2. 8
C H A P T E R
EARLY HOMININS
8-2

3. EARLY HOMININS What Makes Us Human? Chronology of Hominin Evolution
Who Were the Earliest Hominins?
The Varied Australopithecines
The Australopithecines and Early Homo
Oldowan Tools 3

4. EARLY HOMININS
What key traits make us human, and when and how are they revealed in the fossil record?
Who were the australopithecines, and what role did they play in human evolution?
When and where did hominins first make tools?

5. WHAT MAKES US HUMAN?
What determines whether a fossil is a human ancestor?
Look for similarities in DNA
Such key attributes as bipedal locomotion, a long period of childhood dependency, big brains, and use of tools and language
Some physical markers identify certain fossils as early hominins but were lost during subsequent human evolution

6. BIPEDALISM
Ardipithecus (5.8–4.4 m.y.a.): earliest recognized hominin genus; shows capacity for upright bipedal locomotion
Reliance on bipedalism (upright two-legged locomotion) differentiates the early hominins from apes
Traditionally viewed as adaptation to open grassland, however, Ardipithecus lived in humid woodland habitat
Perhaps bipedalism developed in woodlands but became more adaptive in subsequent savanna habitat
Ability to see over long grass, carry items back to a home base, and reduce body’s exposure to solar radiation
Preceded stone tool manufacture and the expansion of the hominin brain
Bipedal but also preserved enough apelike anatomy to make them good climbers

7. Ardipithecus

8. Bipedalism Traditional Theories
Stressed advantages in a habitat increasingly dominated by dry, savanna-like conditions
However, ardipithecus lived in woodland environment
Bipedalism my have developed in the woodlands and became even more advantageous in the savanna habitat

9. Woodlands and Savannah

10. Advantages Ability to see further See predators See food
Arms free to carry items
Tools and weapons
More energy efficient
Requires less fuel
Less body surface area exposed to solar radiation
Facilitates cooling
Reduces fluid loss
Can look for food in sunlight conditions

11. BRAINS, SKULLS, AND CHILDHOOD DEPENDENCY
Early hominins had very small brains compared to modern humans (little bigger than average chimp)
Brain size increased during hominin evolution, especially with genus Homo
Human children have long period of childhood dependency, during which brains and skulls grow dramatically (compared to the young of other primates)
Larger skulls mean larger birth canals, but bipedalism imposes limits on the expansion of human pelvic opening
Pelvis too big – doesn’t provide enough support for the trunk causing problems with locomotion and posture
Pelvis too small – mother and child may die
Natural selection struck balance between structural demands of upright posture and tendency toward increased brain size – the birth of immature and dependent children whose brains and skulls grow dramatically after birth

12. TOOLS Hominin stone tool manufacture dated to 2.6 m.y.a.
Upright bipedalism permitted use of tools and weapons
Primates have abilities to
adapt through learning;
Most likely, early hominins
had even greater cultural
abilities than contemporary apes have

13. TEETH
Big back teeth with thick tooth enamel: an early hominin trait (that has been reduced during subsequent human evolution)
Permitted thorough chewing of tough, fibrous vegetation that would have otherwise been indigestible
Churning, rotary motion associated with such chewing favored reduction of canines and bicuspids
These front teeth are much sharper and longer in the apes than in early hominins

14. Teeth

15. CHRONOLOGY OF HOMININ EVOLUTION
Hominid: the zoological family that includes fossils and living humans, chimpanzees, gorillas, and their common ancestors
Hominin (tribe) describes all human species that have ever existed, excluding chimps and gorillas

16. CHRONOLOGY OF HOMININ EVOLUTION
Hominins appeared late in the Miocene epoch (23 – 5 mya)
The most important epochs for study of hominin evolution are the
Pliocene (5–2 m.y.a.) - Austalopithecus
Pleistocene (2 m.y.a.–10,000 B.P.) – Au. Had evolved into homo
Holocene or Recent (10,000 B.P.–present)
Australopithecus main hominin genus until end of Pliocene
Some form of Australopithecus evolved into Homo by start of Pleistocene

17. WHO WERE THE EARLIEST HOMININS?
Significant recent discoveries in Africa
Kenya
Tanzania
Ethiopia
South Africa
Chad

18. Table 8.1: Dates and Geographic Distribution of Major Hominoid, Hominid, and Hominin Fossil Groups18

19. SAHELANTHROPUS TCHADENSIS
6- to 7-million-year-old skull, two lower jaw fragments, and three teeth; OLDEST POSSIBLE HUMAN ANCESTOR yet found
Also known as “Toumai” (“hope of life”)
Central Africa – Chad (2001)
Time period when humans and chimps were
diverging from common ancestors
Blends ape-like and human characteristics:
Heavy brow ridges
Adult male with chimp-sized brain
Relatively flat, humanlike face
Teeth
Foramen magnum – “big hole” through which spinal cord joins the brain; placement is farther forward than in apes; suggests bipedal locomotion
Moves scientists closer to time when humans and African apes diverged
If hominin, shows hominin evolution not confined to E. Africa’s Rift Valley

