Transcript Ch. 15 The Theory of Evolution

Chapter 15
Evolution
15-1 Darwin’s Theory of Natural
Selection
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Charles Darwin
1809-1882
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As a boy liked nature
study
Flunked out of med
school
Theology degree from
Christ College,
Cambridge
Became minister Church
of England
1831 job as naturalist on
HMS Beagle
5 year world voyage to
chart coasts
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Unique Galapagos Islands
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1000 km off west
coast of South
America
Unique species
animals, similar to
S.A. but not exact
Unique species
animals on each
island, similar to S.A.
and each other but not
exact
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Darwin’s Finches
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Especially interesting
is the number and
variety of these birds
Each island had own
variety dependent on
the food source
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Darwin’s Influenced by:
1.
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Thomas Malthus: human species grows faster
than food supply; competition for food, space,
mates, shelter; struggle to survive
Pigeon breeding: found individual variation,
could breed desirable traits into a population
(artificial selection)
His 13 children: found individual variation
22 years of study after HMS Beagle to formulate
his ideas
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Natural Selection
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Is a mechanism for change in a population
Groups NOT INDIVIDUALS evolve
Occurs when organisms with certain
variations survive, reproduce, and pass
their variations onto the next generation
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Theory of Natural Selection (old)
A.
C.
Organisms produce
more offspring than
can survive
Individuals with
certain helpful
variations survive in
their environment,
reproduce, and pass
helpful variation on
to offspring
Individuals in a
population have
variations
D. Overtime, individuals
with helpful variations
make up more and
more of the
population
B.
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15.1 Darwin’s Theory of Natural Selection
Natural Selection (NEW)
 Individuals in a population show variations.
 Variations can be inherited.
 Organisms have more offspring than can survive
on available resources.
 Variations that increase reproductive success
will have a greater chance of being passed on.
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Origin of Species by
Means of Natural
Selection
By Charles Darwin
Published in 1859
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Other’s Ideas on Evolution
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Alfred Wallace: had same ideas about
natural selection as Darwin, but Darwin
published first (both presented their ideas
in 1858 at a scientific meeting)
Genetics has changed ideas about
evolution; now we measure frequency of
allele in gene pool
Gene pool: all the genes of a population
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Chapter 15
Evolution
15-2 Evidence of Evolution
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Evolution and Natural Selection
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Darwin’s theory of natural selection is not
synonymous with evolution.
It is a means of explaining how evolution
works.
The theory of evolution states that all
organisms on Earth are related; share a
common ancestor.
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Evidence for Evolution
1.
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6.
Fossils
Anatomy
Embryology
Biochemistry
Geographic Distribution
Adaptations
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1. Fossils
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Record of early life
Ancestors of whales
were dog sized land
animals
Record is incomplete
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2. Anatomy
A.
Homologous structures: similar arrangement or
function or both
Evidence that organisms evolved from a
common ancestor
(Analogous structures: body parts do not have
common evolutionary origin but have similar
function)
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Homologous Structures
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2. Anatomy
B. Vestigial structures: body part that has no
function today but probably did in ancestor
eyes of blind mole rat
eyes of blind cave fish
wings of flightless birds
human appendix, little toe, muscles to
move ears…
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3. Embryology
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Embryo: earliest stage
of growth and
development
Similarities for all
vertebrates
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Gill slits
tail
Tail
Gill slits
Suggest a common
ancestor
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4. Biochemistry
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Comparison of DNA, RNA, and/or proteins
Newest RNA evidence is that there are
three types (Domains) of organisms
Archae
Eubacteria
Eukarya
Prokaryote
Prokaryote
Eukaryote
Archaebacteria
Eubacteria
Protista
Fungi
Plants
Ancestral Prokaryote
Animals
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5. Geographic Distribution
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The distribution of plants and animals that
Darwin saw first suggested evolution to
Darwin.
Rabbit
Mara
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5. Geographic Distribution
 Patterns of migration were critical to Darwin
when he was developing his theory.
 Evolution is intimately linked with climate
and geological forces.
 Biogeography is the branch of science that
studies the world distribution of organisms.
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6. Adaptations
A.
Any variation that helps an organisms’
chance for survival
Structural Adaptations: can take millions
of years
mimicry: enables one species to resemble
another species;
harmless look like harmful
all harmful look alike
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6. Adaptations
A.
Structural Adaptations
camouflage: enables species to blend in
with surroundings so that they are not
easily found by predators
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6. Adaptations
B. Physiological adaptations: takes shorter
time
Changes in organisms metabolic processes
(function)
antibiotic resistant bacteria
pesticide resistant insects (head lice)
herbicide resistant weeds
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6. Adaptations
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Not all features of an organisms are
necessarily adaptive.
Example: helplessness of human babies.
Human babies are born at a much earlier
stage of development than other mammals.
This is probably not an adaptation but a
consequence of the larger brains and
upright posture of humans.
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Chapter 15
Evolution
15-3 Shaping Evolutionary Theory
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Population Genetics and Evolution
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Darwin knew NOTHING about genes,
never read the work of Mendel even though
they lived about the same time
Darwin: 1809-1882
Mendel: 1822-1884
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Populations NOT individuals evolve
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Individuals can’t change their genes, can’t
change their genotypes and can’t change
their phenotypes or trait
Individuals can only respond to their
environments as their genes allow
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Natural Selection acts on Phenotypes
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If an individual has a phenotype that is
poorly suited to their environment, the
individual organism may not survive
and/or may not reproduce to pass their
genes on to the next generation
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Natural Selection acts on Phenotypes
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Each member of a population has the
genes that characterize the traits of the
species
All the genes (and alleles) of individuals
make up the gene pool of the population
Evolution occurs as a population’s genes
and their frequencies change over time
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Allelic Frequency
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Allelic frequency: % of any specific allele
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= Number of specific allele
Total number of alleles
Can change over time or stay the same
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Hardy-Weinberg Principle
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Hardy-Weinberg principle states that when
allelic frequencies remain constant, a
population is in genetic equilibrium.
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Hardy-Weinberg Principle
 Equation:
and
p2 + 2pq + q2 = 1
p+q=1
 This equation allows us to determine the
equilibrium frequency of each genotype in the
population.
 Homozygous dominant (p2)
 Heterozygous (2pq)
 Homozygous recessive (q2)
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Genetic Equilibrium
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Frequency of alleles stays the same over
many generations
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Not evolving
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Phenotypes remain the same too
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Changes in Genetic Equilibrium
1.
2.
3.
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5.
Mutations
Genetic Drift
Gene Flow
Nonrandom mating
Natural Selection
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1. Mutations
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Caused by environmental factors like
radiation and chemicals
Caused by random chance
Some mutations are lethal and quickly
eliminated
Some mutations are helpful (useful) and
new allele or gene becomes part of the
population’s gene pool
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2. Genetic Drift
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Alteration of allelic frequency by chance events
Small populations that become isolated by natural
events can evolve differently
Bottleneck effect: disasters such as earthquakes,
floods kill victims unselectively
Founder effect: few individuals colonize an
isolated area (Darwin’s finches)
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3. Gene Flow
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Movement of individuals into or out of a
population
When individuals immigrate or emigrate
their genes go with them
Example: westward expansion in the US
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4. Nonrandom mating
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Usually organism
mate with those in
close proximity. (May
result in inbreeding).
Usually organisms
mate with those of the
same or similar
phenotype.
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5. Natural Selection
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Acts on variation
Some variations increase or decrease an
organism’s chance for survival
Variation can be inherited and are
controlled by alleles
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5. Natural Selection
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Four Types of Natural Selection that act
on variation
A.
B.
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D.
Stabilizing Selection
Directional Selection
Disruptive Selection
Sexual Selection
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Stabilizing Selection
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Favors average
Reduces variation
Example: Large
spiders easy to see
and be eaten while
small spiders have a
hard time getting food
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Directional Selection
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Favors one extreme
Can lead to rapid
evolution
Example: Over time
there were more and
more darker colored
Peppered Moths in the
industrial area of
England in the 1800’s
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Disruptive Selection
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Both extremes are
favored
Average (mean)
disfavored
Leads to the evolution
of two species
Example: Light yellow
butterfly overtime
becomes either nearly
white or orange
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Sexual Selection
Sexual selection operates in populations
where males and females differ significantly
in appearance.
 Qualities of sexual attractiveness appear to
be the opposite of qualities that might
enhance survival.
 Example: tail of mail peacocks, while
beautiful, makes the organism a greater
target for predators.
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The Evolution of Species
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Species: group of organisms that look alike
and can breed to produce fertile offspring
Speciation: process of evolution of new
species
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occurs when members of similar populations no
longer interbreed to produce fertile offspring in
their natural environment
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Reproductive Isolation
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Prezygotic isolation mechanisms make
fertilization unlikely.
Can’t mate to produce fertile offspring
Genetic differences: genetic material too
different so no fertilization results
Behavioral differences: mate at different
times of day or at different season; different
“courting” rituals
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Reproductive Isolation
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Fertilization is possible
between a tiger and a lion
but the offspring is sterile.
Postzygotic isolation
occurs when
fertilization has
occurred but a hybrid
offspring cannot
develop or reproduce.
Prevents offspring
survival or
reproduction.
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Speciation
 In allopatric speciation a physical barrier
divides one population into two or more
populations; geographic isolation.
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Geographic Isolation
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Islands, lava flows, rock slides, rivers
changing course
Populations become physically separated
Over time each small population adapt
differently to environments and have
different gene pool
When gene pool becomes too different
then two species exist
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Speciation
 In
sympatric
speciation a
species evolves
into a new
species without
a physical
barrier.
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Patterns of Evolution
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Divergent Evolution (adaptive radiation):
become different
Convergent Evolution: become the same
Coevolution: the evolution of one species
effects the evolution of another species
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Divergent Evolution
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Adaptative radiation::
one ancestral species
evolves into many
species to fit diverse
habitats
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Convergent Evolution
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Distantly related
organisms evolve similar
traits
Occurs when unrelated
species occupy similar
environments in different
parts of the world
African and American
cactus
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Coevolution
 The relationship
between two species
might be so close that
the evolution of one
species affects the
evolution of the other
species.
 Example: specialized
mouth parts
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Two Theories of Speciation
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Gradualism: species
originate through
gradual, slow change
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Evolution of the horse
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Two Theories of Speciation
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Punctuated
Equilibrium: speciation
relatively quickly (10,
000 years) with long
periods of no evolution
(genetic equilibrium)
High environmental
change
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Evolution of elephants
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