Georgia Performance Standards:
SB5b: Explain the history of life in terms of
biodiversity, ancestry, and the rates of evolution.
SB5d: Relate natural selection to changes in
Essential Questions:
Why is important to understand evolutionary theory?
What is the role of natural selection in speciation?
Why are there species alive now that were not found in the past fossil
4. How does fossil and biochemical evidence support the evolutionary
What scientific explanation can
account for the diversity of life?
• Answer: The evolutionary theory
• Evolution, or change over time, is the
process by which modern organisms have
descended from ancient organisms.
• A theory is a well-supported testable
explanation of phenomena that have
occurred in the natural world.
Charles Darwin
• During his travels, Darwin made numerous
observations and collected evidence that
led him to propose a revolutionary
hypothesis about the way life changes
over time.
• That hypothesis, now supported by a huge
body of evidence, has become the theory
of evolution.
Darwin’s Observations:
• Patterns of Diversity - the many ways in which
organisms survived and produced offspring.
• Living Organisms and Fossils - Why had so
many of these species disappeared? How were
they related to living species?
• The Galápagos Islands - The higher islands
had greater rainfall and a different assortment of
plants and animals
Giant Tortoises of the Galápagos
Section 15-1
Pinta Island
Intermediate shell
Santa Cruz
Santa Fe
Hood Island
Isabela Island
Dome-shaped shell
Saddle-backed shell
Ideas That Shaped Darwin's Thinking
• Hutton’s Theory of Geological Change
– proposed that Earth had to be much more
than a few thousand years old.
• Lyell’s Principles of Geology
– Lyell’s work explained how awesome
geological features could be built up or torn
down over long periods of time.
– Lyell helped Darwin appreciate the
significance of geological phenomena that he
had observed.
Ideas That Shaped Darwin's Thinking
• This understanding of geology influenced
Darwin in two ways.
1. If Earth could change over time, might life
change as well?
2. Darwin realized that it would have taken
many, many years for life to change in the
way he suggested.
Ideas that shaped Darwin’s Thinking:
• Lamarck proposed that
by selective use or disuse
of organs, organisms
acquired or lost certain
traits during their lifetime.
– These traits could then
be passed on to their
– Over time, this
process led to change
in a species.
– Lamarck’s ideas were
incorrect in several ways
(he did not know how traits
are inherited)
– He did not know that an
organism’s behavior has no
effect on its inheritable
– Lamarck was one of the
first to develop a scientific
theory of evolution and
realize that organisms are
adapted to their
– He paved the way for the
work of later biologists.
Ideas that Shaped Darwin’s Thinking
• Malthus & Population Growth reasoned that if the human population
continued to grow unchecked, sooner or
later there would be insufficient living
space and food for everyone.
Checkpoint Questions:
1. What two ideas from geology were important to
Darwin’s thinking?
2. According to Lamarck, how did organisms
acquire traits?
3. According to Malthus, what factors limited
population growth?
4. Why has Lamarck’s theory of evolution been
5. Malthus formed his theory by studying factors
that control the population growth of humans.
How might factors operating on organisms in
nature differ from those of Malthus’s theory?
Darwin’s Conclusions:
• On the Origin of Species.
– In his book, he proposed a mechanism for
evolution that he called natural selection.
– He then presented evidence demonstrating
that the process of evolution has been taking
place for millions of years—and continues in
all living things.
Darwin’s Conclusions:
• Natural variation, defined as differences
among individuals of a species, is found in
all types of organisms. Variation is present
in species in nature
• Artificial selection, nature provided the
variation among different organisms, and
humans selected those variations that they
found useful.
Darwin’s Conclusions:
• Evolution by Natural Selection
– struggle for existence means that members of each species
compete regularly to obtain food, living space, and other
necessities of life.
– The ability of an individual to survive and reproduce in its specific
environment fitness, which is the result of adaptations.
– An adaptation is any inherited characteristic that increases an
organism’s chance of survival.
– Successful adaptations enable organisms to become better
suited to their environment and thus better able to survive and
Darwin’s Conclusions:
• Individuals that are better suited to their
environment—that is, with high levels of fitness—
survive and reproduce most successfully.
• This was a process that Darwin called survival of the
• Because of its similarities to artificial selection, Darwin
referred to the survival of the fittest as natural selection.
– In both artificial selection and natural variation, only
certain individuals of a population produce new
Darwin’s Conclusions:
• Over time, natural selection results in
changes in the inherited characteristics of a
• These changes increase a species’ fitness in
its environment.
– Natural selection cannot be seen directly; it can only
be observed as changes in a population over many
successive generations.
Descent With Modification
• Natural selection produces organisms that have different
structures, establish different niches, or occupy different
• As a result, species today look different from their
• Each living species has descended, with changes, from
other species over time.
