http:www'uweb'ucsb'edujulianlimindex'htm

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http//www.uweb.ucsb.edu/julianlim/index.htm
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Life is Organized. is Complex. is Adjusted to
its circumstances. Reproduces. Why?
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Because of the process that creates it Evolution
by natural selection (Darwin Wallace,1858).
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• How does natural selection shape living things?
• Six-step argument
• Reproduction is exponential.
• 2, 4, 8, 16, 32, 64, 128, 256, 512...

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numbers
time
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Elephants begin to reproduce at 30, have 1
offspring per decade, up to the age of 90
6 offspring per pair 9,000,000 per pair after
750 years
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2. But numbers of organisms tend to be relatively
stable in nature.
numbers
time
Not a ball of elephants expanding outward at the
speed of light!
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• Reproduction is exponential.
• 2. But numbers of organisms tend to be relatively
  stable in nature.
• Therefore
• 3. Many individuals must fail to reproduce

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Which ones succeed and which ones fail? Success
or failure is not a matter of chance 4.
Individuals with advantageous traits are more
likely to survive and reproduce.
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5. Offspring resemble their parents. Successful
parents pass on their advantageous
traits. Unsuccessful parents dont pass on their
disadvantageous traits. So
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4. Individuals with advantageous traits are more
likely to survive and reproduce. 5. Offspring
inherit those traits. 6. Advantageous traits
become more common over the generations.
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What determines whether a traits is
advantageous? The environment, nature. Natural
selection sorts the alternatives in the
population and holds onto whatever works. Thus,
organisms become well adapted to their
environments.
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What works in one environment may fail in
others. Hence there are many kinds of creatures.
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Selection is not an engineer, only a
tinkerer. Selection cant create new variants. It
can only choose among those that already exist.
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And what is advantageous? Any trait that
promotes Reproduction. Survival is a means to an
end, not and end in itself. A type of creature
that lived a long time but died without
reproducing would disappear.
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If we say that natural selection designs
organisms, then it designs them for
reproduction. Adaptations Traits that have been
preserved by selection because they aided
reproduction.
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Are there any limits to the kinds of advantageous
traits selection can spread? Yes! Traits must be
transmitted reliably from parent to
offspring. e.g., genetically based traits.