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Unit 3
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Evolution
[CATCH UO7-P01-OB11USB; Size UO; R; Description of photo to come in addendum photo ms]
Overall Expectations
∙ analyze the economic and environmental
advantages and disadvantages of an artificial
selection technology, and evaluate the impact
of environmental changes on natural
selection and endangered species
∙ investigate evolutionary processes, and
analyze scientific evidence that supports the
theory of evolution
∙ demonstrate an understanding of the theory
of evolution, the evidence that supports it,
and some of the mechanisms by which it
occurs
Big Ideas
∙ Evolution is the process of biological change
over time based on the relationships between
species and their environments.
∙ The theory of evolution is a scientific
explanation based on a large accumulation of
evidence.
∙ Technology that enable humans to
manipulate the development of species has
economic and environmental implications.
UNIT TASK PREVIEW
In this Unit Task you will [t/k]
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Unit 3 Are You Ready?
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CONCEPTS
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SKILLS MENU
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Concepts Review
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Skills Review
Career Pathways
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Chapter
7
The Theory of Evolution
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KEY CONCEPTS
In this chapter you will be able to
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STARTING POINTS
Answer the following questions using your current knowledge. You will have an opportunity to revisit these questions later,
applying concepts and skills from the chapter.
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MINI INVESTIGATION: TITLE T/K
Skills:
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Equipment and Materials:
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7.1
[catch C07-P02-OB11USB;
Size D; Research. Photo of a
snowshoe hare in the snow.]
Figure 1 Snowshoe hares have evolved a number
of adaptations that allow them to survive in
winter: a coat that changes from brown to white
and unusually wide feet for moving on deep soft
snow.
Biological Change Over Time
Everywhere we look we see change. We live on a dynamic Earth, which we
share with millions of other species, comprised of trillions of individual
organisms. We observe life changing over time – individuals grow and mature
and new generations come and go. The physical Earth also changes. Some
changes are rapid, while others are slow and may go unnoticed. For example,
you would observe a forest fire or the birth of an individual, but you might not
observe the daily changes during ecological succession that follows a fire or
the changes as an individual grows. The slower and more gradual the change,
the more difficult it is to observe and investigate. As you learned in the
Diversity unit, biologists are convinced that entire species change over time –
they evolve. How do biologists detect such evolutionary changes in species and
what causes them to occur? How might the environment influence
evolutionary changes in species (Figure 1)?
Change in Living Things
Before discussing the evolutionary change of species in nature, it is useful to
first examine the changes in species with which we are most familiar. Consider
what you already know about genetic variation and change. How can this
information be put to practical use in animal and plant domestication?
All species, including humans, exhibit genetic variation. The original
sources of genetic variation are mutations, which are changes in genetic
information. Mutations create new genes which provide a continual supply of
new genetic information. Mutations that enter populations have an immediate
and direct effect on individuals, and also have the potential to influence future
generations when they are inherited.
Mutations
neutral mutation mutations that do not result in
any selective advantage or disadvantage
harmful mutation any mutation that reduces the
reproductive success of an individual and is
therefore selected against; harmful mutations do
not accumulate over time
beneficial mutation any mutation that increases
the reproductive success of an organism;
beneficial mutations are favoured by natural
selection and accumulate over time
Mutations may be neutral, harmful, or beneficial. Most mutations are neutral
and result in changes in DNA that have no immediate effect. Neutral mutations
are those that provide no benefit or harm to the individual. Harmful mutations
are those that reduce the reproductive success of an organism. Examples of
harmful mutations include those that lead to serious genetic disorders such as
cystic fibrosis or Huntington disease. Beneficial mutations are those that
produce a change in an individual’s phenotype that gives the individual an
advantage. Beneficial mutations give individuals a better chance of survival in
their environment. For example, the sickle-cell allele for example, gives
carriers a high degree of resistance to malaria and dramatically enhances their
chances of survival in malaria endemic regions.
The changes that arise in species through mutation can have significant
consequences. Bacteria that exhibit resistance to antibiotics are becoming
more widespread as less resistant strains are killed off (Figure 2(a)). Similarly,
insect and other pest species that demonstrate resistance to various pesticides
are becoming more common and difficult to control (Figure 2(b)). From the
perspective of a bacteria or pest species, any mutations that confer increased
resistance are beneficial. Humans, however, would consider these mutations
undesirable.
The next two images will be placed side by side in the text measure. Should
have the same orientation.
[catch C07-P03-OB11USB; Size B1; Research. Photo of highly resistant
strain of bacteria (e.g. Staphylococcus aureus)]
[catch C07-P04-OB11USB; Size B1; Research. Photo of a pesticide-resistant
insect. Look for an Ontario example such as the Colorado potato beetle.]
Figure 2 t/k pending image selection.
