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Chapter 17: Human Evolution

Chapter 17: Human Evolution. 17-1 The Study of Human Origins. 17-2 Fossil Evidence of Hominid Evolution. 17-3 Hypotheses of Hominid Evolution. 17-1 The Study of Human Origins. I. The Hominid Fossil Record (understanding HUMAN evolution).

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Chapter 17: Human Evolution

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  1. Chapter 17: Human Evolution 17-1 The Study of Human Origins 17-2 Fossil Evidence of Hominid Evolution 17-3 Hypotheses of Hominid Evolution

  2. 17-1 The Study of Human Origins I. The Hominid Fossil Record (understanding HUMAN evolution) • (1) Revealing our ANCESTRY through FOSSIL records, and • (2) Investigating closest of our living kin (primates). NOTE: Some human behavior AND morphology are SIMILAR to those of other PRIMATES, HOWEVER some remain UNIQUELY human.

  3. (1) Paleoanthropologists (a.ka., biological anthropologists) • Uncover FOSSIL EVIDENCE (including TOOLS, bones of PREY, and PLANT remains) used to support LIFESTYLES of human ancestors.

  4. (2) Hominids (hominid evolution) • Modern humans AND our most recent ancestors; • NOTE: FOSSIL EVIDENCE largely pertains to skulls, teeth, bone fragments, AND also tools (in the more recently evolved hominids).

  5. (3) Pelvis (anatomical EVIDENCE for hominid evolution) • Bones MAKING up the “HIPS” are evidence in SHOWING whether or not an organism can walk UPRIGHT (bipedalism).

  6. II. Primate Characteristics (Order Primata, Class Mammalia) • 2 groups are RECOGNIZED… (1) Anthropoid primates (2) Prosimian primates • NOTE: ALL primates evolved GRASPING hands, acute COLOR vision, FRONT-facing eyes (depth perception) & proportionately LARGE brains.

  7. (1) Anthropoid Primates (majority are GROUND species) • MORE-RECENTLY evolved e.g., marmosets, gibbons, monkeys, apes, and humans.

  8. (2) Prosimian Primates (majority of species are ARBOREAL) • MORE-PRIMITIVE and ANCESTRAL primates e.g., lemurs, lorises, and tarsiers.

  9. (3) Prehensile (adaptation of primate DEXTERITY) • Movable fingers and toes (GRASPING using hands and feet)  ancestral CLAWS have become MODIFIED as flattened NAILS.

  10. (A) Characteristics of Anthropoids (rotating shoulder and elbow joints) • Better DEXTERITY, LARGER and more COMPLEX brain (than prosimians), IMPROVED color vision (evolved with being DIURNAL).

  11. (1) Opposable Thumb (human evolution  LOST opposable big toe) • 2-jointed thumb OPPOSITE to other fingers—allows for a NEW arrangement of fingers better for PRECISION.

  12. (2) Dental Formula (humans and anthropoids SHARE this arrangement) • Includes 2 pairs of INCISORS, 1 pair of CANINES, 2 pairs of PRE-MOLARS, and 3 pairs of MOLARS.

  13. (3) Great Apes (Modern Apes; Chimpanzee and Human = ~98% DNA) • Gibbons, orangutans, gorillas, and chimpanzees  LARGER cranial capacity  MORE complex structure (similar to HUMAN evolution). • NOTE: As primates evolved FROM prosimian TO anthropoid, brain SIZE increased, allowing for complex behaviors and BETTER adaptability)

  14. (B) Characteristics of Humans (Morphological distinctions) • We are distinguished FROM the great apes in SEVERAL ways, including… (1) Human jaw is ROUNDER rather than NARROW U-shaped like great apes. (2) Human pelvis is CUP-shaped rather than the FLATTER ape pelvis. (3) Human spine is S-SHAPED rather than the SINGLE curve of ape spine. (4) Human foot has SHORT, ALIGNED toes rather than the longer, grasping toes (and opposable, big toe) of the ape. NOTE: Characteristics 2-4 work together to support FULL TIME BIPEDALISM in humans; (ONLY MAMMALS CAPABLE OF BIPEDALISM).

