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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.
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:
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.
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-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
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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?
How does natural selection cause evolution?
Summary Questions: