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Honors Biology
Ch. 13 Notes
13.1 Briefly summarize the history of evolutionary
Evolution: The development of new types of organisms
from preexisting types over time.
Modern definition: a heritable change in the
characteristics within a population from one generation to
the next.
Idea as old as ancient Greeks.
Charles Darwin
1830, 22 years old
Served on H.M.S. Beagle: “Ship’s Naturalist”
Around-the-world voyage lasting five years.
Aristocrat so could socialize with Captain.
Despised by the Ship’s Surgeon.
Sought to provide evidence and mechanism for evolution
13.1 Explain how Darwin’s voyage on the Beagle
influenced his thinking.
Anatomy: Cuvier(anatomist/archeologist) reassembled fossil
o Stated:
o Past organisms differed greatly from any living
o Some organisms had become extinct.
o Deeper, older strata hold fossils that are
increasingly different from living species.
o Catastrophism: sudden geologic catastrophes
caused extinction of large groups of organisms at
certain points in the past. (Geologic change and
extinction occurred).
Geology: Lyell
o Shared some of Cuvier’s ideas
o Laws of nature in past same as today:
o “Uniformitarianism”
o Lyell’s geologic evidence fit with Darwin’s
evidence from biology.
Lamarck’s Ideas on Evolution
o Died the year Darwin set sail.
o Supported change over time.
o Spontaneous generation for simple life.
o Simple life becomes more complex.
o Acquire Traits thru experience or behavior then
pass those traits on to offspring.
o “Inheritance of Acquired Characteristics”
Darwin’s Competition:
Scientists don’t argue that evolution occurs, but HOW it
happens or it’s mechanism.
1830-1835 Voyage of the Beagle
1830 Alfred Russell Wallace turns 7 years old, grows up
to be a biologist and also sails around the world.
Both Darwin and Wallace arrive at the same conclusions.
1858 Both present ideas to scientists in London.
1859 Darwin publishes: “On the Origin of Species”
1835  1858 = 23 years
Galapagos Video with Alan Alda
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13.1 Describe the ideas and events that led to Darwin’s
1859 publication of The Origin of Species.
13.2 Explain how the work of Thomas Malthus and the
process of artificial selection influenced Darwin’s
development of the idea of natural selection.
Thomas Malthus: Wrote an essay on human populations:
More individuals are born than can survive to maturity.
Artificial Selection: Selective breeding of animals and crops to
attain traits needed.
13.2 Explain why individuals cannot evolve and why evolution does not
lead to perfectly adapted organisms.
Individuals do not evolve:
They can only pass on traits to
fertile offspring with
varying degrees of success: “fitness”
Evolution does not lead to perfectly adapted organisms:
Not goal oriented
NS results from environmental factors that vary
from place to place and time to time
“fitness” will vary
Adaptations are compromises
ex. blue-footed boobie’s feet
o work great in water
o clumsy on land
Evol: Laryngeal Nerve in Giraffes
13.3 Describe two examples of natural selection known to occur in nature.
Notes three key points about how natural selection works.
Thousands of experiments document evolution in action.
Example #1: Ground Finches’ beaks
20 year study
changes in beak size
eat small seeds
in dry years, fewer seeds, birds eat more large seeds
birds with larger, stronger beaks have the advantage
average beak size in population increases.
during wet years, opposite happens.
Example #2: Pesticide resistance
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Three Key points: Simulation of Natural Selection:
1. N.S. is editing not creative
2. Contingent on time and space: N.S. favors characteristics
that fit current, local environment.
3. Significant evolutionary change can occur in a short time.
13.4 Explain how fossils form, noting examples of each process.
Fig. 13.4 A-F
A. Skull of H. erectus:
actual remains
B. Ammonite casts:
minerals replace
organic molecules,
harden, refilled,
hardens, turned out of
a mold.
1. Petrified trees.
C. Dinosaur tracks: trace
fossils: footprints,
burrows, other traces
that represent
D. Fossilized organic
matter of a leaf: actual
remains preserved by
omitting bacteria and fungi from growing.
E. Insect in amber: fossilized tree sap (actual)
F. Ice Man (otzi): frozen (actual)
G. La Brea tar pits (actual)
H. Peat bogs: Tolund Man (actual)
13.4 Explain how the fossil record provides some
of the strongest evidence of evolution.
The Fossil Record: the sequence in which fossils appear within layers of
sedimentary rocks.
 Strata: layers
 Superposition: oldest is deepest, youngest is shallow
 Fossilization is a rare event
o hard parts fossilize best and most often
o soft parts (skin, feathers) fossilize least often.
