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Chapter 13
Evidence of Evolution
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock
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Clues to Evolution Lie in the Earth,
Body Structures, and Molecules
Life on Earth arose 3.8 billion years
ago. Changes in body structures
and molecules have slowly
accumulated through that time,
producing the variety of organisms
we see today.
Section 13.1
Figure 13.2
Clues to Evolution Lie in the Earth,
Body Structures, and Molecules
Scientists use the geologic
timescale to divide the history of
the Earth into eons and eras. These
periods are defined by major
geological or biological events, like
mass extinctions.
Section 13.1
Figure 13.2
Figure 13.2
Clues to Evolution Lie in the Earth,
Body Structures, and Molecules
Researchers analyze fossils, anatomy, and
molecular sequences to learn how species
are related to one another.
Paleontology is the study of fossil remains
or other clues to past life. Fossils provided
the original evidence for evolution.
Section 13.1
Ge Sun, et al. "In Search of the First Flower: A Jurassic Angiosperm,
Archaefructus, from Northeast China,"
Science, Vol. 282, no. 5394, November 27, 1998, pp. 1601-1772.
©1998 AAAS. All rights reserved. Used with permission
Clues to Evolution Lie in the Earth,
Body Structures, and Molecules
Fossils are the remains of ancient organisms.
Section 13.1
Left fossil: Ge Sun, et al. "In Search of the First Flower: A Jurassic Angiosperm, Archaefructus, from Northeast China,"
Science, Vol. 282, no. 5394, November 27, 1998, pp. 1601-1772. ©1998 AAAS. All rights reserved. Used with permission; Wood:
©PhotoLink/Getty Images RF; Embryo: ©University of the Witwatersrand/epa/Corbis; Coprolite: ©Sinclair Stammers/Science Source;
Trilobite: ©Siede Preis/Getty Images RF; Fish fossil: ©Phil Degginger/Carnegie Museum/Alamy RF; Leaf fossil: ©Biophoto
Associates/Science Source; Triceratops: ©Francois Gohier/Science Source
Figure 13.1
13.1 Mastering Concepts
What is the geologic timescale?
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock
Fossils Record Evolution
Fossils form in many ways.
Section 13.2
Compression fossil of leaf: ©William E. Ferguson
Human skull and bone fossil: ©John Reader/Science Source
Figure 13.4
Fossils Record Evolution
Fossils form in many ways.
Section 13.2
Impression of dinosaur skin: ©Dr. John D. Cunningham/Visuals Unlimited
Horn coral: ©Robert Gossington/Photoshot
Figure 13.4
Fossils Record Evolution
Fossils form in many ways.
Section 13.2
Mosquito trapped in amber: ©Natural Visions/Alamy
Figure 13.4
Fossils Record Evolution
Even though fossil evidence is diverse, it is often challenging—or impossible—to
find fossils of transitional forms between groups.
The fossil record is incomplete, partly because some organisms (such as those
with soft bodies) fail to fossilize. Also, erosion and movement of Earth’s plates
might destroy fossils.
Section 13.2
Ammonite: ©Jean-Claude Carton/Photoshot
Figure 13.3
Fossils Record Evolution
Dating fossils yields clues about the timeline of life’s history.
The simpler, and less precise, method of dating fossils is
relative dating, which assumes that lower rock layers
have older fossils than newer layers.
Section 13.2
Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF
Figure 12.3
Fossils Record Evolution
Absolute dating uses chemistry to determine how long ago a fossil formed.
Radiometric dating is a type of absolute dating that uses radioactive isotopes.
Section 13.2
Woolly mammoth skeleton: ©Ethan Miller/Getty Images
Figure 13.6
Clicker Question #1
Which rock layer (A, B, or C) should have
fossils with the most carbon-14?
A
B
C
Flower: © Doug Sherman/Geofile/RF
Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF
Clicker Question #1
Which rock layer (A, B, or C) should have
fossils with the most carbon-14?
A
B
C
Flower: © Doug Sherman/Geofile/RF
Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF
Clicker Question #2
Researchers used a radioactive isotope
with a 25,000-year half-life to date a
fossil to 100,000 years ago. The fossil
contains ____ as much of the isotope as
does a living organism.
A. 1/2
B. 1/4
C. 1/8
D. 1/16
E. 1/32
Flower: © Doug Sherman/Geofile/RF
Clicker Question #2
Researchers used a radioactive isotope
with a 25,000-year half-life to date a
fossil to 100,000 years ago. The fossil
contains ____ as much of the isotope as
does a living organism.
A. 1/2
B. 1/4
C. 1/8
D. 1/16
E. 1/32
Flower: © Doug Sherman/Geofile/RF
13.2 Mastering Concepts
Distinguish between relative and absolute
dating of fossils.
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock
Biogeography Considers Species’
Geographical Locations
According to the theory of plate tectonics, Earth’s surface consists
of several rigid layers, called tectonic plates, that
move in response to forces acting deep within the planet.
Section 13.3
Figure 13.7
Biogeography Considers Species’
Geographical Locations
Fossils help geographers piece together Earth’s continents
into Pangaea.
Section 13.3
Figure 13.8
Biogeography Considers Species’
Geographical Locations
Biogeography sheds light
on evolutionary events.
Animals on either side of
Wallace’s line have been
separated for millions of
years, evolving
independently.
The result is a unique
variety of organisms on
each side of the line.
