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He found that the birds, tortoises, iguanas, and
many plants he saw on the Galapagos were
found nowhere else in the world
He did not publish his book, On the Origin of
Species, because it challenged the beliefs of that
time, the findings stunned him, and he was
disturbed by them
He did not publish it until 25 years after his
findings
In his book, he presented evolution as natural
selection, that it has been taking place for
millions of years, and continues with all living
things
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He saw that members of each
species vary from one another
in important ways
He spoke with animal & plant
breeders that convinced him
variation existed in nature &
farm
Ex., some plants in the same
species bear bigger fruits than
others, some cows produce
more milk than others
He learned this was heritable
variation- differences passed
from parent to offspring
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He didn’t know how heredity
worked, now we know its
controlled by genes
Darwin said farmers and
animal breeders used
heritable variation to improve
crops and livestock
They would only breed the
large hogs, the fastest
horses, etc.
He called this artificial
selection: nature provides
the variation, & humans
select the variations they find
useful
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Artificial selection worked in nature
High birth rates and shortages of life’s basic needs
would force organisms to compete for these
resources
Struggle for existence: members of each species
compete for food, living space, etc.
Fast predators can catch their prey
Prey that are better camouflaged or better protected
could avoid being caught
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Darwin observed how well an
organism fit into its environment
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Fitness: ability of an individual to
survive/reproduce in its environment
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Fitness is the result of adaptations:
any inherited characteristic that
increases an organism’s chance of
survival
Adaptations can be structural or
anatomical
Ex., porcupine’s sharp quills, plants
able to perform photosynthesis, how
some animals hunt in groups
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Individuals that are
not well-suited to
their environments die
or leave few offspring
and can become
extinct
Individuals well suited,
survive and reproduce
more successfully
Darwin called this
survival of the fittest
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Because of its similarities to artificial selection,
Darwin referred to survival of the fittest as natural
selection
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Over time, natural selection results in changes in
the inherited characteristics of a population.
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Natural selection acts directly on phenotypes (the
way things look)
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He also said that today species look different from
their ancestors
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Each living species has descended with changes
from their ancestors over time: descent with
modification
This also means that all living things are related to
one another: common descent; a single tree of life
links all living things