Human origins

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Human origins
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Human origins

• Who is a large-brained mammal capable of shaping
  and controlling its own environment?
• Who changed the surface of the planet?
• Who altered the entire biosphere?

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Human origins

• What is a primate?
• Not sure structurally generalized
• Non-specialized teeth
• No specialized horns, trunks, antlers, or hoofs

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Human origins

• Some things changed, however
• Progressively larger brain
• Modification of the hand, foot, and thorax
• Even these small changes were significant,
  though enabled the human primate to shape a
  life very different from any other animal

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Human origins

• More specifically
• Opposable thumb allows primates to grasp,
  release, and manipulate objects
• Rotation of the ulna permits the hands to be
  turned at various angles
• Eyes became positioned in the front of the face
  binocular vision meant improved ability to judge
  distances
• to judge accurately the distance to prey?
• Ridges of bone developed around the outer margin
  of the eye orbit protection?

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Opposable thumb
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Modern primates

• Two major groups of primates
• The Prosimii (prosimians) primitive
  characteristics (lemur, tree shrew, bush baby)
• The Anthropoidea (anthropoids) monkeys, apes,
  humans

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Modern primates

• Anthropidea Monkeys are subdivided into two
  groups
• 1) New world forms early branch (not involved
  with the human evolution) spider monkey,
  marmoset, capuchin
• Flat faces, small size, widely separated
  nostrils, prehensile tails
• Originate in the Oligocene

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New World monkeys
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Modern primates

• 2) Old World monkeys mostly in Africa and Asia
• Rhesus monkeys, langurs, baboons, mandrills
• Nostrils are close together and directed downward
  (as in humans)
• The tail is not prehensile

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Old world monkeys
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Modern primates

• Anthropiod apes
• Tail-less primates
• Probably evolved from the same ancestral stock as
  humans diverged about 7-5 Ma ago
• The chimpanzee is our closest relative a 98
  correlation in DNA

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Evolution of primates

• Prosimii (prosimians)
• Contemporary with the last of the dinosaurs
• Ex Plesiadapis (Paleocene) old and new world
• The continents were not yet completely separated
• Dead-end offshoot of the primate family

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Paleocene promisian Plesiadapis
The incisors were rodent-like
Tooth-less gap (diastema)
Claws instead of nails
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Evolution of primates

• Eocene prosimians
• Reduction in length of the muzzle
• Increasing brain size
• Eye orbits to a more forward position
• Grasping big toe

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Primitive Eocene prosimian Notharctus
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The Eocene promisian Notharctus
Lemur-like
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The early anthropoids

• Oligocene anthropoids
• Fossils found in Fayum, Egypt (33-34 Ma)
• Ex Aegyptopithecus arboreal primate with
  monkey-like limbs and tail
• Eye-orbit rotated to the front of the skull

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Aegyptopithecus
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Aegyptopithecus
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The early anthropoids

• How do we know when the transition from monkey
  to ape occurred?
• Each animal is a transitional link, so it is an
  arbitary transition
• One clue look at the cusps of certain molars
  four cusps in monkeys, five cusps in apes

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Monkeys four cusps
Y-shaped depression
Apes five cusps
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The early anthropoids

• Miocene (25-5 Ma) anthropids
• Plate tectonics forced adaptive radiation
• Among the first homonids were Proconsul africanus
  (a dryomorph)
• Discovered by Mary and Louis Leaky in 1948 in
  Kenya
• The skull is ape-like the trunk, arms and finger
  bones are monkey-like

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Proconsul africanus
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Proconsul africanus
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The early anthropoids

• When Africa converged on Eurasia about 18 Ma ago,
  monkeys and apes migrated into Eurasia and
  diversified
• No sequential, gradual change, but instead,
  parallel and diverging branches (like a bush)
• Thus, it is difficult to trace the exact ascent
  of humans

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The emergence of homonids

• Australopithecus africanus famous 4 Ma-old
  fossil found by Raymond dart in South Africa,
  1924
• Interspersed ash and lava layers enables dating
• Recently, a 7 ma-old fossil, Sahelanthropus was
  found in Chad

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The emergence of homonids

• Another famous fossil Australopithecus
  afarensis Lucy
• brain size of a chimpanzee
• walked upright as evidenced by skeletal
  characteristics as well as footprints in layers
  of volcanic ash in East Africa

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Australopithecus afarensis
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Australopithecus afarensis Lucy
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Australopithecus afarensis
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Rich homonid sites, especially Australopithecus
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Australopithecus

• Two types
• Those with smaller teeth, smaller body size, and
  more gracile Australopithecus afarensis
• More robust types (side branches of evolution)
  with big cheek teeth for grinding coarse plant
  food Australopithecus robustus and
  Australopithecus boisei

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The emergence of homonids

• There is no sharp boundary in the transition from
  Australopithecus to Homo (oldest remains 2.5
  Ma)
• Homo has increased height of the cranial vault
  and somewhat larger cranial capacity
• Crude stone tools are found in association with
  Homo

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Homo
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Homo erectus
Australopithecus
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The emergence of homonoids

• Homo erectus (from Java)
• Moved out of Africa into Eurasia
• Ex 1.8 Ma-old lower jaw with teeth from Caucasus
  Mountains
• The skeleton was very similar to modern humans
• The cranial capacity was 775 1300 cm3 (whereas
  Homo sapiens is 1200 1500 cm3)
• The skull is massive and rather flat heavy
  supraorbital ridges existed over the eyes
• Natural selection, thus, favored a large pelvis

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Homo erectus
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The emergence of homonoids

• Homo erectus
• Excellent hunters
• Simple tools - axes, scrapers
• Cannibalism?
• Could have spoken a language, worn clothes, or
  built dwellings
• Perhaps knew how to make fire

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Homo erectus