Transcript Natural Selection

Charles Darwin
1809-1882
S. Stevens 3/20/2007
Darwin explains
Natural Selection
•Mechanism for a change in
populations
•Natural selection occurs at
the population level, not in
individuals
S. Stevens 3/20/2007
Darwin explains
Natural Selection
•When organisms with certain
variations survive, reproduce,
and pass their variations to
the next generation.
S. Stevens 3/20/2007
Evidence of Natural Selection
Darwin collected a closely related
group of 14 finch species in the
Galápagos Islands
– All were similar except for beak
characteristics
– Darwin hypothesized that different beak
shapes were related to food gathering
– Darwin wrote “…one might really fancy
that…one species has been taken and
modified for different ends.”
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S. Stevens 3/20/2007
Overproduction
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Variation
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Competition for Limited Resources
and Survival of the “Fittest
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Inheritance and Descent with
Modification
S. Stevens 3/20/2007
Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass those
advantages to their children
5. Species alive today are descended with
modifications from common ancestors