The puzzle of life’s diversity

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The Theory Evolution via natural selection
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How did different organisms arise? How are they related?
Voyage of the Beagle
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1831, ship sets sail for a
voyage around the
world
Aboard is Charles
Darwin, a 21 yr old
college graduate,
serving as ships’
naturalist (unpaid)
Observations and
evidence collected on
this voyage changed
biology forever.
The voyage of the HMS Beagle
Darwin’s observations
Giant sloth claw
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Land and marine iguanas
Fossils: he finds evidence of extinct animals
Diversity: animals and plants vary widely in similar
habitats
Why are some species widely found, others live only
in one place?
Ideas that shaped Darwin’s thinking
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Lyell: Geology shows evidence of an ancient
earth with geologic processes happening over
extended periods of time
Lamarck: traits of a parent can be passed on to
the offspring
Malthus: population size is determined by
limiting factors: food, living space
Publication of “On the Origin of the
Species”
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In 1859 Darwin proposes
a mechanism to explain
the complexity of life
Theory: evolution has
been going on for billions
of years, and continues
today.
Evolutionary theory
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Inherited variation: all species have individuals that are
slightly different from each other
Over reproduction: species produce excess offspring
Struggle for existence: there is competition to survive
Natural selection: the weak will die off
Survival of the fittest: the members best adapted to
their environment will live to reproduce, and their traits
will be passed on to their offspring
Evolution is Descent
with modification
Each species alive today
descended, with
changes, from other
species
 All species, living and
extinct, were derived
from common ancestors
 A single “tree of life”
links us all together
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Summary
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Write a 5 sentence paragraph (in your own words)
that summarizes the key point of this lecture.

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