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Chapter 15 Evolution
15-1 Darwin’s Theory of Natural Selection
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Charles Darwin1809-1882 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 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 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. Thomas Malthus: human species grows faster
than food supply; competition for food, space, mates, shelter; struggle to survive
2. Pigeon breeding: found individual variation, could breed desirable traits into a population (artificial selection)
3. His 13 children: found individual variation
4. 22 years of study after HMS Beagle to formulate his ideas
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Natural Selection 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)B. Individuals in a
population have variations
D. Overtime, individuals with helpful variations make up more and more of the population
A. Organisms produce more offspring than can survive
C. Individuals with certain helpful variations survive in their environment, reproduce, and pass helpful variation on to offspring
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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.
15.1 Darwin’s Theory of Natural Selection
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Origin of Species by Means of Natural
SelectionBy Charles Darwin
Published in 1859
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Other’s Ideas on Evolution 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 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. Fossils2. Anatomy3. Embryology4. Biochemistry5. Geographic Distribution6. Adaptations
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1. Fossils Record of early life Ancestors of whales
were dog sized land animals
Record is incomplete
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2. AnatomyA. 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. AnatomyB. 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 Embryo: earliest stage
of growth and development
Similarities for all vertebrates Tail Gill slits
Suggest a common ancestor
Gill slits
tail
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4. Biochemistry Comparison of DNA, RNA, and/or proteins Newest RNA evidence is that there are
three types (Domains) of organismsArchae
Prokaryote
Archaebacteria
Eubacteria
Prokaryote
Eubacteria
Eukarya
Eukaryote
Protista
Fungi
Plants
AnimalsAncestral Prokaryote
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5. Geographic Distribution 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. AdaptationsAny variation that helps an organisms’ chance for survival
A. 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. AdaptationsA. Structural Adaptations
camouflage: enables species to blend in with surroundings so that they are not easily found by predators
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6. AdaptationsB. 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 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 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
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
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
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 Allelic frequency: % of any specific allele
= Number of specific allele
Total number of alleles
Can change over time or stay the same
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Hardy-Weinberg Principle Hardy-Weinberg principle states that when
allelic frequencies remain constant, a population is in genetic equilibrium.
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Hardy-Weinberg Principle Equation: p2 + 2pq + q2 = 1
and 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 Frequency of alleles stays the same over
many generations
Not evolving
Phenotypes remain the same too
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Changes in Genetic Equilibrium
1. Mutations2. Genetic Drift3. Gene Flow4. Nonrandom mating5. Natural Selection
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1. Mutations 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 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 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 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 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 Four Types of Natural Selection that act
on variationA. Stabilizing Selection
B. Directional Selection
C. Disruptive Selection
D. Sexual Selection
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Stabilizing Selection 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 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 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 Species: group of organisms that look alike
and can breed to produce fertile offspring Speciation: process of evolution of new
species occurs when members of similar populations no
longer interbreed to produce fertile offspring in their natural environment
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Reproductive Isolation 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 Postzygotic isolation
occurs when fertilization has occurred but a hybrid offspring cannot develop or reproduce.
Prevents offspring survival or reproduction.
Fertilization is possible between a tiger and a lion but the offspring is sterile.
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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 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 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 Adaptative radiation::
one ancestral species evolves into many species to fit diverse habitats
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Convergent Evolution 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 Gradualism: species
originate through gradual, slow change Evolution of the horse
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Two Theories of Speciation Punctuated
Equilibrium: speciation relatively quickly (10, 000 years) with long periods of no evolution (genetic equilibrium)
High environmental change Evolution of elephants