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[BEGIN PAGE]
[catch C07-P05-OB11USB;
Size D; Research. Photo of
someone getting a vaccination.
Would prefer image showing an
ethnic teen.]
Figure 3 Each year millions of Ontarians receive
the seasonal flu shot. A new vaccine is needed
each year because the influenza virus is
continuously changing.
Some mutations have serious consequences to human health. For
example, viruses, like living cells, carry genetic information that can undergo
mutation. This means that populations of disease-causing viruses, such as the
human influenza virus, are genetically variable, and change over time. In rare
instances, a mutation may increase the virulence of a virus or enhance its
ability to spread. The result can be a deadly epidemic. Each year the World
Health Organization and other health agencies try to predict which particular
virus strains poses the greatest threat to humans and they then work to
develop an effective “flu” vaccine (Figure 3).
The most obvious changes to species are those that have occurred with
the domestication of numerous species of plants and animals. In most cases
unmodified members of the original species still remain in the wild but in
some cases such as that of certain breeds of domesticated cattle, the original
species is now extinct. Changes that have occurred during domestication are a
direct result of human manipulation.
Selective Breeding: Artificial Selection of Traits
artificial selection directed breeding in which
individuals that exhibit a particular trait are
chosen as parents of the next generation;
artificial selection is used to produce new breeds
or varieties of plants and animals
The domestication of animals and plants is one of the most important
technological innovations in human history. Domesticated plants and animals
provide humans with the vast majority of our food supply and formed the
basis for the development of modern civilizations.
Domestication is the changing members of a species to suit human needs
through controlled captive breeding. The controlled captive breeding process
is referred to as artificial selection – artificial because it occurs in captivity
rather than in a natural setting and selection because humans choose which
specific animals or plants are bred. The breeder selects individuals that exhibit
a desired trait or traits and uses them as the parents of the next generation.
Humans have been domesticating animals and plants for more than 10
000 years. You might be surprised to learn that the earliest animal to be
domesticated was Canis lupus, the wolf (Figure 4). Of course we no longer
refer to the domesticated variety as wolves but rather as dogs. Genetic
evidence provides compelling evidence that all modern breeds of dogs are
descended from wolves (Figure 5). For this reason, dogs are considered a
subspecies of wolves and given the scientific name Canis lupus familiaris.
[catch C07-P07-OB11USB; Size B; Research. Image of many different dog
breeds.]
[Formatter: place fig4 & fig5 side by side across
page; in the correct order]
[catch C07-P06-OB11USB; Size D; Research.
Photo of a wolf, must be Canis lupis. Would
prefer to see a nice head shot or a clear profile.]
Figure 4 The wolf, Canis lupus, is the ancestral
species to all modern dog breeds.
Figure 5 Thousands of years of artificial selection have produced a great variety of dog breeds. During this time a single
mutation is thought to have produced a dog with achondroplasia – a form of dwarfism. The descendents of this dog have
since given rise to bassets and dachshunds.
[END PAGE]
[BEGIN PAGE]
Plants are equally capable of being selectively bred to suit our needs. For
example, several thousand years of domestication of the wild sea cabbage,
Brassica oleracea, has produced a wide array of vegetables (Figure 6). These
diverse vegetables are, in fact, altered forms of the same original species. They
look and taste different as a result of artificial selection acting over thousands
of generations.
[catch C07-F01-OB11USB; Size B; New. Art showing the seven well-known
domesticated vegetables that are included in the sea cabbage family tree.]
Figure 6 These seven well-known vegetables are domesticated varieties of the wild sea cabbage.
Table 1 Domesticated species and the areas they
originated in.
Region
Domesticated species
Eurasia
[t/k]
North and
South America
[t/k]
Africa
[t/k]
How does artificial selection work? How can animal and plant breeders
turn wolves into Chihuahuas and St. Bernards, and wild cabbage into broccoli
and kohlrabi? The process is surprisingly simple but, with the exception of
modern genetic engineering techniques, very slow. The breeder usually has a
particular feature in mind. For example, native peoples of Mesoamerica
domesticated the tomato. Wild tomato plants produce nutritious but small
fruit (Figure 7). As with any species, these plants exhibited variability – some
were a little larger than others, some produced larger fruits, and some tasted
better than others. Generation after generation, farmers selected seeds from
the best plants to sow the next season. The seeds germinated, grew, flowered,
and then cross pollinated each other producing more fruit with the desired
traits. Again the farmers consumed most of the fruit as food, but carefully
examined the plants and saved seeds from the very best plants for sowing.
These practices happened in many parts of the world (Table 1).
The next two images will be placed side by side in the text measure. Should
have the same orientation.
[catch C07-P08-OB11USB; Size B1; Research. Photo of wild tomatoes.]
[catch C07-P09-OB11USB; Size B1; Research. Photo of domesticated
tomatoes]
Figure 7 Beginning with (a) a wild species of tomato farmers chose only those plants that exhibited the most desirable
characteristics as a source of seeds for the next generation of planting. The result of thousands of generations is (b) the
modern tomato.
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[BEGIN PAGE]
THE SCIENCE OF BREEDING
Most traditional animal and plant breeders would not consider themselves
scientists but what they do is often equivalent to a tightly controlled
experiment. Each time breeders attempt to develop a new breed, they are
testing a hypothesis and following a common set of procedures:
Hypothesis: By selecting for breeding stock individuals with certain favoured
CAREER LINK
Animal or Plant Breeder
Animal or plant breeders ...[t/k] ...... To learn
more about becoming an animal or plant breeder,
Go to Nelson Science.
traits over others, the favoured trait will become more prevalent and more
pronounced.
Independent Variable: Breeding population (selected by the breeder)
Dependent Variable: Appearance of favoured trait in population
Procedure:
1. Choose a useful species that can be bred in captivity.
2. Breed a large number of individuals.
3. Choose a trait that you wish to favour, such as large size, a particular colour,
or sweetness.
4. Identify individuals that exhibit the favoured trait most strongly.
5. Breed only these individuals to produce the next generation of individuals.
6. Repeat Steps 4 and 5 over many generations.
In most cases the hypothesis is confirmed. The favoured trait becomes
widespread throughout the population and also becomes enhanced. What
early breeders likely did not expect was the degree to which the populations
would change. [catch career link icon]
Modern breeding, particularly of crop plants, has undergone a revolution.
Today scientists are routinely using genetic engineering techniques to transfer
what they hope will be beneficial genes from an individual of one species to an
individual of another species. When successful, the genetically modified
individual is often mass-produced by cloning. This practice can result in the
widespread use of genetically modified plants with little or no genetic
diversity. Although the pros and cons of genetic engineering are hotly debated,
one thing is certain: these genes have all arisen in natural populations and a
loss in biodiversity also results in a loss of potentially valuable genes.
THE POWER OF ARTICIFICAL SELECTION
The most unexpected result of artificial selection is the production of
individuals that exhibit characteristics that are far beyond the natural
variability witnessed in the original breeding population. Adult Chihuahuas are
not simply small wolves, they are much smaller than even the smallest of adult
wild wolves and they look very different. Giant red tomatoes can be a hundred
times larger than the largest wild tomato fruit. Looking back to the traits of the
first wild plants and animals used for breeding, no one could have imagined
the power of selective breeding (Figure 8).
The next two images will be placed side by side in the text measure. Should
have the same orientation.
[catch C07-P10-OB11USB; Size B1; Research. Photo of a giant pumpkin with
a person in the photo for perspective]
[catch C07-P11-OB11USB; Size B1; Research. Photo of a Texas longhorn]
Figure 8 Artificial selection can produce surprising results, such as this giant pumpkins or the long horns of this Texas
Longhorn.
[END PAGE]
[BEGN PAGE]
Artificial selection methods can also lead to the reduction in genetic
diversity within a population. If breeders only favour certain traits within a
population, then the many alleles linked to other versions of a particular
characteristic are reduced or eliminated. Such a loss in diversity makes a
population more vulnerable to disease. For example, large cobs of sweet corn
might be favoured by plant breeders but might also be favoured by insect
pests. In addition, some favoured traits can be linked to alleles that are
detrimental. For example, some breeds of dogs are more prone to genetic
disorders such as hip dysplasia or cancer because the alleles associated with
these disorders are inherited along with the same alleles that produce the
favoured traits of those particular breeds.
[FORMAT AS 2 COLUMNS WITH FULL PAGE MEASURE AND
INCLUDE WHEAT FIGURE IN BOX.] RESEARCH THIS: THE RICH
HISTORY OF DOMESTICATION
Skills: [tk]
[catch Skills Handbook icon: t/k]
Many species have been the subject of artificial selection. They include livestock, pets, food crops, and ornamental plants
(Figure 9). Each has a fascinating history that began in some part of the world where the original wild species lived. In this
activity, you are to choose a domesticated species and investigate its past.
[catch C07-P12-OB11USB; Size D; Research. Photo of wheat clearly showing an individual head of wheat.]
Figure 9 Wheat originated in Turkey. It was selected for large seed size and non-shattering heads, so that farmers could
collect the seeds before they dispersed.
