Change
Over Time
7.3 Biological evolution accounts for the diversity of species developed through
gradual processes over many generations. As a basis for understanding this
concept:
a. Students know both genetic variation and environmental factors are causes of
evolution and diversity of organisms.
b. Students know the reasoning used by Charles Darwin in reaching his
conclusion that natural selection is the mechanism of evolution.
c. Students know how independent lines of evidence from geology, fossils, and
comparative anatomy provide the bases for the theory of evolution.
d. Students know how to construct a simple branching diagram to classify living
groups of organisms by shared derived characteristics and how to expand the
diagram to include fossil organisms.
e. Students know that extinction of a species occurs when the environment
changes and the adaptive characteristics of a species are insufficient for its
survival.
Darwin
• He discovered many fossils of extinct animals that were similar to
modern species
• Found many variations in plants and animals that led to the
formations of his theories
• Species- a group of organisms that resemble one another and
are able to reproduce among themselves
• Traits- genetic characteristics among similar organisms in a
species that is passed from one generation to another
• Offspring- child of a parent
Darwin’s Voyage
Charles Darwin sailed on the Beagle, from England to the
Galápagos Islands.
 Discovered many fossils of extinct animals that were similar to
modern species
 Found many variations in plants and animals that led to the
formations of his theories
Overproduction and Variation
Natural selection is the process by which individuals who are better
adapted to their environment are more likely to survive and reproduce
than other members of the same species.
Variations- a difference in a characteristic or trait from one
organism in a species to another in the same species
Competition and Selection
Variations among turtles make some of them better able to survive.
Turtles that survive to become adults will be able to reproduce.
 Survival of the fittest- theory of natural evolutionary processes that
enables organisms that are best suited for their environment to survive
 Evolution- overall change of a population’s gene pool over time
through processes such as mutation and natural selection
Section 2: Evidence of
Evolution
Forms of Evidence
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Key concept: Similar body structures, patterns of early
development, molecular structure, and fossils all provide
evidence that organisms have changed over time.
Homologous structures- similar structures that related species
have inherited from a common ancestor
Comparative anatomy- comparison of the structures of different
organisms
The structure of the bones in a dolphin’s flipper, a bird’s wing, and a
dog’s leg is similar. Homologous bones are shown in the same color.
Forms of Evidence
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Early Development- how
different species develop
before birth
Scientists make
inferences about
relationships based on
early development
Similarities in DNA and
proteins- if two species
have similar DNA and
proteins, probably
evolved from same
ancestor
How Do Fossils Form?
Most fossils form when organisms that die become
buried in sediments.
How Do Fossils Form?
 Mold-
hollow area in sediment in the shape of an
organism or part of an organism
 Cast- solid copy of the shape of an organism
 Cast is the opposite of a mold
 Petrified fossils- fossils in which minerals replace all
or part of an organism
 Trace fossils- fossils that provide evidence of the
activities of ancient organisms, like footprints
 Preserved remains- processes that preserves the
remains of organisms with little or no change (tar,
amber, and freezing
Learning From Fossils
The fossils record
provides evidence
about the history of
life and past
environments on
Earth. In addition,
scientists use fossils to
study the rate at
which evolution has
occurred.
Learning From Fossils
 Paleontologists-
scientists who study fossils
 Fossils build a picture of Earth’s past
environments
 Fossils show how an environment has changed
 Gradualism- proposes that evolution occurs
slowly but steadily
 Punctuated equilibria- accounts for gaps in the
fossil record, periods of rapid change separated
by long periods of little or no change
Section 3: Evolution of Species
What factors have contributed to the diversity of
species?
How do new species form?
How do scientists infer evolutionary relationships
among species?
What causes the extinction of species?
A Variety of Species
 Key
concept: Over time, different
environments and genetic variation have
produced, through natural selection, the
variety of organisms that exist today.
 Over millions of years, natural selection
has produced different species with
adaptations enabling them to live in
specific habitats
 habitats- specific environment that
provides the things organisms need to live,
grow, and reproduce
A Variety of Species
 Genetic
diversity- organisms within the
same species are not identical
 Some genetic diversity is because of
mutations in DNA
 Some genetic diversity is caused by
rearrangement of genes during meiosis
 Species that have a lot of variety adapt
to changes in the environment
 Most organism are genetically similar, they
have a difficulty surviving environmental
change
How Do New Species Form?
 Key
concept: A new species can form
when a group of individuals remains
isolated from the rest of its species long
enough to evolve different traits.
 Geographic Isolation is one of the main
ways new species form
 Sometimes a group is separated by a
river, volcano, or mountain range
 A wave can sweep members of a species
out to sea and wash them up on an island
Kaibab and Abert’s Squirrels
 Two
kinds of squirrels
isolated from one
another by the Grand
Canyon for a long time
 This isolation may result
in two different species
 They belong to the
same species but have
different characteristics
*an example of Geographic Isolation
Kaibab
Abert’s
Inferring Species Relationships
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Key concept: Scientists have combined the
evidence from DNA, protein structure, fossils,
early development, and body structure to
determine the evolutionary relationship
among species.
Compare genes to determine how closely
related species are
More similar DNA is more closely related
organisms are
In most cases evidence from DNA and protein
structure confirm hypotheses on fossils,
embryos and body structures
A Branching Tree
This branching tree shows how scientists now think
that raccoons, lesser pandas, giant pandas, and
bears are related.
Extinction of Species
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Key concept: Extinction is caused by
a change in species' environment.
The members of a species may not
have adaptations that allow them to
survive and reproduce in the
changed environment.
Extinct- no members of the species
are still alive
Causes of extinction: disease,
predators, humans, climate change
Not all climate changes cause
extinction, some species have been
able to adapt
Just like we saw in the Beak game, many organisms can survive but if
the organism doesn’t get enough of what it needs it will not be able to
reproduce and the species will become extinct.
Section 5: Branching Trees
How does a branching tree diagram
show evolutionary relationships?
A Branching Tree
Branching Trees Diagram- show probable
evolutionary relationships between groups of
organisms. It also shows the order in which specific
characteristics may have evolved.
Shared Derived Characteristics
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Key concept: A branching tree diagram shows
evolutionary relationships by grouping organisms
according to shared derived characteristics.
Shared Derived Characteristics- homologous
structures that are shared by all organisms in a
group
Amphibians
Fishes
Reptiles
Egg with shell
Invertebrates
Four limbs
Backbone
Ancestor of animals
Constructing a Branching Tree
 Organism
with none of the characteristics are at
the bottom
 Next fork put group with one shared derived
characteristics
 Branch above that put organism with two shared
derived characteristics
 Continue until you end
with the organism that has
the most shared derived
characteristics
Reading a Branching Tree Diagram
1. Did crocodiles evolve
from amphibians?
No they are on
different branches of
the branching tree.
2. Are rodents more closely
related to primates or
crocodiles?
Primates they are on a
branch together with
other.
3. Name a common ancestor
between crocodiles and
dinosaurs.
Two post-orbital fenestrae
Essay Question
 You
are a wild rabbit and your species
currently lives in the desert. Most of the
rabbits are brown but there are a few that
are white. An asteroid hits the Earth and
the environment you live in suddenly
becomes very cold. It begins to snow
leaving snow covering the ground. Will
your species be able to adapt and live in
the new environment? Explain and give
details (what happens to white rabbits
and brown rabbits).