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Biology 11 Answer Key Unit 3 • MHR TR 1

Answer Key

Unit 3 Evolution

Unit Preparation Questions (Assessing Readiness)(Student textbook pages 290–3) 1. c 2. a 3. Th e major steps followed during a scientifi c 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.

4. a 5. a. Repeat the experiment several times.

b. Revise your hypothesis. 6. e 7. c 8. a 9. a true; b true; c false; Meiosis leads to four genetically

diff erent 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

10. e 11. c 12. Th e 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.

16. Comparison of Genotype and Phenotype

Term Description Example

Genotype The combination of alleles in an individual organism

The combination of alleles for any given trait, such as Ss or AaBb

Phenotype The outward expression of an organism’s genotype; an organism’s phenotype is its physical and physiological traits

A physical characteristic, such as pea shape; a physiological characteristic, such as sickle cell anemia; or a behavioural characteristic, such as territorial behaviour

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.

18. c 19. a 20. a 21. Answers may include predators, food availability,

competition, weather factors, and disease. 22. Comparison of Biotic and Abiotic Factors

Term Description Example

Biotic factor

Living features of an ecosystem

Plants, animals, micro-organisms

Abiotic factor

Non-living features of an ecosystem

Water, rocks

23. a. Th e carrying capacity b. Th e 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

Answer Key

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2 MHR TR • Biology 11 Answer Key Unit 3

25. Th ere may be time lags or delays in the eff ect that a carrying capacity has on population growth. For example, it may take time for birth rates in rabbits to slow down aft er the rabbits eat too much of the food supply.

26. Urban sprawl:

Defi nition:

• Expansion of human communities into undeveloped areas surrounding urban centres

Eff ects:

• Alters habitat and ecosystems, usually making them uninhabitable for other species

• Changes how the water cycle and nutrient cycle function in the aff ected areas

Examples:

• Development of suburbs around cities

• Increased pavement and road systems, housing developments, and density of human populations in areas previously used for agriculture

Non-examples:

• Protection of large tracts of land as conservation areas

• Land held and maintained for natural or agricultural purposes

27. a 28. c 29. a. A physiological adaptation

b. Th e 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: Th e 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 EvolutionLearning Check Questions(Student textbook page 299) 1. An adaptation is a structure, behaviour, or

physiological process that helps an organism survive

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 fi nd prey easily and increases its chances of survival given that it does not need to depend solely on sight to locate its prey.

3. Th e fl y’s adaptation is mimicry: its coloration resembles that of a stinging insect such as a bee. Th e advantage of this adaptation is that predators will leave it alone.

4. Students should create a cause-and-eff ect chart using the information on pages 298 and 299 of the student text: trees covered with light-coloured lichen → fl ecked moths fl ourished, few black moths → environment changed (tree trunks darkened due to soot from Industrial Revolution) → black moths began to fl ourish, fl ecked moths began to decrease in number → environment changed (tree trunks lightened due to lichen growing on trees aft er clean-air legislation) → fl ecked 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 off spring. In this way, the proportion of the diff erently 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 eff ect 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 off spring.

8. Th e 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. Th ose individuals that survive will reproduce and pass on their alleles to their off spring. Th e 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 fl owchart 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). → Th ose 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. → Th is 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 off spring that will survive long enough to reproduce. A highly fi t organism survives and reproduces, passing on its advantageous genes to its off spring. Natural selection is the pressure that determines an organism’s relative fi tness in a given environment.

Caption QuestionsFigure 7.1 (Student textbook page 296): Th e camoufl age 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 camoufl age trait is heritable, the genes for camoufl age will likely be passed on to a number of its off spring; 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): Camoufl age: Th e fl ecked moths were better hidden (camoufl aged) when they rested in the trees whose trunks were covered with light-coloured lichen, and the black moths were better camoufl aged 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. Th e wild mustard plant was modifi ed to produce more desirable traits that led to six agricultural plants that look very diff erent 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. Th e 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. Th e 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. Th rough 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 camoufl age 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 (greyish-white and black) helped certain varieties of the peppered moth around Manchester survive changing environmental conditions that aff ected the colour of their habitat. It is likely that fl ecked moths appeared fi rst, 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 fl ecked moths, so they fl ourished 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 camoufl aged. 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 eff ects 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 off spring with unique genetic information. Mutation is the ultimate source of genetic variation, as new, previously non-existent alleles are formed.



