Origins of Humanity

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Origins of Humanity

• Earliest Beginning
• Characteristics of Ancestors
• Early Behavior

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Earliest Beginnings

• Ca. 25-5 million years ago (mya)
• Miocene primates
• Ca. 6-2 mya
• Hominids, early culture

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Miocene Primate Evolution

• The Miocene epoch (25-5 mya) - "The Golden Age of
  Apes"
• Two major hominoid radiations
• The dryopiths - Early to Middle Miocene (25-15
  mya)
• The ramapiths - Middle to Late Miocene (15-5 mya)

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Dryopithecus
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Ramapiths (Sivapithecus)
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Gigantopithecus

• 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
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Size Differences
http//www.unmuseum.org/bigape.htm
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Our Last Common Ancestor?

• 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.

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Scientific Evidence

• Earliest humans (hominids)
• Evolved 5-6 million years ago in Africa
• Very similar to apes, but
• Characteristics
• Bipedal
• Small brain size
• Relatively small body size
• Between 3 and 4 feet
• 60-100 pounds

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Bipedality Evidence
Anatomy of Bipedalism
Early hominid pelvis on left, modern human on
right.
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Comparisons
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Basal Hominids (6-4 mya)

• 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.

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What did they look like?
tchadensis
tugenensis
anamensis
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Australopithecines

• Australopithecus afarensis
• Australopithecus africanus
• Australopithecus garhi

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Australopithecus afarensis (ca. 3.5mya)
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Australopithecus afarensisLucy
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.
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Other Evidence Laetoli footprints

• 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.

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Laeotoli

• 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.

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Laetoli

• 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_0
  71_03.html

http//www.jqjacobs.net/anthro/paleo/bipedalism.ht
ml
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Why Bipedal?

• Three key features differentiate human and
  chimpanzee bipedalism
• Chimpanzees are unable to extend their
  knee-joints 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.ht
m
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Advantages of Bipedalism?

• 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?

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Theories

• 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.ht
ml
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Hunt's postural feeding hypothesis

• 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.
• 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 arm-hanging, 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.ht
ml
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The behavioral model

• The behavioral model, as presented by Lovejoy,
  focuses on social behavioral mechanisms that
  influence survivorship and birthrate.
• 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.ht
ml
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Wheeler's thermoregulatory model

• Wheeler's thermoregulatory model proposes, as the
  selective pressure, bipedalism conferring
  reduction in heat gain and facilitation of heat
  dissipation.
• 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.ht
ml
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Do we really know?
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Timing

• 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.ht
ml
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Paleoenvironment

• 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.ht
ml
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Which is it?

• 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 Hunts feeding model might be most
  appropriate.

http//www.jqjacobs.net/anthro/paleo/bipedalism.ht
ml
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Australopithecus africanus (ca. 3 mya)

• 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.
• 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
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A. africanus

• 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
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Australopithecus garhi

• A. garhi existed 2.5 million years ago. Tim White
  and Berhame Asfaw found it in Bouri, East
  Ethiopia.
• Characteristics
• 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
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Genus Paranthropus

• 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.
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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.
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Paranthropus aethiopicus

• By 2.7 million years ago, a new lineage of early
  humans had evolved in East Africa Paranthropus
  aethiopicus

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http//www.mnh.si.edu/anthro/humanorigins/ha/a_tre
e.html