Section 13.3
Figure 13.9
13.3 Mastering Concepts
How have the positions of Earth’s continents
changed over the past 200 million years?
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock
Anatomical Relationships Reveal
Common Descent
Two structures are
homologous if the
similarities
between them
reflect common
ancestry.
Section 13.4
Figure 13.10
Anatomical Relationships Reveal
Common Descent
All of these animals,
for example, have
similar bones in their
forelimbs.
These similarities
suggests that their
common ancestor had
this bone
configuration.
Section 13.4
Figure 13.10
Anatomical Relationships Reveal
Common Descent
Homologous
structures need not
have the same
function or look
exactly alike.
Different selective
pressures in each
animal’s evolutionary
line have led to small
changes from their
ancestor’s bone
structure.
Section 13.4
Figure 13.10
Anatomical Relationships Reveal
Common Descent
A vestigial structure has lost
its function but is
homologous to a functional
structure in another species.
Vestigial hind limbs in some
snake species and pelvises in
whales are evidence of
these organisms’ ancestors.
Section 13.4
Mexican-boa-constrictor: ©Pascal Goetgheluck/Science Source
Python skeleton: ©Science VU/Visuals Unlimited
Figure 13.11
Anatomical Relationships Reveal
Common Descent
Anatomical structures are
analogous if they are superficially
similar but did not derive from a
common ancestor.
None of these cave animals has
pigment or eyes.
These similarities arose by
convergent evolution, which
produces similar structures in
organisms that don’t share the
same lineage.
Lack of pigment arose
independently in each of these
cave animals.
Section 13.4
Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited
Crayfish: ©Dante Fenolio/Science Source
Figure 13.13
Clicker Question #3
The streamlined shapes of dolphins and
sharks evolved independently. The body
plan of these two animals are
A. homologous.
B. vestigial.
C. analogous.
D. a product of convergent evolution.
E. Both C and D are correct.
Flower: © Doug Sherman/Geofile/RF
Clicker Question #3
The streamlined shapes of dolphins and
sharks evolved independently. The body
plan of these two animals are
A. homologous.
B. vestigial.
C. analogous.
D. a product of convergent evolution.
E. Both C and D are correct.
Flower: © Doug Sherman/Geofile/RF
13.4 Mastering Concepts
What can homologies reveal about
evolution?
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock
Embryonic Development Patterns
Provide Evolutionary Clues
Anatomical similarities are often
most obvious in embryos. Notice
how much more similar human
and chimpanzee skull structure
is in fetuses compared to in
adults.
Section 13.5
Figure 13.14
Embryonic Development Patterns
Provide Evolutionary Clues
Adult fish, mice, and alligators have very different bodies.
Their evolutionary relationships are more obvious in embryos.
How do similar embryos develop into such different organisms?
Homeotic genes provide a clue.
Section 13.5
Fish: ©Dr. Richard Kessel/Visuals Unlimited; Mouse: ©Steve Gschmeissner/Science Source; Alligator: USGS/Southeast
Ecological Science Center
Figure 13.15
Embryonic Development Patterns
Provide Evolutionary Clues
Homeotic genes control an organism’s development. Small differences in gene
expression might make the difference between a limbed and limbless organism.
Homeotic genes therefore help explain how a few key mutations might produce
new species.
Section 13.5
Figure 13.16
Embryonic Development Patterns
Provide Evolutionary Clues
Mutations in segments of DNA
that do not encode proteins
also produce new phenotypes.
Section 13.5
Figure 13.17
13.5 Mastering Concepts
How does the study of embryonic
development reveal clues to a shared
evolutionary history?
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock
Molecules Reveal Relatedness
Comparing DNA and protein sequences
determines evolutionary relationships in
unprecedented detail.
It is highly unlikely that two unrelated species
would evolve precisely the same DNA and
protein sequences by chance.
Section 13.6
It is more likely that the similarities were
inherited from a common ancestor and that
differences arose by mutation after the species
diverged from the ancestral type.
Molecules Reveal Relatedness
Molecular clocks assign dates to evolutionary events.
If a gene is estimated to mutate once every 25 million years, then two
differences from an ancestor might arise in 50 million years.
Section 13.6
Figure 13.20
Molecules Reveal Relatedness
If a gene is estimated to mutate once every 25 million years, then two
differences from an ancestor might arise in 50 million years.
Therefore, two species that derived from the same common ancestor 50 MYA
might have four differences in the nucleotide sequence of the gene.
Section 13.6
Figure 13.20
Clicker Question #4
Mutations in a gene occur at a rate of one
nucleotide every 10 million years. The gene
sequence differs by 6 nucleotides between
two related organisms. How long ago did
these organisms split from a common
ancestor?
A. about 2 million years ago
B. about 30 million years ago
C. about 60 million years ago
D. about 120 million years ago
E. None of the choices is correct.
Flower: © Doug Sherman/Geofile/RF
Clicker Question #4
Mutations in a gene occur at a rate of one
nucleotide every 10 million years. The gene
sequence differs by 6 nucleotides between
two related organisms. How long ago did
these organisms split from a common
ancestor?
A. about 2 million years ago
B. about 30 million years ago
C. about 60 million years ago
D. about 120 million years ago
E. None of the choices is correct.
Flower: © Doug Sherman/Geofile/RF
13.6 Mastering Concepts
How does analysis of DNA and proteins
support other evidence for evolution?
Fossil: ©Lou Mazzatenta/National Geographic Stock
Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock