Origins of Humanity
Earliest Beginning
Characteristics of Ancestors
Early Behavior
Earliest Beginnings
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Ca. 25-5 million years ago (mya)
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Miocene primates
Ca. 6-2 mya
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Hominids, early culture
Miocene Primate Evolution
The Miocene epoch (25-5 mya) "The Golden Age of Apes"
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Two major hominoid radiations
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The dryopiths - Early to Middle Miocene
(25-15 mya)
The ramapiths - Middle to Late Miocene
(15-5 mya)
Dryopithecus
Ramapiths (Sivapithecus)
Gigantopithecus
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Gigantopithecus is known to have lived in what is
now China and Southeast Asia.
Gigantopithecus was the largest primate that ever
walked the Earth. He would have risen 9 to 10 feet
high if he choose to stand up on only his hind legs,
and probably weighed about 600 lbs (a mountain
gorilla male weigh about 400 lbs).
Some suggest that Gigantopithecus is not extinct,
but is hiding in remote areas of the Himalaya
Mountains or the forests of North-West America.
Could a Gigantopithecus, or his descendants, be
the source of the Yeti or Bigfoot tales?
http://www.unmuseum.org/bigape.htm
Size Differences
http://www.unmuseum.org/bigape.htm
Our Last Common Ancestor?
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Unable to determine exact specimen as
yet (Dryopith or Ramapith)
Molecular data suggests split occurred
between 6 and 5 million years ago.
Extensive genetic diversity in
hominoids during the Miocene makes
things complicated.
Scientific Evidence
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Earliest humans (hominids)
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Evolved 5-6 million years ago in Africa
Very similar to apes, but:
Characteristics
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Bipedal
Small brain size
Relatively small body size
 Between 3 and 4 feet
 60-100 pounds
Bipedality Evidence
Anatomy of Bipedalism
Early hominid pelvis on left,
modern human on right.
Comparisons
Basal Hominids (6-4 mya)
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Sahelanthropus tchadensis
Ardipithecus ramidus
Australopithecus anamensis
Orrorin tugenensis
Recent specimens that date to this
time period may represent the earliest
on the human line, but not a lot of data
yet. Most have small brains and were
probably bipedal.
What did they look like?
tchadensis
tugenensis
anamensis
Australopithecines
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Australopithecus afarensis
Australopithecus africanus
Australopithecus garhi
Australopithecus afarensis
(ca. 3.5mya)
Australopithecus afarensis
“Lucy”
Discovered by Donald Johanson and
Tom Gray in 1974 at Hadar in
Ethiopia (Johanson and Edey 1981;
Johanson and Taieb 1976). Its age is
about 3.2 million years. Lucy was an
adult female of about 25 years. About
40% of her skeleton was found, and
her pelvis, femur (the upper leg bone)
and tibia show her to have been
bipedal. She was about 107 cm (3'6")
tall (small for her species) and about
28 kg (62 lbs) in weight.
Other Evidence: Laetoli footprints
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In 1976, members of a
team led by Mary
Leakey discovered the
fossilized footprints of
human ancestors in
Laetoli, Africa.
The footprints were
formed 3.5 million
years ago when at
least two individuals
walked over wet
volcanic ash. The wet
ash hardened like
cement and was then
covered by more ash.
Laeotoli
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Some analysts have noted that the smaller
of the two clearest trails bears telltale signs
that suggest whoever left the prints was
burdened on one side -- perhaps a female
carrying an infant on her hip.
The detailed interpretation of the prints
remains a matter of debate, they remain an
extraordinary and fascinating fossil find,
preserving a moment in prehistoric time.
Laetoli
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Paleoecological reconstructions for that time include bushland
and aquatic fauna at Laetoli and closed woodland at Hadar.
Direct evidence of bipedality in Australopithecus anamensis
dates from between about 3.9 and 4.2 mya (Leakey, et. al.
1995).
http://www.pbs.org/wgbh/evolution/library/07/1/l_071_03.html
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Why Bipedal?
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Three key features differentiate human and
chimpanzee bipedalism:
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Chimpanzees are unable to extend their kneejoints to produce a straight leg in the stance
phase.
Muscular power has to be exerted to support the
body.
The constantly flexed position of the
chimpanzee leg also mean there is no toe off
and heel strike in the swing phase.
http://www.stanford.edu/~harryg/protected/chp15.htm
Advantages of Bipedalism?
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With its radically different anatomy, bipedalism
clearly was an adaptation to terrestrial living, but
was it an advantage over quadrapedalism?
Not necessarily faster, but likely sustainable over
long distances
Protection from predators?
Latest evidence for earliest hominids puts them in
forested environment, not open habitat
Did free hands for tool-using, but what tools; or
possibly food transport?
Theories
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The postural feeding hypothesis (Hunt
1996) is an ecological model.
The behavioral model (Lovejoy 1981)
attributes bipedality to the social, sexual and
reproductive conduct of early hominids.
The thermoregulatory model (Wheeler
1991) views the increased heat loss,
increased cooling, reduced heat gain and
reduced water requirements conferred by a
bipedal stance in a hot, tropical climate as
the selective pressure leading to bipedalism.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Hunt's postural feeding hypothesis
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Hunt's postural feeding hypothesis asserts that the
arboreal food gathering postures of arm-hanging
and vertical climbing, a shared adaptation and
postural specialization of apes, are sufficiently
common to influence anatomy.
