Answer Key
Unit 3 Evolution
16. Comparison of Genotype and Phenotype
Term
Unit Preparation Questions
(Assessing Readiness)
(Student textbook pages 290–3)
1. c
2. a
3. The major steps followed during a scientific inquiry
are: making observations, asking questions, forming
a hypothesis, making a prediction, performing an
experiment/investigation, analyzing data, drawing
a conclusion, and supporting or rejecting/revising
the hypothesis.
Genotype
Description
The combination of
alleles in an individual
organism
Phenotype The outward expression
of an organism’s
genotype; an organism’s
phenotype is its
physical and
physiological traits
Example
The combination of
alleles for any given
trait, such as Ss or AaBb
A physical characteristic,
such as pea shape;
a physiological
characteristic, such
as sickle cell anemia;
or a behavioural
characteristic, such as
territorial behaviour
5. a. Repeat the experiment several times.
b. Revise your hypothesis.
17. Mendel’s discovery of the allele is so important because
the laws that Mendel developed through his work on
pea plants formed the foundations of our modern
theory of inheritance and his discovery explained the
mechanism underlying evolution and natural selection.
6. e
18. c
7. c
19. a
8. a
20. a
9. a true; b true; c false; Meiosis leads to four genetically
different daughter cells. d false; Meiosis is important
for generating genetic variation among the daughter
cells and each cell will have half the number of
chromosomes. e true
21. Answers may include predators, food availability,
competition, weather factors, and disease.
4. a
10. e
11. c
12. The original source of all new alleles is
genetic mutation.
13. b
14. Black with a long tail
15. Because the allele for dimples is dominant, a dimpled
adult may be heterozygous—carrying the non-dimpled
allele. If both parents carry the recessive allele, they
have a 25% chance of having a child with no dimples.
22. Comparison of Biotic and Abiotic Factors
Term
Description
Example
Biotic
factor
Living features of an
ecosystem
Plants, animals, microorganisms
Abiotic
factor
Non-living features of
an ecosystem
Water, rocks
23. a. The carrying capacity
b. The carrying capacity is the point at which the
environment supports the maximum population
size. Growth slows because resources become
limited. For example, if a species needs to nest
in a particular habitat, the environment reaches
its carrying capacity for that species once all the
required nesting habitat is occupied.
24. b
Biology 11 Answer Key Unit 3 • MHR TR
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25. There may be time lags or delays in the effect that
a carrying capacity has on population growth. For
example, it may take time for birth rates in rabbits
to slow down after the rabbits eat too much of the
food supply.
26. Urban sprawl:
Definition:
Effects:
• Expansion of human
communities into
undeveloped areas
surrounding urban centres
• Alters habitat and
ecosystems, usually making
them uninhabitable for other
species
• Changes how the water cycle
and nutrient cycle function
in the affected areas
Examples:
Non-examples:
• Development of suburbs
around cities
• Protection of large tracts of
land as conservation areas
• Increased pavement and
road systems, housing
developments, and density
of human populations in
areas previously used for
agriculture
• Land held and maintained
for natural or agricultural
purposes
27. a
28. c
29. a. A physiological adaptation
b. The chemical may frighten predators so the
caterpillar will likely not get eaten and will
survive longer.
30. c
31. Sample answers: In fall, some plants shed their leaves
and some birds migrate; in winter, some animals
change colour.
32. Sample answer: The thick stem of a cactus stores water
for the plant.
33. e
34. a
35. a. A fossil is the remains and traces of past life found in
sedimentary rock that reveal the history of past life
on Earth.
b. Extinction means that the species has died off and
will not reappear again.
Chapter 7 Introducing Evolution
Learning Check Questions
(Student textbook page 299)
1. An adaptation is a structure, behaviour, or
physiological process that helps an organism survive
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MHR TR • Biology 11 Answer Key Unit 3
and reproduce in a particular environment. Examples
include an owl’s sharp talons and keen vision.
2. Yes, its excellent sense of smell allows a shark to find
prey easily and increases its chances of survival given
that it does not need to depend solely on sight to locate
its prey.
3. The fly’s adaptation is mimicry: its coloration resembles
that of a stinging insect such as a bee. The advantage of
this adaptation is that predators will leave it alone.
4. Students should create a cause-and-effect chart
using the information on pages 298 and 299 of the
student text: trees covered with light-coloured lichen
→ flecked moths flourished, few black moths →
environment changed (tree trunks darkened due to
soot from Industrial Revolution) → black moths began
to flourish, flecked moths began to decrease in number
→ environment changed (tree trunks lightened due
to lichen growing on trees after clean-air legislation)
→ flecked moths increased in number, black moths
decreased in number
5. As the environment changed, the peppered moths
that were able to blend in with the changing colour of
the tree trunks survived at a greater rate and passed
on their survival traits to their offspring. In this way,
the proportion of the differently coloured moths in
the population changed in response to the changes in
the environment.
6. Sample answer: DNA variation in sequences that are
not part of genes that are expressed may not have an
effect on an individual or its species. Sample answer:
DNA variation in sequences that are not part of genes
may have no advantage or disadvantage for individuals.
(Student textbook page 307)
7. Natural selection is the process by which characteristics
of a population change over many generations as
organisms with heritable traits survive and reproduce,
passing on their traits to offspring.
8. The ability of individuals with advantageous and
heritable traits to survive and reproduce leads to
changes in the characteristics of populations over time.
An example is the development of pesticide resistance
in a population of plants.
9. Genetic variation in a population increases the chances
that those individuals with favourable, heritable traits
will survive changing conditions. Those individuals
that survive will reproduce and pass on their alleles
to their offspring. The characteristics of a population
will therefore change over time due to this process of
natural selection.
10. Adaptations are products of natural selection because
as environments change, the genetic characteristics
that result in favourable traits in a given environment
are selected for and their frequency of occurrence in a
population increases.
11. A flowchart should show the following steps:
Individual plants within a population show variation.
→ Some variations are genetic, such as the trait
that permits growth in shade (low light levels). →
Those seedlings that can grow in an environment
with low light levels will survive and reproduce more
successfully than plants that cannot grow well in shady
environments. → This leads to changes in the plant
population over time, with higher percentages of plants
that can grow well in low light levels.
12. Fitness is the contribution that an individual makes
to the gene pool of the next generation by producing
offspring that will survive long enough to reproduce.
A highly fit organism survives and reproduces, passing
on its advantageous genes to its offspring. Natural
selection is the pressure that determines an organism’s
relative fitness in a given environment.
Caption Questions
Figure 7.1 (Student textbook page 296): The camouflage
of an individual stick insect increases its chances of
survival. If the insect survives, it has a better chance of
reproducing. As long as the camouflage trait is heritable,
the genes for camouflage will likely be passed on to a
number of its offspring; this provides new individuals that
will maintain or increase the population and thus increase
the population’s chances of survival.
Figure 7.3 (Student textbook page 299): Camouflage: The
flecked moths were better hidden (camouflaged) when
they rested in the trees whose trunks were covered with
light-coloured lichen, and the black moths were better
camouflaged when they rested in the trees whose trunks
were darkened by pollution (soot).
Figures 7.9 and 7.10 (Student textbook pages 308–309):
Both Figures show that desirable traits increase or decrease
as humans choose which plants to breed. The wild mustard
plant was modified to produce more desirable traits that
led to six agricultural plants that look very different from
each other. Selective breeding for oil content in corn plants
has resulted in an increase in the percentage oil content in
the plants with the highest oil content in the kernels.
Section 7.1 Review Questions
(Student textbook page 304)
1. a. The shape and coloured dots look like a snake’s head
and eyes.
b. Mimicry: the caterpillar mimics a snake; also,
physiological adaptation: the caterpillar swells up the
front part of its body so it resembles a snake’s head
and eyes
c. The caterpillar’s resemblance to a snake frightens
predators; thus, the caterpillar will likely not get eaten.
2. Adaptations are the result of a gradual change in the
characteristics of members of a population over time.
A variation that helps an individual in a population
survive is likely to be passed on from survivor to
survivor. Through generations of survivors, this
variation will become more common, perhaps so
common that eventually it is considered to be a
characteristic, or trait, of the population.
3. Both camouflage and mimicry involve changes in
body form and coloration that match aspects of the
environment in order to increase an organism’s ability
to survive and reproduce.
4. Sample answer: Mutations in coloration (greyishwhite and black) helped certain varieties of the
peppered moth around Manchester survive changing
environmental conditions that affected the colour of
their habitat. It is likely that flecked moths appeared
first, but there would have been a recessive gene
controlling dark colour as well. Unpolluted trees are
the natural condition, and the light-coloured lichen on
the trees provided a selective advantage for the flecked
moths, so they flourished and reproduced. Only later,
when the trees were blackened by soot, would this
environmental change result in a selective advantage
for the black moths.
5. Sample answer: I would present potential predators
a group of walking sticks on native twigs from their
habitat so that they are camouflaged. I would also
present some walking sticks to predators on native
twigs that have been painted red so that the insects
stand out. As a control group, I would have walking
sticks presented to predators on native twigs that have
been painted with a clear paint to control for the effects
of the paint. For the experiment, I would compare
survival rates in all three populations of walking sticks.
6. Sexual reproduction mixes genotypes of parents,
resulting in offspring with unique genetic information.
Mutation is the ultimate source of genetic variation, as
new, previously non-existent alleles are formed.
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7. If all sparrows have exactly the same size of beak, then
they are in direct competition with one another for
food resources. However, since some have smaller
beaks and others have larger beaks, they are able to
partition the food resources up and most individual
sparrows should be able to find food and survive.
8. Sample answer: A population of mosquitoes may have
some individuals with a mutation that allows them
to survive an application of insecticide. This is an
example of a selective advantage. A beaver could have
a mutation such that its tail is not shaped properly and
it cannot swim as well as the rest of the population of
beavers. This is an example of a selective disadvantage.
a. Selective advantage will exist if the alleles are not
evenly distributed throughout the population.
Only some organisms that have the particular allele
will survive.
b. A previous disadvantage could become an
advantage if the environment changes and the
selective advantage shifts to benefit the previously
disadvantaged genotype.
9. Sample answer: A cat has sharp retractable claws that
allow it to hunt effectively. A cat also has large eyes
that see well in the dark, allowing it to hunt effectively
at night or in low-light conditions. Students’ sketches
should show the claws and the eyes.
10. Disagree. Individuals do not adapt; rather, populations
adapt. The wording in the article is scientifically
inaccurate.
11. Using these products might result in bacterial
resistance to the antibiotic that is contained in the soap
or spray, resulting in bacteria that are not affected by it.
12. Some AZT-resistant viruses must have been present
at the start of treatment and those strains reproduced
more successfully than the non-resistant strains during
the course of treatment.
13. Mutation creates new alleles and is the original source
of genetic variation.
14. Since the same colonies survived the antibiotic,
the experiment generates the conclusions that the
bacteria did not develop a mutation in response to the
antibiotic but, rather, two of the bacteria colonies have
a mutation that made them resistant to the antibiotic,
so they were the only colonies that survived.
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MHR TR • Biology 11 Answer Key Unit 3
Section 7.2 Review Questions
(Student textbook page 311)
1. Natural selection is a process by which individuals with
favourable variations survive and/or reproduce more
successfully than those individuals without such traits.
If favourable variations are genetically based, then they
can be passed on to offspring and cause changes in
populations over time.
2. The term selective pressure refers to environmental
conditions that put pressure upon the varying
individuals in an environment to survive and
reproduce. Particular environmental conditions will
select some individuals to survive compared to other
individuals—in other words, the conditions will
preferentially allow the survival of individuals with
traits that enhance survival and reproductive success.
