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Chapter 23
Lecture Outline
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Human Evolution
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Points to ponder
• What is chemical evolution?
• 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.
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Points to ponder
• How are humans classified?
• What characteristics do primates have in
common?
• Explain the evolution of hominids.
• Who was Lucy?
• Explain the evolution of humans.
• What is the most widely accepted hypothesis
for the evolution of modern humans?
• Compare and contrast Cro-Magnons and
Neandertals.
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23.1 Origin of Life
Origin of life through chemical evolution
•
Steps of chemical evolution
– 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; this is supported by the fact
that RNA can act as enzymes called
ribozymes (RNA-first hypothesis).
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23.1 Origin of Life
Origin of life through chemical evolution
– 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.
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23.1 Origin of Life
Origin of life through chemical evolution
Biological Evolution
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cell
Stage 4
DNA
RNA
origin of
genetic code
protocell
Stage 3
plasma
membrane
polymers
Stage 2
Chemical Evolution
polymerisation
small organic molecules
energy
capture
Stage 1
abiotic
synthesis
inorganic chemicals
early Earth
Figure 23.1 Chemical and biological evolution.
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23.2 Biological Evolution
Biological evolution
•
Biological evolution – change in population or
species over time
•
Two important points
1. Living things descended from a common
ancestor and thus have common chemistry.
2. Livings things adapt to their environment.
•
Adaptation – a characteristic that enables an
organism to survive and reproduce in its
environment
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23.2 Biological Evolution
Natural selection
•
Natural selection is a theory by Charles
Darwin that describes a mechanism by
which a species becomes adapted to its
environment.
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23.2 Biological Evolution
Natural selection
•
Three vital elements
• 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
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23.2 Biological Evolution
Natural selection
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Lamarck’s proposal
Figure 23.3 The two major
mechanisms for evolutionary
change in the nineteenth century.
Darwin’s proposal
Originally, giraffes had
short necks.
Originally, giraffe neck
length varied.
Giraffes stretched their necks
in order to reach food.
Competition for resources
causes long-necked giraffes
to have the most offspring.
With continual stretching, most
giraffes now have long necks.
Due to natural selection, most
giraffes now have long necks.
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23.2 Biological Evolution
Evidence to support the theory
of evolution by common descent
1.
2.
3.
4.
Fossil record
Biogeographical evidence
Anatomical evidence
Biochemical evidence
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23.2 Biological Evolution
1. What are fossils?
•
Fossils are the traces of past life.
•
Fossils allow us to trace the descent of a
particular group.
•
Charles Darwin, an English naturalist, relied
on fossils to formulate the theory of evolution.
•
Transitional fossils have characteristics of two
different groups.
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23.2 Biological Evolution
Transitional fossils
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Amphibian
tetrapod
360
Early
amphibian
Millions of years ago (MYA)
Expanded ribs
Flat head,
eyes on top
Neck
370
Scales
Tiktaalik
roseae
Fins
377
380
Figure 23.4 Transitional fossils.
Rounded head,
eyes on sides
Fish
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23.2 Biological Evolution
What have we learned from the
fossil record?
• The fossil record tells us that life progressed
from simple to more complex.
• Prokaryotes are the first life forms seen in the
fossil record, followed by unicellular
eukaryotes, and then multicellular eukaryotes.
• Fishes evolved before terrestrial plants and
animals.
• Nonflowering plants preceded flowering plants.
• Amphibians preceded reptiles.
• Dinosaurs are directly linked to birds.
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23.2 Biological Evolution
Fossils
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
wing
wing
head
tail
a. Ambulocetus
50
MYA
b. Basilosaurus
40
MYA
feathers
feet
Archaeopteryx fossil
teeth
tail with vertebrae
claws
artist depiction of Archaeopteryx
(fossil, left): © Jean-Claude Carton/PhotoShot; (drawing, right): © Joe Tucciarone
modern
c. Right whale
a (fossil Ambulocetus foot): © J.G.M. Thewissen, Northeastern Ohio Universities College of Medicine
Figure 23.5 Archaeopteryx.
Figure 23.6 Evolution of the whales.
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23.2 Biological Evolution
2. Biogeographical evidence
•
•
•
•
Biogeography is the study of the distribution
of plants and animals throughout the world.
It supports the hypothesis that organisms
originate in one locale and then may spread
out.
Different life forms are expected whenever
geography separates them.
