Early Hominids

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Early Hominids

• Chronology of Hominid Evolution,The Varied
  Australopithecines, Beginning of Homo and Tools

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Chronology of Human Evolution

• If we compare Earths History to a 24 hour day
  Earth originates at midnight.
• The earliest fossils were deposited at 545am
• The first vertebrates appeared at 902 pm
• Earliest mammals at 1045pm
• Earliest primates at 1143pm
• The earliest hominids (australopithecines) at
  1158pm
• Homo Sapiens arrives 36 seconds before midnight.
• For the study of Hominid evolution, the
  Pliocene(5 to 2 m.y.a), Pleistocene (2 m.y.a to
  10,000 B.P.) and Recent (10,000 B.P. to present)
  epochs are most important.
• Until the end of the Pliocene, the main hominid
  was Australopithecus (Africa), by the start of
  the Pleistocene they evolved into Homo.

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Pleistocene

• The Pleistocene is considered the epoch of human
  life, sub-divided into lower, middle and upper.
  Each subdivision is associated with a particular
  group of hominids.
• Late Australopithecus and early Homo lived during
  Lower.
• Homo Erectus spanned most of Middle, and Homo
  sapiens appeared late in the Middle and was the
  sole hominid of the Upper.
• During the 2nd million years of this era, there
  were several ice ages, or glacials, major
  advances of continental ice sheets in Europe and
  N. America. These periods were separated by
  interglacials, long warm periods between major
  glacials.
• During interglacials, the climate warmed up
  forests returned to the areas. Hominid fossils
  found in association with animals known to occur
  in cold and warm climates.

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The varied Australopithecines

• We still dont know the identity of our Miocene
  ancestors, we do know that they evolved into a
  varied group of Pliocene-Pleistocene hominids
  known as the australopithecines.
• Today the distinction between the
  australopitecines and later hominids is made at
  the genus level.
• Most significant fossils in this genus were found
  East Africa(Table 6.1)
• Ardipithecus ramidus is recognized as the
  earliest known hominid, which evolved into A.
  anamensis, a bipedal hominid, which evolved into
  A. afarensis, which is considered ancestral to
  all the later australopithecines as well as to
  homo.

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Species of Australopithecus

• A. amamensis (4.2 m.y.a)
• A. afarensis (3.8? To 3.0 m.y.a)
• A. africanus (3.0 to 2.5 m.y.a)
• A. robustus (2.6 to 2.0 m.y.a)
• A. boisei (2.6 to 1.2 m.y.a)
• Homo appeared around 2 m.y.a.

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Australopithecus afarensis

• Earliest hominid species. Fossils found in
  northern Tanzania and parts of Ethiopia.
• Lucy was one of these fossil finds.
• Similar in many ways to chimps and gorillas that
  are common ancestry with African apes must be
  very recent (no more than 8 m.y.a)

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Dentition of A. afarensis

• Like apes, unlike modern humans, A. afarensis had
  sharp canine teeth that projected beyond the
  other teeth. Lower premolar was pointed and
  projecting to sharpen the upper canine.
• It had one long cusp and one tiny bump that is
  like a bicuspid premolar that eventually
  developed in hominid evolution.
• Evidence shows powerful chewing associated with
  savanna vegitation was entering their feeding
  pattern.
• Massive back teeth, jaws, and facial and cranial
  structures suggest a diet demanding extensive
  grinding and powerful crushingSee pg 173 Fig 7.2

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What makes us Human?

• Bipedal locomotion, big brains, childhood
  dependency, use of language and tools?
• We can be defined from features we have lost
  big back teeth.
• Bipedalism has characterized human evolution
  since it split from African Apes.
• Skull of A afarensis contrasts with those of
  later hominids brain case is very small. Very
  similar to a chimp.

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Bipedalism

• Bipedalism-upright two-legged locomotion-is the
  key feature differentiating earlier hominids from
  the apes. May be more than 5 m.y.a
• The structure of the hip, pelvic, leg and foot
  bones confirm that upright bipedalism was A.
  afarensiss mode of locomotion. Actually started
  with A. anamensis (4.2 m.y.a)
• Considered an adaptation to open grassland.
• Preceded tool manufacture and expansion of
  hominid brain.
• Early hominids also preserved enough of their
  ape-like anatomy to take to the trees to sleep at
  night and keep away from predators

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Advantages of Bipedalism

• Ability to see over long grass
• Carrying items back to home base
• Reducing bodies exposure to sunlight

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Why did we adapt to bipedalism?

• Change in climate to cooler and drier,
  shrinking the aboreal habitat.
• Deepening of Rift Valley-caused split environment
  which may have caused the split in hominoids and
  chimps. (174)
• To protect brains from overheating.
  Quadrupedalism exposes body to 60 more UV
  radiation.
• Upright body can catch cooler breeze above ground.

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Sexual Dimorphism in A. afarensis

• Difference in jaw size of male and female
• Females stood between 3 and 4 feet, whereas males
  reached 5 feet.
• Males weighted twice as much as females
• Both males and females had more robust muscles
  and bones than modern humans.
• Mixture of apelike and hominoid features in both
  sexes

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How we walk

• Hominids alternating swing and stance for each
  foot.
• Old World Monkeys (not humans) always supported
  by 2 limbs. Bipeds-are supported by one limb at
  a time.
• Homo pelvises are much smaller than
  Australopithecine, which shows an adaptation to
  bipedalism.
• Spines were similar but not identical to ours.
• Expansion of the birth canal is a trend in
  hominid evolution, due to our larger brain.

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Early Homo

• Between 3 and 2 m.y.a, ancestors of Homo split
  off and became reproductively isolated from the
  later australopithecines that coexisted with Homo
  until 1.2 m.y.a .
• 1.7 m.y.a there were two hominid groups. 1) Homo
  erectus- had a larger brain which had an increase
  in areas of the brain that regulate higher mental
  functions. These were our ancestors-they hunted
  and gathered, made sophisticated tools and soon
  displaced A. boisei.

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Separation between A. boisei and early Homo

• One theory proposes that A. afarensis split into
  2 groups.
• One group, the ancestors of Homo, became
  reproductively isolated from other hominids
  between 3 and 3 m.y.a. This group became Homo
  habilis (2-1.7 m.y.a) which evolved to H.erectus.
  
• The other groups of A. afarensis evolved into the
  various kinds of australopithecines.

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H. rudolfensis and H. habilis

• A skull found in 1972 unusual combination of a
  large brain and very large molars. Created much
  controversy and debate. (183)
• In 1986-it was named H. rudolfensis.
• Some think rudolfensis lived earlier than and is
  an ancestor to habilis.
• Some think that rudofensis and habilis are male
  and female members of the same species-habilis.
• Some think they are separate, but coexisted. And
  others think that one of them gave rise to H.
  erectus.

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Tools

• Tool making may have had something to do with the
  split between A. boisei and Homo.
• Oldowan pebble tools are pieces of stone about
  the size of a tennis ball. Flakes were struck
  off both sides to form a cutting edge.
• Early homo also used tools that they did not
  make naturally chipped or cracked objects.

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A. Garhi and Early Stone Tools

• 1999 new species of hominid discovered along with
  earliest traces of butchery. Fossils date to 2.5
  m.y.a
• May be the link between Australopithecus and
  Homo.
• Species named A. Garhi surprise.
• Important for 3 reasons 1) new potential
  ancestor to humans. 2) show that the femur had
  elongated by 2.5 m.y.a., which was a million
  years before the forearm shortened. 3) evidence
  that large animals were being butchered shows
  early stone technology was aimed at getting meat
  and marrow from big game dietary revolution.
  

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A little more on tools

• Tools show that Australopithecines were
  toolmakers with the capacity for culture.
• Australopithecines evolved to Homo, which became
  the most efficient exploiter of the savanna
  niche.
• H. erectus eventually expanded into Asia and
  Europe.Next Modern Humans!!!