If these traits are passed on to the individuals’
offspring, then over time the population changes.
3. Every time the insecticide is applied, some individuals
in the population will survive due to the presence of
alleles that provide protection against the effects of the
insecticide. These insects will be the only survivors;
therefore, they will be the only insects that reproduce,
and they will likely pass on the genetic information
related to resistance to the insecticide to their offspring.
The resulting new generation will have a higher
percentage of individuals with the allele for resistance
to the insecticide, and so the population shifts over
time to be fully resistant to the insecticide.
4. As an environment changes, individuals with genetic
characteristics that are best adapted to the environment
are selected for. Therefore, populations become
adapted to their environment over generations through
natural selection.
5. Fitness is measured by how many viable offspring an
individual produces. Since the chipmunk produced
more babies compared to a typical litter of chipmunks
and they all survived, she would have high fitness.
6. Blueberries in the store are farmed and selectively bred
for large size. Wild blueberries are not selectively bred
for size.
7. In artificial selection, humans rather than the
environment exert selective pressure on populations to
improve or select for desirable traits.
8. Sample answer: People have used selective breeding
to produce varieties of corn that have a higher oil
content compared to other varieties of corn. This is
economically beneficial because the oil is an important
product that can be sold. Another consequence of
selective breeding is the reduced genetic variation
in the new variety of corn, which makes more of the
individuals in that variety susceptible to new pests.
9. This quote is fairly accurate in that natural selection
only works on the genetic material found in the
population. However, natural selection works as a
result of changing environmental pressures, so there is
no proper or correct outcome, whereas a copy editor
makes corrections to achieve a particular outcome—a
well written, error-free piece of writing.
10. Students should show and explain that domesticated
plants and animals are artificially selected and therefore
the genetic diversity in the gene pool is reduced.
11. Our domesticated crops are now genetically very
similar, so there is little variation. Thus, if a new
disease attacked a food crop, there may not be enough
variation for any plants to have a mutation that would
protect the plant from damage due to the disease. The
whole crop could be lost, whereas if there were more
variation, some plants might survive.
12. Farmers can take advantage of the genetic changes
brought about by artificial selection in the crops they
would plant in a monoculture. Monoculture crops are
selectively bred to have high yields, and to be easy to
grow and/or harvest. These characteristics would all be
beneficial for farmers.
13. a. During the dry years (years 1, 4, and 6), the beak
depth is larger. During the wet year (year 8), the
beak depth is smaller.
b. Birds with deep beaks gather more food and pass
along their genes that code for large beak depth to
their offspring in drought years, when the seed size
is large. Birds with less deep beaks gather more food
and pass along their genes that code for less deep
beaks to their offspring in wet years, when the seed
size is small.
14. Sample answer: Selective breeding of vegetables –
advantages: a plentiful food crop to feed an expanding
population; the vegetables can be bred for size, thus
making them more economically viable; disadvantages:
loss of genetic diversity makes the crop susceptible to
new pests and diseases
Quirks and Quarks: From Mosquito
Control to Malaria Control
(Student textbook page 303)
1. Sample answer: Just as for antibiotic-resistant bacteria,
pesticides that target all mosquitoes would wipe out
mosquitoes that are not resistant, leaving only the
mosquitoes that have a genetic mutation that codes
for resistance to the pesticide to reproduce. New
pesticides would have to be developed to combat what
is an adaptation to the environmental challenge of
the pesticides. Dr. Read’s method avoids creating an
environmental change for the population at large, and
the younger mosquitoes should not pass on the genetic
mutation that codes for resistance to pesticide to
their offspring.
2. Essential skills would include attentiveness to detail,
the ability to use microscopes and other laboratory
equipment, the ability to work in the field taking
samples, and the ability to analyze data, interpret
findings, and communicate results.
Chapter 7 Review Questions
(Student textbook pages 319–21)
1. d
2. e
3. b
4. d
5. b
6. a
7. d
8. c
9. Individuals’ traits vary. Individuals with variations
that are favourable in a particular environment will
survive and reproduce more successfully, leading to a
greater proportion of individuals with those traits in
the population.
10. If the mutation is in an individual’s somatic (body)
cells, it could affect the individual, but it will not be
passed on to the next generation. If the mutation is
in one of the parent’s sex cells (gametes), it could be
passed on to the next generation.
11. A field mouse’s colour might help it blend in with its
environment, thus preventing the mouse from being
seen and eaten by predators. On the other hand, if a
field mouse’s colour does not help it blend in with its
environment, the mouse might stand out and it would
be noticed and eaten by predators.
Biology 11 Answer Key Unit 3 • MHR TR
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12. The case of the peppered moths shows how different
environmental conditions (light-coloured or darkcoloured bark on trees) selects for different colours
of moths (light or dark). When the tree bark changes
colour, the moths that blend in best are not eaten as
prey, so their survival rates increase, they reproduce,
and their offspring are more likely to be the colour that
blends in successfully with the environment.
13. Natural selection is the process in which environmental
pressure acts upon a population, and members of the
population with certain variations are able to survive
compared to other members.
14. A mutation present in a small population that provides
a selective advantage could become quickly passed
on to, and become advantageous to, individuals in a
population, such as a bacterium with a mutation that
protects it from an antibiotic. Subsequent generations
of bacteria could inherit the mutation and remain
protected from the antibiotic.
15. No. Only the mutations in gametes that get passed
down from generation to generation can affect the
biological change of a population.
16. If there is an allele that provides resistance to the
pesticide, so that some houseflies can withstand the
pesticide, then the offspring of the surviving houseflies
will also carry the genetic resistance to the pesticide.
Over time, the population of houseflies would be made
up only of individuals that carry the allele for resistance
to the pesticide. This is a selective advantage for the
surviving houseflies, but not for the humans that are
applying the pesticide.
17. Variation is necessary for natural selection to have
something to act on. Otherwise, all individuals would
die or all would survive. The food source for eagles
changed over time, and it became advantageous
for those eagles with talons that are slightly longer
compared to eagles with talons that are slightly shorter
to obtain more food and to live longer, reproduce, and
pass that trait on to their offspring.
18. a. Streptomycin, because antibiotic-resistant bacteria
were identified the same year in which the antibiotic
was introduced.
b. Vancomycin, because it took 31 years before bacteria
resistant to it were identified.
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MHR TR • Biology 11 Answer Key Unit 3
19. a. The horses’ performance times have not improved
significantly since around 1940.
b. Since all the horses were selectively bred from three
original ancestors, there is not enough variation in
the gene pool.
20. Hypothesis 1 is correct. The individual beetles do not
develop a mutation. The beetles with the mutation
already exist in the population. These beetles are the
ones that will survive, reproduce, and pass on the
genetic advantage to the next generations.
21. a. IHO and SHO
b. RHO and ILO
c. Artificial selection to increase its oil content,
although it started with very low oil content.
22. Sample answer: Compare fitness, or the number of
reproductively viable offspring, of larger finches in
wet years and in dry years. Factors to measure would
be the amount of precipitation, the size of the finches,
the number of offspring, and the survival rate of
the offspring.
23. Answers should include selective breeding of parents
with high milk production and a way to measure milk
production in cows.
24. Sample answer: I would measure the lengths of tails
in a population of birds to see if there is variation. It
is important to sample non-siblings, if possible (that
is, individuals that are not from the same parents), so
that a greater range of variation is possible. Siblings
share genetic material, so only the variation present in
their parents’ genotypes that was passed on to them
would be measurable. As a result, you might not get
the full range of the trait’s variation throughout the
whole population.
25. Genetic variation provides the raw material that the
environment acts on. Selective pressure selects for
certain genetic variations that are both heritable and
advantageous to the bearer, so over time, populations
change and evolve as a result of the genetic variations
in individuals that survived particular environmental
conditions and were then passed on to offspring in the
next generation.
26. Students will likely choose a Venn diagram as a
graphic organizer, as it allows the differences to be
clearly shown. They must also then include at least one
similarity, as shown below.
Adaptations
Similarities
Variations
- Traits or processes Related to genetic - The total number of
traits that are in the
material that is
that increase
population
heritable
an organism’s
chances of
- Only present as
survival and
different alleles
successful
- The more variations
reproduction
(differences
- Can be structural,
between
behavioural, or
individuals) present
physiological
in the population,
the more likely some
variations will be
adaptive for some
individuals
27. The flowchart should show that selective breeding can
improve crop yields, thereby increasing the economic
benefit of farming. An example would be selective
breeding for early maturing crops (i.e., selecting for
faster developmental times).
28. Answers will depend on the specific adaptations that
students choose, but should show that an adaptation
can be a structure, a behaviour, or a physiological
process that helps an organism survive and reproduce
in a particular environment.
29. The Venn diagram should include the following points:
Natural selection
Similarities
Artificial selection
The mechanism by
which populations
change as a result
of environmental
pressure
Both natural
selection and
artificial selection
are the result of
changes in the
genetic material in
a population.
Selection applied
by humans in order
to improve or
modify particular
desirable traits
30. Students’ graphic organizers should include two
sections, “Adaptation and Variation,” and “Natural
Selection and Artificial Selection,” reflecting the
two sections of Chapter 7. Answers should show
an understanding of how sexual reproduction and
inherited mutations contribute to adaptation and
variation in individuals in populations, as well as
how natural selection is the mechanism by which
populations change while artificial selection is the
result of human choice.
31. This example of natural selection favouring greater bill
depth was due to the fact that finches with greater beak
depth were better able to eat the remaining larger seeds
compared to varieties of finches with smaller beaks,
and thus large-beaked finches survived and the smallbeaked finches died.
32. More small-beaked birds will survive and produce
offspring that also have small beaks. The proportion
of small-beaked birds should increase over time.
33. a. Yes, in this case breeders are selectively breeding
organisms (racing greyhound dogs) for a particular
trait (speed).
b. Yes, the person is selectively breeding organisms
(Persian cats) for a particular trait (long fur).
c. Yes, the farmer is making the choice of breeding and
crossing the plants to increase the desired condition
of higher variability in the plant species’ fat content.
d. No, the development of chemical defences in plants
over time is a product of natural selection.
e. Yes, the breeders are selectively breeding crop plants
for a particular trait (resistance to pests).
34. The insect is exhibiting camouflage.
35. On the basis of knowing how certain traits are
inherited, the plant breeder could choose desirable
traits and practise selective breeding.
36. The beak shape and wing size of the blackcap warbler
are changing in the United Kingdom as a result of
warmer climates and the use of bird feeders. Source:
The Globe and Mail news online.
37. Sample answer:
a. Chickens now lay more eggs and lay them more
frequently than earlier chickens.
b. Chickens have been selectively bred to increase the
productivity of their egg laying.
c. A reduction in the genetic variability within the
different species of farm animals makes them
vulnerable to disease. If one animal is susceptible,
they will all probably be susceptible. Selecting
for some traits can have the consequence of also
selecting for less desirable traits at the same time.
This is a possible danger that might decrease an
animal’s chances of survival.
Biology 11 Answer Key Unit 3 • MHR TR
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d. The traits being selected for are a result of the goals
of the farmer, so it can be hard to determine if one
or more traits should be selected for at the same
time. It is only possible to select multiple traits if
they are not in conflict with each other. For example,
selecting for an increase in overall muscle mass
cannot occur at the same time as selecting for a
decrease in size.
e. The selective breeding program would have to
include maintaining a certain level of genetic
variation, perhaps by bringing in new animals
on a regular basis to support genetic diversity.
