Download - 9: Early Hominins
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Hominins
• Most paleoanthropologists believe a common ancestor to the modern African Apes (Chimps, Gorillas, Bonobos) and the Hominins existed approximately 6-7 million years ago.
• Hominins are habitually bipedal primates. Modern humans are the only extant (living) species of hominin.
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Bipedalism
• The early ancestors of humans and the ancestors of the African apes appear very similar.
• The key point of difference between early hominins and early apes were how they walked: early hominins were bipedal, early apes were quadrapedal.
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Sivapithecus (12.5-8.5 million years ago). possible ancestor of modern Orangutans (quadruped)
Paranthropus Boisei (2.3-1.2 million years ago) . Hominin (upright walker)
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Bipedalism: Advantages
• We are taller and more intimidating to predators.
• Walking on two legs is more efficient in terms of calories used.
• We are able to use our front limbs to carry, use tools and to hunt and gather more efficiently.
• We expose less of our bodies to direct sunlight, allowing for more efficient cooling.
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Bipedalism
• Given the similarities of early apes and early hominins, the primary task is to examine the skeleton to figure out how this organism walked.
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Anatomical marks of bipedalism
• Pelvis
• Femur
• Spine
• Foot
• Foramen Magnum
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Human Pelvis
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Chimp Pelvis
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Chimp Skeleton
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Spine/Quadruped
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Chimp Foot
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Human Foot
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Spine/Biped
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Sahelanthropus tchadensis“Toumai” 7 millions years old
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Orrorin tugenensis“Millenium Man” ~6 million years ago
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Orrorin tugenensis
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Difficulties in building a family tree
• Creating a “family tree” for extinct species is very difficult for two major reasons:
• A) The fossil record is incomplete (not all organisms leave behind a record of their existence and
• B) Many fossils are too old to derive DNA from, making genetic comparisons impossible.
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Difficulties in building a family tree
• Family trees of hominin and non-hominin fossils are constantly being redrawn as new discoveries are made.
• Additionally, different fossils may be interpreted as the same species by one anthropologist…and different species by another.
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Lucy
• 1974: Donald Johanson discovered “Lucy”, a 3 foot 8 inch hominin later classified as Australopithecus afarensis.
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Lucy: (AL 288-1) 3.2 mya
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Comparative anatomy
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The Laetoli footprints
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A. afarensis cranium (AL- 444)
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Modern Chimp Skull
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Australopithecus afarensis (left) Chimpanzee (right).
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Big Brains and Bipedalism
• Bipedalism emerged long before big brains.
• What started us on the journey to becoming human was how we moved, rather then the way we thought. Brain changes came later.
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Early Hominins
• The term Early Hominins is used to describe the hominins that lived before Genus Homo. They are all found only in Africa.
• The fossil record indicates that there were a variety of species of early hominins adapted to various environments in sub-Saharan Africa.
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Robust vs. Gracile
• Hominins and other primates are described as robust or gracile.
• A robust body is heavy in skeletal structure and muscle. A gracile body is more slender and fine-boned.
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Robust Skull: Paranthropus robustus
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Gracile Skull: Australopithecus Afarensis
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Speech
• Examinations of australopithecines have determined their vocal tracts were very similar to apes.
• As such it is unlikely that they used spoken language.
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Culture
• While it is safe to assume that the majority of early hominins (like the majority of primates) were social creatures we know only so much about their culture.
• It does seem to be the case that they DID NOT make stone tools: that came later in human evolution.