Transcript Natural Selection ppt A

Natural Selection
Natural Selection
Objective- You should be able to:
Explain how species change overtime
 Define natural selection
 Describe Charles Darwin’s observations
 Describe the peppered moth case study

Natural Selection
Important Vocabulary
 Variation
 Adaptation
 Traits
 Survival of the Fittest
 Evolution
 Natural Selection
Natural Selection

An important process in explaining how
species change overtime.

Helps maintain healthy populations.
Charles Darwin’s Observations
1. Organisms have
the ability to
produce more
offspring than
can usually
survive.
Charles Darwin’s Observations
2. Members of the
same species
normally have slight
differences called
variations. (They
are not all
identical!)
Charles Darwin’s Observations
3. Members of a species must compete with
each other and with other species to
survive. Some organisms cannot
successfully compete for limited
resources.
Charles Darwin’s Observations
4. Some members of a species have traits
that are helpful for survival, called
adaptations. Other traits are not helpful
for survival.
Charles Darwin’s Observations
5.Those organisms
with traits that
are helpful for
survival are more
likely to survive
and reproduce
than those
without these
traits.
Charles Darwin’s Observations
6.The ability to successfully reproduce
establishes the population for the next
generation.
Survival of the Fittest
Natural selection is
sometimes referred to as
“survival of the fittest.”
 Being “fit” means that an
organism has adaptations
or traits that help it to
survive.
 More importantly, being
“fit” means that the
organisms are able to pass
their genes onto the next
generation.

Remember This!!!
Natural Selection explains how a species
may change over time.
 The change is created because of
successful reproduction.
 The organism most “fit” for an
environment is most likely to be the one
to successfully reproduce and have
offspring that mature into adults and
reproduce.

Interesting Science Fact
After talking to local farmers, Charles Darwin
discovered that the farmers had been using
artificial selection for centuries.
The farmers and ranchers never allowed their
stock to reproduce on their own.
Instead the farmers and ranchers always allowed
their best plants and animals to reproduce, but did
not allow the weak ones to reproduce.
This type of reproduction creates stronger, better
produce and livestock.
The Process of Natural Selection
Traits are passed from parents to offspring
 Those organisms that survive pass on the genes
for those traits that helped them survive.
 Organisms without those traits helpful for
survival are less likely to reproduce, so their
genes are not likely to be passed on to the next
generation.
 Organisms that can survive long enough to
reproduce are able to determine the
characteristics of the next generation.

??? Questions ???
1. How does the successful reproduction of
an organism affect the next generation?
2. How does the unsuccessful reproduction
of an organism affect the next generation?
Remember This!!!

Only those organisms able to
reproduce affect the next
generation.

Organisms that reproduce pass
their unique traits in the form of
genes on to the next generation;
therefore the next generation
inherits genes that helped the
previous generation to survive.
Natural Selection and the
Environment
If the environment stays the same, then natural
selection favors organisms with certain
adaptations.
 Organisms with these adaptations (traits)
survive and reproduce.
 Organisms that do not possess these traits may
not survive long enough to reproduce.
 The population adjusts to the environment over
time through reproduction or the failure to
reproduce.

Natural Selection and the
Environment
What happens if the environment changes?
When the environment changes (which it
almost always does), then other
adaptations might be favored.
 The traits that helped an organism survive
in one environment may not help in
another situation.

Natural Selection and the
Environment
Example: Peppered Moth Study

There are two types of peppered moths:




White
Dark
Normally, they are found in equal amounts in
forested areas of England.
During the Industrial Age, the white variety almost
became extinct in areas around the factories
because the factories produced large amounts of
black soot that covered everything for miles.
Natural Selection and the
Environment
Peppered Moth Continues…
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The dark moths were able to hide on trees and it
became hard for their predators to find them.
The white variety was very easy to see and the
predators had no trouble finding and eating them.
Therefore, only the dark moths survived long
enough to reproduce.
Natural Selection and the
Environment
And the Pepper Moth Story continues…
 As
the environment changed, it favored the
dark color over the white color.
 In areas where the environment had not
changed, both moth variations were found
with the same population numbers.
 The environment determined which variation
would survive long enough to reproduce.
 The next generations were almost exclusively
dark colored peppered moths.
??? Questions ???
3. Predict what might happen to the population of the
white and dark moths if the factories covered the
landscape with a white soot instead of a black soot.
4. Explain how a changing environment affects the
population of the organisms living in that area.
5. Compare how a changing population and a nonchanging population affect the organisms that live in
the area.
Evolution
There is much evidence that the Earth has
changed greatly over the last 4.6 billion
years. Natural selection has continually
favored the survival of organisms with
adaptations that make them suited to their
environment. However, since the
environment has changed, the species
have changed. This is referred to as
evolution.
Test Yourself: Matching Test Yourself:
Matching
________ 1. natural selection
________ 2. variation
________ 3. adaptations
________ 4. fit
________ 5. survival of the fittest
a. Traits that help an organism survive
b. An organism that has adaptations
c. A phrase to describe natural selection
d. The process that explains how species change over time
e. Differences among individuals of the same species
Test Yourself: True or False
_____ 1. In order to understand natural selection, several observations must
be understood together.
_____ 2. Organisms have the ability to produce very few offspring.
_____ 3. Organisms have the ability to produce more offspring than can
usually survive.
_____ 4. Variations are traits that help an organism survive.
_____ 5. Variations are traits that do not help an organism survive.
_____ 6. Variations are differences among members of the same species.
_____ 7. All members of the same species are identical.
_____ 8. Members of a species must compete only with organisms of other
species.
_____ 9. Members of a species must compete with members of their own
species and members of other species.
Test Yourself: True or False Cont.
______ 9. Members of a species must compete with members of their own
species and members of other species.
______ 10. Adaptations are traits that do not help an organism survive.
______ 11. Adaptations are differences among members of the same species.
______ 12. Adaptations are traits that help an organism survive.
______ 13. Organisms have an equal chance of surviving and reproducing.
______ 14. Organisms with adaptations have a better chance of surviving
and reproducing than organisms without adaptations.
______ 15. A fit organism is more likely to survive and reproduce than a less
fit organism.
______ 16. Evolution is the changing of species over time.
______ 17. Natural selection has little to do with evolution.
______ 18. Natural selection explains how species can change over time.
Test Yourself: Fill in the Blank
Natural selection
Adaptation
Reproduction
evolution
variation
compete
fit
survive
1.
______________ is the process often describe as “survival of the fittest.”
2.
3.
4.
_____________ is the changing of species over time.
Organisms must _______________ to survive.
Those organisms that are more ________ have more traits that help them
survive.
A trait that helps an organism survive is called an __________________.
Since there is ______________ in a population, not all organisms are
identical.
Some organisms are more likely to ________ because of their adaptations.
Organisms that survive long enough to _______________ can pass on the
genes for their adaptations to their offspring.
5.
6.
7.
8.
Test Yourself: Short Answer
1. What is a variation?
2. What is an adaptation? Give an example.
3. What are the five observations that explain natural selection?
4. How does natural selection change a population?
The End!!!