The Government of Canada BioBasics website
(www.biobasics.gc.ca) has information on
selective breeding that might help students answer
this question.
38. a. Inbreeding occurs when closely related individuals
breed together.
b. Because close relatives share similar genotypes,
inbreeding makes homozygous genotypes more
common. Homozygous refers to two identical
alleles for a characteristic. This means that harmful
recessive alleles, which are often masked by a
dominant allele in heterozygous individuals, are
more likely to be expressed.
Chapter 7 Self-Assessment Questions
(Student textbook pages 322–3)
1. b
2. c
3. e
4. d
5. a
6. d
7. b
8. e
9. e
10. c
11. A physiological adaptation is a physiological process
that helps an organism survive and reproduce
in a particular environment. An example of a
physiological adaptation is the biochemical processes
that a Richardson’s ground squirrel’s body undergoes
during hibernation.
12. Sample answer: A mutation that does not change
a gene. For example, a mutation that changes a
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MHR TR • Biology 11 Answer Key Unit 3
nucleotide in a non-coding region of DNA will be
neutral to the organism.
13. Each puppy could inherit a different combination of
alleles from its parents.
14. Selective pressure occurs when environmental
conditions select for certain characteristics of
individuals and select against other characteristics.
A selective advantage is a characteristic that improves
an organism’s chances of survival, usually in a
changing environment.
15. You can most directly measure an organism’s fitness by
counting the number of the organism’s offspring that
are viable and that survive to reproduce.
16. No, because the offspring of these species cannot pass
on genes to the next generation.
17. Natural selection selects for individuals with
traits that are adaptive, thereby increasing the
population’s ability to survive and/or reproduce in a
particular environment.
18. Sample answer: A selection factor changed,
for example, predation decreased or food
availability increased.
19. A trait in one environment at one specific time may
have no apparent relevance to survival or might even
reduce the chances of survival. However, that same
trait at a different time in a different environment
might be favourable and might help certain individuals
in a population survive and reproduce.
20. Sample answer: Students’ diagrams might show the
following steps: A population of plants varies in flower
colour from light pink to dark red. Red flowers are
easier to find by pollinating bees. Therefore, red flowers
have greater reproductive success and produce more
offspring than lighter-coloured flowers. Eventually,
the flower population has a greater proportion of
individuals with red flowers.
21. Students’ answers may include size, sugar content,
ripening time, and/or resistance to disease.
22. Students’ answers should highlight that a major
difference is that natural selection occurs when the
environment creates selective pressure for individuals
with adaptive traits that allow them to survive and
reproduce more successfully. In artificial selection,
however, the parents are chosen for a particular trait by
the person doing the selecting, regardless of whether or
not the trait is adaptive.
23. Students may suggest that selective breeding allows
people to enhance traits they desire in plants or
animals, such as better resistance to disease in
agricultural crops. Disadvantages include the fact that
selective breeding can result in a loss of variation and
this loss can lead to greater susceptibility to disease.
5. Sample answer: Cuvier’s idea that catastrophic events
in Earth’s history caused species extinction does not
necessarily suggest that organisms change over time
(evolve), especially since Cuvier explained the origin
of new species as being immigrants from nearby
geographical areas unaffected by the catastrophes.
24. a. Answers should suggest a way to choose only
varieties of Brassica with large leaves and to breed
them with each other to produce a population with
larger leaves.
b. The new variety with large leaves may not be as
fit compared to the wild plant species for various
reasons; for example, it provides more abundant
food for leaf-eating insects.
6. Sample answer: Many of the geological processes that
operate today—for example, volcanoes, earthquakes,
glacier formation, and erosion—also existed in the
past. However, the rates at which these events occur
may be different today compared to rates in the past.
25. Sample answer: No, not necessarily; natural selection
has no will, purpose, or direction, it does not anticipate
change in the environment, and it is situational. A
trait that at one time in one situation seems to have no
apparent relevance to survival may be the trait that, at
a different time in a different situation, helps certain
individuals in a population to survive and reproduce.
Chapter 8 Developing a Theory
of Evolution
Learning Check Questions
(Student textbook page 327)
1. The empirical system is a system of learning
about the natural world through observation
and experimentation.
2. During Buffon’s time, it was generally accepted that life
forms did not change and that Earth was about 6000
years old. Buffon suggested that life forms changed and
that Earth was older than 6000 years.
3. Catastrophism suggests that Earth experienced
many destructive events such as floods, diseases, and
droughts, which caused localized extinctions of species.
Uniformitarianism, however, suggests that geological
processes occur at the same rates in the past as they do
today, slowly and continuously, and not as a result of
destructive events.
4. Cuvier’s explanation of the appearance of fossils of
species that did not exist anymore is important because
it shed light on the fact that some species disappeared
(became extinct) and new species appeared over the
passage of time, and his ideas allowed for the field
of paleontology—the study of ancient life through
fossils—to develop and grow.
(Student textbook page 336)
7. The fossil record is the remains and traces of past life
that are found in sedimentary rock and that reveal the
history of life in Earth and the kinds of organisms that
were alive in the past.
8. The fossil record shows that fossils found in young
layers of rock are much more similar to existing species
than are fossils found in older, deeper layers of rock;
fossils appear in chronological order in the rock layers,
thus showing changes and transitional links between
groups of organisms; not all organisms appear in
the fossil record at the same time, indicating that all
organisms did not co-exist on Earth at the same time.
9. Transitional fossils link the past with the present
by providing information about the intermediary
relationships between groups of organisms in terms of
the evolutionary process.
10. According to Lamarck’s idea of use and disuse,
the vestigial pelvic bones should have disappeared
eventually because they were not being used. However,
vestigial structures still remain despite disuse.
11. In the Paleocene epoch, the animal is small, with a
short tail that is pointing up, as well as colour banding
on the body. In the Eocene epoch, the animal is bigger.
The body shape and head shape are quite different
from that in the Paleocene epoch. There is some colour
banding on half the body. The tail is a little shorter and
pointing down. In the Oligocene epoch, the animal
is bigger still. The body is a little rounder, and the
banding is gone or less distinct. The shape of the head
is similar to that in the Eocene epoch. In the Miocene
epoch, the animal is larger and the appearance of a
hump is clear. The neck is longer, as is the tail. In the
present, the tail is long with a tassel at the end; the
hump is obvious; the neck shape is different, with a
bend in it. The head shape is different, and the ears
are smaller.
Biology 11 Answer Key Unit 3 • MHR TR
9
12. Species that arrive on islands evolve from mainland
immigrants, so that populations adapt over time to the
unique environmental conditions of their new island
home, giving rise to unique organisms.
Caption Questions
Figure 8.10 (Student textbook page 338): Differences: The
chicken embryo is enclosed in a pouch-like structure in the
first illustration; the shapes are very different in the second
illustration of each embryo, with the fish shape becoming
obvious in the fish embryo; in the third illustrations,
the pouch is still evident in the chicken embryo but is
not noticeable in the fish embryo. Similarities: Both
embryos show a large eye; both show a pouch in the
second illustrations.
Section 8.1 Review Questions
(Student textbook page 331)
1. Deep rock strata are older than strata that are closer to
the surface of Earth. In the diagram, different species of
fossilized organisms are seen in different rock strata.
2. Students’ letters should feature terms associated
with Cuvier’s work, for example, revolutions, or
catastrophes, that killed species each time they
occurred and that corresponded to the boundaries
between rock strata.
3. Students’ graphic organizers should show how
catastrophism proposed occasional catastrophic events
that killed species, which were then replaced with
new species. Uniformitarianism proposed long, slow
change in which geological forces act as they act today.
Uniformitarianism explained that such slow changes
have big results.
4. If Earth is slowly changing, naturalists wondered
whether slow, subtle changes also occurred in
populations of organisms.
5. Over time, as the elephant used its trunk to reach for
and grasp food or drink water, the trunk would have
stretched. The elephant would pass on the stretched
trunk to its offspring.
6. No, because the broken leg could not be inherited as
a limp.
7. Malthus explained that populations grew faster than
their food supply, so some members of the population
would die. The best adapted members would survive
and reproduce; in so doing, they had the greatest
evolutionary “fitness.”
10
MHR TR • Biology 11 Answer Key Unit 3
8. a. Cuvier founded the science of paleontology and
proposed the idea of catastrophism.
b. Malthus proposed that there were limited resources
for the offspring born in populations, and many
individuals died in the struggle to obtain resources.
Thus, populations were eventually reduced by
starvation or disease.
c. Wallace independently proposed the theory of
evolution, forcing Darwin to publish his work.
d. Lyell was a geologist who proposed that slow, steady
changes in geology result from the same forces we
see acting today. Darwin applied this idea to
a theory to evolution.
e. Lamarck suggested that adaptations to the
environment result in changes in species over time.
9. Students’ concept maps should include the
following information:
• Georges-Louis Leclerc, Comte de Buffon—Author of
the 44-volume Histoire Naturelle, in which he publicly
challenged the idea that life forms are unchanging
and that Earth was 6000 years old
• Mary Anning—A fossil hunter who discovered the
first plesiosaur fossil in England
• Georges Cuvier—A French naturalist who founded
the science of paleontology and proposed the idea
of catastrophism
• Charles Lyell—A Scottish geologist who proposed
that slow, steady changes in geology result from
the same forces we see acting today in a process he
called uniformitarianism
• Jean-Baptiste Lamarck—A French naturalist who
suggested that an organism’s adaptations to the
environment resulted in characteristics that could be
inherited by offspring
• Thomas Malthus—An economist who proposed that
there were limited resources for the offspring born in
populations, and that many individuals therefore died
in the struggle to obtain resources. Thus, populations
were eventually reduced by starvation or disease.
• Charles Darwin—A British naturalist who explored
the natural history of many different countries and
locations, making careful observations. He merged
his observations with the work of many previous
individuals and developed the theory of evolution by
natural selection.
• Alfred Russel Wallace—A British naturalist who
independently proposed conclusions that were
similar to Darwin’s, thereby forcing Darwin to
publish his work.
10. There were too many trout in the lake to be supported
by too few resources.
11. Darwin thought the word evolution implied progress,
the idea that each generation was somehow improving
in some way, whereas descent with modification implied
no demonstration of progress and no set direction.
12. The finches and other animals Darwin saw on the
Galapagos Islands closely resembled animals he had
observed on the west coast of South America. Through
his experiments with artificial selection (breeding
pigeons and studying breeds of dogs and varieties of
flowers), Darwin realized it was possible for traits to
be passed on from parent to offspring and that sexual
reproduction resulted in many variations within
a species.
13. Students should include the following four main ideas:
Organisms produce more offspring than can survive
and must therefore compete for limited resources;
much of the extensive variation in a population
is heritable; individuals that are better suited to
local environmental conditions survive to produce
more offspring; and processes for change are slow
and gradual.
14. a. The species on islands were related to or arose from
ancestral populations on nearby continents.
b. There is variation among individuals in
a population.
c. Organisms compete for limited resources.
15. You would observe that traits do get passed on from
parent to offspring.
Section 8.2 Review Questions
(Student textbook page 340)
1. Darwin was the first to bring together all of the ideas
on evolution that were in existence and to see the
significance of these ideas on a large scale. He was also
the first to publish his work, although he probably
would not have if Alfred Russel Wallace had not been
preparing to publish the same ideas.
2. The order of the main groups in the fossil record
supports the idea that organisms evolved at different
time periods in evolutionary history, rather than all
at the same time.
3. Transitional fossils show the in-between stages in the
fossil record, allowing gaps to be filled as early forms
transition into later forms.