20. ORRORIN TUGENENSIS Kenya - 2001
6-million-year-old fossils from at least five individuals suggest upright bipedalism and tree-climbing skills
Close to time of common ancestor
between humans and chimps
Chimp-sized creature that climbed
easily and walked on two legs when on
the ground
Teeth more like a female chimpanzee
Other dental and skeletal features, especially bipedalism, led discoverers to assign Orrorin to hominin lineage – it is debated issue
Lived after Toumai but before Ardipithecus kadabba
Hominin status of Ardipithecus more generally accepted

21. ARDIPITHECUS Dates to at least 4.4 m.y.a.
Subsequently, FOSSILS from 5.8 m.y.a. found in Ethiopia (Ardipithecus kadabba) (1992 – 1994)
At least five individuals represented
Apelike in size, anatomy,
and habitat (mixture of woods
and grasslands)
Because of its probably upright
bipedalism, Ardipithecus kadabba
has been recognized as the earliest hominin
Ardipithecus ramidus (4.4 m.y.a.) is earliest known hominin SKELETON 21

22. ARDIPITHECUS Ardipithecus ramidus - “Ardi”; female - Ethiopia – 2009
Fairly complete skeleton; earliest known hominin skeleton; almost 1.2 million years older than Lucy; fossils date from 5.8 to 4.4 mya
Skeleton:
Seems to be transitional between earlier
arboreal primates and later terrestrial ones
Pelvis – transitional; suited for arboreal
climbing and bipedal locomotion
Brain no larger than that of modern chimp
Retained arboreal heritage in lower pelvis
Strong hamstrings for climbing
Lack of arched feet
Long arms and short legs
Wooded environment
Teeth suggest omnivorous diet less dependent on fruits (ate plants, nuts, and small mammals); no heavy chewing specializations of later australopithecus species
Reduced sexual dimorphism – canines resemble modern humans rather than chimps or gorillas (smaller and less tusk-like)

23. KENYANTHROPUS
Maeve Leakey’s Kenyanthropus platyops complicates picture
Kenya – 1999
Flat faced “man”
of Kenya
Nearly complete
skull and partial jawbone
3.5 million year old find represents a new branch on early human family tree
Shows at least two hominin lineages existed as far back as 3.5 m.y.a. (au. afarensis, “Lucy”, and Kenyanthropus); THEY WERE NOT ALONE
Kenyanthropus has flattened face and small molars, suggesting to Leakey a new taxon (very different from au. afarensis)

24. Figure 8.1: Phylogenetic Tree for African Apes, Hominids, and Hominins24

25. THE VARIED AUSTRALOPITHECINES
Australopithecus had at least 7 species
A. anamensis (4.2–3.9 m.y.a.)
A. afarensis (3.8–3.0 m.y.a.)
A. africanus (3.0?–2.0? m.y.a.)
A. garhi (2.5 m.y.a.)
A. robustus (2.0?–1.0? m.y.a.)
A. boisei (2.6?–1.2 m.y.a.)
A. sediba (1.98–1.78 m.y.a.)

26. Austalopithecus

27. Australopithecus

28. AUSTRALOPITHECUS ANAMENSIS
Ardipithecus ramidus may or may not have evolved into Au. anamensis
Fossils (78 fragments) from two sites, reported first by Leakey and Walker, date to 4.2–3.9 m.y.a.
Strong jaws
Molars have thick enamel
Large apelike canines
Suggests, at times, ate hard, abrasive food (probably preferred fruits and nuts)
Weighed about 110 pounds
Bipedal
May be ancestral to A. afarensis, which is usually considered ancestral to all later australopithecines as well as Homo species

29. Austalopithecus Anemensis

30. AUSTRALOPITHECUS AFARENSIS
A. afarensis lived 3.8–3.0 m.y.a.
Fossils found at two sites (Laetoli in northern Tanzania and Hadar in Ethiopia)
Very similar to chimps and gorillas; indicates common ancestry with African apes must be recent (no more than 8 m.y.a.)
“Lucy” – from Hadar; approximately 3.2 million years old

