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UNIT 4 REVIEW
(Pages 640–643)
Understanding Concepts
1. (a) Lyell established the principles of modern scientific geology and the theory of uniformitarianism. His book Principles
of Geology had a strong influence on Darwin’s understanding and interpretation of observations on the voyage of the
Beagle.
(b) Lamarck was the first prominent scientist to recognize the important role played by the environment in influencing and
directing evolutionary change and adaptations. He formulated a theory for evolution based on the inheritance of
acquired characteristics.
(c) Cuvier was a highly regarded anatomist who established that many fossils were of extinct species. He also proposed a
theory of catastrophism that posited mass extinctions and multiple creation events.
(d) Eldredge and Gould formulated the theory of punctuated evolution. The theory accounts for some common patterns in
the fossil record—particularly that associated with the pace of evolution surrounding mass extinction events.
2. (a)
• The specimen usually contains hard body parts such as bones or a shell.
• The specimen dies or leaves remains in soft sedimentary deposits or some other soft material such as volcanic ash,
tree sap, or tar.
• The specimen becomes covered such that decomposition is greatly slowed or prevented by cutting off oxygen supply.
• Over long periods the specimen becomes covered in deep sediments that become compressed.
• Dissolved minerals often replace the original organic remains, resulting in a permineralized fossil.
• The sediments of other substrate in which the remains are located form hardened rock, amber, and so on.
(b) Generally the deeper the fossil is in the deposit, the older it is. Strata that are assumed to form as sediments are
deposited in layers—one on top of the other. The top layers are therefore assumed to be the youngest, the deepest, the
oldest. Students should recognize that occasionally tectonic movements flip strata over, causing this pattern to be
inverted. These assumptions and exceptions can be easily tested and identified using standard radiometric dating or
other simple techniques.
3. Species differ dramatically in their likelihood of being fossilized. Common, hard-bodied marine species, for example, are
much more likely to be preserved in the fossil record than rare soft-bodied animals living in barren rocky terrestrial
environments.
4. Fossils provide direct evidence, as they are the remains of actual individuals that were alive at some time in the past.
5. These techniques provided an explanation for the internal source of heat within the Earth and provided a natural “clock”
that could be used to accurately date rock.
6. Like Darwin, Lamarck realized that species changed over time and that the environment played a key role in such change.
However, Lamarck thought individuals changed (adapted to the environment) during their own lifetimes and passed on
these changes to their offspring. In contrast, Darwin believed that individuals inherited differences (variations) from their
parents and that these differences influenced their reproductive success, because the environment “favoured” some more
than others.
7. Darwin discovered the unique sets of species that lived on these remote islands. He noted the many finches,
mockingbirds, tortoises, marine iguanas, and other endemic species. He was particularly struck by the geographic
distribution of organisms on remote islands and their uncanny resemblance to species on the closest mainland. Students
should recall that many of his important findings came during later analysis and interpretation of data, rather than at the
initial time of his visit.
8. Answers will vary. Suggested responds include the following:
(a) All forelimbs of terrestrial vertebrates are homologous to some degree with bird wings. Analogous features would include
the wings of other nonvertebrate organisms such as insects.
(b) All mammalian noses are homologous to an elephant’s trunk. Analogous features might include long bills in birds, the
tongues of butterflies, or the mouthparts of a mosquito. Even the arms of an octopus are used in a somewhat similar
manner to a trunk. Of course, in the case of the octopus, the muscles of the legs do have at least some homologous
relationship to those within the trunk.
(c) All true leaves of higher plants are homologous to cactus spines. Other nonleaf spines or needles are analogous, such as
those of euphorbia and even porcupine needles and sea urchin spines.
(d) All true mammalian hairs are homologous to cat whiskers. Analogous features would include the antennae of insects and
other arthropods.
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(e) Homologous features include all the mineral shells of the molluscs as well as the internal shell of the cuttlefish, and oyster
and clamshells. Analogous features include turtle shells and the hard exoskeleton of arthropods such as beetles and
lobsters.
9. Answers will vary. Vestigial features and anatomical oddities suggest an evolutionary past. Examples include the fact that
vestigial hipbones in pythons and whales are rudimentary structures. These species had ancestors that had hind legs
supported by hipbones. The dewclaws of dogs are also vestigial. At some time in the past, these would have been
functioning toes. The webbed feet of upland geese and frigate strongly suggest that at one time ancestors of these birds
used them for swimming—behaviour no longer displayed by the present species.