4. Sample answer: The Archaeopteryx fossil shows
an extinct form of bird that has characteristics of
both birds and dinosaurs, making it a transitional
fossil between two, now separate, groups. This fossil
provides information about how long birds have been
in existence and provides evidence that they share
characteristics with dinosaurs.
5. Finding a whale with hind legs shows that whales
evolved from terrestrial mammal ancestors that
had limbs.
6. You would expect to find organisms similar to those
in Africa near where the island of Madagascar split
from it; organisms could have drifted or flown from the
continent to the island or been carried by wind from
the African continent to the island of Madagascar.
7. Students could hypothesize that the species on
Madagascar would have to compete with existing
African species, and would either expand into
new habitats and diversify or become extinct. This
hypothesis could be tested by sampling biodiversity
over a long period of time and observing any changes.
8. Comparing anatomy can show homologous structures
that provide evidence of shared ancestral history, and
also vestigial structures show that organisms share
structures with an ancestor, even if they do not need
these structures.
9. Homologous structures
10. Analogous structures perform similar functions
even though the organisms do not share a recent
common ancestor. Homologous structures have
similar structural elements and origins, but may have
different functions.
11. They are analogous structures because they
share a similar function but have different
evolutionary origins.
12. A vestigial structure is a structure that is the reduced
form of a functional structure in an organism’s
ancestors. For example, ancestors of the modern whale
had hind limbs; therefore, they also had pelvic bones
in order to use the limbs. Some modern whales do not
have hind limbs but they do have a pelvic bone.
13. Vertebrates are related to each other, so they share
similar early stages.
14. Students should include evidence from the fossil
record, from biogeography, from anatomy, from
embryology, and from comparative DNA studies in
their concept map.
Biology 11 Answer Key Unit 3 • MHR TR
11
15. Scientific facts are the data that scientists gather, and
scientific theories attempt to explain facts and connect
them together in a comprehensive way. Facts that
support the theory of evolution include the presence of
homologous structures, transitional fossils in the fossil
record, biogeography, and DNA relationships.
16. These animals share a common ancestry with
other mammals.
17. Sample answer: First, a giraffe population varies in
neck length from short to long and this variation is
heritable. → Long-necked giraffes are more successful
at reaching leaves in the high canopy of trees. → There
is competition for food and there is not enough food
for all giraffes. → Long-necked giraffes compete more
successfully for food, survive longer, and produce more
offspring compared to short-necked giraffes. Over a
long period of time, the giraffe population has a greater
proportion of individuals with long necks.
Chapter 8 Review Questions
(Student textbook pages 343–5)
1. e
2. b
3. c
4. b
5. a
6. b
7. c
8. d
9. Darwin had gathered a lot of evidence to support his
theory but he could not explain exactly how natural
selection works because the science of genetics was not
advanced enough at that time.
10. They show that as organisms evolved from a common
ancestor, the same structures were put to different uses
and became modified into the structures visible today.
11. Darwin’s observations included the following:
• The flora and fauna of the different regions the Beagle
visited were distinct from the flora and fauna that
Darwin had studied in England and Europe.
• Some fossils of extinct organisms looked very similar
to living animals.
• Organisms on the Galapagos Islands closely
resembled animals he had observed on the west coast
of South America.
• Galapagos species looked identical at first, but they
varied slightly between islands.
12
MHR TR • Biology 11 Answer Key Unit 3
• Darwin had significant experience with artificial
selection, so he knew that traits could be passed from
parent to offspring and that sexual reproduction
resulted in many variations within a species.
12. Lamarck would say that the fish lost their sight
because they did not use it. Darwin would say that
eyes had no advantage for survival, so eyes were not
selected for and they therefore became vestigial and the
fish became blind.
13. Embryology shows that many different species exhibit
a common embryological development, supporting the
idea that they shared a common ancestor.
14. a. They do not overrun the Earth because resources
are limited so individual insects must compete with
other insects for resources and not all survive.
b. This was significant because it made him consider
the idea that there was a struggle for survival, and
only some individuals in the population will survive
the struggle and go on to reproduce.
15. The more similar their DNA sequences are, the more
closely related the organisms are.
16. A functionless or rudimentary version of a body part
in a species is evidence that the species was descended
with modification from an ancestor with a fully
developed and functional structure. Hence, organisms
with vestigial structures are related to ancestral
organisms that had functioning structures.
17. The strata correspond to different times or eras, with
the fossils from earlier times and eras appearing below
the fossils from later times that would have been laid
down on top of older strata. These strata and the fossils
in them provide a sequence of evolutionary events
and can show major changes, such as the movement
of organisms from aquatic environments onto land,
as well as which types of organisms arose from earlier
ancestors. Rock strata and the fossils in them can also
highlight mass extinction events.
18. Like Lamarck, Darwin emphasized the importance of
the adaptation of organisms to their environment.
19. Red Island will have species that were able to cross the
500 km between Red Island and South America, and
the animals will be very similar to the South American
animals. Blue Island will have species that have evolved
from animals that were once South American, but that
were isolated after the separation of Blue Island from
the continent. Thus, the animals on Blue Island will be
very different from animals in South America.
20. No, these species are separated so extensively
geographically that they descended from different
ancestors; however, they responded to similar
environmental pressures, thus making them appear
very similar.
27. Answers should include evidence from the fossil
record, biogeography, anatomy, DNA, and embryology.
21. The fossils in the lower strata are older than the fossils
in the rocks in the upper strata, but the fossil species
did not undergo significant evolutionary change.
Fossils found at different times can be compared
to see if there are any common features. If so, this
indicates that there has been either slow or little
evolutionary change.
29. Students’ presentations will vary depending on the
format they choose, but the content should show
that they understand the key points of the theory of
evolution by natural selection. All life descended from
some unknown organism and as the descendents
spread out over different habitats, they developed
adaptations that helped them survive in their local
environments. Populations of individual species
become better adapted to their local environments
over time. They do so because organisms compete for
limited resources, there is heritable variation present
among individuals in a population, individuals that are
better suited to local environmental conditions survive
and produce more offspring, and the entire process can
occur over very long periods of time.
22. Students’ answers should include that all of these
organisms need food and an environment in which
to grow, and the plants and animals need mates and
water. These are all factors that might limit the growth
of their populations.
23. a. Number of seeds = number of pumpkins × number
of seeds/pumpkin = (70 × 2) pumpkins × 70 seeds/
pumpkin = 9800 seeds
b. Number of seeds = number of seeds available (9800
seeds) × number of pumpkins/seed (2) × number
of seeds/pumpkin (70) = 9800 seeds × 2 pumpkins/
seed × 70 seeds/pumpkin = 1 372 000 seeds
c. Populations are eventually reduced by lack of
sufficient resources, such as physical space, nutrients
or food, or by disease.
24. It would have been easier. Darwin reached his
conclusions about evolution without understanding
how the mechanism of natural selection worked.
Genetics would have explained that mechanism.
25. a. The number of digits must have been reduced from
five to four during the evolution of chickens and
other birds, but the fifth digit still appears for a short
period during the early development of birds.
b. Since most living vertebrates have five digits, the
temporary fifth digit during the early development
of chickens and other birds shows shared ancestry
with other vertebrates.
26. Sample answer: No, evolution does not mean that
organisms are becoming progressively better with
each generation. Instead, they are just becoming
better adapted to their environments. The changes in
organisms are random, and they are based only on the
selective pressure of the organisms’ environments.
Genetic variation provides the raw material that the
environment acts on. Selective pressure selects for
certain genetic variation, and, over time, populations
change and evolve.
28. Students’ answers should include the fact that
homologous structures have a common origin and
analogous structures have a common function.
30. Students’ diagrams should communicate the following
information: There is variation among individuals of
the same species, species adapt to local conditions,
which are variable among locations, and different traits
are better suited to different local conditions.
31. Sample dialogue:
Darwin: “All organisms exhibit variation, and variation
is essential for evolution to occur. Nature selects for
individuals with favourable variations as they survive
and reproduce more successfully than others without
these variations.”
Lamarck: “Variation is important but variation can be
environmentally induced in individuals within their
lifetime and this acquired variation can be passed on
to offspring.”
Darwin: “I disagree. Variation must first exist in
populations and selection shows favouritism among
this variation.”
32. The points should include the four main ideas
comprising Darwin’s theory of evolution by natural
selection; links could include web pages providing
evidence that supports the theory; personal interest
links, links to Darwin, Lamarck, Cuvier, and other
scientists, and so on.
Biology 11 Answer Key Unit 3 • MHR TR
13
33. Facts are individual pieces of information based on
observational evidence. A theory is developed from
a group of facts that all support and strengthen a
particular idea. Students’ graphic organizers will show
that combined facts that support a single conclusion
are comprehensively grouped into a single theory.
Theories, in the scientific sense, are never based on
a single fact or a few facts, and for a statement to be
called a theory, there must be no dissenting facts. If
there were, the theory would need to be revised to
account for the discrepant facts.
34. The fossil record captures what happened in a
particular location at a particular time. In that way, it is
like a picture or a snapshot.
35. Students’ graphic organizers should include two
sections, “Scientific Contributions to a Theory of
Evolution” and “Sources of Evidence for Evolution,”
reflecting the two sections of Chapter 8. Answers
should show an understanding of the work of the many
thinkers who supported Darwin’s direct observations
and that led to Darwin’s formulation of the theory of
evolution by natural selection, and also how many
different lines of scientific evidence from before,
during, and after Darwin’s time all support the theory
of evolution by natural selection.
Question
Yes
Is the body shape
streamlined?
Yes
Yes
Does the animal have
teeth?
Yes, coneshaped
Yes, several rows
of very sharp teeth
The similarities are analogous because the ancestral
conditions are not common to both dolphins (a dolphin is
a mammal) and sharks (a shark is a fish).
40. a. Archaeopteryx
b. Bird ancestors had clawed appendages.
41. The fossil record could be examined to see where the
extinct animal fits into the evolutionary sequence.
Biogeography could be helpful, depending on where
the remains of the organism were found and where
other related organisms have been found. The
organism’s brain tissue could be used in DNA analysis
to indicate shared evolutionary relationships between
this organism and other organisms.
Chapter 8 Self-Assessment Questions
(Student textbook pages 346–7)
1. c
2. b
37. Homologous structures, such as the anatomy of joints
and the interior of bones, support the idea that birds
and dinosaurs have a common ancestor. Finding
a transitional fossil provided the most compelling
evidence for this relationship.
5. e
38. Dawkins means that natural selection does not have
a particular end goal, so it has no purpose in terms
of influencing future events. Natural selection occurs
in response to changes in local conditions, not in
response to potential future conditions that are as
yet unknown.
9. b
Question
Dolphin
Shark
How does each animal
breathe?
Comes to
surface for air
Gills
Does the animal nurse its
young?
Yes
No
What is its skeleton made Bone
of?
Cartilage
Is the animal a mammal?
No
14
Yes
MHR TR • Biology 11 Answer Key Unit 3
Shark
Yes
36. Disagree. The pelvic bones are vestigial features that
would have served as the point of attachment for an
animal with legs. This shows that snakes evolved from
an ancestor that had legs.
39. Comparison of Dolphins and Sharks
Dolphin
Does the animal have a
fin on the top?
3. e
4. a
6. a
7. a
8. a
10. c
11. It is a similar structure in related species due to
common ancestry, but structures may have different
functions. Examples may include the forelimb
in vertebrates.
12. a. layer A
b. layer A
c. layer D
13. Answers might include evidence from the fossil record
and from the fields of embryology, genetics/DNA,
anatomy, and biogeography.