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 fi nd 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. Th is 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. Th is 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 shift s to benefi t the previously disadvantaged genotype.

9. Sample answer: A cat has sharp retractable claws that allow it to hunt eff ectively. A cat also has large eyes that see well in the dark, allowing it to hunt eff ectively 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. Th e wording in the article is scientifi cally 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 aff ected 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.

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 off spring and cause changes in populations over time.

2. Th e 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’ off spring, 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 eff ects of the insecticide. Th ese 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 off spring. Th e resulting new generation will have a higher percentage of individuals with the allele for resistance to the insecticide, and so the population shift s 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. Th erefore, populations become adapted to their environment over generations through natural selection.

5. Fitness is measured by how many viable off spring an individual produces. Since the chipmunk produced more babies compared to a typical litter of chipmunks and they all survived, she would have high fi tness.

6. Blueberries in the store are farmed and selectively bred for large size. Wild blueberries are not selectively bred for size.

7. In artifi cial 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. Th is is economically benefi cial 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. Th is 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 artifi cially 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. Th us, 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. Th e 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 artifi cial 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. Th ese characteristics would all be benefi cial 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 off spring 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 off spring 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 off spring.

2. Essential skills would include attentiveness to detail, the ability to use microscopes and other laboratory equipment, the ability to work in the fi eld taking samples, and the ability to analyze data, interpret fi ndings, 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 aff ect 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 fi eld 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 fi eld 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.



12. Th e case of the peppered moths shows how diff erent environmental conditions (light-coloured or dark-coloured bark on trees) selects for diff erent 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 off spring 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 aff ect the biological change of a population.

16. If there is an allele that provides resistance to the pesticide, so that some housefl ies can withstand the pesticide, then the off spring of the surviving housefl ies will also carry the genetic resistance to the pesticide. Over time, the population of housefl ies would be made up only of individuals that carry the allele for resistance to the pesticide. Th is is a selective advantage for the surviving housefl ies, 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. Th e 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 off spring.

18. a. Streptomycin, because antibiotic-resistant bacteria were identifi ed the same year in which the antibiotic was introduced.

b. Vancomycin, because it took 31 years before bacteria resistant to it were identifi ed.

19. a. Th e horses’ performance times have not improved signifi cantly 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. Th e individual beetles do not develop a mutation. Th e beetles with the mutation already exist in the population. Th ese 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. Artifi cial selection to increase its oil content,

although it started with very low oil content. 22. Sample answer: Compare fi tness, or the number of

reproductively viable off spring, of larger fi nches in wet years and in dry years. Factors to measure would be the amount of precipitation, the size of the fi nches, the number of off spring, and the survival rate of the off spring.

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 off spring in the next generation.



26. Students will likely choose a Venn diagram as a graphic organizer, as it allows the diff erences to be clearly shown. Th ey must also then include at least one similarity, as shown below.

Adaptations Similarities Variations

- Traits or processes that increase an organism’s chances of survival and successful reproduction

- Can be structural, behavioural, or physiological

Related to genetic material that is heritable

- The total number of traits that are in the population

- Only present as diff erent alleles

- The more variations (diff erences between individuals) present in the population, the more likely some variations will be adaptive for some individuals

27. Th e fl owchart should show that selective breeding can improve crop yields, thereby increasing the economic benefi t 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 specifi c 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. Th e Venn diagram should include the following points:

Natural selection Similarities Artifi cial selection

The mechanism by which populations change as a result of environmental pressure

Both natural selection and artifi cial 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 Artifi cial Selection,” refl ecting 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 artifi cial selection is the result of human choice.

31. Th is example of natural selection favouring greater bill depth was due to the fact that fi nches with greater beak depth were better able to eat the remaining larger seeds compared to varieties of fi nches with smaller beaks, and thus large-beaked fi nches survived and the small-beaked fi nches died.

32. More small-beaked birds will survive and produce off spring that also have small beaks. Th e 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. Th e insect is exhibiting camoufl age. 35. On the basis of knowing how certain traits are

inherited, the plant breeder could choose desirable traits and practise selective breeding.

36. Th e 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: Th e 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

diff erent 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. Th is is a possible danger that might decrease an animal’s chances of survival.



d. Th e 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 confl ict 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. Th e 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. Th e 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. Th is means that harmful recessive alleles, which are oft en 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

nucleotide in a non-coding region of DNA will be neutral to the organism.

13. Each puppy could inherit a diff erent 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 fi tness by counting the number of the organism’s off spring that are viable and that survive to reproduce.