10.(a) The source of new variation is both genetic recombination and mutation. However, as artificial selection is performed
over a relatively short timeframe, there is very little likelihood that mutation plays a role in the changes produced by
breeding. Instead, breeders rely on the potential variation inherent in genetic recombination. Natural selection in
contrast has been working over millions of years, providing ample opportunity for new genetic variation to arise
through mutation events.
(b) Yes, both forms of selection act on favoured traits. In the case of artificial selection, breeders chose traits of interest
such as the stature of dog breeds. In the case of natural selection, individual traits are not handpicked but are still
favoured by the environment. For instance, a desert environment selects for plants better able to survive drought
conditions. In this way reduced leaf surface area has been selected consistently.
(c) Both processes often select against certain features. Breeders intentionally choose not to interbreed individuals that
display features that they consider undesirable, such as poor flavour in food plants. Similarly, natural selection acts to
reduce the reproductive success of any individual that is not as well suited to environmental conditions. For example,
those plants with a thinner wax coating may not do well in drought conditions.
(d) Artificial breeders most often apply directional selection pressure. A specific trait, such as enhanced sweetness or
disease resistance in fruit plants, is often chosen as the target of a breeding program. Individuals exhibiting extremes of
such traits are selected as breeding stock for the next generation. Over time, however, the combined efforts of many
breeding programs do produce results analogous to disruptive selection (and adaptive radiation), as many dog breeds or
colour variations in flowers are produced. Natural selection is much more variable. In environments that have exhibited
little change, stabilizing selection most commonly acts on species that have become well adapted to their ecological
niches. In new or changing environments, or after the arrival of new species, disruptive and directional selection
pressures are common. Examples include the fruit flies of the Hawaiian Islands.
(e) Artificial selection operates much faster than natural selection in most cases. Selection pressure is maximized when
breeders are able to select a small number of individuals as breeding stock for the entire next generation. In wild
populations, many individuals contribute offspring to succeeding generations, making change more gradual while
maintaining greater genetic diversity in the population. Students will be aware of the risks of inbreeding in
domesticated animals in which a relatively small number of individuals are used as breeding stock.
11. Malthus’s essay on population growth used mathematical models to demonstrate the potential for rapid population growth
in populations when all offspring survive to reproduce in each generation. Darwin realized that if large numbers of
individuals in all species die before reproducing, there must be intense competition and a potentially unequal contribution
of inherited information from generation to generation.
12. The two fundamental questions that could not be answered by Darwin or his cotemporaries were how are variations
passed on from generation to generation? and what is the source of new inherited variations?
13.(a) Generally, the larger the genome, the greater the potential for increased genetic variability.
(b) The greater the number of genes, the greater the potential for genetic recombination and variability.
(c) The greater the homozygosity, the lower the genetic variability of a population.
(d) Genetic recombination greatly enhances phenotypic variability.
(e) The greater the number of mutations, the greater the genetic variability of the population.
(f) Generally, the greater the population size, the greater the genetic variability of the population. Very small populations
can result in drastic reductions, or bottlenecks, in genetic variability.
14. Evolution is a measurable change in the gene (or allele) frequencies of a species.
15. The necessary conditions to maintain Hardy–Weinberg equilibrium are as follows:
A very large population size
Equal mating opportunities
No mutation
No migration
No natural selection
16. Because harmful mutations lower an individual’s fitness and reproductive success, they are less likely to be passed on to
future generations. This results in their being gradually eliminated from the gene pool or maintained in very low numbers.
In contrast, beneficial mutations enhance the success of an individual and in so doing, increase their own chances of being
passed on to future generations. Such new beneficial genes gradually increase in frequency and spread throughout the
population.
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17.(a) Disruptive selection
(b) Runaway selection
(c) Directional selection
(d) Stabilizing selection
(e) Directional selection
(f) Sexual selection
18.(a) Moose: large size of males and their antlers
(b) Mallard ducks: males are more brightly coloured than females
(c) Chorus frogs: the mating calls of male frogs
(d) Lions: males are large and have thick manes
19. There is frequently a kinship relationship. The helping individual usually provides a benefit to another individual that is a
close relative.
20.(a) Mechanical isolation occurs when two species are not physically capable of breeding. This occurs frequently in insects
that have highly specialized genitalia.
(b) Ecological isolation occurs when two species do not come in contact with each other, because they inhabit different
environments, such as prairie ground squirrels and alpine marmots.