31. Lucy

32. Lucy’s Baby “Lucy’s Baby” - female Ethiopia; 2000
Lived 100,000 years before Lucy; 3.3 million years ago
Remains include: almost complete skull, baby teeth, fingers, torso, kneecap, foot
Monkey size face with smooth brow
Skull and upper body appear ape-like
Lower body confirms bipedalism
Upper body includes two complete shoulder blades similar to a gorilla’s (better at climbing than humans)
World’s oldest fossil child – sheds light on growth cycle of Australopithecus brain:
Growth cycle similar to chimps; allows less time for guidance and socialization
Chimps reach puberty around age 7 and males leave their mother around age 10
Reached adulthood earlier than modern humans
Developed rapidly - lifespan would have been shorter than ours

33. Lucy’s Baby

34. Australopithecus Afarensis

35. AUSTRALOPITHECUS AFARENSIS
CHARACTERISTICS:
Skull and upper body are ape-like; Llwer body confirms bipedalism
Teeth and Face
- Canines, premolars and skulls were more ape-like
Longer and sharper canine teeth (compared to Homo) that projected beyond other teeth; canines were smaller than ape’s tusk-like canines
Lower premolar – pointed and projecting to sharpen upper canine teeth; had one long cusp and one tiny bump that hints at bicuspid premolar that eventually developed in hominins
Molars, chewing apparatus, and cheekbones foreshadowed later hominin trends
Massive back teeth, jaws and facial and cranial structures suggest diet demanding extensive grinding and powerful crushing (hard, gritty, fibrous vegetation of grasslands and semi-desert) (back teeth change to accommodate heavy chewing stresses)
Cheekbones large and blare out to the side for attachment of powerful chewing muscles

36. AUSTRALOPITHECUS AFARENSIS
Bipedalism – predates Au. Afarensis
Structure of pelvic, hip, leg, and foot bones confirm bipedalism
Pelvis is more similar to Homo than to ape’s (but not identical)
Blades of Australopithecine pelvis are shorter and broader than those of apes
Sacrum is larger, as is Homo
Lower spine (lumbar) curve characteristics of Homo; curvature helps transmit weight of upper body to pelvis and legs
Skull - Brain capacity only slightly larger than modern chimp

37. Au. Afarensis Foramen Magnum
“Big hole” through which spinal cord joins the brain
Placement is farther forward in Australopithecus and Homo
Represents adaptation to upright bipedalism
Arms
Muscular
Longer arms relative to legs
Likely spent some time in trees
ADAPTATIONS TO LIVING BOTH IN TREES AND ON THE GROUND HELPED AUSTRALOPITHECUS AFARENSIS SURVIVE FOR ALMOST A MILLION YEARS.

38. AUSTRALOPITHECUS AFARENSIS
Birth Canal
- Most significant contrast
Narrower in Australopithecus than in Homo
Expansion of birth canal is trend in hominin evolution
Width of birth canal is related to size of brain and skull
Australopithecine skull grew after birth to accommodate a growing brain (like Homo) but it expanded less than ours do
Sexual Dimorphism
Very marked; males weighed perhaps twice as much as females (Lucy stood between 4-5 feet tall; male Australopithecus might have reached 5 feet)

39. Au. Afarensis Childhood
Young would have depended on parents and kin for nurturance and protection
Years of childhood dependency would have facilitated social learning by providing time for observation, teaching, and learning
Suggests possibility of rudimentary cultural life
Au. anamensis and Ardipithecus indicate bipedalism; thus, bipedalism predates Au. afarensis as well as larger brain size

40. RECAP 8.1: Facts about the Australopithecines Compared with Chimps and Homo40

41. Figure 8.3: Comparison of Homo sapiens and Pan troglodytes (the Common Chimp)41

42. Figure 8.4: A Comparison of Human and Chimpanzee Pelvises42

43. Figure 8.5: A Comparison of the Skull and Dentition (Upper Jaw) of Homo and the Chimpanzee43

44. GRACILE AND ROBUST AUSTRALOPITHECINES
Two groups of South African australopithecines (3–1 m.y.a.)
Gracile (A. africanus): smaller and lighter;
Robust (A. robustus): larger than gracile, robust
A. boisei - hyperrobust
3 Conflicting models:
1.) Africanus and robustus as separate species; life spans were overlapping
2.) africanus and robustus as sequential; africanus was ancestral to robustus
3.) both groups were part of single species; each represents opposite extremes of variation within one species
Both gracile and robustus probably descended from A. afarensis