16. No, because the off spring 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 specifi c time may have no apparent relevance to survival or might even reduce the chances of survival. However, that same trait at a diff erent time in a diff erent 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 fl ower colour from light pink to dark red. Red fl owers are easier to fi nd by pollinating bees. Th erefore, red fl owers have greater reproductive success and produce more off spring than lighter-coloured fl owers. Eventually, the fl ower population has a greater proportion of individuals with red fl owers.

21. Students’ answers may include size, sugar content, ripening time, and/or resistance to disease.

22. Students’ answers should highlight that a major diff erence 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 artifi cial 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.

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. Th e new variety with large leaves may not be as fi t compared to the wild plant species for various reasons; for example, it provides more abundant food for leaf-eating insects.

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 diff erent time in a diff erent situation, helps certain individuals in a population to survive and reproduce.

Chapter 8 Developing a Theory of EvolutionLearning Check Questions(Student textbook page 327) 1. Th e empirical system is a system of learning

about the natural world through observation and experimentation.

2. During Buff on’s time, it was generally accepted that life forms did not change and that Earth was about 6000 years old. Buff on suggested that life forms changed and that Earth was older than 6000 years.

3. Catastrophism suggests that Earth experienced many destructive events such as fl oods, 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 fi eld of paleontology—the study of ancient life through fossils—to develop and grow.

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 unaff ected by the catastrophes.

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 diff erent today compared to rates in the past.

(Student textbook page 336) 7. Th e 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. Th e 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. Th e body shape and head shape are quite diff erent from that in the Paleocene epoch. Th ere is some colour banding on half the body. Th e tail is a little shorter and pointing down. In the Oligocene epoch, the animal is bigger still. Th e body is a little rounder, and the banding is gone or less distinct. Th e 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. Th e 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 diff erent, with a bend in it. Th e head shape is diff erent, and the ears are smaller.



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 QuestionsFigure 8.10 (Student textbook page 338): Diff erences: Th e chicken embryo is enclosed in a pouch-like structure in the fi rst illustration; the shapes are very diff erent in the second illustration of each embryo, with the fi sh shape becoming obvious in the fi sh embryo; in the third illustrations, the pouch is still evident in the chicken embryo but is not noticeable in the fi sh 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, diff erent species of fossilized organisms are seen in diff erent 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. Th e elephant would pass on the stretched trunk to its off spring.

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. Th e best adapted members would survive and reproduce; in so doing, they had the greatest evolutionary “fi tness.”

8. a. Cuvier founded the science of paleontology and proposed the idea of catastrophism.

b. Malthus proposed that there were limited resources for the off spring born in populations, and many individuals died in the struggle to obtain resources. Th us, 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 Buff on—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 fi rst 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 off spring

• Th omas Malthus—An economist who proposed that there were limited resources for the off spring born in populations, and that many individuals therefore died in the struggle to obtain resources. Th us, populations were eventually reduced by starvation or disease.

• Charles Darwin—A British naturalist who explored the natural history of many diff erent 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. Th ere 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 modifi cation implied no demonstration of progress and no set direction.

12. Th e fi nches and other animals Darwin saw on the Galapagos Islands closely resembled animals he had observed on the west coast of South America. Th rough his experiments with artifi cial selection (breeding pigeons and studying breeds of dogs and varieties of fl owers), Darwin realized it was possible for traits to be passed on from parent to off spring and that sexual reproduction resulted in many variations within a species.

13. Students should include the following four main ideas: Organisms produce more off spring 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 off spring; and processes for change are slow and gradual.

14. a. Th e species on islands were related to or arose from ancestral populations on nearby continents.

b. Th ere 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 off spring.

Section 8.2 Review Questions (Student textbook page 340) 1. Darwin was the fi rst to bring together all of the ideas

on evolution that were in existence and to see the signifi cance of these ideas on a large scale. He was also the fi rst to publish his work, although he probably would not have if Alfred Russel Wallace had not been preparing to publish the same ideas.

2. Th e order of the main groups in the fossil record supports the idea that organisms evolved at diff erent 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 fi lled as early forms transition into later forms.

4. Sample answer: Th e 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. Th is 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 fi nd organisms similar to those in Africa near where the island of Madagascar split from it; organisms could have drift ed or fl own 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. Th is 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 diff erent functions.

11. Th ey are analogous structures because they share a similar function but have diff erent 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.