(c) Behavioural isolation occurs when courtship behaviours are not recognized by different species, such as the mating
displays of birds such as frigates.
(d) Gametic isolation results when the sperm of one species is incapable of fertilizing the eggs of another. This is common
among wind-pollinated plants.
(e) Temporal isolation occurs when species’ mating seasons are at different times—for example, day-blooming and nightblooming cacti.
21. Allopatric speciation is likely to occur more rapidly on distinct islands, as the different environmental conditions will
produce disruptive selection pressures. On similar islands species experience the same selection pressures and the key
factor becomes genetic drift.
22. In 1991, Julius Rebek showed that some RNA molecules were capable of self-replication under laboratory conditions. In
living systems RNA molecules are involved in transcription and translation of DNA into proteins and in the synthesis of
DNA via the process of reverse transcription.
23. Both mitochondria and chloroplasts have their own DNA loops and cell membranes that are strikingly similar to those
found in bacteria. In addition, both organelles replicate independently of the rest of the cell.
24.(a) Sudden disappearances of large numbers of species from the fossil record from around the globe suggest that global
mass extinction events have occurred. The discovery of particular chemical clues (iridium) suggests that at least some
of these catastrophes have been caused by the impact of large meteorites. Large impact craters have also been
discovered that date to the times of some of these events.
(b) Mass extinction events dramatically reduce competition for the species that do survive. This creates many new
opportunities and empty niches, promoting adaptive radiation and rapid evolutionary change.
25. Earliest life evolves, first eukaryotic cells, Cambrian explosion, first land plant, largest mass extinction, first dinosaurs,
first flowering plants
26.(a) The wasps feed on and reproduce within the specialized fig flowers. The figs are pollinated by the fig wasps.
(b) The leaf-cutter ants feed on the fungi that are able to grow on plants the ants cannot eat. The fungi and fed and tended
by the ants. The ants carry small quantities of the fungi with them when they establish new colonies.
27. They may be closely related species whose evolutionary paths diverged a relatively short time ago. However, their
similarity may be the result of convergent evolution. In this case, they represent two more distantly related species that
have both evolved similar features in response to the same selective pressures.
28. Bipedal motion has been strongly favoured. This may have provided the benefit of freeing the hands for carrying infants
or making and using tools. A large brain is our most notable feature. A large brain allowed for a dramatic increase in the
capacity to learn and to communicate through complex language. Highly dextrous hands provided the ability to fashion
complex and valuable tools.
29.(a) D and E are most closely related. They share the most recent common ancestor.
(b) C and E would be expected to share the SINE. This is because we would conclude that both B and D inherited the
SINE from their most common recent ancestor. This species is also an ancestor of C and E.
(c) D and E and equally closely related to C.
Applying Inquiry Skills
30. The fossils are just older than two half-lives of 40K or a little more than 2.6 billion years old.
31.(a) Fossils at high elevation suggest environments have changed dramatically over long periods.
(b) The fossil record of whales shows many excellent transitional forms from a four-limbed mammal to an ocean-going
mammal, with the gradual loss of the hind limbs and reduction of the hipbones.
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Unit 4 Review 291
(c) Chromosome banding patterns are extremely similar in many primate species, including humans and chimpanzees.
This similarity suggests we are closely related to each other.
(d) Limbs that are used for very different functions, but the flipper of a whale, the wing of a bat, the foot of a horse, and
the hand of a human all share strikingly similar anatomical features. This suggests they have been inherited from a
common ancestor.
(e) Rudimentary eyes in fish that are blind are considered vestigial traits that were functioning eyes in a distant ancestor.
(f) Bacteria can be shown to evolve antibiotic resistance under laboratory conditions and in the wild in relatively short
periods.
32. Breeders simply select those individuals that express the most extreme phenotype for the character they want to enhance.
For example, they would select those plants with the highest protein content and use them to produce seeds for the next
generation. By repeating this process over and over they would eventually be able to produce plants with a much higher
protein yield that the original population.
33. Darwin concluded that, since the species inhabiting these archipelagos most closely resembled species on the nearest
mainland (Ecuador in the case of the Galapagos, and Africa in the case of the Canary Islands), the pioneer populations
had originally arrived from these landmasses and had subsequently undergone evolutionary changes.
34. The key features of such islands are their unusual environments that generally differ markedly from other landmasses.
