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Darwin’s Theory
1. Individual organisms differ and
some of this variation is heritable.
2. Organisms produce more
offspring than can survive.
3. They compete for limited
• Food
• Water
• Shelter
• Mates
4. Individuals best suited for the
environment will survive/reproduce
• These surviving and
organisms will leave
the most offspring.
• Their traits will be
inherited and move
on to the next
5. Descent With Modification
• Organisms alive
today are descended
from ancestors who
lived in the distant
• Modifications are
changes that allow
diverse species to
have a common
• On HMS Beagle went to the Galapagos
and wondered if the various species from
each island had once been members of
the same species.
• Organisms are considered to be the same
species if they mate and have fertile
• Published “The Origin of Species”
James Hutton and Charles Lyell
• Both were Geologists and knew the Earth
was Millions of years old, not thousands
as most believed at that time.
• Both knew forces shaped the Earth over
long periods of time
• Lyell said that the same forces that worked
on shaping the Earth in the past were still
happening in the present time.
• Statistician – Used math to analyze
• Predicted that the human population would
grow faster than the resources necessary
to support it (Like food and places to live)
Jean-Baptiste Lamarck
• Traits are inherited
• Organisms became more complex and
more perfect
• These “Acquired Traits” could be passed
to offspring. This was ultimately proven
• If fruit fly wings were clipped, the offspring
would not be born without wings.
• Published “The Theory of Natural
• Pressured Darwin to publish his work on
the “Origin of Species”
Natural Selection
• Struggle for existence
• Survival of the fittest
• Descent with
Artificial Selection
• Nature provides the
• Humans select the
variations they find
attractive or useful
What happens if there is no
• Selective breeding can reduce the variation in a
• What are some of the risks?
Adaptation = Survival
• If you are not well adapted you may not
survive to have offspring.
• Variation means that there are many
different adaptations.
• When there is less variation one disease
or predator could kill the whole population
• Variation = A better chance for the
population to survive