15. Scientifi c facts are the data that scientists gather, and scientifi c 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. Th ese animals share a common ancestry with other mammals.

17. Sample answer: First, a giraff e population varies in neck length from short to long and this variation is heritable. → Long-necked giraff es are more successful at reaching leaves in the high canopy of trees. → Th ere is competition for food and there is not enough food for all giraff es. → Long-necked giraff es compete more successfully for food, survive longer, and produce more off spring compared to short-necked giraff es. Over a long period of time, the giraff e 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. Th ey show that as organisms evolved from a common ancestor, the same structures were put to diff erent uses and became modifi ed into the structures visible today.

11. Darwin’s observations included the following:• Th e fl ora and fauna of the diff erent regions the Beagle

visited were distinct from the fl ora 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 fi rst, but they varied slightly between islands.

• Darwin had signifi cant experience with artifi cial selection, so he knew that traits could be passed from parent to off spring and that sexual reproduction resulted in many variations within a species.

12. Lamarck would say that the fi sh 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 fi sh became blind.

13. Embryology shows that many diff erent species exhibit a common embryological development, supporting the idea that they shared a common ancestor.

14. a. Th ey do not overrun the Earth because resources are limited so individual insects must compete with other insects for resources and not all survive.

b. Th is was signifi cant 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. Th e 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 modifi cation 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. Th e strata correspond to diff erent 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. Th ese 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 aft er the separation of Blue Island from the continent. Th us, the animals on Blue Island will be very diff erent from animals in South America.



20. No, these species are separated so extensively geographically that they descended from diff erent ancestors; however, they responded to similar environmental pressures, thus making them appear very similar.

21. Th e fossils in the lower strata are older than the fossils in the rocks in the upper strata, but the fossil species did not undergo signifi cant evolutionary change. Fossils found at diff erent 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.

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. Th ese 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 suffi cient 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. Th e number of digits must have been reduced from fi ve to four during the evolution of chickens and other birds, but the fi ft h digit still appears for a short period during the early development of birds.

b. Since most living vertebrates have fi ve digits, the temporary fi ft h 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. Th e 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.

27. Answers should include evidence from the fossil record, biogeography, anatomy, DNA, and embryology.

28. Students’ answers should include the fact that homologous structures have a common origin and analogous structures have a common function.

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 diff erent 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. Th ey 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 off spring, and the entire process can occur over very long periods of time.

30. Students’ diagrams should communicate the following information: Th ere is variation among individuals of the same species, species adapt to local conditions, which are variable among locations, and diff erent traits are better suited to diff erent 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 off spring.”

Darwin: “I disagree. Variation must fi rst exist in populations and selection shows favouritism among this variation.”

32. Th e 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.



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. Th eories, in the scientifi c 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. Th e 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, “Scientifi c Contributions to a Th eory of Evolution” and “Sources of Evidence for Evolution,” refl ecting 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 diff erent lines of scientifi c evidence from before, during, and aft er Darwin’s time all support the theory of evolution by natural selection.

36. Disagree. Th e pelvic bones are vestigial features that would have served as the point of attachment for an animal with legs. Th is shows that snakes evolved from an ancestor that had legs.

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.

38. Dawkins means that natural selection does not have a particular end goal, so it has no purpose in terms of infl uencing future events. Natural selection occurs in response to changes in local conditions, not in response to potential future conditions that are as yet unknown.

39. Comparison of Dolphins and Sharks

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 of?

Bone Cartilage

Is the animal a mammal? Yes No

Question Dolphin Shark

Does the animal have a fi n on the top?

Yes Yes

Is the body shape streamlined?

Yes Yes

Does the animal have teeth?

Yes, cone-shaped

Yes, several rows of very sharp teeth

Th e similarities are analogous because the ancestral conditions are not common to both dolphins (a dolphin is a mammal) and sharks (a shark is a fi sh). 40. a. Archaeopteryx

b. Bird ancestors had clawed appendages. 41. Th e fossil record could be examined to see where the

extinct animal fi ts 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. Th e 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 3. e 4. a 5. e 6. a 7. a 8. a 9. b 10. c 11. It is a similar structure in related species due to

common ancestry, but structures may have diff erent 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 fi elds of embryology, genetics/DNA, anatomy, and biogeography.



14. a. Lamarck would say that they would pass this learned behaviour on to their off spring, 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.

15. Archaeopteryx showed an important link between two groups of organisms once thought to be unrelated: birds and reptiles.

