1. Window on Humanity Conrad Phillip Kottak Third Edition
Chapter 5
The First Hominins
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2. Overview What makes us human? Early hominin evolution
Australopithecines
Gracile vs. robust
Early Homo
Oldowan tools
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3. 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
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4. 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
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5. 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)
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6. 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
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7. 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.
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8. 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
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9. CHAPTER 5 The First Hominins
A. afarensis
Fossils from Laetoli, Tanzania ( m.y.a.), and Hadar, Ethiopia ( 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
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10. 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
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11. 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
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12. 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
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13. 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)
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14. 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
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15. 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
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