This provides a unique set of selective pressures. In addition, as they are small and isolated, only small populations are
likely to find and inhabit them. Small population sizes enhance the effects of genetic drift. Their island nature also acts as
a strong selective screen to keep out entire groups of organisms that are not capable of reaching them. This results in
unusual mixes of species and allows species to evolve and fill ecological niches usually filled by others.
35.(a) For all calculations, frequency of A = (AA × 2) + (Aa)/200
Frequency of a = (Aa) + (aa × 2)/200
Example: Population X, frequency of A = (25 × 2) + (50)/200
= 50 + 50/200
= 0.5
For population X, A = 0.5, a = 0.5; for population Y, A = 0.5, a = 0.5; for population Z, A = 0.2, a = 0.8.
(b) Population Y is not at Hardy–Weinberg equilibrium. We would expect the ratios of phenotypes to be the same as in
population X. This may indicate disruptive selection, as both homozygous genotypes are being favoured. Students
might note that if this is the case, the A and a alleles would not represent a simple dominance and recessive influence.
36. Let A represent the normal hemoglobin allele and a the sickle cell allele. Recall that p2 + 2pq + q2 = 1
Where p = frequency of A and q = frequency of a.
In this case q2 = 1/64 or q = 0.125. Therefore, p = 0.875. The normal hemoglobin allele frequency is 87.5% and the sickle
cell allele frequency is 12.5%. Note: the expected phenotype frequencies are AA = 76.6%, Aa = 21.9%, and aa = 1.5%.
37.(a) With such a small population, Hardy–Weinberg equilibrium will not be maintained. Genetic drift will result in changes
to allele frequencies.
(b) Each year mutations add new alleles to the virus population, thus upsetting Hardy–Weinberg equilibrium.
(c) Natural selection that favours one trait over another produces a change in allele frequencies in the next generation,
thereby upsetting the Hardy–Weinberg equilibrium.
38.(a) The females may benefit from obtaining extra nutrients for egg production. The males may benefit by increasing the
number and success of the young by providing nutrients to the female, or they may be able to prolong sperm transfer
by allowing themselves to be eaten, thus passing on more of their genetic information to the next generation.
(b) Unless males are able to survive they will pass no genes on to the next generation. Any male born with “gentle” genes
and unwillingness to fight over females will never pass such traits on to the next generation. In contrast, those males
that are willing to fight for females are sometimes able to mate and have young.
39.(a) We might expect symmetry to be of more influence for mate selection by females. In most species females are the sex
that selects the males rather than vice versa.
(b) Student experimental designs might involve using photocopiers to create “mirror image” samples that could be viewed
by experimental subjects. Students could be asked to select images that they found most attractive from among an
assorted collection of both symmetrical and nonsymmetrical images.
Students could choose 20 images of people's faces. For one set of trials they could make the first 10 faces
“symmetrical” by scanning and cutting and pasting two identical halves together. The second 10 faces could be “cut in
half” and then realigned using similar technology so that they also appeared to have been manipulated. Students could
then be asked to pick their preferred face from each of 10 pairs (symmetrical and nonsymmetrical). In a second set of
trials students could perform the identical experiment, except they could switch images so that copies of the first 10
images are manipulated and left as normal and the second 10 are manipulated to be symmetrical. This eliminates the
possible bias of the actual faces themselves.
40. It may be possible that males with the larger gift offerings have a better set of genes for “hunting” prey. This might make
them preferred candidates for mating.
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41. Because females produce eggs, they have far fewer and much larger gametes than males. Males in contrast are able to
produce large numbers of sperm at much smaller “cost” to the individual; therefore, they could theoretically have an
almost unlimited number of offspring. From the perspective of the female—she will have a limited number of young so
the best mate is important. From the perspective of the male—evolutionarily, the more offspring a male, has the greater
the biological success. In many species, a large proportion of males never get an opportunity to mate, while almost all
reproductively fit females mate successfully.
42. The longer a group has been in a particular region, the greater the genetic diversity might be, as long as the region can
support a large population. The reason that young populations are genetically less diverse is that they are usually founded
by a small number of individuals with reduced diversity—the founder effect.
