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Evolution
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Natural Selection I.
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BI. 8. a. Students know how natural selection
determines the differential survival of groups
of organisms.
BI8. b. Students know a great diversity of
species increases the chance that at least
some organisms survive major changes in the
environment.
BI.7 a. Students know why natural
selection acts on the phenotype rather than
the genotype of an organism.
BI7. d. Students know variation within a
species increases the likelihood that at least
some members of a species will survive
under changed environmental conditions.
Standards:
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BI8. a. Survival of the fittest and the struggle for
existence.
BI8. b. The more variety of organisms there are in
an environment the better the chances are that
some organisms will survive any major
environmental changes.
BI7. a. NS acts on the physical or physiological
traits of an individual.
BI7. d. The more genetic variation a species has
the better chance they will have of surviving a
changing environment because at least some
individuals will have the characteristics needed to
survive.
Standard Summary
SWBAT…
 Explain how natural selection determines the
differential survival of groups of organisms.
 Explain how variation within a species increases the
likelihood that at least some members of a species
will survive under changed environmental
conditions.
 Apply their understanding of natural selection
to various scenarios to determine which adaptations
(phenotypes=physical traits) will increase or
decrease an organisms’ chances of survival.
Objectives:
Natural variations appear in populations
because of genetic variations.
 These natural variations can lead to
beneficial adaptations.
 Beneficial adaptations will appear in
future generations because of the
principles of natural selection.
 These “ natural selections” drive
evolution by changing the inherited
characteristics of the population.
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Review-What we know so
far….
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Natural Selection-inherited adaptations
provide an advantage
Evolution-change in a species over time
Natural Selection vs.
Evolution
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Natural selection-mechanism by which
individuals that have inherited beneficial
adaptations produce more offspring on
average than do other individuals.
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These adaptations occur over many
generations in a population (descent with
modification)
What is natural selection’s role
in evolution?
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NS explains how evolution can occur
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Natural selection acts on phenotypes (physical
traits), not on genetic material.
What is natural selection’s role
in evolution?
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Overproduction-jaguar produces more
offspring than can survive
Variation-some jaguars are born with larger
teeth and jaws
Adaptation-jaguars with larger teeth and jaws
are able to eat shelled reptiles, and leave more
offspring
Descent with modification-large teeth and
jaws are inherited and become more common
The Four Principles of Natural
Selection
Shell Crushers!! (700 psi)
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What causes the natural variations that occur in
a population?
Does natural selection act on the genotype or
phenotype of organisms?
Where do species get their adaptations from?
Explain the relationship between natural
selection and evolution.
Summarize standard 7a in your own words.
Summary Questions: