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Evolution
Pre-AP Biology
Charles Darwin
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Known as the Father of Evolution
Wrote book On the Origin of Species
Sailed the world on a ship called the
Beagle
Darwin
Evidence for Evolution
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The fossil record – show biodiversity, mass
extinctions and episodic speciation
Geographic Distribution of Living Species –
shows similarities among species living on
different continents
Homologous Body Structures – structures that
have different mature forms but come from the
same embryonic tissue.
Similarities in Early Development – embryos of
many vertebrates are very similar.
Embryology
Fossils and Evolution
Natural Selection
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Over time natural selection results in
changes in the inherited characteristics of
a population. These changes increase a
species’ fitness (ability to survive and
reproduce) in its environment.
Natural Selection causes struggles for
existence and survival of the fittest.
Natural Selection act on the phenotype
rather than the genotype of a species.
Gene Pools
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A gene pool is the combined genetic information of
all the members of a particular population.
A gene pool typically has two or more alleles for a
given trait.
Homozygous lethal traits can be carried by
heterozygous individuals and thus remain in a gene
pool.
Relative Frequency is the number of times an allele
occurs in a gene pool compared with the number of
times other alleles occur.
Microevolution is evolution on its smallest scale;
change in the relative frequencies of alleles in a
population over generations.
What are gene pools?
Sources of Variation
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Two main sources are mutations and gene
shuffling.
Mutations – changes in DNA sequence.
These may or may not affect an
organisms fitness.
Gene shuffling – is the random shuffling of
genes caused by sexual reproduction.
Natural Selection on Single-Gene
Traits
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Natural selection on single-gene traits can
lead to changes in allele frequencies and
thus to evolution.
If the change is beneficial to the
organism, the change may cause the
original form to fade out and the newer
organisms to be more fit and take over.
Natural Selection on Polygenic
Traits
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Natural Selection can affect the
distribution of phenotypes in a population
in any of three ways: directional,
disruptive and stabilizing.
The 3 selections
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Directional
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Stabilizing
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One phenotype is favored (Larger Beak)
The average is best fit (Medium Beak)
Disruptive
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Both extremes are favored (Small and Large)
Can lead to separate species
Directional Selection
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Directional Selection –
Evolution causes an
increase in the
number of individuals
with the trait at one
end of the curve.
Graph of Directional Selection
Stabilizing Selection
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Individuals in the
center of the curve
and more fit and thus
the curve narrows
Graph of Stabilizing Selection
Disruptive Selection
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Individuals at the
ends of the curve are
more fit than the ones
in the middle causing
two curves to form
and possible new
species to form.
Genetic Drift
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In small populations, individuals that carry
a particular allele may leave more
descendants than other individuals, just by
chance. Over time, a series of chance
occurrences of this type can cause an
allele to become common in a population.
Hardy-Weinberg
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Genetic equilibrium takes place when allele
frequencies remain constant.
In order for genetic equilibrium to take place,
five factors must remain true.
1. random mating
2. Large Population
3. No movement in or out of the population
4. No Mutations
5. No Natural Selection
Hardy-Weinberg
H-W Conditions
Speciation
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Reproductive Isolation occurs when
members of two populations cannot
interbreed. At that point, they have
different gene pools.
Types of Isolation
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Behavioral Isolation – Two populations
capable of interbreeding but have
differences in courtship rituals or other
types of behavior.
Geographic Isolation – Populations are
separated by geographic barriers such as
rivers, mountains, or bodies of water.
Temporal Isolation – Species reproduce at
different times of the year.
Speciation
Galapagos Finches
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Speciation in the Galapagos Finches
occurred by founding of new populations,
geographic isolation, gene pool changes,
reproductive isolation, and ecological
competition.
Survival
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Variation within a species help insure that
some will survive major changes in the
environment.
Major diversity of species also insure that
some of the species will survive major
environmental changes.
MACROEVOLUTION
Evolutionary change on a grand
scale, including the origin of
new species and large scale
evolutionary trends.
Mass Extinction
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Mass Extinction means that MOST, but
NOT ALL species went extinct during a
short time period.
Because of GREAT BIOLOGICAL
DIVERSITY before a catastrophic event,
some individuals of some species survive
the event.
Macroevolution Patterns
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Adaptive Radiation: When many species
disappear, habitats and ecological
opportunities are left open for survivors take
over
The result seems to be a burst of evolution
that produces many new species
For example, when the dinosaurs went
extinct, that cleared the way for evolution of
modern mammals and birds
Let’s pretend that this is a small
population of rhinos
Macroevolution Patterns
Macroevolution = large scale evolutionary
changes
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Mass Extinction
Adaptive Radiation
Convergent Evolution
Coevolution
Punctuated Equilibrium
Changes in developmental genes
Mass Extinction
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Extinction occurs all the time: more than 99% of
all species that ever lived on Earth are now
extinct!
Mass extinction = huge numbers of species
disappear
Mass extinctions extinguish species and also
wipe out whole ecological systems
It is difficult to determine the causes of mass
extinctions, possibly volcanoes, continental
shifts, changing sea level, asteroids?
Mass extinctions often result in bursts of
evolution producing many new species
Adaptive Radiation
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A single species or a small group of
species evolved into several different
forms that live in different ways
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For example, Darwin’s finches
When dinosaurs became extinct, it made way
for adaptive radiation of mammals
Convergent Evolution
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Groups of different (unrelated) organisms
can undergo adaptive radiation in different
places or at different times but in similar
environments and natural selection may
mold different body structures to look very
similar
So, unrelated organisms come to resemble
one another
 Analogous structures = structures which
look and function similarly, but do not
share a common evolutionary history
Coevolution
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Organisms that are closely connected to
one another by ecological interactions can
evolve together in response to each
other’s changes over time
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For example, flowers and pollinators
Punctuated Equilibrium
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Evolution can occur at different rates for different
organisms at different times during Earth’s history:
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Gradualism = biological changes occur slow and steady or gradually
over time
Equilibrium = little or no change over time
Punctuated equilibrium = new species produced by period of rapid
change after long periods of equilibrium
 Can be due to isolation, genetic variation, mass extinctions, etc
Phylogenic Tree
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A diagram that indicated probable
pathway of evolution.
Branches were species separate and form
new species.
The more branches shared, the closer the
relationship.
Review
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Explain what happened to the gene
pool of the moths color during the
Industrial Revolution.
What would you expect to happen to
the color of the moths if natural
selection did not act on color?
Natural selection acts on the
(phenotype/genotype). Genes only
help pass on the traits.