 Speciation requires little time (geologic time scale)
 Fossil record is incomplete as one should expect.
 Bacteria is oldest fossilized life form
 Transitional fossils: fig. 13.4H
o Terrestrial mammals to
o Vestigial pelvis
o Share ankle bone design
unique to: pigs, hippos,
cows, camels, and deer.
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Evidence of Evolution:
 Fossils (“Comparing Primate
Fossils” or “Skulls Lab” Activity)
Biogeography: Wallace established
biogeography: the study of the
past and present geographical
distribution of organisms
Comparative anatomy
o homologous features: Blast
Animation “Homologous Structures”
o analogous features
o embryonic development:
gill slits
“Ontogeny recapitulates Phylogeny
o vestigial features
Boelens Python Vestigial
Pelvis 
Whale evolution video:
Molecular biology
AA sequence in proteins (“Biochemical Evidence” activity)
Chromosomes (“Comparing Primate Fossils” Activity)
Ken Miller: Chromosomal Evidence for Evol. 4:22min.
Important molecules: Cytochrome c highly conserved.
Excellent review:
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13.6 Explain how evolutionary trees are constructed and
used to represent ancestral relationships.
 Darwin was the first to view the history of life as a tree,
with multiple branches from a common ancestral trunk to
the descendant species at the tips of the twigs.
 Fig. 13.6 Evolutionary Tree
 Homologous structures, both anatomical and molecular,
can be used to determine the branching sequence of
such a tree.
 Genetic Code: (A, T, C, G) is a homology shared by all
species because they date to the deep ancestral past.
 Characteristics that evolved more recently are shared
only within smaller groups of organisms. (Tetrapods all
share basic limb bone structure but their ancestors do
13.7 Define the gene pool, a population, and
Gene Pool: The total collection of genes in a population at
any one time. Used to study evolution at the population level.
Population: A group of individuals of the same species living
in the same place at the same time.
Microevolution: Evolution on its smallest scale, occurring in
the gene pool of a population. When the relative frequencies
of alleles in a population change over a number of generations.
13.8 Explain how mutation and sexual recombination
produce genetic variation.
Mutation: A chance event, not a mechanism (controlled
by genes.)
New alleles originate by a change (mutation) in the nucleotide
sequence of DNA.
 Ultimate source of genetic variation
 Most mutations occur in body cells and are not passed on.
 Only mutations in gametes are passed on.
 Chromosomal mutations:
o that delete, disrupt or rearrange many gene loci
are usually harmful.
o Duplication of part of a chromosome is an
important source of genetic variation.
Extra genes that can be mutated.
Olfactory receptor genes in mammals
allows for greater range of scent
Mice = 1,300 receptors
Humans = 1,000 receptors
Sexual Recombination
Fresh assortments of existing alleles:
 Crossing over during Prophase I.
 Independent orientation of homologous chromosomes Metaphase I of meiosis
 Segregation of alleles
 Random Fertilization
Review Questions:
1. What is the ultimate source of genetic variation?
2. What is the source of most genetic variation in a population that reproduces sexually?
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1. mutation
2. Unique combinations of alleles resulting from sexual reproduction.
13.8 Explain why prokaryotes can evolve more quickly than eukaryotes.
 Prokaryotic mutations can multiply rapidly due to rapid reproduction rate.
o Bacteria are haploid, one gene per character, a new allele can have
immediate effect.
o Generation time: 20 min. under ideal conditions
o Simultaneous Transcription and Translation allows for more rapid
response to environmental changes.
 Mutation Rate:
o Animals and plants average 1/100,000 genes per generation.
o Considered a low mutation rate.
o Long time spans between generations,
o diploid genomes prevent most mutations from significantly affecting
genetic variation in plants and animals from generation to
13.11 Define genetic drift and gene flow. Explain how the bottleneck effect and
the founder effect influence microevolution.
Mech.of Evol. 7:40min.
Non-random Mating
Genetic drift: Small population size.
A change in the gene pool of a population due to chance.
 The smaller the population, the greater the effect.
 Alleles may be lost to the population due to chance
 This reduces variation by such losses.
 Examples are:
o Bottleneck Effect
o Founder Effect
Bottleneck Effect:
 Catastrophe may kill indiscriminately and leave few survivors.
 Reduced gene pool variation affects population
 Less variation reduces population’s fitness
Founder effect:
 When a few individuals colonize as isolated island or other new habitat.
 The smaller the group, the less likely the genetic makeup will represent
larger population they left.
 Genetic difference between large pop. and founder pop. is founder effect.
Gene Flow (Immigration/emigration)
 Allele frequencies can change as a result of fertile individuals move into or
out of a population.