16. Lamarck’s idea was that characteristics acquired during an organism’s lifetime can be passed on to its off spring. Th e 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 off spring.

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 modifi cation 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. Th ese 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 modifi cation. Diff erences include: homologous structures have a common ancestral origin but diff erences in function; analogous structures have a diff erent ancestral origin, but have a common function; and vestigial structures show a reduced version of a fully functioning structure in a related ancestor.

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.

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. Th is 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.

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.

Chapter 9 Evolution and SpeciationLearning 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. Th e greater the migration between populations, the greater the mixing of the gene pools of these populations, which results in the reduction of genetic diff erences between these populations.

5. Answers should refl ect the content shown in Figure 9.1 and the diagram should be titled or captioned with reference to eastern grey squirrels.



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 fi tness 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. Th erefore, random events can cause genetic drift by aff ecting 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 aff ecting individuals will probably have a larger eff ect.

9. Th e diff erences 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 eff ect.

10. Changes to the gene pool that result from a rapid decrease in the size of a population is known as the bottleneck eff ect.

11. Generally, the founder eff ect 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.

(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 off spring.

14. Th e Venn diagram should be made up of two circles labelled “Pre-zygotic Isolating Mechanisms” and “Post-zygotic Isolating Mechanisms.” Th e area of overlap should include “Mechanisms that prevent the production of viable and fertile off spring.” Th e independent portions of each circle should include the correct listings of mechanisms for that grouping.

15. Reproductive isolation is maintained because part of the eff ect of reproductive isolation is the prevention of the production of fertile off spring.

16. Th e reproductive isolating mechanism is temporal isolation.

17. Th ey would be considered diff erent species. Aside from the fact that these two diff erent species cannot produce viable, fertile off spring, the biological species defi nition requires that individuals of populations must interbreed in nature, and the defi nition does not include artifi cial conditions.

18. Th e 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. Th e two diff erent 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:• Th ey become isolated on the periphery of their

species range, where local environmental conditions may be diff erent 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.

• Th ey are likely to have greater genetic diff erences between themselves and the average parental species population.

• Th eir 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. Th is is what happened to the fi nches that reached the islands and were then separated from their parental species by the ocean.

28. Adaptive radiation is the diversifi cation of a common ancestral species into a variety of diff erently 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 diff erent 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 eff ects 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 QuestionsFigure 9.2 (Student textbook page 351): Scientists might have diffi culty defi ning distinct grey wolf populations in North America because gene fl ow 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): Th e off spring would not be viable according to the biological species defi nition, given that these two zebras are members of two diff erent species.

Section 9.1 Review Questions (Student textbook page 359) 1. Mutations are the only source of new genetic

variation. Th ey contribute new alleles to the gene pool, increasing variation.

2. Microevolution is the changing percentages, or frequencies, of alleles within populations. Individuals are not aff ected 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. Th is 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, shift ing the curve in that direction; and disruptive selection favouring both extremes over the intermediate, resulting in the elimination of the intermediate form.



5. Sample answer: In left -hand portion of Venn diagram: founder eff ect; 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 eff ect; change in gene pool as a result of a rapid decline in population size.

6. a. Th e 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 eff ect would be the most likely mechanism. Th e bottleneck eff ect 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. Th e bottleneck eff ect. One example is the cheetah population; another is the northern elephant seal population, both of which have little to no genetic variation.

8. Th e diagram should show the two separate gene pools merging and becoming one, so that there are no diff erences 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.

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. Th e 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 off spring will not be able to reproduce, so the shared genetic material will not be maintained past the one generation of off spring.

3. Yes, the mice would possibly become two separate species because they are now geographically isolated from each other and cannot interbreed. Th e birds would not become two separate species because they can fl y over the river, are not geographically isolated, and can continue to interbreed.

4. Th is 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 fi rst to a tree fi nch that was strictly vegetarian in its diet. Th at species gave rise to one species (woodpecker fi nch) 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 fi nch remained tree-living species.



6.

Comparison of Isolating Mechanisms

Type of Isolating

Mechanism

Description Example

Behavioural isolation

Pre-zygotic mechanism that prevents diff erent species from mating because of species-specifi c signals or behaviours

Diff erences in the mating calls of frogs

Temporal isolation

Pre-zygotic mechanism that prevents diff erent species from mating because of timing barriers

Flowers that bloom at diff erent times in a season

Ecological/habitat isolation

Pre-zygotic mechanism that prevents diff erent species from mating because individuals from diff erent species do not encounter each other

Some fi sh that live in shallow water compared to fi sh that live in deep water

Mechanical isolation

Pre-zygotic mechanism that prevents fertilization between diff erent species because of anatomical incompatibility

Genital anatomy may vary enough that the species’ parts do not fi t together.