14. a. Lamarck would say that they would pass this learned
behaviour on to their offspring, so it would become
a natural trait.
b. No, I do not agree because looking both ways before
crossing the street is a learned behaviour, not a
heritable genetic trait, so it will not be passed on to
the next generation.
24. Lyell proposed the process of uniformitarianism, in
which geological processes operated at the same rates
in the past as they do in the present. This led to the
conclusion that the Earth was much older than people
thought at the time, and that therefore slow, subtle
changes could also occur in populations as well as in
geological processes.
15. Archaeopteryx showed an important link between two
groups of organisms once thought to be unrelated:
birds and reptiles.
25. Sample answer: Biogeography is the study of the
geographical distribution of species, in the present
and in the past, and correlating that distribution with
their ancestral relationships. For example, species that
are very similar are probably located near each other
because they may have arisen from a shared common
ancestor. Species that are very dissimilar are probably
located far apart from each other and do not share a
common ancestor.
16. Lamarck’s idea was that characteristics acquired during
an organism’s lifetime can be passed on to its offspring.
The idea is not a theory because the individual facts
do not support it. It is incorrect because acquired
characteristics are not genetically based and are
therefore not heritable by offspring.
17. Embryology can reveal similarities in related species
and thus provide evidence of evolutionary relationships
between organisms.
18. a. Birds and reptiles must have a common ancestor.
b. Feathers may have evolved from scales.
19. Yes, Darwin would support the idea that evolution
does not necessarily lead to more advanced species, but
rather leads to descent with modification over time due
to natural selection shaping traits in species over a long
period of time.
20. Non-indigenous specimens might be well adapted to
local conditions here in Canada and they might be able
to outcompete native species. These types of organisms
are called invasive species and they can decimate
natural native Canadian species.
21. Answers may include that a functionless gene due to
a gene mutation could be considered a vestigial trait if
the gene once functioned in a related ancestor.
22. Answers should show that these structures provide
evidence for evolution and descent with modification.
Differences include: homologous structures have a
common ancestral origin but differences in function;
analogous structures have a different ancestral origin,
but have a common function; and vestigial structures
show a reduced version of a fully functioning structure
in a related ancestor.
Chapter 9 Evolution and Speciation
Learning Check Questions
(Student textbook page 352)
1. Because evolution is measured by changes to the gene
pool of a population, the population evolves rather
than individuals.
2. If mutations allow a few individuals in a population
to thrive and reproduce at a greater rate in a changing
environment than other individuals in the population,
then these mutations have provided those few
individuals with a selective advantage over the rest.
3. “Allele frequency” is the number of copies of an
allele with respect to the total number of alleles in
a population.
4. When migrating individuals join a new population,
they increase the genetic diversity of the new
population by introducing their genes into the gene
pool of this population. The greater the migration
between populations, the greater the mixing of
the gene pools of these populations, which results
in the reduction of genetic differences between
these populations.
5. Answers should reflect the content shown in Figure 9.1
and the diagram should be titled or captioned with
reference to eastern grey squirrels.
23. Catastrophism proposed occasional catastrophic events
that caused extinction of species, which were then
replaced with new species from nearby geographical
areas. Uniformitarianism proposed long, slow change
during which geological forces act as they act today.
Biology 11 Answer Key Unit 3 • MHR TR
15
6. Random mating describes mating between any two
individuals in a population in such a way that it
cannot be predicted. Non-random mating, on the
other hand, describes mating between two individuals
that can be predicted based on choices of preferred
physical or behavioural traits, or phenotypes. Unlike
random mating, non-random mating is more common
in nature because it increases the fitness of the
mating individuals.
(Student textbook page 356)
7. Inbreeding is a form of non-random mating because it
occurs when closely related individuals breed together,
rather than breeding with unrelated members of their
population at the same frequency.
8. Small populations do not have high levels of genetic
variation because there are not many individuals in a
small population. Therefore, random events can cause
genetic drift by affecting the variation in the gene pool
more so than would be expected in a large population.
In other words, each individual in a small population
represents a larger portion of the population’s gene
pool than each individual in a large population, so
events affecting individuals will probably have a
larger effect.
9. The differences in a gene pool that result from the
founding of a population by a few individuals that do
not completely represent the gene pool of the original
population is known as the founder effect.
10. Changes to the gene pool that result from a rapid
decrease in the size of a population is known as the
bottleneck effect.
11. Generally, the founder effect results in a reduction
in the genetic diversity in the gene pool of the new
population relative to the original population.
However, depending on the genetics of the founders,
some alleles that were at low frequencies in the
original, larger population may increase in frequency
because of the small number of individuals in the
new population.
12. A suitable answer will involve events that demonstrate
a rapid reduction in population size. Such events could
include any two of the following: starvation, disease,
human activities such as overhunting, and natural
disasters such as severe weather.
16
MHR TR • Biology 11 Answer Key Unit 3
(Student textbook page 363)
13. A biological species is a population or a group of
populations in nature whose individual members can
interbreed to produce viable, fertile offspring.
14. The Venn diagram should be made up of two circles
labelled “Pre-zygotic Isolating Mechanisms” and
“Post-zygotic Isolating Mechanisms.” The area of
overlap should include “Mechanisms that prevent
the production of viable and fertile offspring.” The
independent portions of each circle should include the
correct listings of mechanisms for that grouping.
15. Reproductive isolation is maintained because part of
the effect of reproductive isolation is the prevention of
the production of fertile offspring.
16. The reproductive isolating mechanism is temporal
isolation.
17. They would be considered different species. Aside
from the fact that these two different species cannot
produce viable, fertile offspring, the biological species
definition requires that individuals of populations
must interbreed in nature, and the definition does not
include artificial conditions.
18. The reproductive isolating mechanism is
habitat isolation.
(Student textbook page 365)
19. For speciation to occur, a population must either
become divided into at least two populations that are
reproductively isolated from each other, or become
reproductively isolated from its parent species.
20. Sympatric speciation involves the creation of a species
within the same geographical area, while allopatric
speciation involves the creation of a species as a result
of a geographical barrier.
21. Sympatric speciation is more common in plants than in
animals, because animals are typically diploid, whereas
plants are more commonly polyploid.
22. The two different species of squirrels living on either
side of the Grand Canyon are an example of allopatric
speciation, because the Grand Canyon is too large
to allow these animals to journey from one side to
the other.
23. Smaller populations are more likely to undergo
speciation than larger populations for the
following reasons:
• They become isolated on the periphery of their
species range, where local environmental conditions
may be different compared to the average
environmental conditions of the parental species
range. As a result, natural selection is more likely
to occur, which changes the gene pool of the small
population relatively quickly.
• They are likely to have greater genetic differences
between themselves and the average parental
species population.
• Their small population size allows genetic drift to
have a larger impact on the population’s gene pool.
24. No; many isolated populations do not live long enough
or change enough to undergo speciation.
(Student textbook page 370)
25. An ecological niche is the ecological role and the
physical distribution of a species in its environment.
26. It would have been possible because there were no
other land birds on the island, and there were many
unoccupied ecological niches to move into and adopt.
27. Allopatric speciation occurs when a population of
a species becomes reproductively isolated from its
parental species as a result of a geographical barrier.
This is what happened to the finches that reached the
islands and were then separated from their parental
species by the ocean.
28. Adaptive radiation is the diversification of a common
ancestral species into a variety of differently
adapted species.
29. In the “Divergent Evolution” circle of the Venn
diagram, students should write: new species become
distinct from ancestral species due to changing
environmental conditions; in the “Convergent
Evolution” circle, students should write: species with
similar adaptations arise from different ancestral
species due to similar environmental conditions; in the
overlapping area of the Venn diagram, students should
write: new species arise.
30. Gradualism describes evolution as the result of the
slow and steady accumulation of many small changes
over a long period of time. Punctuated equilibrium
describes evolution that occurs suddenly, in a short
period of time, followed by long periods of little
change. Both of these models can be used to explain
evolution by natural selection, because natural
selection accounts for the effects of the pressures that
changing environments exert on the gene pool of a
population, changes that can occur very gradually and
also very suddenly.
Caption Questions
Figure 9.2 (Student textbook page 351): Scientists might
have difficulty defining distinct grey wolf populations in
North America because gene flow between populations has
probably resulted in populations with a wide variety of coat
colours, rather than just one coat colour.
Figure 9.3 (Student textbook page 352): Caribou males
with antlers and any other traits that help them win
more mates are more likely to pass on their traits to the
next generation. In this way, the frequencies of alleles
responsible for “winning traits” increase in the gene pool,
changing the composition of the gene pool.
Figure 9.11 (Student textbook page 360): The offspring
would not be viable according to the biological species
definition, given that these two zebras are members of two
different species.
Section 9.1 Review Questions
(Student textbook page 359)
1. Mutations are the only source of new genetic
variation. They contribute new alleles to the gene pool,
increasing variation.
2. Microevolution is the changing percentages, or
frequencies, of alleles within populations. Individuals
are not affected because they have only their genotype,
which will not change during their lifetime.
3. Non-random mating can create inbreeding, as seen
in self-fertilization in some plants. This increases the
expression of harmful recessive alleles. Non-random
mating in animals can change the phenotype of the
population, as seen in the antlers of caribou.
4. Students’ graphic organizers should show stabilizing
selection as a selection favouring intermediate
phenotypes and not favouring extreme phenotypes;
directional selection favouring the extreme phenotype
on one end of the distribution curve, shifting the curve
in that direction; and disruptive selection favouring
both extremes over the intermediate, resulting in the
elimination of the intermediate form.
Biology 11 Answer Key Unit 3 • MHR TR
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5. Sample answer: In left-hand portion of Venn diagram:
founder effect; extreme example of genetic drift; small
sample of a population is separated from the rest of the
population. In centre of Venn diagram: mechanism of
evolution; type of genetic drift. In right-hand portion
of Venn diagram: Bottleneck effect; change in gene
pool as a result of a rapid decline in population size.
6. a. The current world population of cheetahs has very
little or no genetic variation, so the genetic material
of the donor and the recipient of the skin transplant
would be extremely similar, reducing rejection rates.
b. Genetic drift in the form of the bottleneck
effect would be the most likely mechanism. The
bottleneck effect results from a rapid decrease in
population size.
c. A lack of genetic variation makes them vulnerable
to changing environmental conditions, for example,
the spread of new diseases and parasites. An animal
exchange program between conservation groups
would help maintain the existing genetic variation
in cheetahs.
7. The bottleneck effect. One example is the cheetah
population; another is the northern elephant
seal population, both of which have little to no
genetic variation.
8. The diagram should show the two separate gene
pools merging and becoming one, so that there
are no differences in gene frequencies among the
two populations.
9. Genetic variation would be lost from the gene pool
that loses the individuals with rare alleles. Fewer
homozygous recessive genotypes might remain.
10. Mutation is the ultimate source of genetic variation.
When a new allele arises as a result of a mutation,
it can spread throughout the population, thereby
changing the gene frequencies.
18
MHR TR • Biology 11 Answer Key Unit 3
11. One probable outcome is reduction in frequency of
the green meeps and an increase in frequency of grey
meeps, as they would survive and reproduce more
successfully. The frequency of the allele for the grey
meeps would increase, and the frequency of the allele
for green meeps would decrease.
Section 9.2 Review Questions
(Student textbook page 373)
1. Reproductive isolation means that species are unable
to reproduce with each other, for a variety of possible
reasons, including prevention of mating, prevention of
fertilization, or prevention of the survival of hybrids.
2. Yes, the offspring will not be able to reproduce, so the
shared genetic material will not be maintained past the
one generation of offspring.
