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Chapter 17: Human Evolution

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Chapter 17: Human Evolution 17-1 The Study of Human Origins 17-2 Fossil Evidence of Hominid Evolution 17-3 Hypotheses of Hominid Evolution (A) Multiregional Evolution ... – PowerPoint PPT presentation

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Title: Chapter 17: Human Evolution


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

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(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).

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(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).

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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.

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

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

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

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(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).

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

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(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.

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(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)

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(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).
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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?
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(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 SPEECHimportant
for cultural and intellectual development.
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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.
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(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.
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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.)
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(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).

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(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).
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(B) An Older Hominid? (1995 uncovered an OLDER
hominid)
  • A NEW GENUS that predates Australopithecus by
    200,000 years
  • Ardipithecus ramidus, 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).

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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.

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(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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(B) Homo erectus (upright human 1.8 m.y.a. to
50,000 years ago)
  • Believed to be 1st hominid OUT of Africa ?
    fossils of Java Man found on Island of Java
    (Pacific) (also Europe, Asia).

NOTE Compared to MODERN humans, H. erectus had a
thick skull, large brow ridges, a low forehead,
and large protruding teeth. To survive in COLDER
climates of Europe and Asia, H. erectus may have
used FIRES in caves for warmth and cooking.
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II. Homo sapiens (include TWO lineages ?
Neanderthal and Cro-Magnon)
  • Descended FROM H. erectus 800,000 years ago.
    (Existed until as recently as
    50,000 to 35,000 years ago).

NOTE When H. sapiens AROSE, it is possible they
did NOT replace H. erectus RIGHT AWAY. Findings
(fossils) show coexistence of BOTH SPECIES may
for occurred for 700,000 years.
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(A) Neanderthals (LARGEST C.C., ? evidence of
STONE TOOLS for skins)
  • EARLIEST group of H. sapiens from around
    230,000-30,000 y.a. and were found in parts of
    Europe and Asia.

NOTE Heavy bones, THICK brow ridges, protruding
teeth, AND a very LARGE cranial capacity (larger
than modern humans?!)Are NOT believed to be
ancestral to modern humans and DISAPPEARED (LEFT
NO DESCENDANTS) at the same time that MODERN H.
sapiens evolved in LARGE numbers. (possible
tribal warfares OR disease?)
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Critical Thinking
(2) According to existing fossil evidence,
Neanderthals died out about 30,000 years ago.
Some anthropologists hypothesize that the
Neanderthals were killed off by Cro-Magnons.
Others hypothesize what the two groups interbred.
What evidence would you look for to evaluate
these two hypotheses?
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(B) Homo sapiens (MODERN ? BETTER-developed
tools/weapons)
  • 1st fossils to bear RESEMBLANCE to modern humans
    ? found in southwestern FRENCH CAVES ? 35,000
    years old. (Cro-Magnons)

NOTE Cro-Magnons are distinguished from
Neanderthals by their HIGHER forehead and
RECESSED brow ridge and teeth also stood TALLER
at about 6 feet tall (ADVANCED use of TOOLS).
  • OLDEST modern H. sapiens fossils are about
    100,000 years old and were found in AfricaBUT as
    Neanderthals declined, modern H. sapiens became
    MORE advanced in hunting, habitat-building, and
    survival.

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Critical Thinking
(3) How might the acquisition of language account
for the very fast cultural and intellectual
development that has occurred in the evolution of
humans?
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III. Spread of Modern Humans (TWO theories)
  • ALL modern humans belong to a SINGLE species,
    Homo sapien sapien So HOW did all of our genetic
    VARIATION arise OVER TIME?

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Critical Thinking
(4) From H. habilis to modern H. sapiens, there
has been a trend for brain size to increase. Is
it inevitable that any future descendant species
of H. sapiens will have larger brains than we
have? Explain your answer in terms of some form
of natural selection, such as directional
selection.
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(A) Multiregional Evolution (LESS widely accepted)
  • Gene FLOW existed AMONG different populations
    during TRANSITION from H. erectus ? H. sapiens.

(1) Multiregional Hypothesis of Human Evolution
1 MILLION years AGO
  • PARALLEL populations of H. sapiens evolved
    SIMULTANEOUSLY from DIFFERENT H. erectus
    populations LOCATED around the WORLD.

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(A) Out of Africa (MORE widely accepted,
mitochondrial DNA)
  • MODERN H. sapiens originated about 100,000 to
    200,000 years ago and then, LIKE H. erectus
    before them, LEFT Africa to colonize the WORLD.

(1) Recent African-Origin Hypothesis (supported
by mitochondrial DNA)
  • MODERN H. sapiens evolved IN Africa and SPREAD
    throughout the world, REPLACING populations of H.
    erectus and EARLY H. sapiens.

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Critical Thinking
(5) Compared with humans, apes do not have a
well-developed voice box or well-developed facial
muscles. How might the apes anatomy affect its
ability to use spoken language?
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Extra Slides AND Answers for Critical Thinking
Questions
(1) In social groups with language, information
can be passed on and accumulated, which
significantly speeds up cultural and intellectual
development.
(2) The location of the foramen magnum indicates
the angle at which the spinal cord exits the
skull, a clear indicator of posture.
(3) Fossil evidence of Neanderthals who met a
violent death in areas where Cro-Magnons later
flourished would constitute evidence that the
Neanderthals were killed off by Cro-Magnons.
Fossil evidence of a body type representing a
blend of Neanderthals and Cro-Magnon features
would support the hypothesis that the two groups
interbred.
(4) It is not inevitable that descendant species
of H. sapiens will have larger brains that modern
humans. Stabilizing selection tends to keep
traits in an average range. The size of the
human female pelvis must enlarge along with any
enlargment of the head.
(5) The apes anatomy would restrict its ability
to use spoken language because speed production
requires a great degree of control of the voice
box and facial muscles.
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Revisiting Evolution
  • Evolutionary theory holds that the organisms
    alive on Earth today, including humans, evolved
    from shared ancestors.
  • During their evolution, populations acquired
    characteristics that distinguished them from
    their ancestors and from other populations alive
    today.

Assessing Prior Knowledge
  • What theories are there about how new species
    form? And what are the criteria for becoming a
    new species?
  • Distinguish between species and race, with
    respect to human populations.
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