Yo!
Please get out your Natural Selection outline
you made from the textbook – we’re going to
add to it.
Didn’t do it? Get out a piece of paper.
Everyone – please read the board.
Please pass back the permission slip!
Armand Bayou Nature Center
Natural Selection
Natural Selection –
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Process by which organisms best suited to
their environmental conditions are most likely
to survive and reproduce
It’s HOW evolution works!
Three conditions that must be true for
natural selection to occur:
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Natural variation of a
trait in a population
Trait must be heritable
Trait must lead to
differential
reproduction (must
make you more likely
to reproduce)

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Some male peacocks
have more vibrant tail
displays than others
Tail and display
behavior is encoded in
DNA
Males with more
vibrant displays are
more likely to mate.
Natural selection leads to adaptations

Adaptation: a structure
or behavior that helps
an organism survive in
their environment.
Through natural selection, adaptations
are encoded in DNA.

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An INDIVIDUAL cannot change their
adaptations.
POPULATIONS undergo natural selection
and over many generations, can experience a
change in adaptations.
Some people confuse adaptation with
acclimation!
Coevolution

Read the excerpt from the text, then draw a
cartoon of the steps of coevolution.
Speciation
Speciation

How do new species evolve?
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Divergent selection – in ancestral species,
variation provides ability to survive in different
environments.
If different groups of the species become
physically isolated, they can continue to adapt to
separate environments (microevolution)
Eventually, they may be so different that they
cannot successfully mate = new species.
Geographic Isolation
So what if an entire species can’t
change quickly enough to deal with
changing conditions?
For each individual, either it survives
to reproduce or it dies

So what if an entire
species can’t change
quickly enough to deal
with changing
conditions?
Extinction

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Background extinction
rate: about 1 to 5
species/ year
Mass extinction: the
loss of many species in
a sudden event.

Current extinction rate:
1,000 to 10,000 times
the natural background
rate (dozens a day).
Legal/scientific designations

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Healthy
Threatened
Endangered
Extinct
Grizzlies and Polar Bears diverged
about 150,000 yrs ago.
Check for understanding!
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Why can’t an individual change it’s
adaptations in its lifetime?
What is the better word for an inidividual
getting used to a new situation?
What happens to populations in which no
individual is able to survive?