• If we look far enough back, the logic concludes, we could
find the common ancestors of all living things. This is the
principle known as common descent.
Evidence of Evolution:
• Fossil record - by
examining fossils from
sequential layers of rock,
one could view how a
species had changed and
produced different species
over time, as shown in the
figure at right.
• Geographical distribution
of living species
• Biochemistry
• Similarities in Embryonic
• Homologous structures of
living organisms
– structures that have
different mature forms in
different organisms but
develop from the same
embryonic tissues
– Not all homologous
structures serve
important functions.
– Vestigial organs (the
organs of many animals
are so reduced in size
that they are just
vestiges, or traces, of
homologous organs in
other species.
Homologous Body Structures
Section 15-3
Typical primitive fish
Concept Map
Section 15-3
Evidence of
The fossil record
distribution of
living species
body structures
in early
which is composed of
which indicates
which implies
which implies
remains of
Similar genes
Similar genes
Summary of Darwin’s Theory
Individual organisms in nature differ from one
another. Some of this variation is inherited.
Organisms in nature produce more offspring
than can survive, and many of those that
survive do not reproduce.
Because more organisms are produced than
can survive, members of each species must
compete for limited resources.
Because each organism is unique, each has
different advantages and disadvantages in the
struggle for existence.
Summary of Darwin’s Theory
• Individuals best suited to their environment survive and
reproduce most successfully. The characteristics that
make them best suited to their environment are passed
on to offspring. Individuals whose characteristics are not
as well suited to their environment die or leave fewer
• Species change over time. Over long periods, natural
selection causes changes in the characteristics of a
species, such as in size and form. New species arise,
and other species disappear.
• Species alive today have descended with modifications
from species that lived in the past.
• All organisms on Earth are united into a single tree of life
by common descent.
Checkpoint Questions:
1. How is artificial selection dependent on variation in
2. The theory of evolution by natural selection explains, in
scientific terms, how living things evolve over time.
What is being selected in this process?
3. What types of evidence did Darwin use to support his
theory of change over time?
4. What is the “struggle for existence”? How was this idea
based on Malthus’s work?
5. Compare and contrast Darwin’s theory of evolution with
that of Lamarck. How are they similar? How are they
Patterns of Evolution
• Macroevolution
refers to the
changes that take
place over long
periods of time.
• Six important patterns
of macroevolution
mass extinctions
adaptive radiation
convergent evolution
punctuated equilibrium
changes in
developmental genes.
Mass Extinctions:
• New fossil studies show
that those mass
extinctions not only
extinguished species but
also wiped out whole
ecological systems,
disrupting energy flow
throughout the biosphere
and causing food webs to
• Many paleontologists
think that most mass
extinctions were
caused by multiple
• For the survivors,
there was a new
world of ecological
• Often, the result was
a burst of evolution
that produced an
abundance of new
Adaptive Radiation
• Studies of fossils or of living organisms
can show that a single species or a
small group of species has evolved into
several different forms that live in
different ways.
• This process is known as adaptive
– Implies common descent
Convergent Evolution
• Unrelated organisms that come to
resemble one another, is called
convergent evolution.
• Natural selection may mold different body
structures, such as arms and legs, into
modified forms, such as wings or flippers.
– EX: Streamlined body of penguin, shark,
• The process by which two species evolve in
response to changes in each other over time
is called coevolution.
• An evolutionary change in one organism may
also be followed by a corresponding change in
another organism.
• EX: Many flowering plants, for example, can
reproduce only if the shape, color, and odor of
their flowers attract a specific type of pollinator.
Punctuated Equilibrium
• Evolution has often
proceeded at different
rates for different
organisms at different
times during the long
history of life on
(Rate of Evolution)
• Gradualism - slow,
steady change in a
particular line of
• Punctuated
equilibrium - long,
stable periods
interrupted by brief
periods of more
rapid change
Developmental Genes and Body Plans
• First, molecular studies show that homologous hox
genes establish body plans in animals as different as
insects and humans
• Second, major evolutionary changes—such as the
different numbers of wings, legs, and body segments in
insects—may be based on hox genes.
• Finally, geneticists are learning that even small changes
in the timing of genetic control during embryonic
development can make the difference between long legs
and short ones
Changes in
developmental genes
are one major pattern of
• Fossil evidence shows
that some ancient insects
(top left) had no wings, but
others (top right) had
winglike structures on
many body segments.
• In modern insects
(bottom), genes may turn
off wing development in all
except one or two body
Checkpoint Questions:
• What is macroevolution? Describe two patterns
of macroevolution.
• What role have mass extinctions played in the
history of life?
• Use an example to explain the concept of
• How might hox genes contribute to variation?
• Compare and contrast the theories of
gradualism and punctuated equilibrium.
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