Title: Hominid Evolution
1Hominid Evolution
2Trends in Hominid Evolution
- Bipedalism
- Larger Brains
- Smaller face teeth and jaws
3Bipedalism
- 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.
4Why 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
5Why 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.
6Disadvantages 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.
7Skeletal 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/
8Brain 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.
9Brain 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?
10Brain 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.
11Reduction 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
12Reduction 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
13Dates 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
14The 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.
15Sahelanthropus tchadensis
- 7 mya
- Chad
- Also called Toumai
- Discovered July 2002 by member of French team
16Sahelanthropus 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
17Sahelanthropus 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
18Sahelanthropus 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.
19Ardipithecus 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)
20Ardipithecus 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
21Ardipithecus 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
22Ardipithecus 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.
23Australopithecus anamensis
- 4.2-3.9 mya found during the Pliocene Epoch
- Kenya (East Africa)
24Australopithecus 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.
25Australopithecus anamensis
- Apelike jaw with shallow palate and large canines
26Australopithecus anamensis
- Older than A. afarensis but has a similar
shinbone which suggests bipedalism - Seems to be a bridge between Ardipithecus and A.
afarensis
27Australopithecus afarensis
- 4-3 mya
- East Africa
- (Ethiopia, Tanzania and Kenya)
- The East African Rift Valley
- Hadar and Laetoli
28Australopithecus 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.
29Australopithecus afarensis
- First family
- Thirteen individuals of all ages and both sexes
- Hadar in Ethiopia
- Found in 1975 by Johanson
- Dates to 3.2 mya
30Australopithecus 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
31Australopithecus 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
32Australopithecus 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.
33Australopithecus 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
34AustralopithecusAfricanus
- 3-2.3 mya during the Pliocene Epoch
- Later than A afarensis
- Southern Africa
- Includes Taung Child and Mrs Ples
- Numerous fossils found
35AustralopithecusAfricanus
- 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
36AustralopithecusAfricanus
- 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
37AustralopithecusAfricanus
- Skull
- chinless jaw
- rounded brain case with well-developed forehead
sloping backward - Moderate brow ridges
38AustralopithecusAfricanus
- 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
39AustralopithecusAfricanus
- 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
40AustralopithecusAfricanus
- 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.
41Australopithecus 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
42Australopithecus 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
43Australopithecus 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
44Australopithecus 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
45Australopithecus 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
46Australopithecus 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
47Australopithecus 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
48Australopithecus 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
49Australopithecus 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
50Comparison 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
51Comparison 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
52Early 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)
53Homo 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
54Homo 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
55Homo 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
56Homo 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.
57Oldowan 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
58Oldowan 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
59Homo 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?
60Sources
- 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