Gametic isolation

Pre-zygotic mechanism that prevents fertilization between diff erent 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.

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 off spring from producing viable off spring

Mules are the product of horses and donkeys but are sterile.

Hybrid breakdown

Post-zygotic mechanism that prevents hybrids by preventing second generation off spring from producing viable off spring

Cotton plants produce fertile hybrids, but those off spring do not survive.

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.

8. Human activities may fragment habitats when people build roads and suburbs. Th ese 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 eff ect.

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.

11. Th e diff erent islands all have specifi c local conditions to which the lizards have adapted. Th ese diff erent lizards have undergone adaptive radiation, in which there is diversifi cation from a common ancestor based on diff erent conditions.

12. Th e 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).

13. One ancestral crossbill species was able to extract the seeds from closed cones. Th is allowed subsequent generations to radiate into new habitats and access new sources of food for which there was no competition. Th e crossed bill allowed new species to develop based on the availability of a specifi c type of food.

Chapter 9 Review Questions (Student textbook pages 379–81) 1. d 2. e 3. b 4. d 5. a 6. b 7. d 8. e 9. Th is 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 specifi c resources that were available to them in the absence of competitors.



10. Sample answer: Temporal isolation is a pre-zygotic isolating mechanism that prevents diff erent species from mating because of timing barriers, for example, fl owers that bloom at diff erent times in the season. Hybrid sterility is a post-zygotic isolating mechanism that prevents hybrids by keeping the hybrid off spring from producing viable off spring; for example, mules are the product of horses and donkeys but are sterile.

11. a. Th is is behavioural isolation; distinctive patterns of fl ashes prevent the species from identifying a potential mate.

b. Th is is temporal isolation; because the two species of grasses fl ower at diff erent times, fertilization is prevented.

c. Th is is hybrid breakdown; although the fi rst-generation hybrids of crossed species are viable and fertile, off spring of the next generation are sterile or weak.

d. Th is is ecological/habitat isolation: because the two species live in the same general region but in diff erent 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. Th ere is less genetic variability in small populations, so it is easier for the gene frequencies to change in response to environmental conditions. Th is 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 fi nd the river to be a reproductive barrier.

15. Th e species of fruit fl ies 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 specifi c resources.

16. Th e 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. Th e 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.

18. Th e only way to be completely certain is to compare the DNA of the diff erent birds or to try to crossbreed the birds to see if they can reproduce. Th is second method would take too long, so DNA comparison is the better choice. Some birds of the same species look very diff erent, whereas some birds of diff erent 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. Th is 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 fi res. Th e smoke and particulate matter from the fi res 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 classifi ed as being in diff erent or the same species based on the viability of their off spring. Th ey would need to be classifi ed into species on the basis of other characteristics such as DNA or morphological characteristics.

24. Some limitations include the fact that determining if diff erent species can interbreed may be diffi cult 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. Th ey would probably not be too similar because they exist together on at least one of the islands. Th e two species would need to be able to exploit food on the islands, meaning they are probably eating diff erent things.

b. I would not expect that the morphology would be diff erent in more distantly related species. Th e more signifi cant issue would be what types of resources the diff erent fi nch 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 insuffi cient resources for all individuals means that some individuals but not all will survive and be able to pass along their genes to off spring. Th e process of this diff erential 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 off spring 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’ fl owcharts 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 refl ect the following information:

Th e biological species concept focuses on similar characteristics and the ability of organisms to interbreed in nature and produce viable, fertile off spring. Th e advantage is that this species concept can be widely used by scientists. Th e 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 off spring condition cannot be tested. Th e concept cannot be applied to asexually reproducing organisms, nor to fossil species that are no longer reproducing.

31. Students’ graphic organizers should refl ect 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 refl ect 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 aff ected.

33. Students’ graphic organizers should include two sections, “Mechanisms of Evolution and Th eir Eff ect on Populations,” and “Speciation: How Species Form,” refl ecting the two sections of Chapter 9. Answers should show an understanding of gene fl ow, non-random 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 fi re or hot object, or grabbing for an object if it is about to fall. Students’ visuals for migration patterns should refl ect their research on migration, showing long-term migration patterns over long distances.

35. a. natural selection b. genetic drift —the bottleneck eff ect c. gene fl ow d. gene fl ow e. genetic drift —the founder eff ect

36. I would respond that the Earth has seen fi ve mass extinction events and each time, biodiversity rebounds. Biodiversity tends to increase at some point aft er a mass extinction because there will be resources available for which there will be no competition. Th e diff erence 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. Th e monarch migration requires three to four

generations of monarchs, as the trip is longer than the lifespan of the butterfl y. Th e monarch butterfl y larvae eat milkweed, so as the milkweed population declines, the number of larvae that survive also declines.



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 diff erent 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 fl ow between diff erent populations of grizzlies, increasing their genetic diversity and reducing the impact of genetic drift .

40. Th e 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. Th eir DNA could be compared for similarity or dissimilarity.

12. Th e 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. Th is is a pre-zygotic isolating mechanism called behavioural isolation. Other species of ants will not respond to the chemical signals so diff erent species will not mate.

b. Th is is a pre-zygotic isolating mechanism called temporal isolation. Diff erent timing of mating means the two species will not interbreed.

c. Th is is a post-zygotic isolating mechanism called hybrid inviability. Th e off spring 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 fl ow. Eventually the two groups will not be able to interbreed even if they are reconnected. An example could be a fl uctuation in sea levels that turns an archipelago or a peninsula into an island.

15. Th e rise and fall of the lake levels may create geographic barriers where gene fl ow is disrupted among fi sh 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 eff ect 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 eff ect portion of the Venn diagram, a once large population is drastically reduced by some natural disaster or human activity such as overfi shing.

17. Th is is an example of non-random mating, and it will result in microevolution that produces a population of toads with no size diff erence 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’ fl owcharts 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. Th is is an example of genetic drift . Only two plants reproduced in the second generation, and they happened to be two homozygous dominant plants, eff ectively removing the recessive (white) allele from the population.



21. Th e random probability of getting heads or tails refl ects the random probability of maintaining both alleles in the population. Th e more individuals mating in the population, the more likely that both alleles will be represented in the gene pool in similar numbers. Th is 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 benefi tting 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.

24. No, this is not an example of evolution, because the change in leaves is not permanent. Th e next spring, new green leaves grow again. Th is is part of the deciduous cycle.

25. Burrs getting caught in the fur of mammals and transported to other locations is one example of gene fl ow involving an animal. Birds and bats that eat fruit and drop the seeds when they defecate in diff erent locations is another example.

Unit 3 Review Questions (Student textbook pages 387–91) 1. d 2. b 3. b

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 off spring. 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.

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.

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.

15. Biodiversity is important to maintain because biodiversity contains all of the genetic material in the region being measured. Th e more biodiversity, the more likely that organisms in the region will be able to withstand changing conditions and continue to exist.



16. Selective pressure:Defi nition:Environmental conditions that select for certain characteristics of individuals and select against other characteristics

Characteristics:Can occur as a result of biotic or abiotic environmental conditionsCan be natural or artifi cial (pressure applied by humans)

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.

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. Th e survivors are able to reproduce and pass on their genetic information. Th is genetic information gives the off spring an advantage, and results in the off spring becoming adapted to particular conditions.

19. Embryology is the study of early, pre-birth stages of an organism’s development. Th e similarity of developmental pathways between organisms in diff erent 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 benefi cial, 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.

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 fi ll empty niches, would support the idea that there are periods of very rapid divergence. As the niches fi ll and the rapid increase in biodiversity slows down, a period of stasis would begin.

24. Th e 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. Diff erences 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. Th is is an example of a pre-zygotic reproductive barrier. Th e lacewings are behaviourally isolated.

26. a. I would have to know if they are able to interbreed and produce viable off spring. I could look to see if there are any obvious behavioural barriers, such as diff ering mating calls or timing of reproductive behaviour.

b. I could use DNA analysis to see how closely their genetic information matches. Th e closer the match in terms of genetic information, the more closely related the two species are.

27. a. Th e 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 fl ow 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 off spring of the mutant plants survives, they will have a unique genetic code, with extra chromosomes. Th is 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. Th e Florida Keys are located very close to the mainland, so there is lots of gene fl ow between the populations on the islands and the populations on the continent. Th e Hawaiian Islands do not have regular gene fl ow occurring between the islands and the continent, so the populations there became reproductively isolated and speciated into new species.

31. Th e barriers could be behavioural isolation, where some signal or mating ritual is not shared between the two species. Th e barrier could also be temporal isolation, where the timing of mating is diff erent between the two species.

32. Stripes provide an evolutionary advantage because they camoufl age individual organisms within the herd. Th is 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. Th is 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 refl ect 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 diff erential survival and reproduction in populations. Over time, this diff erential survival

and reproduction shift s the genetic makeup of the population, resulting in evolution.

36. Students’ graphic organizers should indicate that Cuvier infl uenced 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. Th is information was recognized by Darwin as evidence that species do change over time, extinctions occur, and the older the fossils were, the more they diff ered 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 fl owers. Th ere 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. Th is confuses the predator, and gives the newt time to escape. Th e 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. Th ose 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 off spring will inherit the trait and will also be better able to survive the environmental conditions, passing the trait along to their off spring. 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 benefi cial, harmful, or neutral In the overlapping section of the Venn diagram,

students should write the following: – aff ects 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 diff erential survival and reproduction rates

for individuals in the population



40. a. Some off spring will survive, while some will die. b. Th ere 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 that prevents diff erent species from mating because of species-specifi c signals or behaviours

Diff erences in the mating calls of frogs

Temporal isolation

Pre-zygotic mechanism that prevents diff erent species from mating because of timing barriers

Flowers that bloom at diff erent times in the season

Ecological/habitat isolation

Pre-zygotic mechanism that prevents diff erent species from mating because individuals from diff erent species do not encounter each other

Some fi sh that live in shallow water compared to fi sh that live in deep water

Mechanical isolation

Pre-zygotic mechanism that prevents fertilization between diff erent species because of anatomical incompatibility

Genital anatomy may vary enough that the species’ parts do not fi t together.

Gametic isolation Pre-zygotic mechanism that prevents fertilization between diff erent 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 aft er 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.

43. Th e 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 eff ect 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 off spring.

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 off spring.

46. Th is 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. Th ese rare mutations in the population could be explained as a result of genetic drift , in the form of the founder eff ect. Th e founder eff ect 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 fi elds 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 fi rms 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. Th ey 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. Th e 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. Th e fossils from this time are in very good condition, contained in fossil beds that preserved them without signifi cant distortion and damage.

c. Many of the fossils include soft tissue, articulated skeletons, stomach contents, and even twigs and sticks with fl owers 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. Th e mottled grey phenotype should increase as these fi sh will be camoufl aged 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 oft en because it will be more diffi cult for predators to see them. Th ey will go on to reproduce and pass on the allele for green coloration to their off spring. 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 oft en kill many, but not all, of the pests that they target. Th e pests that survive are able to reproduce and pass on the resistance to the pesticide to their off spring. 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. Th is 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 aft er mating because they do not fl y as well. Th e 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 infl uences the evolution of the other.

b. Sample hypothesis: Th e mantis can eat the insects that come to feed from the orchid. Th e 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 fl owers and their pollinators. Th e fl owers evolve particular shapes that are specifi c to the shape of the pollinator’s beak or tongue. Th e pollinator evolves so that the shape of its beak or tongue matches the shape of the fl ower.

55. a. Diffi culty breathing, due to lung infections and scarring

b. Profuse watery diarrhea, severe dehydration, vomiting, abdominal pain

c. Cystic fi brosis is caused by a genetic mutation called CFTR. Th e cholera toxin requires normal CFTR functioning, so individuals with mutated CFTR may show resistance to cholera.

d. Cystic fi brosis is an autosomal recessive disease, meaning that it can be carried in the genotype but not be expressed in the phenotype.

56. Selectional forces aff ecting wild salmon populations could include changes in water temperature, water levels, competition for food, or changes in predator behaviour. Th e 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. Th e type of selection in farmed salmon populations would be directional, selecting for the extreme of larger size and increased growth rate.



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 fi ttest is the struggle between organisms to survive and reproduce. Th ose that are fi t 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 confl icting 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 fl y.

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 diff erent 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. Th e application of the antibiotic kills many of the non-resistant individuals.

C. Th e resulting population aft er the antibiotic has been applied has many more antibiotic-resistant than antibiotic non-resistant individuals.

21. Th is 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 diff erent.

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 modifi cation 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. Th erefore, mountains cannot evolve.

24. Sample answer: Th is quote means that it is diffi cult 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.


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