Islands have many unique life forms because
of geographic isolation.
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23.2 Biological Evolution
Biogeographical evidence
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Sugar glider, Petaurus breviceps,
is a tree-dweller and resembles
the placental flying squirrel.
The Australian wombat, Vombatus,
is nocturnal and lives in burrows. It
resembles the placental woodchuck.
Figure 23.7 Biogeography.
Kangaroo, Macropus, is an herbivore
that inhabits plains and forests. It
resembles the placental Patagonian
cavy of South America.
(sugar glider): © ANT Photo Library/Photo Researchers; (wombat): © Photodisc
Blue/Getty RF; (kangaroo): © George Holton/Photo Researchers
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23.2 Biological Evolution
3. Anatomical evidence
•
Common descent hypothesis offers plausible
explanation for anatomical similarities among
living organisms.
•
Homologous structures – structures
anatomically similar that are inherited by a
common ancestor
• e.g., Vertebrate forelimbs
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23.2 Biological Evolution
3. Anatomical evidence
•
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
•
Vestigial structures – anatomical features fully
developed in one group that are reduced and
may have no function in another group
• e.g., Whales have a vestigial pelvic girdle and legs
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23.2 Biological Evolution
An example of homologous structures
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bird
humerous
ulna
radius
metacarpals
phalanges
bat
whale
Figure 23.8 Vertebrate
forelimbs are homologous
structures.
cat
horse
human
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23.2 Biological Evolution
Homologous structures in
vertebrate embryos
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Pig embryo
pharyngeal
pouches
Figure 23.9 Homologous
structures in vertebrate embryos.
postanal
tail
Chick embryo
(both): © Carolina Biological Supply/Phototake
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23.2 Biological Evolution
4. Biochemical evidence
•
Almost all living things use the same
biochemicals (e.g., DNA and ATP).
•
Living things use the same triplet genetic code.
•
Living things use the same 20 amino acids in
their proteins.
•
Living things share many of the same genes.
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23.2 Biological Evolution
Biochemical evidence describes
evolutionary relationships
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Species
Number of Amino Acid Differences Compared to
Human Cytochrome c
0
human
Cytochrome c is a small protein
that plays an important role in
the electron transport chain
within mitochondria of all cells.
2
monkey
9
pig
11
duck
18
turtle
20
fish
Figure 23.10
Biochemical evidence
describes evolutionary
relationships.
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moth
51
yeast
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22.3 Classification of Humans
The evolution of humans
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23.3 Classification of Humans
3 domains of life
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fungi
plants
animals
EUKARYA
protists
heterotrophic
bacteria
protists
cyanobacteria
ARCHAEA
BACTERIA
Figure 23.11 The three domains of life.
common ancestor
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23.3 Classification of Humans
Primates
•
Characteristics
•
•
•
•
Opposable thumb
Stereoscopic vision (depth perception)
Well-developed brain
Reduced number of offspring (usually a
single birth) with an increased period of
parental care
• Emphasis on learned behavior and social
interactions
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23.3 Classification of Humans
Primates
•
Two major groups (suborders)
• Prosimians – includes lemurs, tarsiers,
and lorises
• Anthropoids – includes monkeys, apes,
and humans
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23.3 Classification of Humans
Asian and African apes
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Asian Apes
African Apes
western lowland gorilla,
Gorilla gorilla
white-handed gibbon,
Hylobates lar
orangutan, Pongo pygmaeus
chimpanzee, Pan troglodytes
(gibbon): © Hans & Judy Beste/ Animals Animals; (orangutan, chimps, gorillas): © Creatas/PunchStock RF
Figure 23.12 Asian and African apes.
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23.3 Classification of Humans
Comparing the human skeleton
to the chimpanzee
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Human spine exits from the skull’s center;
ape spine exits from rear of skull.
Human spine is S-shaped; ape spine has a
slight curve.
Human pelvis is bowl-shaped; ape pelvis is
longer and more narrow.
Human femurs angle inward to the knees;
ape femurs angle out a bit.
Human knee can support more weight than
ape knee.
Human foot has an arch; ape foot has
no arch.
a.
b.
Figure 23.13 Adaptations in the human skeleton allow upright locomotion.
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23.4 Evolution of Hominins
Evolution of primates
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Humans
Hominines
Hominids
Hominoids
Prosimians Anthropoids
hominin
Chimpanzees
common
chimpanzee
Gorillas
western
lowland
gorilla
Orangutans
Bornean
orangutan
Gibbons
white-handed
gibbon
rhesus
monkey
Old World Monkeys
Mammalian
ancestor
enters trees.
capuchin
monkey
Tarsiers
Philippine
tarsier
ring-tailed
lemur
Lemurs
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Figure 23.14 The evolutionary
tree of the primates.
60
50
40
30
Million years Ago
20
(MYA)
10
Prosimians Anthropoids
New World Monkeys
PRESENT
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23.4 Evolution of Hominins
Evolution of hominins
•
Hominins – All species of the genus
Homo and their close relatives
•
Characteristics
• Bipedal
• Flatter face with more pronounced chin
• Brain size
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23.4 Evolution of Hominins
Evolution of hominins
•
Suggested fossils of the first hominins
(6-7 MYA)
• Central African fossil 7 MYA
(Sahelanthropus tchadensis)
• Eastern African fossil 6 MYA (Orrorin
tugenensis)
• Eastern African fossil 5.8-5.2 MYA
(Ardipithecus kadabba)
• Hominins split from the ape line of
descent 7 MYA.
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23.4 Evolution of Hominins
Australopithecines
•
A group of hominins that evolved and
diversified in Africa ~3 MYA.
• Some had slight frames and others were
robust with massive jaws for feeding on
plant materials.
• They walked upright.
• Limbs proportions are apelike.
• They had a small brain.
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23.4 Evolution of Hominins
Australopithecines
•
Famous skeleton named “Lucy” is from
this group .
•
Australopithecus africanus, with a large
brain, is the most likely ancestral
candidate for early Homo.
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23.4 Evolution of Hominins
Australopithecines
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a.
b.
a: © Dan Dreyfus and Associates; b: © John Reader/Photo Researchers
Figure 23.15 Australopithecus afarensis.
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23.5 Evolution of Humans
Characteristics of Homo
1. Brain size is 600 cc or greater.
2. There is evidence of tool use.
3. Jaw and teeth of Homo resemble humans.
Early Homo representatives
•
•
Homo habilis
Homo erectus
Later Homo representatives
•
•
Neandertals
Cro-Magnons
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23.5 Evolution of Humans
Human evolution
Figure 23.16 Human evolution.
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23.5 Evolution of Humans
Early Homo: Homo habilis
•
Lived 2.0-1.9 MYA
•
Large brain with enlarged speech area
•
Omnivorous (hunters and gatherers)
•
Primitive tools
•
May have had culture
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23.5 Evolution of Humans
Early Homo: Homo erectus
•
•
•
•
•
•
•
•
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)
May have had language
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23.5 Evolution of Humans
Homo ergaster
Figure 23.17 Homo ergaster.
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23.5 Evolution of Humans
Modern humans: Homo sapiens
•
Replacement model, or out-of-Africa
hypothesis, is the most widely accepted
hypothesis.
–
–
It proposes that modern humans evolved
from archaic humans only in Africa.
Then, modern humans migrated to Asia
and Europe, where they replaced the
archaic species about 100,000 years BP.
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23.5 Evolution of Humans
Hypothesis for modern human evolution
Figure 23.18 Replacement model.
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Migration of early Homo from
Africa
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23.5 Evolution of Humans
Neandertals
•
Discovered in Germany 200,000 years
ago
•
Massive brow ridges
•
Nose, jaws, and teeth protrude forward
•
Low and sloping forehead, no chin
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23.5 Evolution of Humans
Cro-Magnons
•
•
•
•
•
Lived about 40,000 to 100,000 years ago
Oldest fossils to be designated Homo
sapiens
Modern appearance
Advanced culture including art, tools, and
maybe language
Good cooperative hunters
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23.5 Evolution of Humans
Cro-Magnons
Figure 23.19 The Cro-Magnons.
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23.5 Evolution of Humans
Human variation
•
•
Human variations between populations are
called ethnicities.
Variations evolved as adaptation to local
environments.
– Skin color ranges from dark to light.
– Body shape
•
•
Bergmann’s rule – colder regions mean
bulkier build
Allen’s rule – colder regions mean shorter
limbs, digits, and ears
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23.5 Evolution of Humans
Human variation
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a.
Figure 23.20 Ethnic variations
in modern humans.
b.
c.
© PhotoDisc/Getty RF; 22.20b: © Sylvia S. Mader; c: © Adam Crowley/Getty Images
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