3. Yes, the mice would possibly become two separate
species because they are now geographically isolated
from each other and cannot interbreed. The birds
would not become two separate species because they
can fly over the river, are not geographically isolated,
and can continue to interbreed.
4. This reproductive barrier is a prezygotic isolating
mechanism called ecological/habitat isolation.
5. Sample answer: An example of students’ interpretation
might be to notice that a common ancestor (unnamed,
but belonging to the Genus Camarhynchus) gave rise
first to a tree finch that was strictly vegetarian in its
diet. That species gave rise to one species (woodpecker
finch) that had evolved to include insects in its diet
(students should be able to make this inference). Two
other species diverged from the vegetarian species that
were also adapted for an insectivorous lifestyle, with
one being larger and another smaller—presumably to
take advantage of niches that favoured either larger or
smaller birds. Students might note that all four species
that arose from the vegetarian tree finch remained treeliving species.
6.
Comparison of Isolating Mechanisms
Type of
Isolating
Mechanism
Description
Behavioural
isolation
Pre-zygotic mechanism
that prevents different
species from mating
because of species-specific
signals or behaviours
Differences in the
mating calls of
frogs
Temporal
isolation
Pre-zygotic mechanism
that prevents different
species from mating
because of timing barriers
Flowers that bloom
at different times in
a season
Ecological/
habitat
isolation
Pre-zygotic mechanism
that prevents different
species from mating
because individuals from
different species do not
encounter each other
Some fish that live
in shallow water
compared to fish
that live in deep
water
11. The different islands all have specific local conditions
to which the lizards have adapted. These different
lizards have undergone adaptive radiation, in which
there is diversification from a common ancestor based
on different conditions.
Mechanical
isolation
Pre-zygotic mechanism
that prevents fertilization
between different species
because of anatomical
incompatibility
Genital anatomy
may vary enough
that the species’
parts do not fit
together.
Gametic
isolation
Pre-zygotic mechanism
that prevents fertilization
between different species
because the gametes (egg
and sperm) do not meet
Pollen grains from
one plant may
not survive the
conditions found
on the stigma of
another plant.
12. The small horses may not have been able to compete
with larger horses for food or habitat (hypothesis
related to natural activity). Early humans may
have hunted the small horse for food, reducing the
population and causing its extinction (hypothesis
related to human activity).
Zygotic
mortality
(Figure 9.12)
or hybrid
inviability
(page 363)
Post-zygotic mechanism
that prevents hybrids by
stopping the zygote from
developing
Hybrid embryos
between sheep and
goats die in early
development.
Hybrid
sterility
Post-zygotic mechanism
that prevents hybrids
by keeping the hybrid
offspring from producing
viable offspring
Mules are the
product of horses
and donkeys but
are sterile.
Post-zygotic mechanism
that prevents hybrids
by preventing second
generation offspring from
producing viable offspring
Cotton plants
produce fertile
hybrids, but those
offspring do not
survive.
Hybrid
breakdown
Example
8. Human activities may fragment habitats when
people build roads and suburbs. These barriers may
geographically isolate some species, encouraging
speciation events. Unregulated hunting can cause large
and rapid species decline, leading to genetic drift in the
form of the bottleneck effect.
9. Students’ graphic organizers may resemble Figure 9.19.
Gradualism proposes slow and steady change from
one form to another, whereas punctuated equilibrium
proposes long periods of no change (stasis)
interspersed with periods of rapid divergence.
10. A mass extinction is a sharp decline in the number
of species.
13. One ancestral crossbill species was able to extract the
seeds from closed cones. This allowed subsequent
generations to radiate into new habitats and access new
sources of food for which there was no competition.
The crossed bill allowed new species to develop based
on the availability of a specific type of food.
Chapter 9 Review Questions
(Student textbook pages 379–81)
1. d
2. e
3. b
4. d
7. No, rodents and anteaters do not share a common
ancestor, and thus the spiny skins are a result of
convergent evolution, whereby environmental
conditions cause similar adaptations to occur.
5. a
6. b
7. d
8. e
9. This is a result of adaptive radiation. Species were
isolated on the islands, and as a result they were
able to diversify as they took advantage of specific
resources that were available to them in the absence
of competitors.
Biology 11 Answer Key Unit 3 • MHR TR
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10. Sample answer: Temporal isolation is a pre-zygotic
isolating mechanism that prevents different species
from mating because of timing barriers, for example,
flowers that bloom at different times in the season.
Hybrid sterility is a post-zygotic isolating mechanism
that prevents hybrids by keeping the hybrid offspring
from producing viable offspring; for example, mules
are the product of horses and donkeys but are sterile.
11. a. This is behavioural isolation; distinctive patterns
of flashes prevent the species from identifying a
potential mate.
b. This is temporal isolation; because the two species
of grasses flower at different times, fertilization
is prevented.
c. This is hybrid breakdown; although the firstgeneration hybrids of crossed species are viable and
fertile, offspring of the next generation are sterile
or weak.
d. This is ecological/habitat isolation: because the
two species live in the same general region but in
different habitats, they rarely encounter each other.
12. If the environment is stable, gradualism, or even stasis,
can occur. However, periods of rapid environmental
change will produce periods of rapid divergence, as
seen in punctuated equilibrium.
13. There is less genetic variability in small populations,
so it is easier for the gene frequencies to change in
response to environmental conditions. This shift in
gene frequencies is the cause of microevolution.
14. Rivers can be geographically isolating if species are
unable to cross them to interbreed with populations
on the other side. Non-swimming species would be
isolated by a river. Birds or species that can swim
across the river would not find the river to be a
reproductive barrier.
15. The species of fruit flies would probably be the result
of adaptive radiation, whereby increased species
diversity is possible due to a lack of competition from
other species over time, so ancestral species are able to
diverge to take advantage of specific resources.
16. The bird’s call can be a pre-zygotic isolating
mechanism, called behavioural isolation, whereby the
call attracts mates of the same species but not of others.
17. The model on the left represents gradualism,
characterized by slow, steady change; the model on the
right represents punctuated equilibrium, characterized
by periods of no change followed by events of
sudden change.
20
MHR TR • Biology 11 Answer Key Unit 3
18. The only way to be completely certain is to compare
the DNA of the different birds or to try to crossbreed
the birds to see if they can reproduce. This second
method would take too long, so DNA comparison is
the better choice. Some birds of the same species look
very different, whereas some birds of different species
look very similar, making visual inspection uncertain.
19. Biodiversity increases as a result of microevolution
working on the surviving species that did not become
extinct. Natural selection would drive evolution, and
the lack of competition would allow for adaptive
radiation to occur.
20. Adaptive radiation would be more likely to occur on
islands that are remote, because there would be less
chance of organisms from nearby continents arriving
and competing for resources.
21. This is an example of non-random mating, where
females select mates on the basis of their strength
in head-butting. If males do not participate at all,
they will not reproduce at all, so this behaviour has
evolutionary advantages even if some individual males
may not survive.
22. Students’ charts should show that this extinction
event was the result of an asteroid impact that caused
massive forest fires. The smoke and particulate matter
from the fires would have blocked the sun for months
or even years, reducing the availability of food and,
as a result, the dinosaurs became extinct.
23. Species that do not reproduce sexually are clones of the
parents, meaning that they cannot be classified as being
in different or the same species based on the viability
of their offspring. They would need to be classified into
species on the basis of other characteristics such as
DNA or morphological characteristics.
24. Some limitations include the fact that determining if
different species can interbreed may be difficult or even
impossible (due to time or observational constraints),
as well as the fact that this method is not useful for
asexually reproducing organisms or fossil organisms.
25. a. They would probably not be too similar because
they exist together on at least one of the islands. The
two species would need to be able to exploit food
on the islands, meaning they are probably eating
different things.
b. I would not expect that the morphology would be
different in more distantly related species. The more
significant issue would be what types of resources
the different finch species need.
26. Students’ presentations need to highlight that
geographical barriers reduce the potential for mating
between populations, leading to reproductive isolation
and ultimately speciation.
27. Students’ essays should show that they understand
that genetic variation is the raw material that natural
selection can act on. Changing environmental
conditions and insufficient resources for all individuals
means that some individuals but not all will survive
and be able to pass along their genes to offspring. The
process of this differential survival drives changes in
gene frequencies, which results in microevolution.
28. Students’ illustrations should show that sea stars
with the largest muscles are able to access the most
food and, therefore, survive and reproduce more
successfully than sea stars with smaller muscles.
Over time, the sea stars should develop progressively
larger muscles as the offspring inherit the alleles for
large muscles.
29. Since post-zygotic isolating mechanisms are essentially
reproductive dead ends and since natural selection
involves heritable traits, this would suggest that
natural selection cannot favour post-zygotic isolating
mechanisms. Students’ flowcharts or diagrams would
have to indicate some sense of “ongoing-ness” to
prezygotic isolating mechanisms and a sense of
termination for post-zygotic isolating mechanisms.
30. Students’ graphic organizers should reflect the
following information:
The biological species concept focuses on similar
characteristics and the ability of organisms to
interbreed in nature and produce viable, fertile
offspring. The advantage is that this species concept
can be widely used by scientists. The disadvantages
are that the concept cannot be used in all cases. For
example, if two species never have the chance to
interbreed based on geographical separation, the viable
offspring condition cannot be tested. The concept
cannot be applied to asexually reproducing organisms,
nor to fossil species that are no longer reproducing.
31. Students’ graphic organizers should reflect the idea that
gradualism suggests evolutionary change to be slow
and steady, whereas punctuated equilibrium proposes
that evolutionary change occurs in bursts of rapid
diversity interspersed with long periods of stasis.
32. Students’ diagrams should reflect an initial population
with relatively low variation in the gene pool. Students
can show how removing a small number of individuals
can reduce the variation in the gene pool even further
if individuals with rare alleles are affected.
33. Students’ graphic organizers should include two
sections, “Mechanisms of Evolution and Their Effect
on Populations,” and “Speciation: How Species Form,”
reflecting the two sections of Chapter 9. Answers
should show an understanding of gene flow, nonrandom mating, genetic drift, natural selection, and
stabilizing, directional, and disruptive selection.
Answers should also show an understanding of
reproductive isolating mechanisms, sympatric and
allopatric speciation, adaptive radiation, convergent
and divergent evolution, and gradualism versus
punctuated equilibrium.
34. Students’ visuals for taxis might include the instinct to
pull away quickly from a fire or hot object, or grabbing
for an object if it is about to fall. Students’ visuals for
migration patterns should reflect their research on
migration, showing long-term migration patterns over
long distances.
35. a. natural selection
b. genetic drift—the bottleneck effect
c. gene flow
d. gene flow
e. genetic drift—the founder effect
36. I would respond that the Earth has seen five mass
extinction events and each time, biodiversity rebounds.
Biodiversity tends to increase at some point after
a mass extinction because there will be resources
available for which there will be no competition.
The difference between the current extinctions and
previous mass extinction events is that this one is being
caused by human activity, whereas previous events
were naturally occurring.
37. a. pre-zygotic—temporal isolation
b. pre-zygotic—behavioural isolation
c. post-zygotic—hybrid sterility
d. pre-zygotic—habitat isolation
e. pre-zygotic—behavioural isolation
38. a. reduction in habitat; pesticide use
b. The monarch migration requires three to four
generations of monarchs, as the trip is longer than
the lifespan of the butterfly. The monarch butterfly
larvae eat milkweed, so as the milkweed population
declines, the number of larvae that survive
also declines.