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Both chimpanzee behavior and australopithecine anatomy inform
the model.
Eighty percent of chimpanzee bipedalism is during feeding with
arm-hanging stabilizing the posture 93% of the time in terminal
branches and 52% in the central parts of trees.
Torso form in australopithecines features adaptations to armhanging, inferring australopithecine adaptation to arboreal
bipedal fruit gathering.
According to Hunt, this early and specialized origin of bipedalism
only later evolved into habitual bipedal locomotion.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
The behavioral model
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The behavioral model, as presented by
Lovejoy, focuses on social behavioral
mechanisms that influence survivorship and
birthrate.
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Human sexual behavior and anatomy are
hypothesized as implying a monogamous
mating structure, a social form seen as
prerequisite to male provisioning.
Provisioning behavior with the upper limbs used
to transport food to a mate and offspring is seen
as a strong selection factor for bipedality by
directly improving offspring survivorship and
increasing reproductive rate.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Wheeler's thermoregulatory model
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Wheeler's thermoregulatory model
proposes, as the selective pressure,
bipedalism conferring reduction in heat gain
and facilitation of heat dissipation.
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Bipedalism raises the mean body surface higher
above the ground, where more favorable wind
speeds and temperatures prevail.
Greater wind flow translates to higher convective
heat loss.
Bipedalism reduces evaporative cooling
requirements and conserves body water.
Vertical orientation also minimizes direct solar
exposure during the time of day when the solar
radiation is most intense.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Do we really know?
Timing
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The timing of the appearance of bipedalism is of
critical importance in assessing these competing
hypothesis.
The models all present plausible selective
pressures needed for evolutionary change: food
access, provisioning, survivorship assurance,
increase in offspring, predator and injury avoidance
and energy and water conservation.
Under different conditions the individual importance
of these pressures will change. The important
question is what conditions prevailed at the time
that bipedalism appears in the fossil record.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Paleoenvironment
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Vrba's "turn-over pulse" hypothesis supports a
major climate change, with onset of drier
conditions and diminution of wooded habitats,
beginning in the Pliocene around 2.5 mya.
Habitat reconstruction based on faunal
associations with hominid fossils demonstrate
that Australopithecus species lived in wooded
and well watered environments (Reed 1997).
Homo is the first hominid known to have
adapted to open, savannah-like habitats, well
after the evolution of bipedality.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Which is it?
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Thus, from an paleoecological perspective, the
thermoregulatory model does not fit the evidence.
With the behavioral model, which hypothesizes
monogamous pair bonding and reduction in mate
competition as changing social factors antecedent
to bipedalism, one would expect an earlier
reduction in canine size, in parallel with the
evolution of bipedalism.
Arm-hanging anatomy persists long after the onset
of bipedal characteristics, indicating occupation of
wooded niches for the early bipedal hominids, so
Hunt’s feeding model might be most appropriate.
http://www.jqjacobs.net/anthro/paleo/bipedalism.html
Australopithecus africanus
(ca. 3 mya)
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South Africa was the home to the
species Australopithecus africanus,
which lived 3.3 to 2.5 million years
ago.
This species was the first of the
australopiths to be described;
Raymond Dart named the genus
and species in 1925 after his
discovery of the famous Taung
child.
Many features of the cranium of A.
africanus are more evolved than
that of earlier A. afarensis.
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These features include a more
globular cranium and slightly higher
ratio of brain size to body size.
Also the teeth and face appear less
primitive.
http://www.mnh.si.edu/anthro/humanorigins/ha/afri.html
A. africanus
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For years researchers considered the
evolution of early humans to pass from A.
afarensis to A. africanus and lead to early
Homo.
However, some researchers now believe
that facial features link A. africanus to the
"robust" early human species of southern
Africa, Paranthropus robustus
http://www.mnh.si.edu/anthro/humanorigins/ha/afri.html
Australopithecus garhi
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A. garhi existed 2.5 million years ago. Tim White and Berhame
Asfaw found it in Bouri, East Ethiopia.
Characteristics:
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cranial capacity of 450ml.
canines and premolars like Homo genus
huge molars
no diastema
prognathic
ape-like arms and legs
The importance of this hominid is that it was found with many
tools and an array of slaughtered animals. Tool use has been the
defining criteria that separated the Homo genus from the
Australopithecines.
http://www.humboldt.edu/~mrc1/main.shtml
Genus Paranthropus
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Robust Early Hominids (2.5-1.5 mya)
Extinct branch/lineage
Highly specialized features
Heavy brows
 Large teeth, particularly back
 Large muscle attachment areas
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Paranthropus robustus
DNH 7, "Eurydice",
Paranthropus robustus.
Discovered by André
Keyser in 1994 at the
Drimolen cave in South
Africa. Estimated age is
between 1.5 and 2.0
million years.
Paranthropus boisei
OH 5, "Zinjanthropus",
"Nutcracker Man",
Paranthropus boisei
Discovered by Mary Leakey
in 1959 at Olduvai Gorge in
Tanzania (Leakey 1959).
Estimated age is 1.8 million
years.
Paranthropus aethiopicus
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By 2.7 million years
ago, a new lineage
of early humans
had evolved in East
Africa:
Paranthropus
aethiopicus
http://www.mnh.si.edu/anthro/humanorigins/ha/a_tree.html