Hominid Evolution

1
Hominid Evolution

• Part 1

2
Trends in Hominid Evolution

• Bipedalism
• Larger Brains
• Smaller face teeth and jaws

3
Bipedalism

• Probably developed between 8 and 4 million years
  ago in Africa, but we are still unsure of the
  exact time
• Between 16 and 11 mya, there was a drying period
  in Africa.
• During this time, tropical forest cover was
  replaced in some parts of the continent by
  tropical grasslands, called savannah,
  interspersed by dense forest.

4
Why bipedalism

• Bipedalism may have been an adaptation to living
  in the savanna. If this is the case, however,
  why are baboons not bipedal?
• Better dispersion of body heat.
• The ability to use the hands, to carry food for
  instance, while the legs are moving (walking or
  running).
• Making, carrying and using tools for gathering
  plants foods, hunting and weapons

5
Why bipedalism

• Fitted a scavenger lifestyle because it was an
  efficient way to cover long distances walking at
  a slow pace.
• Scavenging would have encouraged the use of tools
  to cut meat efficiently and quickly.
• Ultimately we cannot know why bipedalism
  developed, we can only speculate.

6
Disadvantages of bipedalism

• Bipedal walking has benefits but also costs. The
  benefits had to outweigh the costs for these
  animals to become and remain bipedal.
• One cost is that blood flow to the brain becomes
  harder to sustain.
• Bipedal posture puts enormous pressure on the
  back, hips and pelvis, especially for females
  when pregnant.

7
Skeletal changes to support bipedalism

• Skullforamen magnum position placed skull over
  the spinal column
• Pelvisrounded rather than flat and long as in
  apes
• Knock-kneed legs helps us move our legs when
  walking and running and maintain the centre of
  balance at the mid-line of our bodies.
• Hominid feet have a robust heel and ankle bones
  as well as an arch.
• See http//www.becominghuman.org/

8
Brain size increases

• Brain size as seen through cranial capacity has
  increased over time
• Australopithecus africanus 440 cc
• Homo erectus 1000 cc
• Homo sapiens 1300 cc
• Bipedalism came first and then brain development.
• Some of the increase in brain size is due to
  increase in over all body size.

9
Brain size

• Between 4 mya and 2 mya the relative size of the
  brain did not increase but between 2 mya and the
  present it doubled in relative size and tripled
  in actual size.
• Brain size increase due to
• Tool use?
• Language development?
• Increased lifespan?

10
Brain size

• The size of human brains is limited by the size
  of the female pelvis.
• As brains became larger, children were born less
  developed and more dependant on their parents,
  particularly their mothers.

11
Reduction of face, teeth and jaws

• After 2 mya we see substantial changes in face,
  teeth and jaws
• Australopithecines had
• Large molars relative to their body size
• Large and strong jaw bones
• Large faces that projected below the eyes
• These features may well have been related to
  their food supply, mostly plants food requiring
  chewing and grinding

12
Reduction of face, teeth and Jaws

• Smaller faces, teeth and jaws in various Homo
  species after 2 mya
• Probably related to
• tool use
• greater dependence on meat as a food source
• use of fire

13
Dates to remember

• 4 million years ago
• Clear evidence of bipedalism with
  Australopithecus afarensis
• 2.5 million years ago
• First stone tools which have been associated with
  Homo habilis, the first of the genus Homo
• 1.8 to 1.6 million years ago
• Earliest evidence for Homo erectus

14
The Sivapithecines

• 18-8 mya found during the Miocene Epoch
• East Africa and Eurasia (China, Hungary,
  Pakistan)
• Hominoids (possibly hominids)
• Ancestral to orangutans and probably chimpanzees,
  gorillas and humans.
• By 8 mya the hominid line had probably branched
  off.

15
Sahelanthropus tchadensis

• 7 mya
• Chad
• Also called Toumai
• Discovered July 2002 by member of French team

16
Sahelanthropus tchadensis

• DNA evidence from modern apes and humans suggest
  a single ancestral species at about 6-7 mya
• Environment would have been partially wooded
  savanna
• Mix of ape-like and hominid features
• Cranial capacity of 350cc

17
Sahelanthropus tchadensis

• Because of short face, massive brow ridge, mouth
  and jaw that protrude less than apes and small
  canines, face considered relatively
  modern-looking, even more modern than Lucy A.
  afarensis at 3.6-2.9 mya

18
Sahelanthropus tchadensis

• But dental remains almost identical to
  Ardipithecus
• Could Toumai be a direct ancestor of H habilis
  making Australopithecines a hominid branch that
  became extinct?
• - Was this animal bipedal? Difficult to tell
  because no post-skeletal material.

19
Ardipithecus ramidus

• 4.4 mya during the Pliocene Epoch (Pliocene
  begins 5.2 mya and ends 1.6 mya)
• Subsequent finds date to 5.8-5.2 mya (Miocene era)

20
Ardipithecus ramidus

• Ethiopia, Awash region
• Found in early 1990s (1992, 1993, 1994)
• Represented by the pieces of 17 individuals with
  finds that show almost a complete skeleton

21
Ardipithecus ramidus

• Has apelike relatively small molars and large
  canines, like a chimpanzee
• Latest finds of bones form lower part of body
  such that it was semi-bipedal
• Seems to be a precursor to Australopithecus

22
Ardipithecus ramidus

• The environment in which Ardipithecus ramidus
  lived would have been tropical forest
• Since this animal was semi-bipedal, this find
  suggests to some paleoanthropologists that
  bipedalism was not an adaptation to savannah
  environments as previously thought.

23
Australopithecus anamensis

• 4.2-3.9 mya found during the Pliocene Epoch
• Kenya (East Africa)

24
Australopithecus anamensis

• Small number of finds including upper and lower
  jaws, cranial fragments, and the upper and lower
  parts of a leg bone (tibia) found in 1995 when
  the species was named as well as an armbone
  (humerus) found in 1965.

25
Australopithecus anamensis

• Apelike jaw with shallow palate and large canines

26
Australopithecus anamensis

• Older than A. afarensis but has a similar
  shinbone which suggests bipedalism
• Seems to be a bridge between Ardipithecus and A.
  afarensis

27
Australopithecus afarensis

• 4-3 mya
• East Africa
• (Ethiopia, Tanzania and Kenya)
• The East African Rift Valley
• Hadar and Laetoli

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Australopithecus afarensis

• Lucy (AL 288-1) with bones from all parts of a
  partial skeleton
• Dates to 3.2 million year ago
• Found by D. D. Johanson at Hadar, Ethiopia in
  1974.

29
Australopithecus afarensis

• First family
• Thirteen individuals of all ages and both sexes
• Hadar in Ethiopia
• Found in 1975 by Johanson
• Dates to 3.2 mya

30
Australopithecus afarensis

• Laetoli footprints in fossilized volcanic ash at
  Laetoli site in Tanzania
• Found by Mary Leaky in 1976
• Shows that these ape like Australopithecines
  walked like us at 3.5 mya.
• Heel strike.
• A well-developed arch.
• Big toe, in front of the ball of the foot and
  parallel to the other toes.
• A deep impression for the big toe shows toe-off.
• http//www.pbs.org/wgbh/evolution/library/07/1/l_0
  71_03.html

31
Australopithecus afarensis

• Skull
• Cranium low
• Forehead sloped backwards
• Pronounced brow ridge
• Flat nose
• Chinless with large jaws relative to skull size
• Saggital crest and temporo-nuchal crest across
  lower back of skull
• Apelike face

32
Australopithecus afarensis

• Cranial capacity about 310-500 cc
• Height 3.5 to 5 ft.
• Weight 29-45 kg
• Locomotion Bipedal and climbing,
• Sexual dimorphism
• Extreme. This is seen in size of body and in
  dentition where males tend to have a more molar
  like, two cusped 1st premolar while females do
  not have this.
• May be due to female eating better quality food
  in trees.

33
Australopithecus afarensis

• Dentition
• Generally show features reminiscent of late
  Miocene sivapithecines
• Incisors and canines larger than in A. africanus
  and canine protrudes more
• First lower molars are less like molars
• Dental arch less rounded than in A Africanus
• Evidence of grinding plant food

34
AustralopithecusAfricanus

• 3-2.3 mya during the Pliocene Epoch
• Later than A afarensis
• Southern Africa
• Includes Taung Child and Mrs Ples
• Numerous fossils found

35
AustralopithecusAfricanus

• Taung Child
• Found in 1925 by Raymond Dart
• Taung Cave at edge of Kalahari Desert
• Skull of a child, probably 3 to 4 years old
• http//www.mnh.si.edu/anthro/humanorigins/ha/taung
  1.html
• Doubt about the fossil came from beleief that
  hominids originated in Asia

36
AustralopithecusAfricanus

• Mrs Ples
• 2.6 mya
• Found in 1947 in Transvaal region of southern
  Africa
• Validated the Taung child skull
• http//www.mnh.si.edu/anthro/humanorigins/ha/sts5.
  html

37
AustralopithecusAfricanus

• Skull
• chinless jaw
• rounded brain case with well-developed forehead
  sloping backward
• Moderate brow ridges

38
AustralopithecusAfricanus

• Cranial capacity 428-510 cc (size of large chimp
  brain and 1/3 size of modern human brain)
• Brain organization more like an ape than like a
  human

39
AustralopithecusAfricanus

• Height 3.5-4.5 ft.
• Dentition
• Broad incisors and short canines (like modern
  humans)
• Larger premolars and molars than modern humans
  but similar in shape.
• Jaw is increasingly parabolic in shape

40
AustralopithecusAfricanus

• Skeletal features and locomotion
• Similar pelvis to modern humans and therefore
  probably bipedal
• Similar S-shaped spine, hip joints a femurs to
  modern humans suggesting that they walked in a
  similar fashion.

41
Australopithecus boisei

• Called Paranthropus boisei by some
  anthropologists who think this hominid is a
  different species from Australopithecus because
  it is so robust
• 2.2-1.3 mya
• Found in East Africa
• Omo Basin, Ethiopia
• Lake Turkana, Kenya
• Olduvai Gorge, Tanzania

42
Australopithecus boisei

• First specimen was the OH 5 skull (Zinj) found
  at Olduvai Gorge (Tanzania) in 1959 by Mary
  Leakey and named Zinjanthropus boisei
• http//www.mnh.si.edu/anthro/humanorigins/ha/oh5.h
  tml

43
Australopithecus boisei

• Skull known as KNM ER 406
• Adult male
• Cranial capacity of 510 cc
• Dates to 1.7 mya
• Found by Richard Leaky at Koobi Fora, Kenya in
  1969
• http//www.mnh.si.edu/anthro/humanorigins/ha/er406
  .html

44
Australopithecus boisei

• Dentition
• Enormous molars and premolars and palate like A.
  robustus but bigger
• Skull
• More massive than A. robustus with enormous
  sagittal crest
• Prominent brow ridgeslarger than A. robustus
• Efficient chewing machine

45
Australopithecus boisei

• Cranial capacity 500-530 cc
• Weight 34-49 kg
• Skeletal features Heavy bones. Larger than A.
  robustus
• Geneaology
• Probably evolved from A. afarensis ancestor
  rather than A. africanus ancestor
• Not an ancestor or modern humans. Evolutionary
  deadend
• Co-existed in East Africa with Homo habilis

46
Australopithecus robustus

• Like Australopithecus boisei, this hominid is
  also sometimes called Paranthropus.
• This is because it is thought to be a different
  genus than the gracile Australopithecines

47
Australopithecus robustus

• 2-1.5 mya ((1.8 to 1 mya in your text Ember et
  al.)
• Found beginning in the 1930s in South African
  caves
• Kromdraai
• Swartkrans
• http//www.mnh.si.edu/anthro/humanorigins/ha/rob.h
  tm

48
Australopithecus robustus

• Skeletal features
• Similar to A. africanus in size but thick bones
  with markings where strong muscles were attached.
• Body would have been bigger and more muscular
  than that of A africanus
• Skull
• Sagittal crest running from front to back along
  top to hold jaw muscles needed for eating
• Efficient chewing machine

