Download Natural Selection - Solon City Schools

Darwin vs. Lamarck
Lamarck
Darwin
Jean-Baptiste LaMarck
• French, Early 1800’s
Theory of
Inheritance of
Acquired Characteristics
• Two main points…
1. Principle of Use & Disuse:
•
Most used body structures develop, unused
structures waste away
2. Inheritance of Acquired
Characteristics:
•
Once the structure is modified, the new
trait can be inherited (passed to
offspring)
Explain the picture below as if
you were LaMarck…
Why we don’t believe him…
• Experiments: show that changes
that occur in an animal’s life are not passed on
to its offspring
• Genetics: Gregor Mendel discovered
that traits are passed down through GENES
(which aren’t affected by the outside world in
that way)
Charles Darwin
“The Father of Evolution”
• 1831- sailed on the HMS Beagle to
the Galapagos Islands.
• Studied many species of finches.
• Published book in 1845:
• “On the Origin of Species by
Natural Selection”
Darwin’s Theory of
Evolution
(don’t copy all this it’s on your handout) 
“Natural Selection”
“Survival of the Fittest”
Natural Selection
• Process by which favorable heritable
traits become more common in
successive generations of a population
of reproducing organisms, and
unfavorable heritable traits become less
common.
Natural Selection
Four main points…
• 1. More organisms are produced than
can survive…leads to COMPETITION
OVER RESOURCES
• Ex’s of resources…
•
•
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Water
Food
Habitat
Mates
2. Individuals within a population
vary, and some of these traits are
heritable.
3. Some variations are
FAVORABLE (increase chances for
survival/ reproduction)
• Male vs. Female
Cardinals
• Male color attracts
female=
reproductive
advantage
4. Better adapted individuals
survive and reproduce
• These are the individuals that will pass
on their genes to the next generation.
• This can change the GENE POOL:
• Includes all the genes of every
reproductive member of a population
What The theory of evolution IS
NOT!!!
• It does NOT occur in
INDIVIDUALS…only populations!
• It does NOT happen quickly…the Earth
has a Looooooong history!
• It does NOT explain how life came to be
on Earth, just how it evolved after it was
here.
• It does NOT have any driving force
except the competition for limited
resources.
Species…
• A group of organisms that are
genetically similar enough to produce
healthy, fertile offspring.
Darwin’s Finches…p 558
• Illustrate SPECIATION: when a
species breaks into two (or more)
• The organisms in the two species can no
longer…
• INTERBREED
• What could cause this to happen?
• Geographic barriers
• Occupy a new niche/habitat
• Reproductive Isolation-
Natural selection
What would Darwin say to
explain why giraffe’s have such
long necks?
• See pg. 553
•
Types of Natural Selection
• Stabilizing Selection
• Occurs when natural selection works
against the 2 extremes of a trait to make
the population more uniform.
Stabilizing Selection
Stabilizing Selection
• Birth weight of babies
• Babies that are too big or too small might
have less chance of being born healthy.
Natural Selection
• Directional Selection
• Selects the extreme of 1 trait.
Directional Selection
• In a population of plants, flowers with
the brightest color might be selected for
in order to attract the most pollinators.
Natural Selection
• Disruptive Selection
• Selects against the mean of the population.
Disruptive Selection
• If there are 2 types of seeds to eat for a
population of birds, either of 2 different beak
shapes (sharp or blunt) might be selected for,
but a beak that’s the average of the 2 shapes
might not be particularly good at eating either
seed, so it would be selected against.
Evolution- “Change Over Time”
• All of the changes that have occurred in living things
since the beginning of life on Earth
History of the Earth
4.5 bya
3.5 bya
2.1 bya
• Earth forms
st
•1
PROKARYOTES
• 1st EUKARYOTES
700 million years ago…
• Evolution occurs over MANY
generations
• Evolution occurs within POPULATIONS
(NOT individuals)
• Evolution involves genetic changes in a
SPECIES
• (Members of a species interbreed to
produce healthy, fertile offspring)
The process by which favorable heritable traits
become more common in successive
generations of a population of reproducing
organisms, and unfavorable heritable traits
become less common.
1.
2.
3.
4.
Evolution
Natural Selection
Adaptations
Genetic
Recombination
Consider, for example, a population of shellfish called limpets. The shell color of
these limpets ranges from white, to tan, to dark brown. As adults, limpets live
attached to rocks. On light-colored rocks, white-shelled limpets have an
advantage because their bird predators cannot easily see them. On darkcolored rocks, dark-colored limpets have the advantage because they are
camouflaged. On the other hand, birds easily see tan-colored limpets on either
the light or dark backgrounds. These tan-colored limpets will be at a selection
disadvantage and will most likely become extinct from the population. This type
of natural selection is known as:
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1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
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Consider a population of spiders in which the average
size is a survival advantage. Predators in the area might
easily see and capture spiders that are larger than
average. However, small spiders may find it difficult to
find food. Therefore, in this environment, average-sized
spiders are more likely to survive. This type of natural
selection is known as:
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1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
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Imagine a population of woodpeckers pecking holes in trees to
feed on the insects living under the bark. Suppose that a species
of insect that lives deep in tree tissues invades the trees in a
woodpecker population’s territory. Only woodpeckers with long
beaks could feed on that insect. Therefore, the long-beaked
woodpeckers in the population would have a selective advantage
over woodpeckers with very short or average-sized beaks. This
type of natural selection is known as:
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1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
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The smallest unit that can evolve
is:
A genome
An individual
A community
A population
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Genetic Equilibrium
• Not all populations are in an active state
of “natural selection”
• GENETIC EQUILIBRIUM
• This means that there is no change in the
gene pool = no evolution
Genetic Equilibrium
• 1.) Population size is large
• 2.) No gene flow in the population
• No new organisms introducing more alleles
• 3.) No mutations
• 4.) No environmental factors causing
natural selection
• No trait is favorable over another
• 5.) Random mating must occur
So what factors exist to make
a population evolve?
• It must NOT be in GENETIC
EQUILIBRIUM
• Something that knocks the population
out of genetic equilibrium is called a
MECHANISM OF EVOLUTION
Mechanisms of Evolution
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1.
2.
3.
4.
5.
Natural Selection
Sexual Selection / Non-random mating
Mutation
Gene Flow (Migration)
Genetic Drift- reduces population size
• Bottleneck effect
• Founder effect
How does reproduction affect
natural selection
• Discuss with your partner:
• How would a population that
reproduces asexually “evolve”
differently than one that
reproduces sexually? WHY?
A note on sexual reproduction…
• Sexual reproduction can produce many
different phenotypes
• Sexual reproduction does NOT change
relative frequency of alleles in a
population
• Think about shuffling a deck of cards
• Shuffling cards gives you different hands
• It won’t change the number of kings in a
deck