Download Evolution by Natural Selection

16.3
 Describe the condition under which
natural selection occurs.
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
Explain the principle of common descent.
• Malay Archipelago
• Darwin and himself both read
Malthus essay
• Wrote to Darwin in 1858 and
explained his idea of “Survival of
the Fittest”
• Gave Darwin confidence to
publish his book in 1859
1. Struggle of Existence
- competition for food and living space is a part
of life
2. Variation and Adaptation
- some variations better suited for environment
- inheritable traits that increase ability to survive
and reproduce called adaptations
Monarch
Viceroy
3. Survival of the Fittest
- adaptations affect
fitness
- fitness is how well an
organism survives and
reproduces in its
environment
- better adaptations =
higher fitness
4. Natural Selection
- Process by which organisms with variations best
suited for environment will survive and leave
more offspring
- environment influences fitness
- Process does not make organisms “better” and
does not act in a fixed direction
For Natural Selection to occur, three criteria must
be met:
1. Variation
2. Differential reproductive success (fitness)
3. Heritability
- genes (unit of evolution) passed to offspring
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Under what conditions does natural selection occur?
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Natural selection occurs in any situation in which more
individuals are born than can survive (the struggle for
existence), there is natural heritable variation (variation
and adaptation), and there is variable fitness among
individuals (survival of the fittest).
Evolution by Natural Selection
• descent with modification
- traits modified gradually
in species from a common
ancestor
- happens over LONG
periods of time
• all species, living and
extinct, are descended from
ancient common ancestors

Morphological – organisms structure

Behavioral – how the organism acts

Physiological – functions of organism
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http://wildamerica.com/videos/transcripts
/s34.html
“Designs for Defense” (VHS clip)