Making Connections
43. Answers will vary. The most probable geographic centres of origin of these common domesticated plants and animals are
as follows:
Corn: Mesoamerica
Wheat: Southwest Asia (fertile crescent)
Rice: China
Cattle: Southwest Asia and possibly North Africa
Peanuts: South America
Chickens: China
Pigs: Southwest Asia, China
Rubber: South America
Cotton: Mesoamerica
Sheep: Southwest Asia
44. Darwin was already a celebrity in England and Europe. He was famous for his travel writing of the Voyage of the Beagle,
and he was from a wealthy, well-known, and respected family. Wallace had spent much of his research life in tropical
jungles and so was not a well-known individual by comparison. In addition, Darwin had accumulated a vast body of
supporting evidence for the theory during 20 years of ongoing and exhaustive work.
45.(a) This is an example of directional selection for toxin-resistant individuals. This can lead to sympatric speciation as the
plants are living in the same area.
(b) Plants that have evolved this resistance in one set of mine tailings could be introduced into other regions that needed
rehabilitation.
(c) Yes. Artificial breeding programs might be able to “speed up” the evolutionary process and yield more toxic-resistant
forms much faster than waiting for nature to follow its course.
46. The results may be genetic bottlenecks occurring in many isolated pockets. The result will be an increase in homozygosity
of species and a loss in genetic diversity. This effect would be much more pronounced in large mammal species that have
very small population sizes compared with insects, which often have very large populations.
47. Such discoveries suggest that perhaps some or all of the first building blocks of life had an extraterrestrial origin rather
than an earthly one. It also provides a little more evidence that life may have evolved elsewhere in our solar system. The
discovery of such organic compounds in space also suggests that perhaps in future space exploration, such compounds
might actually be used as a source of raw materials for humans and other life aboard spacecraft.
48. This suggests that the drug-resistant strains have lower fitness than the nonresistant forms in the absence of the drugs.
Therefore, when drugs are not administered, the nonresistant HIV forms out compete and “take over.” The medical
benefit is that if these strains are very successful at competing with the drug-resistant strains, they will reestablish a
population of viruses that can be destroyed by proper drug applications.
49. Consumers would be concerned that as pests become increasingly resistant to insecticides, they will be used in increasing
quantities, threatening the food, as well as the environment, with contamination. In addition, the cost of the potatoes
would increase as the yields drop and the costs of production increase. Ecologists would be particularly concerned with
the potential for environmental damage as pesticides were used in increasing quantities. They would also be concerned
about the possible effects on other nontarget species and the potential for impact on food chains. Pesticide companies
would be concerned that their products would not longer be marketable if insects evolved resistance to them. They would
attempt to develop pesticides for which the evolution of resistance is more difficult. Organic farmers in contrast may feel
that such results are proof that organic approaches are better for the environment and the consumer. Such farmers would
continue to look for natural pest control measures instead of pesticides. Plant breeders would see the importance of trying
to breed food plants that are not palatable to the Colorado potato beetles and other insect pests.
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Unit 4 Review 293
50. By accelerating the process of evolution, medical researchers may be able to develop new varieties of the drugs currently
produced by living organisms. For example, bacteria that produce an antibiotic or other pharmaceutical product may be
able to produce a modified and improved form brought about by mutation. Similarly many plant characteristics, such as
pest resistance or nutritional value, might be improved through mutations. Morphogenics simply increases the rate of
formation of brand new alleles that have potential benefits.
Extension
51. Evidence appears to support both hypotheses. This is a fascinating topic and one that has played a fundamental role in
human history. When European explorers contacted these peoples, they inevitably passed on severe epidemic diseases that
often lead to the deaths of a large percentage of the Indigenous population. Measles and smallpox, for example, wiped out
about 95% of South Americans in the sixteenth century. Europeans were thought to be gods because the diseases didn’t
affect them. When Cortez took over Mexico City, 1000 people were dying each day! In contrast, although Europeans
often contracted new diseases in tropical countries, they were not highly contagious diseases but rather parasitic and often
chronic diseases such as malaria and sleeping sickness.
Many links to the history and evolution of epidemic diseases have been compiled at
<http://www.mic.ki.se/HistDis.html>.
The topic is addressed in the context of the history of human populations in Chapter 15, page 702. This question
provides an excellent lead in to the study of population biology and highlights the significance of evolution in human
history.
An excellent comprehensive “must have” resource is Guns, Germs and Steel by Jarod Diamond, 1999, Norton.
Students might be quite interested to note that Bill Gates (CEO of Microsoft) has a keen interest in this topic and wrote a
review of Diamonds book—posted on the Web at <http://www.edge.org/documents/archive/edge38.html>.
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