  15. Critical Thinking (1) When analyzing fossils, scientists examine the foramen magnum, the opening for the spinal cord in the base of the skull. What does the location of the foramen magnum on a skull tell about the posture of an animal?

  16. (1) Bipedalism (defines the Hominid lineage, from QUADRUPEDAL) • An adaptation to GRASSLANDS  ability to walk primarily on TWO legs, a UNIQUELY human trait. NOTE: An ENLARGEMENT of human BRAIN has been shown to hold extensive areas devoted to production and understanding of SPEECH—important for cultural and intellectual development.

  17. 17-2 Fossil Evidence of Hominid Evolution I. The First Hominids (evidence of bipedalism separates PRE-hominids) • Hominid gene pool has EVOLVED towards a LARGER BRAIN and BIPEDALISM (e.g., improved vision, freed-up forelimbs). NOTE: Fossils of hominids, UNLIKE those of apes (PRE-hominids) and their ancestors, show ADAPTATIONS for UPRIGHT walking.

  18. (1) Quadrupedal (advantages VS. disadvantages) • Modern NON-human anthropoids walk on FOUR limbs (anatomy varied). NOTE: Recent fossil evidence (on A. afarensis) has SUPPORTED a belief that UPRIGHT walking evolved BEFORE any other adaptation (i.e., did NOT require a LARGE brain) making hominids UNIQUE among anthropoids.

  19. II. Australopithecus (a hominid GENUS) • 1974: 3 m.y.o. PARTIAL skeleton of a PRIMATE found in the Afar Valley of eastern Africa by Donald Johanson. NOTE: Fossil named Australopithecus afarensis (A. afarensis)—southern APE of the Afar Valley. Fossil was nicknamed Lucy, (estimated to be 3.0-3.9 m.y.o.)

  20. (1) Lucy (hominid fossil ~ 3.2 m.y.a., ~ 475 cc  skull ) • Smaller CRANIAL CAPACITY (than humans) ALSO with SHORTER stature than humans (~ Lucy was the HEIGHT of a chimpanzee).

  21. (A) Other Australopithecines (different hominids COEXISTED (same TIME) *(ANCESTOR) A. anamensis (~3.5 m.y.a.  OLDER than Lucy?)—A possible ancestor of Lucy, found in 1995; presence of a SHINBONE may indicate *BIPEDALISM*. (DESCENDANT) A. africanus (2.3-3.0 m.y.a.)—A possible DESCENDANT of Lucy, taller/heavier with a slightly LARGER cranial capacity (~430-550 cc). (DESCENDANT) A. robustus and A. boisei (1.0-2.6 m.y.a.)—More RECENT descendant (BUT non-human) HEAVY and LARGE SKULLS and larger TEETH (~450-600 cc).

  22. (B) An Older Hominid? (1995 uncovered an OLDER hominid) • A NEW GENUS that predates Australopithecus by 200,000 years— • Ardipithecusramidus, a *BIPEDAL* and the EARLIEST FOUND hominid. • NOTE: Human evolutionists do NOT believe human evolution occurred in a SINGLE, uninterrupted parade of increasingly humanlike forms. • Rather evidence suggests SEVERAL hominid forms arose AND some died out, leaving NO descendants. Thus the HUMAN EVOLUTIONARY TREE contains many branches (like a BUSH).

  23. 17-3 Hypotheses of Hominid Evolution NOTE: As RESEARCH continues, we are observing DEAD-END branches of human evolution AND evidence that DIFFERENT hominids COEXISTED. I. Early Members of Homo, The Human Genus (20th century fossils) • HUMAN-LIKE morphology resulted in NEW human genus, Homo (1) LARGER Cranial Capacity (700 CC), (2) TOOL Use.

  24. (A) Homo habilis (“handy human,” tool MARKS on animal bones) • 1.6-2.5 m.y.a.:  1st to make tools and weapons (also have larger SKULL)

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