Biology 11 Answer Key Unit 3 • MHR TR
21
39. a. Grizzlies (or the opportunity to see them) are a
tourist attraction, so economically there could be
reduced tourist dollars. Politically, grizzlies are a
symbol of the Canadian wilderness, so many people
would be upset about their extinction and would
push for different and improved species-at-risk plans
and legislation. Socially, again grizzlies are a symbol
of the Canadian wilderness, and it would diminish
the Canadian identity if grizzlies no longer existed in
the wild.
b. Wildlife corridors would allow gene flow between
different populations of grizzlies, increasing their
genetic diversity and reducing the impact of
genetic drift.
40. The implications have primarily to do with the
vulnerability of small populations to genetic drift.
It is easy to lose genetic diversity, which then makes
populations vulnerable to changes in the environment,
or to diseases.
Chapter 9 Self-Assessment Questions
(Student textbook pages 382–3)
1. b
2. c
3. b
4. d
5. c
6. c
7. b
8. d
9. b
10. b
11. a. Data on the iguanas’ reproductive success if they
have opportunities to interbreed would help
you decide.
b. Their DNA could be compared for similarity
or dissimilarity.
12. The graphic organizer should be arranged so
that species are a result of reproductive isolation,
and so that both pre-zygotic and post-zygotic
isolating mechanisms are a way to maintain
reproductive isolation.
13. a. This is a pre-zygotic isolating mechanism called
behavioural isolation. Other species of ants will not
respond to the chemical signals so different species
will not mate.
22
MHR TR • Biology 11 Answer Key Unit 3
b. This is a pre-zygotic isolating mechanism called
temporal isolation. Different timing of mating
means the two species will not interbreed.
c. This is a post-zygotic isolating mechanism called
hybrid inviability. The offspring will not survive and
cannot pass along genetic material.
14. Allopatric speciation occurs when a population is split
into two or more isolated groups due to a geographical
barrier that prevents gene flow. Eventually the two
groups will not be able to interbreed even if they are
reconnected. An example could be a fluctuation in sea
levels that turns an archipelago or a peninsula into
an island.
15. The rise and fall of the lake levels may create
geographic barriers where gene flow is disrupted
among fish populations, for example, if the lake level
drops so that land is exposed, thus creating isolated
pools of water where allopatric speciation can occur.
16. In the founder effect portion of the Venn diagram, the
new population is started by only a few individuals
that become isolated from the larger population. In the
shared portion of the Venn diagram, both are examples
of genetic drift. In the bottleneck effect portion of the
Venn diagram, a once large population is drastically
reduced by some natural disaster or human activity
such as overfishing.
17. This is an example of non-random mating, and it will
result in microevolution that produces a population
of toads with no size difference between males
and females.
18. One model, called gradualism, suggests evolutionary
change to be slow and steady, whereas the other
model, called punctuated equilibrium, proposes that
evolutionary change occurs in bursts of rapid diversity
interspersed with long periods of stasis.
19. Students’ flowcharts should show that non-random
mating, where individuals choose mates based on
physical or behavioural traits, can result in increased
levels of homozygosity if the preferred trait is recessive.
20. This is an example of genetic drift. Only two plants
reproduced in the second generation, and they
happened to be two homozygous dominant plants,
effectively removing the recessive (white) allele from
the population.
21. The random probability of getting heads or tails reflects
the random probability of maintaining both alleles in
the population. The more individuals mating in the
population, the more likely that both alleles will be
represented in the gene pool in similar numbers. This
is analogous to an increasing number of coin tosses
making it more likely that both heads and tails will be
equally represented in the results of the coin tosses.
22. An ecological niche is the ecological role and physical
distribution of a species in its environment. When
species are able to expand their niches, perhaps by
exploiting a new resource or by benefitting from a lack
of competition, these advantages drive adaptations to
the new niche and therefore microevolution.
23. Students’ spider maps may contain the following
information:
directional selection—phenotypes of one extreme are
favoured, and the distribution curve will shift towards
that extreme
stabilizing selection—the intermediate phenotype is
favoured and the distribution curve gets narrower
disruptive selection—the phenotypes on both extremes
are favoured and the distribution curve forms two peaks
sexual selection—typically based on competition
between males and choices made by females. Preferred
phenotype will increase in the population.
4. a
5. d
6. c
7. a
8. d
9. b
10. e
11. Genetic diversity, or variation, is the raw material
that natural selection acts on. Genetic diversity allows
some individuals in a population to be better able to
survive certain environmental conditions, such as
food scarcity, and thus those individuals will be able
to reproduce, passing the genetic information on to
their offspring. Over time, natural selection will shift
the genetic information in the population, resulting
in evolution.
12. Individual organisms do not evolve—their genetic
makeup stays the same over their entire life span.
Populations do evolve, however—the alleles in the
population will change in terms of their frequency in
the gene pool over time.
24. No, this is not an example of evolution, because the
change in leaves is not permanent. The next spring,
new green leaves grow again. This is part of the
deciduous cycle.
13. A geographical barrier is a physical barrier such
as a glacier, a mountain range, or a body of water
that separates populations and keeps them from
interbreeding. A behavioural barrier is a behavioural
or physiological barrier such as mating dances, songs,
or pheromones, that separates populations and keeps
them from interbreeding even though they may
overlap in range.
25. Burrs getting caught in the fur of mammals and
transported to other locations is one example of gene
flow involving an animal. Birds and bats that eat fruit
and drop the seeds when they defecate in different
locations is another example.
14. No, the same thing does not happen in natural
selection because if non-desirable traits arise from
natural selection, these traits will reduce the chances
that the individual will survive and the individuals will
then not reproduce.
Unit 3 Review Questions
(Student textbook pages 387–91)
15. Biodiversity is important to maintain because
biodiversity contains all of the genetic material in the
region being measured. The more biodiversity, the
more likely that organisms in the region will be able to
withstand changing conditions and continue to exist.
1. d
2. b
3. b
Biology 11 Answer Key Unit 3 • MHR TR
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16. Selective pressure:
Definition:
Environmental conditions that
select for certain characteristics of
individuals and select against other
characteristics
Examples:
Bacteria surviving the application
of an antibiotic. The application of
the antibiotic produced a selective
pressure that some bacteria survived
and some didn’t. Those bacteria that
did survive were able to reproduce
and pass on the characteristic that
helped them survive.
Characteristics:
Can occur as a result
of biotic or abiotic
environmental
conditions
Can be natural or
artificial (pressure
applied by humans)
Non-examples:
New mutations that
increase the genetic
variability in the
population
17. Mimicry is a structural adaption in which a harmless
species resembles a harmful species in coloration or
structure. Mimicry is an adaptation because predators
that avoid the harmful species will now also avoid the
harmless species, allowing members of the harmless
species to survive and reproduce.
18. Natural selection results in some organisms surviving
and other organisms not surviving. The survivors
are able to reproduce and pass on their genetic
information. This genetic information gives the
offspring an advantage, and results in the offspring
becoming adapted to particular conditions.
19. Embryology is the study of early, pre-birth stages
of an organism’s development. The similarity of
developmental pathways between organisms in
different groups, such as vertebrates, points to a
common ancestral origin.
20. a. True
b. False—Individuals are selected.
c. False—Populations evolve.
21. Mutations can be positive, negative, or neutral in terms
of their impact on the individual. If the mutation is
negative, the organism will die and obviously will not
reproduce. If the mutation occurs in a body cell, it will
be neutral and it will disappear from the gene pool
when the individual dies. If the mutation is positive
or beneficial, it will give the individual a selective
advantage and it will spread in the population as the
individual survives and passes the mutation on to the
next generations.
24
MHR TR • Biology 11 Answer Key Unit 3
22. a. disruptive selection
b. stabilizing selection
c. disruptive selection
d. directional selection
e. stabilizing selection
f. directional selection
23. Punctuated equilibrium is the idea that evolutionary
change involves long periods of stasis interrupted by
periods of rapid divergence. A mass extinction event,
followed by a period of rapid adaptive radiation, during
which survivors of the extinction event rapidly diverge
to fill empty niches, would support the idea that there
are periods of very rapid divergence. As the niches fill
and the rapid increase in biodiversity slows down, a
period of stasis would begin.
24. The evolutionary history of elephants supports the idea
of punctuated equilibrium, with long periods of little
evolutionary change, and then multiple instances of
divergence into new species.
25. a. Differences in the three auditory signals include
the number of signals in the same period of time
(the frequency of signals) and the amplitude of
the signals.
b. No, because they would not recognize each other’s
auditory signals.
c. This is an example of a pre-zygotic reproductive
barrier. The lacewings are behaviourally isolated.
26. a. I would have to know if they are able to interbreed
and produce viable offspring. I could look to see
if there are any obvious behavioural barriers,
such as differing mating calls or timing of
reproductive behaviour.
b. I could use DNA analysis to see how closely their
genetic information matches. The closer the match
in terms of genetic information, the more closely
related the two species are.
27. a. The key genetic implication is that geographical
barriers are reproductively isolating the populations,
making them more vulnerable to genetic drift as a
result of small population sizes.
b. Natural corridors of habitat could be developed,
allowing gene flow between populations, thus
increasing the genetic diversity and reducing the
vulnerability to genetic drift.
28. a. Plant breeders might use this chemical to
reproductively isolate a particular plant species and
reduce the risk that it will be pollinated with other
plants that have less desirable traits.
b. If the offspring of the mutant plants survives,
they will have a unique genetic code, with
extra chromosomes. This would reproductively
isolate them from other populations, creating a
new species.
29. a. Grizzly bears and polar bears are more closely
related (they share a more recent common ancestor)
compared to grizzly bears and black bears.
b. No, they are not the same species because
their ranges do not overlap and they do not
naturally interbreed.
30. The Florida Keys are located very close to the
mainland, so there is lots of gene flow between the
populations on the islands and the populations on
the continent. The Hawaiian Islands do not have
regular gene flow occurring between the islands
and the continent, so the populations there became
reproductively isolated and speciated into new species.
31. The barriers could be behavioural isolation, where
some signal or mating ritual is not shared between
the two species. The barrier could also be temporal
isolation, where the timing of mating is different
between the two species.
32. Stripes provide an evolutionary advantage because they
camouflage individual organisms within the herd. This
results in predators’ inability to identify individual prey
items, and also results in the herd looking like one very
large organism that may intimidate the predator and
keep it from hunting the zebra.
33. Monocultures are extensive plantings of the same
varieties of a species over large expanses of land.
This makes it easier to manage the crops (planting,
fertilizing, harvesting), but because the plants are so
similar and there is little genetic variation in the crop,
the plants are vulnerable to disease and pests and other
possible changes in the environment such as drought.
34. Students’ graphic organizers should reflect the fact that
variations are the raw material for natural selection to
act on, and natural selection results in adaptations.
35. Students’ illustrations need to show that evolution
occurs as a result of changes in the environment.
Changing environments produce selective pressure,
which causes differential survival and reproduction
in populations. Over time, this differential survival
and reproduction shifts the genetic makeup of the
population, resulting in evolution.
36. Students’ graphic organizers should indicate that
Cuvier influenced Darwin because he was the father
of paleontology, the study of ancient life through the
examination of fossils. Cuvier found that each layer
of rock was characterized by a unique group of fossil
species, and new species appeared and old species
disappeared throughout the strata. This information
was recognized by Darwin as evidence that species
do change over time, extinctions occur, and the older
the fossils were, the more they differed from current
modern forms.
37. Sample answer: First example of adaptation:
Hummingbirds have very long beaks and tongues
that allow them to access the nectar from particular
flowers. There is no competition from other species
for the nectar because other species do not have the
adaptation to exploit the resource. Second example of
adaptation: Some species of newt lose their tails when
attacked by a predator. This confuses the predator, and
gives the newt time to escape. The newt grows a new
tail back.
