Download Summing up Natural Selection

Charles Darwin
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From his observations he started writing:
On the Origin of Species by Means of Natural Selection.
Two main points:
 Species were not created in their present form, but evolved with
modifications from ancestral species.
 Proposed a mechanism for evolution: NATURAL SELECTION
Jean-Baptiste Lamarck
(1 7 4 4 -1 8 2 9 )
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First to hypothesize a mechanism for changes in organisms because they were
adapted to their environments.
But, his Theory of Inheritance of Acquired Characteristics, incorrectly stated
that animals can pass on traits that they developed during their lifetime.
Thomas Malthus (1766- 1834)
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Social Economist, author of Essay on the Principles of Population (1798).
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Argued that food supply increased in a linear fashion, while population
increased “geometrically” (exponentially).
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Example of limited resources causing competition.
Species variation…..
Variation…..
Adaptations
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Characteristics that make an individual suited to its environment
and way of life.
P u t t i n g i t a l l t o g e t h e r ……
Struggle for survival….
Survival = more babies!!
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Individuals that are better adapted tend to survive and produce
more offspring while the less well adapted tend to die or produce
fewer offspring.
Heritable traits
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Individuals that reproduce pass on characteristics to their
offspring.
Summing up Natural Selection
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Natural selection increases the frequency of characteristics that
make individuals better adapted and decreases the frequency of
other characteristics leading to changes within the species.
Adaptable…….
Natural selection in action
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Insecticides
 Apply insecticide.
 Non resistant insects die.
 Resistant survivors live to reproduce.
 Resistance is inherited.
 Insecticide becomes less
& less effective.
 New population allele frequency emerges.
Antibiotic resistance in bacteria
While on the Galapagos Islands Darwin noticed….
The Galapagos Finches
Adaptive Radiation
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Genetic studies have shown that Darwin’s hypothesis was correct.
We call this adaptive radiation.
 Emergence of numerous species from a common ancestor introduced to new and
diverse environments.