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Modern Evolutionary Theory:
Evidence for evolution
“Modern Evolutionary Theory”
• A combination of Darwin’s ideas and newer
discoveries of fossils, anatomy and genetics.
Evidence for Evolution
1. Fossil Record
shows change in organisms over time
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Even if there were no fossil
record, the evidence from living
organisms would be more than
sufficient to demonstrate the
historical reality of evolution
Evidence for Evolution
2. COMPARATIVE ANATOMYMany anatomical similarities can be found
between different species
a) Homologous structures
•similar characteristics in different species
The underlying design of each structure is similar despite
their functional differences
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Frogs, birds, rabbits and lizards all have
different forelimbs, reflecting their
different lifestyles.
But those different forelimbs all share the
same set of bones - the humerus, the
radius, and the ulna.
These are the same bones seen in
fossils of the extinct transitional animal,
Eusthenopteron, which demonstrates
their common ancestry.
c) Vestigial Structures
• Features that have no apparent function
• Typically have an important function in related
Vestigial structures
species
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Ex: Hindlimb
joints in whales
and snakes
Vestigial Structures in Humans
Tailbone
Wisdom Teeth
Appendix
Evidence for Evolution
3. Embryonic Development
Similarities in the way different species
develop from embryos supports the
theory of a common ancestor
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Embryos show evolutionary history
Homologous structures in adults develop from homologous groups
of cells in embryos --> they share developmental pathways
Evidence for Evolution
4. BIOGEOGRAPHY
• SIMILAR ENVIRONMENTS SHAPE THE
EVOLUTION OF ORGANISMS IN SIMILAR WAYS
Emu (Australia)
Rhea
(S. America)
Ostrich (Africa)
Evidence for Evolution
5. Biochemical Evidence• shows DNA similarities and relatedness
between species
Molecules reflect evolutionary divergence
Evolution forms new species, but what
is a species?
• Species
– Closely related group of organisms
– Individuals can interbreed to produce fertile offspring
• Ex. Horses and Donkeys produce sterile mules
• Individuals do not evolve
• Populations do evolve
Is evolution directional? >>>>NO
• Not always bigger, better, faster, stronger
– Ex. Sloth
Speciation
• The formation of a new species as a result of
changes in a population.
• Can begin with a population splitting into two
groups
Two Types of Evolution
• 1. Microevolution- processes by which the genetic
traits change over time in a population
Processes:
– Natural selection- best traits for a specific environment
–
increase in the population
Microevolution Contd.
– Migration- New genes brought into
a population
– Mate choice-Sexual selection increases or
decreases certain alleles
• ex. bower birds, songbirds
– Mutation
chance introduction of new traits
• rare, passed on if beneficial
Bower Birds
Bowerbird Bachelor Pad
• 2. Macroevolution- patterns in which new species
evolve
Processes of macroevolution:
– Convergent evolution
• Unrelated species produce similar adaptations
– Divergent evolution
• Related species produce different adaptations
Macroevolution Contd.
– Coevolution
• Species evolve together
– Adaptive radiation
• One species produces
many new species
Ex. Galapagos Finches
• Why are these finches considered new species?
• Extinction- species fail to survive and reproduce
ex. Ice age, catastrophic events
Macroevolution Contd.
– Gradualism
• Formation of new species gradually over a long time
– Punctuated Equilibrium
• When species evolve suddenly
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What is Fitness?
5
• Fitness is a measure of
reproductive
success.
• Any trait that
promotes survival
increases fitness.
• Such traits are called
adaptations.
Population Genetics
• The study of changes in the number and types
of alleles in a population
• Biologists study the distribution of alleles in a
population
• Ex. Normal distribution of Height
• Gene pool- combination of
alleles in a population
Gene pool
• If the gene pool in a population changes
–  microevolution has occurred
– Review processes of microevolution:
•
•
•
•
Natural Selection
Mate Choice
Migration
Mutation- the major source of new alleles in a population
Review Questions 11/4/10
• 1. Identify 2 pieces of evidence for evolution and
explain how each supports the theory.
• 2. What is coevolution? Give an example.
• 3. Explain the difference between microevolution
and macroevolution. Identify two processes that
cause each type of evolution.
• 4. Give an example of how mate choice can cause
changes in the phenotype of a population.
• 5. What is the difference between convergent and
divergent evolution?
• 6. What is a gene pool?
• 7. Give an example of adaptive radiation.
Hardy-Weinberg Principle
• States that allele frequencies in populations
will change if the following processes occur:
– 1. gene flow- migration
– 2. non-random mating- sexual selection
– 3. genetic drift- chance loss of alleles
– 4. mutation- chance appearance of new alleles
– 5. natural selection
• If all of these processes occur evolution
Sexual Selection (mating is not random)
• Causes certain alleles to
Become more common
Mates chosen based on
Phenotype and females
Often do the choosing
Ex. More bright colors and
Features in male species
Pheromones and the Sweaty Tshirt Study
• http://www.pbs.org/wgbh/evolution/library/0
1/6/l_016_08.html
• What traits do humans select for?
Population Size and Evolution
• Changes in allele frequency impact small
populations more
– Why? Because the gene pool of a small population
is not very diverse
– Changes are more noticeable in small populations
Patterns of Natural Selection
• 1. Directional Selection- traits become more
extreme or exagerated
– Move away from the normal distribution
• 2. Stabilizing selection- alleles for extreme
traits are eliminated
– Traits become more “normal”
• 3. Disruptive Selection- bell curve is disrupted
into two peaks
– Selects for both extremes
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Types of Speciation
• 1. Geographical separation• populations are separated
by a physical barrier and
become different species
• http://www.nodvin.net/snhu/SCI219/demos/
Chapter_4/Chapter_04/Present/animations/2
3_2_4_1.html
• 2. Temporal- different mating seasons,
reproduction takes place at different times of
the year
• 3. Behavioral- species are not recognized as
mating partners
– Ex. Songbirds, frog croaking, mating behaviors
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Biological Resistance
• When organisms are no longer
affected by a drug.
• First documented around 1952
• Causes: Natural consequence
of selective pressures in the
environment.
Resistance in Bacteria
Read page p403.
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• Bacteria- Antibiotic
resistance
• Many insects have
developed a
resistance to
insecticides. (simple
point mutations)
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