38. Students’ answers should include the following
information: Biological evolution is the process of
biological change over time based on the relationships
between species and their environments. As the
environment changes, it creates a selective pressure
such that only some individuals in the population will
survive. Those that survive are able to pass on the genes
that gave them the advantage, assuming the advantage
was a heritable genetic trait. If so, the offspring will
inherit the trait and will also be better able to survive
the environmental conditions, passing the trait along
to their offspring. Over time, this results in populations
that are adapted to their environments.
39. In the “Mutations” section of the Venn diagram,
students should write the following:
– the only new source of genetic material
– can be beneficial, harmful, or neutral
In the overlapping section of the Venn diagram,
students should write the following:
– affects genetic variation in populations
In the “Natural Selection” section of the Venn diagram,
students should write the following:
– acts on genetic variability
– the result of environmental conditions
– results in differential survival and reproduction rates
for individuals in the population
Biology 11 Answer Key Unit 3 • MHR TR
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40. a. Some offspring will survive, while some will die.
b. There is variation within populations and that
variation may increase the chances for some
individuals to survive if it gives those individuals
some type of advantage.
c. Individuals must compete for scarce resources.
41. Types of Pre-zygotic Isolating Mechanisms
Type of Isolating
Mechanism
Description
Example
Behavioural
isolation
Pre-zygotic mechanism Differences in the
that prevents different mating calls of
frogs
species from mating
because of speciesspecific signals or
behaviours
Temporal
isolation
Pre-zygotic mechanism
that prevents different
species from mating
because of timing
barriers
Flowers that
bloom at different
times in the
season
Ecological/
habitat isolation
Pre-zygotic mechanism
that prevents different
species from mating
because individuals
from different species
do not encounter each
other
Some fish that live
in shallow water
compared to fish
that live in deep
water
Mechanical
isolation
Pre-zygotic mechanism
that prevents
fertilization between
different species
because of anatomical
incompatibility
Genital anatomy
may vary enough
that the species’
parts do not fit
together.
Gametic isolation
Pre-zygotic mechanism
that prevents
fertilization between
different species
because the gametes
(egg and sperm) do
not meet
Pollen grains from
one plant may
not survive the
conditions found
on the stigma of
another plant.
42. Students’ diagrams should resemble Figure 9.19.
Gradualism is a model of evolution that views
evolutionary change as slow and steady, both before
and after a divergence. Punctuated equilibrium is a
model of evolution that views evolutionary history
as composed of long periods of time with no or little
change interrupted by periods of rapid divergence.
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MHR TR • Biology 11 Answer Key Unit 3
43. The terms should be
1. natural selection
2. geographic isolation
3. reproductive isolation
4. frequency of alleles
5. speciation
6. gradualism
7. punctuated equilibrium
44. Some students will state that the case against feeding
birds is valid, and others will state that the case is not
strong enough to support the idea of not feeding birds.
A key piece of information that must be provided in
students’ rationale for their position is whether or
not bird feeders have a large enough impact overall
to effect large scale changes in the gene pool of a
particular bird population.
45. a. Lamarck would say that the ancestors of the Ord’s
kangaroo rat learned how to jump away from
predators, and this acquired characteristic was
passed down to offspring.
b. Darwin would say that the Ord’s kangaroo rat’s
ability to jump was a trait that was not learned, but
rather a result of genetics and because this jumping
ability helped the individual to survive, it was passed
on to offspring.
46. This is an example of sexual selection, which is a
type of natural selection. It is a result of non-random
mating in which individuals with preferred phenotypes
are able to contribute to the gene pool of the
next generation.
47. These rare mutations in the population could be
explained as a result of genetic drift, in the form of the
founder effect. The founder effect is the change in a
gene pool that occurs when a few individuals start a
new isolated population. Alleles that were originally
rare may become common and spread through
the growing population at a higher frequency than
expected in larger populations that were not part of the
founder population.
48. Sample answer:
a. Biologist—students’ research will show that there is
a great deal of breadth to career choice as biologists.
Professional biologists usually end up specializing in
fields such as aquatic biology, forestry, mammalian
biology, marine biology, and so on.
b. To be a professional biologist, students would need
to achieve a Master’s of Science or a PhD in Biology.
Depending on education and where they would
choose to work, starting salaries would range from
$40,000 to $60,000 per year. Biologists are hired by
governments to run wildlife programs, by consultant
firms to perform environmental assessments, by
high schools to teach biology courses (although
biology teachers also need a degree in Education),
and by universities and colleges as researchers
and professors.
c. Students’ advertisements will depend on the
particular career they have in mind. They should
include the roles and responsibilities of the job, the
products (such as reports or research results) that
are expected, and the salary range.
49. a. The name means “long shin bird” and it is relevant
because Longicrusavis has hind limbs that are long
relative to its forelimbs.
b. Jehol Biota is an ecosystem that existed in
Northeastern China from 133 to 120 million years
ago in the Lower Cretaceous period. The fossils from
this time are in very good condition, contained in
fossil beds that preserved them without significant
distortion and damage.
c. Many of the fossils include soft tissue, articulated
skeletons, stomach contents, and even twigs and
sticks with flowers still on them.
50. Students’ modelling should show a pattern like that
seen with the peppered moths, where over time
the coloration of the population changes due to the
selective pressure of changing backgrounds. The
mottled grey phenotype should increase as these fish
will be camouflaged against the bottom of the ocean.
51. Students’ diagrams should show that there is selective
pressure applied to the population by the change in
habitat. Insects that have some green in their coloration
will survive more often because it will be more difficult
for predators to see them. They will go on to reproduce
and pass on the allele for green coloration to their
offspring. Over time, more and more members of the
population will have the green coloration, resulting in
an evolutionary change from tan to green colour.
52. Pesticides often kill many, but not all, of the pests that
they target. The pests that survive are able to reproduce
and pass on the resistance to the pesticide to their
offspring. Over time, the entire population will become
resistant and a new pesticide will need to be applied.
Shoppers are indirectly applying the selection pressure
for resistance to pesticides.
53. This is a case of sexual selection versus natural
selection. Sexual selection will result in the phenotype
changing to long wings, because only those males
selected by females will be able to mate. However,
those males may not survive after mating because
they do not fly as well. The more important feature is
to reproduce and pass on is the genes for long wings.
Surviving with short wings does not matter if the genes
are not passed on to the next generation.
54. a. Coevolution is the interaction of two species in such
a way that each influences the evolution of the other.
b. Sample hypothesis: The mantis can eat the insects
that come to feed from the orchid. The orchid gains
the protection of the mantis that eats pests and other
insects that could damage it.
c. Students’ answers will depend on their research.
Common examples of coevolution are the
relationships between flowers and their pollinators.
The flowers evolve particular shapes that are specific
to the shape of the pollinator’s beak or tongue. The
pollinator evolves so that the shape of its beak or
tongue matches the shape of the flower.
55. a. Difficulty breathing, due to lung infections
and scarring
b. Profuse watery diarrhea, severe dehydration,
vomiting, abdominal pain
c. Cystic fibrosis is caused by a genetic mutation called
CFTR. The cholera toxin requires normal CFTR
functioning, so individuals with mutated CFTR may
show resistance to cholera.
d. Cystic fibrosis is an autosomal recessive disease,
meaning that it can be carried in the genotype but
not be expressed in the phenotype.
56. Selectional forces affecting wild salmon populations
could include changes in water temperature, water
levels, competition for food, or changes in predator
behaviour. The type of selection in wild salmon
populations might be any of the three types—
directional, stabilizing, or disruptive—depending
on what the environmental pressures are. The type
of selection in farmed salmon populations would be
directional, selecting for the extreme of larger size and
increased growth rate.
Biology 11 Answer Key Unit 3 • MHR TR
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Unit 3 Self-Assessment Questions
(Student textbook pages 392–3)
1. a
2. b
3. d
4. b
5. b
6. b
7. c
8. c.
9. a
10. d.
11. a. Sample answer: Evolution is the genetic change
in populations, not individuals. Natural selection
works on individuals, has no direction, and is an
important evolutionary mechanism, although not
the only mechanism.
b. Sample answer: Survival of the fittest is the struggle
between organisms to survive and reproduce.
Those that are fit and “win” are not necessarily
the biggest or strongest, but the best adapted to a
particular environment.
12. In the “Adaptation” section of the Venn diagram,
students should write:
– Adaptations are traits that increase an organism’s
chances of survival and successful reproduction
In the overlapping section of the Venn diagram,
students should write:
– Variation is required for adaptations to evolve.
In the “Genetic Variation” section of the Venn diagram,
students should write:
– Genetic variation is the raw material for adaptation.
– Genetic variation is diversity in the genes of an
individual or a population.
13. Students might suggest that traits can only evolve as
much as existing genetic variation allows them to.
Natural selection has no direction or purpose, so traits
are not necessarily going to be perfect. Also, there
may be conflicting selection factors or traits that are
genetically linked that cause constraints. One trait
may be favoured by females, such as long tails in male
birds, but this trait might cause another maladaptive
physiological trait to occur, such as the inability to fly.
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MHR TR • Biology 11 Answer Key Unit 3
14. Gradualism is gradual change in species over a long
period of time and in a linear fashion. Punctuated
equilibrium is spurts of speciation followed by long
periods of no change.
15. Hummingbird moths and hummingbirds do not
share a common ancestor, yet both organisms have
evolved similar characteristics in response to similar
environmental conditions.
16. Natural selection is not progressive, nor does it
necessarily lead to perfect designs. It simply works with
the existing variation to “weed out” traits that are not
adaptive and selects for individuals with traits that are
adaptive within a particular environment.
17. Convergent evolution results in unrelated species
with similar characteristics due to adaptation to
similar environments. Divergent evolution results in
related species with dissimilar characteristics due to
different environments.
18. Genetic drift is the random change in alleles that
occurs in small breeding populations. Genetic drift
is random. Natural selection is the process by which
individuals with traits that are adaptive survive better
and have greater reproductive success than those
without these traits, and so these individuals are
selected for. Natural selection is not random and leads
to adaptations.
19. If environmental conditions change so that the neutral
mutation provides a selective advantage, it would
spread quickly within the population.
20. A. A population of bacteria contains antibiotic-resistant
and antibiotic non-resistant individuals.
B. The application of the antibiotic kills many of the
non-resistant individuals.
C. The resulting population after the antibiotic has
been applied has many more antibiotic-resistant
than antibiotic non-resistant individuals.
21. This is an example of disruptive selection, where
selection favours the extremes of the phenotype,
resulting in two populations of the same species that
look very different.
22. A vestigial structure is a functionless or rudimentary
version of a body part in a species that is evidence
that the species has descended with modification
from an ancestor with a fully developed and
functional structure. An example is the pelvic bone
in some whales.
23. No, this is not an example of evolution. Evolution
is biological change over time. Mountains do not
change for genetic reasons; they change as a result of
other forces, such as erosion by weather. Therefore,
mountains cannot evolve.
24. Sample answer: This quote means that it is difficult
to understand the origin of an organism’s trait
or its function without an evolutionary context
that addresses why a trait has evolved. Within an
evolutionary framework, the existing biodiversity
surrounding us is easy to understand and explain.
25. Evolutionary change is a long, slow process, similar to
the processes that shape the geology of the Earth. It is
only on this scale that the processes can occur, because
processes for change are slow and gradual. Only in very
rapidly reproducing populations, such as insects and
bacteria, can evolutionary processes be observed in
relatively short periods of time.
Biology 11 Answer Key Unit 3 • MHR TR
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