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Evolution
Chapters 16,17,19.2
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Voyage of the Beagle-(1831-1836)
Charles Darwin (1809 - 1882)

While ship was docked, Darwin would make observations
about the plant and animal life
 Kept

a journal of his observations.
Noted 3 distinctive patterns of Biological Diversity:
 1.
Species vary globally
 2. Species vary locally
 3. Species vary over time

The Galapagos Islands – close together, but had different
environments and different animals and plants

tortoise shell and finch beak
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Charles Darwin Observations
Finch Beak
Tortoise Shell
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Voyage of the Beagle-(1831-1836)
Charles Darwin (1809 - 1882)

Living Organisms and Fossils
 Darwin
collected fossils, once living organisms, and noted that
some fossils of extinct animals were similar to some living
species, while others were different.
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Contributions to Theories of
Evolution
Evolution – a change over a long period of time.
Theory – a well supported, testable explanation of
phenomena
Geology and Fossils
 Lyell
(1785) & Hutton (1833) helped shape Darwin’s
research
 Helped scientists recognize that earth is millions of
years old, and the processes that changed Earth in
the past are the same processes that operate in the
present
 Uniformitarianism:

Processes that change Earth in past are same as today
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Contributions to Theories of
Evolution
Living Organisms Change

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
Lamarck (1809)
Proposed that organisms could change during their
lifetime by selectively using or not using various parts of
their bodies.
Also suggested that individuals could pass these acquired
traits on to their offspring, enabling species to change
over time.
Stated organisms have an inborn drive to become
perfect.
Lamarck incorrect:


Organisms do not have a tendency towards perfection
Acquired traits can not be passed on to offspring
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Contributions to Theories of
Evolution
Population Growth
 Malthus
(1798)
 If the human population continued to grow
unchecked, sooner or later there would be
insufficient living space and food for everyone.
 More births than deaths.
 Applied to plants and animals more than to humans
 Human populations limited by:
 Limited resources
 Adverse conditions
 Artificial Selection
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Charles Darwin
“On The Origin of Species”
 Prompted
to publish by Alfred Russel
Wallace
 Published a short essay in 1858
 Darwin published in 1859
 Proposed the mechanism for evolution
 Evolution has been taking place for
millions of years- and continues in all
living things
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Inherited Variation and
Artificial Selection
 In
artificial selection, nature provides the
variation, and humans select those
variations that they found useful
 Selectively breeding only the largest hogs,
fastest horses, or cows that produce most
milk.
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Evolution by Natural Selection
1. The struggle for existence

Members of each species compete regularly to obtain
food, living space and other necessities of life.
2. Variation and Adaptation

Result of adaptations- inherited characteristic that increases
an organism’s chance of survival
3. Survival of the fittest – how well you can survive and
reproduce.
4. Natural selection

Over time, natural selection results in changes in inherited
characteristics of a population
5. Descent with modification

Todays organisms look different than their ancestors
because the changes are inherited.
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Adaptations
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Natural Selection
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Evidence of Evolution
1. Fossil Record


Remains of ancient life
Different layers of rock formed at different times
 Trilobite
2. Biogeography = Geographic Distribution of living
species


Existence of similar but unrelated living organisms.
Island Finches- descendants with modifications from
common mainland ancestor.
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Evidence of Evolution
3. Homologous body structures


Structures that are shared by related species and that
have been inherited from a common ancestor.
Structures that develop from same embryonic tissue.
 Same
structure but different function!
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Evidence of Evolution
4. Analogous structures – Body parts that share a
common function, but not structure.
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Evidence of Evolution
5. Vestigial Structures – inherited from ancestors but
have lost much or all of their original function due to
different selection pressures acting on the
descendant.
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Evidence of Evolution
6. Embryology – Similar patterns of embryological
development provide further evidence that
organisms have descended from a common
ancestor.
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Summary of Darwin
 There
is variation in organisms (which is heritable).
 Organisms produce more offspring than can
survive.
 There is competition for limited resources.
 Natural selection is always taking place.(Those
that are most “fit” survive to reproduce, and
those that are not, die.
 Species living today are descended, with
modification, from ancestor species.
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Chapter 17
Evolution of Populations
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Evolution of Populations
 Combined
the work of Mendel and Charles
Darwin in the 1930’s
 Populations, not individual organisms,
evolve.
 Fitness is an organism’s success in passing
genes to next generation.
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Evolution is a change in the
relative frequency in a gene pool.
 Gene
pool: all genes including the different alleles
that are present in a population
 Allele frequency: Number of times that the allele
occurs in a gene pool, compared to the total
number of alleles in that pool for the same gene.
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Sources of genetic Variation
1. Mutations
 Any change in the sequence of DNA of a cell.
 Could be a gene change or a chromosomal
change.
 Most mutations are neutral.
2. Genetic Recombination in Sexual Reproduction
 Individuals are not exact copies of parents.
 Crossing over and independent assortment
during meiosis occurs creating more variety
among gametes.
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Single and Polygenic Genes
 Single
gene trait- Controlled by one gene that has
two alleles
 Polygenic trait- controlled by two or more genes

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Height
Skin color
Eye color
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Natural Selection on Single Gene Traits
 Lead
to changes in allele frequency and thus
changes in phenotypic frequencies hence
evolution.

A brown lizard experiences a mutation that produces
red and black forms
 What
 Why
would happen?
did the black lizard grow in population size?
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Natural Selection on Polygenic traits.
 More
complex then single-gene traits
 Phenotypes can be affected in three ways:
 1. Directional selection

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Individuals at one end of the curve have higher fitness
Some individuals fail to survive/reproduce
Bell curve will shift in either direction depending on the
favorite.
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Natural Selection on Polygenic traits.
 2.



Stabilizing selection
Individuals near the center of the
curve have higher fitness
Bell curve doesn’t move, but
narrows
Birth Weight
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Natural Selection on Polygenic traits.
 3.


Disruptive selection
When individuals at both ends of the curve are fitter
than individuals in the middle.
Bell curve dips in the center, acts against the
intermediate type.
 Bird
Seed
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Natural Selection on Polygenic traits.
Genetic Drift
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 Natural
selection is not the only source of evolution
 Genetic Drift- changes in the allele frequency due
to a random event or by chance.


Only in small populations
2 types
1. Bottleneck effect – a natural disaster or disease can
dramatically reduce the size of a population
2. Founder effect – the allele frequencies change as a
result of the migration of a small subgroup of a population.
- Colonizing a new habitat
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Hardy-Weinberg equilibrium

Genetic Equilibrium - allele frequencies in its gene pool
do not change.
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If allele frequency remains same: population won’t evolve
Hardy-Weinberg predicts 5 Conditions that can disturb
genetic equilibrium and cause evolution to occur:
1. Small population size - genetic drift occurs, a small
population will be impacted over a large population.
2. Non-Random mating - selection of mates regardless
of their traits.
3. Mutations – introduce new alleles into the gene pool.
4. Immigration or emigration – introduce new alleles or
remove alleles from a population.
5. Natural selection – different genotypes and
phenotypes have a different fitness.
5 fingers of evolution video
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Formation of Species: Speciation

Species – can interbreed and produce fertile offspring.

When the members of two populations cannot interbreed and
produce fertile offspring
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Example: Mule Horse + Donkey
Speciation – the formation of a new species
Reproductive Isolation – A population has split into two groups,
and the changes in one of those gene pools cannot spread to
the other and the two groups can no longer breed.
3 Mechanisms for Reproductive Isolation to occur:
1. Behavioral Isolation - Can interbreed, but have
developed different mating rituals
2. Geographic isolation - Separated by geographic
barriers such as rivers, mountains, lakes, etc.
3. Temporal Isolation - Reproduce at different times
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Speciation in Darwin’s Finches
1. Founders Effect

Birds arrive to islands from
mainland
2. Geographic Isolation

On different islands
3. Changes in gene pool

Overtime, each finch became
adapted to local environment
4. Behavioral reproductive isolation

Don’t have desirable traits or
courtship rituals to other finches.
5. Competition & Continued
Evolution

Natural selection
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Ch 19.2
Patterns of Evolution
1. Extinction
 99% of all species are
extinct. Why?
2. Gradualism

A slow, steady change in a
particular line of descent.
3. Punctuated Equilibrium
 Involves stable periods
interrupted by rapid
changes.
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Patterns of Evolution
3. Adaptive Radiation
 The process by which a
single species or a small
group of species evolve
over a short time into
several different forms that
live in different ways.
4. Convergent Evolution
 Evolution produces similar
structures and
characteristics in distantly
related organisms.
 Unrelated organisms
resemble each other

Examples: Penguin (Bird),
Dolphin (Mammal), Shark
(Fish).
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Patterns of evolution
5. Coevolution
 Two specifies evolve together in response to
changes in each other over time.
 The evolution of organisms that are ecologically
connected to each other and can’t survive without
each other.
 As one evolves, the other will evolve with it
 Acacia tree and fire ants
 Bees Pollinate the flowers