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Unit 05
13.4 The study of fossils provides
strong evidence for evolution
• The fossil record shows that organisms have
evolved in a historical sequence
– The oldest known fossils are prokaryote cells
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The oldest eukaryotic fossils
are a billion years younger
Tappania, a unicellular
eukaryote
Multicellular
fossils are even
more recent
Dickinsonia
costata
2.5
cm
1
B Ammonite casts
E Insect in amber
D Fossilized organic
matter of a leaf
C Dinosaur tracks
A Skull of Homo erectus
F “Ice Man”
2
13.4 The study of fossils provides
strong evidence for evolution
– Many fossils link early extinct species with
species living today
– A series of fossils documents the evolution of
whales from a group of land mammals
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Pakicetus (terrestrial)
Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
Dorudon (fully aquatic)
Pelvis and
hind limb
Balaena (recent whale ancestor)
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Pakicetus (terrestrial)
Rhodocetus (predominantly aquatic)
Pelvis and Dorudon (fully aquatic)
hind limb
Pelvis and
hind limb
Balaena (recent whale ancestor)
13.5 A mass of other evidence
reinforces the evolutionary view
of life
– Biogeography, the geographic distribution of
species, suggested to Darwin that organisms
evolve from common ancestors
– Darwin noted that animals on islands resemble
species on nearby mainland more closely than
they resemble animals on similar islands close to
other continents
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– Comparative anatomy is the comparison of body
structures in different species
– Homology is the similarity in characteristics that
result from common ancestry
– Vertebrate forelimbs
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Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
– Which of the following pairs are homologous
structures?
Human limb and whale flipper
X
Insect wing and bat wing
Human thumb and chimpanzee thumb
Oak leaf and oak root
Oak leaf and lichen
X
X
Oak leaf and maple leaf
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– Comparative embryology is the comparison of early
stages of development among different organisms
– Many vertebrates have common embryonic structures,
revealing homologies
– When you were an embryo, you had a tail and pharyngeal
pouches (just like an embryonic fish)
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Human embryo
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5
– Some homologous structures are vestigial organs
– For example, the pelvic and hind-leg bones of
some modern whales
Pelvis and Dorudon (fully aquatic)
hind limb
Pelvis and
hind limb
Balaena (recent whale ancestor)
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 Molecular biology: Comparisons of DNA and amino acid
sequences between different organisms reveal evolutionary
relationships
– All living things share a common DNA code for the
proteins found in living cells
– We share genes with bacteria, yeast, and fruit flies
Head
Thorax
Abdomen
(a) Adult
0.5 mm
Dorsal
BODY
AXES
Anterior
Right
Posterior
Left Ventral
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13.6 Homologies indicate patterns of
descent that can be shown on an
evolutionary tree
 Darwin was the first to
represent the history of life
as a tree
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 Homologous structures and genes can be used to
determine the branching sequence of an evolutionary
tree
Lungfishes
Mammals
2
Tetrapod limbs
Amnion
Tetrapods
Amniotes
Amphibians
1
Lizards
and snakes
3
4
Crocodiles
Ostriches
6
Feathers
Birds
5
Hawks and
other birds
THE EVOLUTION
OF POPULATIONS
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13.7 Populations are the units of
evolution
• A population is a group of individuals of the same
species living in the same place at the same time
• Evolution is the change in heritable traits in a
population over generations
• Populations may be isolated from one another (with
little interbreeding), or individuals within populations
may interbreed
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8
• A gene pool is the total collection of genes in a
population at any one time
• Microevolution is a change in the relative
frequencies of alleles in a gene pool over time
• Population genetics studies how populations
change genetically over time
• The modern synthesis connects Darwin’s
theory with population genetics
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MAJOR EVENTS
IN THE HISTORY
OF LIFE
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on
ic e Cenozoic
ozo
ner
Pha
oe
M s
zoic
ic
Humans
zo
o
le
Pa
Colonization
of land
Origin of solar
system and
Earth
Animals
1
4
Proterozoic Archaean
eon
eon
Bil
lio
ns
2
of
o
ag
ars 3
ye
Multicellular
eukaryotes
Single-celled
eukaryotes
Prokaryotes
Atmospheric
oxygen
9
– Prokaryotes lived alone on Earth for 1.5 billion years
– They created our atmosphere and transformed Earth’s
biosphere
– Virtually all metabolic pathways evolved within
prokaryotes
– Atmospheric oxygen appeared 2.7 billion years ago due to
prokaryotic photosynthesis
– Cellular respiration arose in prokaryotes, using oxygen to
harvest energy from organic molecules
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15.4 The origins of single-celled and
multicelled organisms and the
colonization of land are key events in
life’s history
– The eukaryotic cell probably originated as a
community of prokaryotes, when small
prokaryotes capable of aerobic respiration or
photosynthesis began living in larger cells
– Oldest fossils of eukaryotes are 2.1 billion years
old
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– Multicellular forms arose about 1.5 billion years
ago
– The descendents of these forms include a variety of
algae, plants, fungi, animals
– The oldest known fossils of multicellular
organisms were small algae, living 1.2 billion
years ago
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– The diversity of animal forms increased
suddenly and dramatically about 535–525
million years ago in the Cambrian explosion
– Fungi and plants colonized land together 500
million years ago
– Roots of most plants have fungal associates that
exchange water and minerals for nutrients
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– Arthropods and tetrapods are the most
widespread and diverse land animals
– Human lineage diverged from apes 7–6 million
years ago
– Our species originated 160,000 years ago
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15.5 The actual ages of rocks and
fossils mark geologic time
– Radiometric dating measures the decay of
radioactive isotopes
– “Young” fossils may contain isotopes of
elements that accumulated when the organisms
were alive
– Carbon-14 can date fossils up to 75,000 years old
– Potassium-40, with a half-life of 1.3 billion
years, can be used to date volcanic rocks that are
hundreds of millions of years old
– A fossil’s age can be inferred from the ages of the
rock layers above and below the strata in which
the fossil is found
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Fraction of Carbon-14
remaining
1
–
2
1
–
4
0
5.7
1
–
8
1
––
16
11.4
22.8
17.1
Time (thousands of years)
1
––
32
28.5
15.6 The fossil record documents
the history of life
– The fossil record documents the main events in
the history of life
– The geologic record is defined by major
transitions in life on Earth
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