45. GRACILE AND ROBUST AUSTRALOPITHECINES
Trend toward enlarged back teeth, chewing muscles, and facial buttressing continues
However, canines are reduced and premolars are fully bicuspid
Front teeth are more marked than Homo
Chewing muscles are strong enough to produce sagittal crest (bony ridge on top of skull
Cheekbones were elongated, massive structures that anchored large chewing muscles running up the jaw
Brain size increased slightly from A. afarensis (430 cm3) to A. Africanus (490 cm3) to A. robustus (540 cm3); compare to Homo sapiens (1,350 cm3)
The skulls, jaws, and teeth of australopithecines indicate their diet was mainly vegetarian, requiring extensive crushing and grinding; they may also have hunted small and slow moving game or scavenged
Living in open savanna, they probably sought safety and companionship in groups; maintained social bonds though play and mutual grooming
Sexual dimorphism is evident; observed through size of canine teeth
Sexual dimorphism was much more pronounced in early hominins than in Homo Sapiens
Later australopithecines had bigger back teeth than earlier ones; trend of enlarged back teeth ended with early Homo (who had much smaller back teeth, reflecting dietary change)

46. GRACILE AND ROBUST AUSTRALOPITHECINES
The 1985 discovery of “black skull” (2.6 m.y.a.) apparently an early A. robustus
Walker and Leakey view skull as an early hyperrobust A. boisei
Gives more possible models of divergence between Homo and Australopithecines
Has mixture of Au. features
Ape like jaw and relatively small brain
Sagittal crest (like hyper-robusts)
Shows that some anatomical features did not change much during more than 1 million years

47. Figure 8.6: Skulls of Robust (left) and Gracile (Right) Australopithecines, Showing Chewing Muscles47

48. THE AUSTRALOPITHECINES AND EARLY HOMO
Homo ancestors became reproductively isolated from later australopithecines by 2 m.y.a.
Hominin teeth fossils from 2 m.y.a. are two very different sizes
Very large teeth belonged to Au. boisei
Smaller teeth belonged to members of genus Homo
By 1.9 m.y.a., fossil evidence shows different hominin groups occupied different ecological niches (Homo and Au. boisei coexisted in East Africa) (early Homo habilis and Homo erectus)
Johanson and White (1979) propose that Au. afarensis split into two populations: other australopithecines and early homo
Homo had a larger brain and reproportioned skull (increase in areas of brain that regulate higher mental function), hunted and gathered, made sophisticated tools, and eventually displaced its cousin species, A. boisei

49. Homo Trends The distinctive early Homo trends are
1. A rapid increase in brain size and reproportioned skull (increased areas of function),
2. Increasingly elaborate toolmaking
3. Increasing emphasis on hunting and gathering
There remains considerable debate as to when and in what population these trends led to speciation, from an australopithecine to Homo habilis.
Homo erectus likely displaced cousin Au. Boisei

50. OLDOWAN TOOLS Oldest manufactured tools; found by Leakeys
First tools found were from Olduvai Gorge (found in 1931) are about 1.8 m.y.a.
Older Oldowan tools found in Ethiopia, Congo, Kenya, and Malawi (2.6-2 million years old)
Stone tools consist of cores and flakes and choppers
Core: piece of rock from which flakes are removed
Flake: piece that is knapped or chipped off of a core
Chopper: tool made by flaking the edge of such a core on one side (byproduct of flaking the core) (not a preconceived form)

51. Oldowan Tools
Core tools and choppers are not the most common stone tools; FLAKES are!
Choppers used for:
Food processing (pounding, breaking, bashing)
Dismember game carcasses
Break open marrow cavities
Oldowan sites have also produced pieces of bone and horn with scratches indicating they were used for digging up tubers or insects

52. OLDOWAN TOOLS
Oldowan pebble tools represent world’s oldest formally recognized stone tools
For decades, anthropologists have debated the identity of early toolmakers.
It has been widely accepted that homo habilis was the first hominin toolmaker; however it is likely that at least one kind of australopithecine also made and used stone tools

53. A. GARHI AND EARLY STONE TOOLS
In 1999, new hominin species, A. garhi (means “surprise”), was found in Ethiopia; dates to m.y.a.
Associated with stone tools, remains of butchered animals (antelopes and horses butchered with earliest stone tools)
Important discovery for three reasons:
Added new species to human family tree
Demonstrated thigh bone elongated 1 million years before forearm shortened, to create current human proportions
Evidence of butchering of large mammals shows early stone technologies were aimed at getting meat and marrow from big game; may be the beginning of dietary revolution that eventually led to occupation of new habitats and continents
The association of Au. garhi with animal butchery combined with the earliest stone tools suggests that australopithecines were tool-makers with some capacity for culture

54. Oldowan Hominins at the Kanjera Site
Provides the earliest, and very complete, evidence for “persistent” reliance on meat within the hominin diet (don’t know which species of hominin though)
A regular diet of red meat was a key factor that allowed the growth of the hominin body and brain and the spread of hominins beyond Africa