49
Australopithecus robustus

• Cranial capacity 490-530 cc
• Weight 32-40 kg.
• Dentition
• Larger molars and premolars but smaller incisors
  than A. africanus
• Geneaology
• May have been descended from A. africanus
• NOT an ancestor of modern humans. Evolutionary
  dead end

50
Comparison of A. boisei, A. robustus and other
Australopithecines

• A boisei had larger molars, expanded pre-molars,
  thicker jaw and cheekbones and a larger sagittal
  crest than A robustus.
• This is probably evidence of great chewing
  capability

51
Comparison of A. boisei, A. robustus and other
Australopithecines

• Robust forms were of similar body size to gracile
  forms, but skulls were more robust
• Was robust form a vegetarian while gracile forms
  were omniverous? Recent evidence makes us
  question this assumption.
• Both A robustus and A boisei died out about 1.2
  to 1 mya so could not have been our ancestors

52
Early Homo species habilis and rudolfensis

• 2.5-1.5 mya
• Mostly in east Africa (Kenya and Tanzania) but
  have also been found in southern Africa
• Some anthropologists place both in the same
  species, H habilis
• Homo habilis is thought to be in direct ancestral
  line to modern humans
• Lived in the same places and at the same time as
  the robust australopithecines (A robustus and A
  boisei)

53
Homo habilis

• Earlier than A rudolfensis beginning 2.3 mya
• OH 7 was the first fossil evidence of Homo
  habilis at Olduvai Gorge
• http//www.mnh.si.edu/anthro/humanorigins/ha/oh7.h
  tml
• OH 24 Twiggy was the oldest H habilis fossil
  skull found at Olduvai Gorge
• http//www.mnh.si.edu/anthro/humanorigins/ha/oh24.
  html

54
Homo habilis

• Larger brain than australopithecies at 630-640 cc
• Reduced molars and premolars
• Body similar to australopithecines
• Long arms may indicate that they were still
  partly arboreal

55
Homo rudolfensis

• Contemporary with H habilis
• Many anthropologists place them in the same
  species (H habilis)
• Brain the same size as H habilis and larger than
  the australopithecines
• Modern limb proportions
• Cheek teeth thickly enamelled
• Flat, Broad face
• KNM ER 1470
• http//www.mnh.si.edu/anthro/humanorigins/ha/er147
  0.html

56
Homo habilis, the first tool maker?

• Stone tools first found at Olduvai Gorge in the
  1930s with no associated fossil bones
• Stone tools found from sites in East Africa date
  to 2.5 mya and on, about the same time as H
  habilis
• Assumption has been made that H habilis was the
  first tool maker
• Tools found at Olduvai Gorge and from other sites
  date from 2.5 to 1.5 mya and are referred to as
  Oldowan.

57
Oldowan Tools

• Flakes and cobble or core tools
• Percussion flaking
• Choppers at Olduvai Gorge were core tools that
  had been partially flaked and may have been used
  for chopping
• Scrapers are core tools flaked on one side
• Most Oldowan tools were unifacial rather than
  bifacial

58
Oldowan tools

• After 2 mya hominids were cutting up animal
  carcasses
• They were probably scavengers rather than hunters
• These hominids were mobile, with the Olduvai
  Gorge site used only in the dry season
• Hominids used many kinds of animalsfrom wild
  pigs to elephants

59
Homo habilis

• Homo habilis had culture
• Culture is learned and shared
• Culture is adaptive
• Culture is always changing
• Home bases?
• Sharing food
• Making tools
• H habilis was a social being with culture
• Language?

60
Sources

• Ember, Carol, Melvin Ember, Peter Peregrine and
  Robert Hoppa (2006) Physical Anthropology and
  Archaeology, 2nd Canadian Edition. Toronto
  Pearson/Prentice Hall.
• Haviland, William A. (1997) Anthropology, 8th
  edition. Fort Worth Harcourt Brace.
• http//www.talkorigins.org/faqs/homs/
• http//www.mnh.si.edu/anthro/humanorigins/ha/ances
  _start.html
• http//www.pbs.org/wgbh/evolution/library/07/1/l_0
  71_03.html