Transcript How does evolution occur by natural selection?

Aim: How does evolution occur by
natural selection?
Ice Age
• “Survival of the Fittest”
How Does Evolution Occur?
• EVOLUTION is a slow change in a
species over time.
• Evolution occurs by a process called
NATURAL SELECTION.
Read this cartoon, what do you think NATURAL SELECTION is?
Lamarck’s theory of Evolution
Lamarck believed that by the selective USE or
DISUSE of characteristics, organisms lost or
acquired certain traits that would be passed
on to the offspring.
Darwin
• Considered the “father” of evolution.
• Charles Darwin traveled to the Galapagos
island, an uninhabited environment, where he
studied evolution (Darwin’s Finches)
Natural Selection
• NATURAL SELECTION is the KEY to
Darwin’s theory.
• According to this theory, evolution is
controlled by NATURE. Only the
organisms that are able to SURVIVE and
REPRODUCE will pass on their genes.
Natural Selection vs.
Artificial Selection
People select the desirable
traits that will appear in the
Offspring.
Environment selects
the desirable traits
that will appear in
the offspring.
Conditions that are vital to
Evolution:
• Overproduction
• Variation
• Struggle For Survival
• Best Adapted To Survive
• Darwin did NOT have knowledge of the
genetic basis of inheritance
Overproduction
• More offspring are produced than can
survive (most die young).
Overproduction leads to
COMPETITION!!
• Organisms
such as bacteria, fish, insects,
and rabbits have high reproductive rates
because the chance that their young will
survive is minimal.
Variation
• Variation: Individuals have differences in
their appearance, structure, or genes.
• Source of variation:
+
=
– Sexual Reproduction (sperm + egg)
– Meiosis (Indp. Ass. & Crossing Over)
– Mutation (Change in DNA)
Mutations
• Mutations change the base
sequence of DNA.
• Most mutations are
HARMFUL, but some can help
the organism SURVIVE.
Adaptive Value
• Adaptive Value: a change that produces a
trait that helps an organism survive.
– Ex: Camouflage
• If all the members of a species were the
same then an environmental change
would wipe out the entire species.
VARIATION increases the chance that
some members of a species will survive.
Best Adapted To Survive
• The ENVIRONMENT chooses which traits
have adaptive value.
• An individual that has traits favorable in a
certain environment will live to reproduce
and pass on those traits, others will die
out.
Struggle For Survival
• “Survival of the fittest”
• Only those BEST suited will survive
because of competition for finite (limited)
resources (oxygen, water, food, and
shelter)
Conditions that lead to Evolution:
Patterns Of Change
•
Species with SHORT reproductive cycles that
produce MANY offspring tend to evolve more
quickly than species with LONG life spans and
FEW offspring.
•
Types:
1) Gradualism – evolution occurs steadily
through time (Slow & Continuous) .
2) Punctuated Equilibrium- species stay the
same for long periods of time and then change
rapidly.
No Change
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No Change
-----------
No Change
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Examples of Natural Selection
• Industrial Melanism
• Antibiotic / Pesticide Resistance
Antibiotic Resistance
Ex: Punctuated Equlibrium
• When bacteria are exposed to an antibiotic
there is a chance that a few will have a
gene that makes them resistant.
• The bacteria WITHOUT the resistance will
be killed, while those that are RESISTANT
will survive and pass on their genes for
antibiotic resistance. The antibiotic is the selecting agent
Resistant
Bacteria
Antibiotic X
Why should we be concerned about
antibiotic overuse?
Why does evolution matter now?
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
Pesticide Resistance
Insect A- Has resistance
to A
Insect B- Has resistance
to B
Insect C- Has resistance
to C
• What would happen to
the population if
insecticide A were
sprayed on the field?
The pesticide selected
only those flies that
were resistant to
pesticide A to survive.
In other words, some
insects had a
MUTATION that
allowed them to
survive the presence of
the insecticide. These
insects were then able
to reproduce and pass
their mutation into the
next generation.
Extinction
• The disappearance of an entire species
(ex. Dinosaurs)
• It can be caused by temperature changes,
pollution, or landscape changes.