Transcript Chapter 22

Chapter 22
Human Evolution
Points to Ponder
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What is the chemical evolution of life?
What is biological evolution?
What is natural selection and what three elements are vital for this?
What was Darwin’s contribution to evolution?
What have we learned from the fossil record?
Explain the fossil, biogeographical, anatomical and biochemical
evidence that supports the theory of evolution by common descent?
What are analogous, homologous and vestigial structures? Give
examples of each.
How are humans classified?
What characteristics do primates have in common?
Explain the evolution of hominids.
Who is Lucy?
Explain the evolution of humans.
What are the 2 hypotheses for modern man?
Compare and contrast Cro-Magnons and Neandertals
22.1 Origin of life
Origin of life through chemical evolution
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Steps of chemical evolution:
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Gases of the primitive atmosphere formed small
organic molecules
Molecules combined to form macromolecules
Only RNA might have been needed to form the first
cells and is supported by the fact that RNA can act
as enzymes called ribozymes (RNA-first hypothesis)
Protocells made of proteins and lipids could
metabolize by using oceanic organic molecules but
could not reproduce
The true cell can reproduce and has DNA as its
genetic material
22.1 Origin of life
Origin of life through chemical evolution
22.2 Biological evolution
Biological evolution
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Biological evolution – change in population or
species over time
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2 important points:
1. Living things descended from a common ancestor
and thus have common chemistry
2. Livings things adapt to their environment
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Adaptation – a characteristic that makes an
organism to survive and reproduce in its
environment
22.2 Biological evolution
Evidence to support the theory of
evolution by common descent
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Fossils in the fossil record
Biogeographical evidence
Anatomical evidence
Biochemical evidence
22.2 Biological evolution
1. What are fossils?
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Fossils are the traces of past
life
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Fossils allow us to trace the
descent of a particular group
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Charles Darwin, an English
naturalist, relied on fossils to
formulate the theory of
evolution
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Transitional fossils have
characteristics of two
different groups
22.2 Biological evolution
What have we learned from the
fossil record?
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Fossil record tells us that life progressed from simple to more
complex
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Prokaryotes are the first life forms seen in the fossil record
followed by unicellular eukaryotes and then multicellular
eukaryotes
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Fishes evolved before terrestrial plants and animals
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Nonflowering plants preceded flowering plants
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Amphibians preceded reptiles
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Dinosaurs are directly linked to birds
22.2 Biological evolution
Fossils
22.2 Biological evolution
2. Biogeographical evidence
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Is the study of the distribution of plants and animals
throughout the world
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Supports the hypothesis that organisms originate in
one locale and then may spread out
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Different life forms are expected whenever geography
separates them
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Islands demonstrate this because they have many
unique life forms because of geographic isolation
22.2 Biological evolution
3. Anatomical evidence
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Common descent hypothesis offers plausible explanation for
anatomical similarities among living organisms
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Homologous structures – structures anatomically similar that are
inherited by a common ancestor
e.g. Vertebrate forelimbs
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Analogous structures – structures that serve the same function but
they do not share a common ancestry and thus are not
constructed the same
e.g. Wings of a bird and wings of an insect
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Vestigial structures – anatomical features fully developed in one
group but are reduced and may have not function in another group
e.g. Whales have a vestigal pelvic girdle and legs
22.2 Biological evolution
An example of homologous structures
22.2 Biological evolution
4. Biochemical evidence
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Almost all living things use the same
biochemicals (e.g. DNA and ATP)
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Living things use the same triplet code
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Living things use the same 20 amino acids in
their proteins
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Living things share many of the same genes
22.2 Biological evolution
Natural selection
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A theory by Darwin that describes a
mechanism by which a species becomes
adapted to its environment
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3 vital elements:
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Variation – there must be physical variations that can
be passed from generation to generation
Competition – there must be competition for limited
resources (food, mates, shelter) and those better
adapted will survive and reproduce
Adaptation – subsequent generations will see an
increase in individuals with the same adaptations as
long as the environment remains unchanged
22.2 Biological evolution
Natural selection
22.3 Classification of humans
The arrival of humans on earth
22.3 Classification of humans
Primates
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Characteristics:
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Opposable thumb
Stereoscopic vision (depth perception)
Well-developed brain
Reduced # of offspring (usually a single birth) with
an increased period of parental care
Emphasis on learned behavior and social
interactions
Two suborders:
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Prosimians – includes lemurs, tarsiers and lorises
Anthropoids – includes monkeys, apes and humans
22.4 Evolution of hominids
Evolution of primates
22.4 Evolution of hominids
Evolution of hominids
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Hominids – human lineage on the evolutionary tree
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Characteristics:
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Bipedal
Flatter face with more pronounced chin
Brain size
Suggested fossils of the first hominids (~ 6-7 MYA):
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Central African fossil ~7 MYA (Sahelanthropus tchadensis)
Eastern African fossil ~ 6 MYA (Orrorin tugenensis)
Eastern African fossil ~ 5.8-5.2 MYA (Ardipithecus kadabba)
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Hominids split from the ape line of descent ~ 7 MYA
22.4 Evolution of hominids
Australopithecines
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A group of hominids that evolved and diversified in
Africa ~ 3 MYA
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Some had slight frames and others were robust with massive
jaws that fed on plant materials
Walked upright
Limbs proportions are ape-like
Small brain
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Famous skeleton named “Lucy” is from this group
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Australopithecus africanus has a large brain is is the
most likely ancestral candidate for early Homo
22.4 Evolution of hominids
Australopithecines
22.5 Evolution of humans
Characteristics of Homo
1. Brain size is 600 cm3 or greater
2. Evidence of tool use
3. Jaw and teeth resemble humans
Early Homo representatives:
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Homo habilis
Homo erectus
Later Homo representatives:
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Neandertals
Cro-Magnons
22.5 Evolution of humans
Human evolution
22.5 Evolution of humans
Early Homo: Homo habilis
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Lived ~ 2.0-1.9 MYA
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Large brain with enlarged speech area
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Omnivorous (hunters and gatherers)
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Primitive tools
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Culture may have existed
22.5 Evolution of humans
Early Homo: Homo erectus
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Lived ~ 1.9-0.3 MYA
Larger brain than H. habilis
Flat face with the nose projected
Tall and stood erect
Striding gait
May have migrated from Africa to Europe and
Asia
Advanced tools and fire (systematic hunters)
Language may have evolved
22.5 Evolution of humans
Later Homo individual
22.5 Evolution of humans
Modern Humans: Homo sapiens
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2 hypotheses:
1. Multiregional continuity – suggests that
modern humans evolved from H. erectus in
several geographic places
2. Out-of-Africa hypothesis – modern humans
evolved from H. erectus most likely only in
Africa and later migrated to Europe and Asia
(this hypothesis has the most support)
22.5 Evolution of humans
Hypotheses for modern human evolution
22.5 Evolution of humans
Neandertals
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Discovered in Germany
~2000 years ago
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Massive brow ridges
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Nose, jaws and teeth
protrude forward
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Low and sloping
forehead, no chin
22.5 Evolution of humans
Cro-Magnons
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Lived about 40,000 to
10,000 years ago
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Oldest fossils to be
designated Homo sapiens
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Modern appearance
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Advanced culture including
art, tool and maybe
language
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Good cooperative hunters
22.5 Evolution of humans
Human variation
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Human variations between populations
are called ethnicities
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Variations evolved as adaptation to local
environments:
– Skin color: range of dark to light
– Body shape: Bergmann’s rule and Allen’s
rule
22.5 Evolution of humans
Human variation