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Evolution Notes
Evolution
What is a Theory versus a Hypothesis?
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Hypothesis
Theory
Origins of Evolutionary Thought
1. 1785 - James Hutton: Proposed earth is shaped by geological forces taking place over extremely long periods of
time. Estimates Earth to be millions – not thousands – of years old.
2. 1798 – Thomas Malthus: Predicts that the human population will grow faster than the space and food supplies
needed to sustain it.
3. 1809 – Jean-Baptiste Lamarck: Proposed the inheritance of acquired traits. His ideas are wrong, but he is still
one of first to propose a new mechanism of how organisms change over time.
4. 1833 – Charles Lyell: Explained that processes occurring now have shaped Earth’s geological features over long
periods of time.
Charles Darwin
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Variation Adaptations -
Some of Darwin’s Most Important Insight to Natural Selection
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
Darwin noticed lots of variation of species in nature & on farms.
 This was due to Artificial selection –
After all his studies in the Galápagos Islands what was Darwin’s proposed mechanism called?
__________________________________
Darwin’s Conclusions
Evolution Occurs by Natural Selection
1. ___________________________________________
 Competition among members of a species exist for food, living space, and the other necessities of life.
 Survival of the Fittest – Individuals that are better suited to their environment – that it, with adaptations
that enable fitness – survive and reproduce more successfully; Darwin referred to this as natural
selection
 Fitness –
2. Adaptation
 Certain variations allow individuals to adapt and survive better in
their environment. Those more successful will live longer and share
those adaptations to future generations.
 Natural Section cannot be seen ______________ - only observed as
changes in a _________________ over many generations.
3. Descent with Modification
 Each
4. Variation
 Many genes have at least two genes or alleles.
Evidence of Evolution
comes primarily from these sources….
1.
2.
3.
4.
5.
Fossil record
Geographical distribution of living species
Structural similarities of related life forms
Chemical similarities in DNA
Embryology
1. Evidence of Evolution: Fossil Record
Age of Fossils
Relative Dating
 In relative dating, the age of a fossil is determined
by comparing its _______________ with that of
fossils in other layers of rock.
 Paleontologists estimate the age
Radioactive Dating
 Scientists use radioactive decay to assign _______________ ages to rocks.
 Radioactive elements decay, or break down, into nonradioactive elements at a steady
rate, which is measured in a unit called a half-life.
 A half-life is the length of time required for half of the radioactive atoms in a sample to
__________.
2. Evidence of Evolution: The Geographical Distribution of Living Species
 Similar, but unrelated species exist. Similar animals in different locations were the product of
different___________ of evolutionary descent.
3. Evidence of Evolution: Structural Similarities of Living Things
i. Homologous Structures
ii. Vestigial Structures
iii. Analogous Structures
(i) Homologous Structures of Living Organisms
 Examples:
 Homologous Structures - Structures that have
different mature forms in different organisms but
develop from the ___________ embryonic tissues.
 Same development – different
__________________.
 Provide strong evidence that all four-limbed
vertebrates have descended, with
modifications, from _________________
ancestors.
(ii) Vestigial Organs
Vestigial Organs – Organ that serves no useful ______________ in an organism; Traces of
____________________ structures.
Examples:
(iii) Analogous Structures
Analogous Structures - Structures that evolve separately to perform a _____________ function.
 Different development – same _________________.
 Provides evidence for ___________evolution because they have very similar structures even though they
were completely independently derived to fill a similar purpose.
 Examples:
4. Evidence of Evolution: Chemical Similarities
 Despite the great diversity of life on our planet, the simple language of the DNA code is the
____________ for all living things.
Amino Acid Comparison
 The more closely related two species are, the more amino acid sequence _______________ should be
seen.
5. Evidence of Evolution: Similarities in Embryology
 The early stages, or embryos, of many animals with backbones
are very ________________.
EVOLUTION OF POPULATIONS
Variation increases chance of survival

Genetic variation is studied in ___________________.
 A ________________ is a group of individuals of the same species that interbreed.
 Gene Pool – consists of _____________________, including all the different alleles, that are present in a
population.
Sources of Genetic Variation

The two main sources of genetic variation are:
1. Mutations – Any ______________ in a sequence of DNA.
 Can occur because of _________________ in the replication of DNA or as a result of radiation or
chemicals in the environment.
2. Recombination - The natural formation in offspring of genetic ___________________ not
present in parents.
 Independent assortment occurs during the production of _________________ – each
homologous pair moves independently during meiosis.
 Crossing over during meiosis further increases _________________.
Natural Selection acts of Distribution of Traits
Natural selection can affect the distributions of phenotypes in any of three ways:
1. Directional Selection
2. Stabilizing Selection
3. Disruptive Selection
1. Directional Selection
 Directional Selection – Takes place when individuals at ___________of the curve have higher fitness than
individuals in the middle or at the other end.
Sketch an example:
2. Stabilizing Selection
 Stabilizing Selection – Takes place when individuals near the _____________ of the curve
have higher fitness than individuals at either end of the curve.
Sketch an example:
3. Disruptive Selection
 Disruptive Selection – Takes place when individuals at the _______________and _______________ ends of the
curve have higher fitness than individuals near the middle.
Sketch an example:
Other Mechanisms for Evolution besides natural selection
 ______________ - the movement of alleles (genes) from one population to another.
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Affected by:
1.
2.
3.
Genetic Drift
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Genetic Drift – Random change in allele frequencies that occurs in small populations due to ___________.
 Unlike natural selection because:
 It happens by _____________ - caused by big event live overhunting or a natural
disaster (fire, landslide or lightning strike).
 Doesn’t work to produce __________________ like natural selection does.
How Does Genetic Drift Occur?
In each generation, some individuals may, just by chance, leave behind a few more descendants (and genes, of
course) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not
necessarily the healthier or “better” individuals. It happens to all populations – there’s no avoiding the vagaries
of chance.
Evolution vs. Genetic Equilibrium

Are there any conditions under which evolution will not occur?
Hardy-Weinberg Principle
Hardy Weinberg Equation: p2 + 2pq + q2 = 1
p+q=1
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Five conditions are required to maintain genetic equilibrium from generation to generation:
1. There must be random mating.
2. The population must be very large.
3. There can be no movement into or out of the population.
4. There can be no mutations.
5. There can be no natural selection.
The Hardy-Weinberg Equation
p2 = Frequency of AA
2pq = Frequency of Aa
q2= Frequency of aa
p = Frequency of A
q = Frequency of a
For example: If the frequency of two alleles in a gene pool is 90% A , and 10% a, what is the frequency of
individuals in the population with the genotype Aa?
Solve:
The Process of Speciation

Speciation – formation of a new species (Group of organisms that breed with one another and produce
___________ offspring)
Speciation & Reproductive Isolation
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The gene pools of two populations must become _______________ for them to become new species.
As new species evolve, populations become reproductively isolated from each other.
Reproductive Isolation - When the members of two populations ______________ interbreed and produce fertile
offspring.
Reproductive Isolation
Reproductive isolation can occur in a variety of ways, including:
1. Behavioral Isolation
2. Geographic Isolation
3. Temporal Isolation
1. Behavioral Isolation
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 Example: mating courtship songs of Eastern and Western Meadowlarks
2. Geographic Isolation
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 Example: The Abert & Kaibab Squirrel seperated with Colorado River
3. Temporal Isolation
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Example: Orchids in rainforest polinating on seperate days
Patterns of Evolution
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Some large-scale evolutionary patterns and processes that occur over _______ periods of time are:
1. Extinction
4. Gradualism
2. Convergent Evolution
5. Punctuated Equilibrium
3. Divergent Evolution
6. Coevolution
(1.) Extinction
 When does an animal go extinct: Most likely when: __________________________ but also when
______________________________________.
(2.) Convergent Evolution
Convergent Evolution – Process by which unrelated organisms come to
_________________ one another.
(3.) Divergent Evolution
Divergent Evolution – The process of two or more related species becoming more
and more _________________.
(4.) & (5.) Gradualism vs. Punctuated Equilibrium
 How quickly does evolution occur?
 Gradualism – Long time with ______________ change.
 Punctuated Equilibrium - Long, stable periods interrupted by brief periods of more _______________
change.
 Think about this…How did a tiger get its stripes? Gradually or with a huge, quick change?
Gradualism
(6.) Coevolution -
Punctuated Equilibrium
Common Misconceptions
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Humans did not come from monkeys. Instead, humans
and primates share a common _______________.
Darwin is not the only evolutionary theorist. Darwin
utilized evidence from other evolutionists to draw
his _______________.
Evolution does not happen quickly – it occurs over
____________________ of time.
Change does not occur at the individual level – it occurs in
___________________.
Cladogram
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Cladogram – Diagram that shows the evolutionary relationships among a group of organisms.
 Is constructed using derived characters, which are characteristics that appear in recent parts of a lineage
but not in older members.
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Phylogeny - Study of evolutionary relationships among organisms.
 Biologists now group
organisms into categories
that represent lines of
evolutionary descent, or
phylogeny, not just physical
similarities.