1 m.y.a. – gracile (A. africanus) and robust (A. robustus) Both were probably descendants of A. afarensis A third, hyperrobust group existed in East Africa Some scholars believe this was a separate species (A. boisei) Others believe this group was a regional variant of A. robustus Competing models of the relationship between graciles and robusts: Separate species; graciles ancestral to robusts Separate species overlapping in time Represent continuum of variation in a single polytypic species © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Gracile and robust australopithecines A. africanus was as sexually dimorphic as A. afarensis Changes in the teeth, jaw, face, and skull indicate that the australopithecine diet increasingly focused on coarse vegetation Overall robustness, especially in the chewing apparatus, increased through time – most pronounced in A. boisei Made and used simple tools Little increase in cranial capacity, but australopithecine endocranial casts are more human than apelike – increasing reliance on learning, memory, and intellectual association © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Australopithecines and early Homo Scholars still do not know exactly why, how, and when the split between Australopithecus and Homo occurred Two sets of teeth dating to 2 m.y.a. constitute the earliest evidence of the split Smaller set – H. habilis (first species of the genus Homo) Larger set – A. boisei, which coexisted with Homo until around 1.0 m.y.a. Johanson and White propose that 3-2 m.y.a., A. afarensis split into two groups: H. habilis – evolved into H. erectus by 1.7 m.y.a. Second group that evolved into the various australopithecines (A. africanus, A. robustus, and A. boisei) © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Oldowan tools Oldowan core and flake tools (around 1.8 m.y.a.) – discovered by the Leakeys in 1931 at Olduvai Gorge, Tanzania Older stone implements (2.5-2 m.y.a.) found in Ethiopia, Congo, Malawi Debate over identity of the earliest stone tool makers A. garhi and early stone tools Fossils from a new hominin species, A. garhi, dating to 2.5 m.y.a. were found in Ethiopia in 1999 Associated with remains of butchered animals Stone tools also dating to 2.5 m.y.a. were found at a nearby site, suggesting that they were manufactured by A. garhi © 2008 McGraw-Hill Higher Education. All right reserved.

CHAPTER 5 The First Hominins Australopithecines and early Homo Evidence that australopithecines had some capacity for culture: Bipedalism Long period of childhood dependency Association of A. garhi with the earliest stone tools Cultural abilities developed exponentially with the appearance and expansion of Homo Increasing reliance on hunting, tool making, and other cultural abilities Homo became the most efficient exploiter of the savanna niche A. boisei may have been marginalized by competition with Homo and eventually driven to extinction © 2008 McGraw-Hill Higher Education. All right reserved.