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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.
Video on Natural Selection
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
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Genetic diversity- organisms within the same
species are not identical
Organisms have different traits, don’t all look the
same
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
With the larger variety there is a better chance
that some individuals have the trait needed to
survive in new conditions
Kaibab and Abert’s Squirrels
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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 Isolationsome members of a
species become cut off
from the rest of the
species
How Do New Species Form?
These two kinds
of squirrels have
been isolated
from one
another for a
long time.
Eventually this
isolation may
result in two
different
species.
A Branching Tree
This branching tree shows how scientists now think
that raccoons, lesser pandas, giant pandas, and
bears are related.
Inferring Species Relationship
 Key
Concept: “Scientists have
combined the evidence from DNA,
protein structure, fossils, early
development, and body structure to
determine evolutionary relationships
among species.”
Extinction of Species
Key Concept- “Extinction is
caused by a change in a
species’ environment. The
members of the species may
not have adaptations that allow
them to survive and reproduce
in the changed environment.”
 Extinct- no members of a
species are still alive
 Ways an environment can
change: disease strikes a
species, predators kill so many
prey that the prey become
extinct
 Most species that are fossils are
now extinct
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Environmental Changes
 Climate
change is #1 cause of extinction
 Destroys habitats
 Example: Wooly Mammoths
Had traits to live in cool climate- thick coats
 Climate becomes warmer
 Thick coats are no longer helpful
 Environmental change doesn’t always cause
extinction
 Some organisms have traits that help them survive
 Peppered Moth and Mutation
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Section 5: Branching Trees
How does a branching tree diagram
show evolutionary relationships?
A Branching Tree
Branching trees show relationships between groups
of organisms. It also shows the order in which
specific characteristics may have evolved.
Shared Derived Characteristics
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Shared derived characteristics- a trait that is
shared by all organisms in a group
A branching tree diagram shows evolutionary
relationships by grouping organisms according
to shared derived characteristics.
Amphibians
Fishes
Reptiles
Egg with shell
Invertebrates
Four limbs
Backbone
Ancestor of animals
Constructing a Branching Tree
 Branching
Tree Video