 Gene flow reduces differences between populations.
 Compare to similarities in a closed society like the Amish.
Natural Selection
13.11 Explain how genetic bottlenecks threaten the survival of certain
 Ice age: Human population estimates 600 breeding individuals at one time
in S. Africa. Genetic variation between individual humans about 30% less
than between individual chimpanzees.
 Florida panther
 African cheetah
 Illinois greater prairie chicken reduced by agriculture and development from
millions in 19th C. to 50 individuals in 1993. Flocks from neighboring states
added into Illinois flock. Regained hatching success from 50% to 90% due
to added alleles.
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1814, 15 people founded British
colony, Tristan da Cunha on island in
One of the 15 was a het for retinitis
In 1960, of the 240 descendants, 4
had RP, 9 were hets.
Frequency 10x higher than parent
13.12 Explain why natural selection is the only mechanism that leads to
adaptive evolution.
Chance Events:
 Genetic drift (bottleneck, founder effects)
 non-random mating
 mutation
 gene flow
Chance + sorting:
 natural selection
o chance: random collection of genetic variation
o sorting: some alleles are favored over others.
o sorting makes in adaptive
o improves the match between organisms and their environment.
o environments change
o “fitness” is a moving target
o adaptive evolution dynamic process
13.13 Distinguish between and describe an
example of:
stabilizing selection:
 most common type
 favors intermediate phenotypes
 stable environment
 conditions reduce phenotypic variation
 example: human infant weight averages
6.5-9 pounds, extremes have higher infant
directional selection:
 shifts the overall makeup of the popul. by
selecting against individuals at one of the
phenotypic extremes.
 example: insects exposed to pesticide
disruptive selection:
 environmental conditions are varied and
favors individuals at both extremes.
 leads to two or more contrasting
13.14 Define and compare intrasexual selection and intersexual
Intrasexual selection or within the sex usually between males
 “Winner takes all”
 Male wins territorial rights to a group of females.
 Usually agonistic or ritualized
 Example: lions, elk, mountain sheep
Intersexual selection or mate choice
 between males and females
 Females choose male
 Males display adornments
o plumage
o courtship dance
o song
o “Choose Me!”
o studies show it relates to overall male
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13.15 Explain how antibiotic resistance has evolved. (6 min. TB
in prisons)
13.16 Explain how genetic variation is maintained in
Diploidy: having two sets of chromosomes
 helps to prevent populations from becoming
genetically uniform.
 Recessive alleles hide from selection forces as Hets
 Maintains presence of recessive alleles in gene pool
Balancing Selection: When natural selection maintains
stable frequencies of two or more phenotypic forms in a popul.
 heterozygote advantage:
o homozygotes are selected against
o NN = susceptible to malaria/ nn =
susceptible to sickle-cell
 frequency-dependant selection: most common
phenotype selected against
o scale-eating fish in Lake Tanganika, Africa
o attack other fish from behind to steal scales
o right-mouthed/left-mouthed
o easier to defend against most common attacker
o those numbers go down from lack of food
o less common #’s go up from greater food
13.16 Explain what is meant by neutral variation.
 Mutations that have no effect, + or -, on the individual
 Mutation occurs in non-coding region of DNA
 Occurs but doesn’t change protein significantly
13.17 Give four reasons why natural selection cannot
produce perfection.
1. Selection can act only on existing variations
a. can use only phenotypes available
b. may not be ideal trait for environment
c. advantageous alleles do not arise on demand
d. extinction happens
2. Evolution is limited by historical constraints.
a. co-opts existing structures and adapts them to
new situations
b. Example: environmental changes favor flight;
TEDed: Evolution of the Human Eye
wings would be best but nature must use the
– Joshua Harvey (4:43min)
parts available. Bats and birds did not evolve a set of appendages, they changed what they
evolution-of-the-human-eye-joshuaalready had.
3. Adaptations are often compromises
a. Each organism must do many different tasks but..
b. …adaptations may be better suited for some
tasks than others
c. Example: blue-footed booby uses webbed feet to
swim after prey well, but they are clumsy on land.
4. Chance, natural selection, and the environment
a. Chance plays a bigger role than once thought
b. Example: a storm blows insects out to sea. A
few land on an island, many perish. The few that
survived may not be the individuals that would be
best adapted to the new environment.
Question: Humans owe much of their physical versatility and athleticism to their flexible limbs and joints.
But we are prone to sprains, torn ligaments, and dislocations.
a. Which one of the four reasons given for why natural selection cannot produce perfect organisms best
explains this?
b. Explain how your chosen reason applies specifically to humans.
End Ch.13 notes
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