1. Choose a domesticated plant or animal.
2. Research the history of the plant or animal’s domestication.
3. Research the various breeds or varieties that currently exist. Are the breeds rare? popular? newly established?
4. Consider the benefits and/or harm caused by the domesticated species.
A. How is the domesticated species of value to humans today?
B. How long has the species been under domestication and in what part of the world did it originate?
C. How much has the species been altered as a result of artificial selection?
D. Is there evidence that artificial selection has caused a serious loss in genetic diversity within the population?
E. How many different breeds or varieties exist today and how do they differ from each other?
F. Comment on the overall influence of the domesticated species on humans and on the environment. Do you think that
species domestication was a good idea? [END Research This]
THE HUNDRED YEAR EXPERIMENT
The longest running formal experiment in artificial selection is being
conducted by the Illinois State Agricultural Research Station. The experiment
began in 1896 and it still underway. The purpose of the experiment was to test
the effect of artificial selection on oil content of corn seeds. The design
involved two separate breeding experiments. In the first, corn plants were
selected for high oil content, whereas in the second experiment they were
selected for low oil content. Over 76 years, the oil content increased from 5%
to more than 18% in the first experiment while it dropped to less than 1% in
the second (Figure 10).
[catch C07-F02-OB11USB;
Size D; New/Permissions.
Graph of experimental results
for the hundred year
experiment. ]
Figure 10 Artificial selection can increase or
decrease the oil content in corn.
LIMITATIONS OF ARTIFICIAL SELECTION: THE INFLUENCE OF
MUTATIONS
Not all attempts at artificial selection have been successful. Breeders cannot
create traits that do not already exist in some form within the population. If
there are no genes for blue roses (long sought after by flower lovers), then no
amount of cross breeding will create one. Breeders must work with the genetic
diversity that already exists in the population. This does not mean that new
mutations cannot arise however and when this happens the breeder has new
material with which to work. There is always room for hope that someday a
mutation will occur that gives rise to a truly blue rose.
Beneficial or neutral mutations have a good chance of being passed on to
future generations because they are either favoured or go unnoticed. In
contrast, mutations that cause harm, or produce an undesirable trait in an
individual, have little influence on the potential success of artificial selection
efforts. Breeders simply do not choose such individuals for breeding and
therefore the harmful mutations are not passed on to the next generation. In
rare circumstances an undesirable trait may accompany a beneficial one. An
interesting example occurred in the breeding of strawberries. Breeders were
able to develop plants with high quality berries held on elevated stocks making
them much easier to harvest. Unfortunately the berries were purple in colour!
Attempts at commercialization failed. A number of farmers produced these
berries but consumers simply rejected them based on their odd colour.
[END PAGE]
[BEGIN PAGE]
Implications for Natural Populations
How can we apply our current understanding about genetics and artificial
selection to the millions of species that exist in the wild? We should first recap
what we already know about genetics:
• Individuals of all species exhibit genetic variation.
• Mutations produce heritable changes in individuals and these changes may
be beneficial, harmful, or neutral.
• Some species, such as bacteria and insects, can change over relatively short
periods of time.
• Some domesticated species have changed dramatically under the influence of
artificial selection.
These observations are based on a large number of species that have been
domesticated over relatively short periods of time – at most over several
thousand years. How, then, might similar processes influence the populations
of all species on Earth? If we can begin with a population of wolves, and change
them into hundreds of distinct breeds of dog, what might happen to a species
over thousands or millions of years living under natural conditions?
One of the challenges faced by biologists trying to answer these questions
is how and where to obtain useful evidence. You can imagine that one of the
most useful places for biologists to look would be back in time. Biologists do
not have time machines but fortunately Earth keeps some records of the past
history of life. A history that is recorded in the rocks and in at least some
locations, actually opened to views of the past (Figure 11).
7.1 SUMMARY
[catch C07-P13-OB11USB; Size D; Research.
Photo of the grand canyon, illustrating that it was
formed by erosion.]
• Mutations create new genetic information and add genetic diversity to species
• Beneficial mutations can have significant consequences for species.
• Artificial selection works by choosing individuals with particular favoured traits in each generation as the breeding stock
for next generation.
• When practiced over many generations, artificial selection can produce dramatic changes in the traits of a population.
• Artificial selection is limited by the genetic variability within the breeding population.
• Artificial selection methods can reduce the overall genetic diversity of the population and therefore contribute to the
loss of biodiversity.
7.1 QUESTIONS [FORMATTER: RUN IN TWO COLUMNS ACROSS
PAGE]
Figure 11 The grand canyon was formed by
erosion. The Colorado river has cut through and
exposed sedimentary deposits that are hundreds
of millions of years old.
1. The chances of any one individual being born with a beneficial mutation is very low. How then is it possible for
mutations to play such a key role in evolution? [K/U]
2. How might it be possible for a neutral mutation to play an important role in the evolution of a species? [K/U]
3. Explain why harmful mutations do not accumulate over time and cause harm to populations. [K/U]
4. Use the sickle-cell allele to show how a mutation may be beneficial or harmful depending on the environment. [K/U]
4. Use the evolution of antibiotic resistant to show how a mutation that is advantageous for one species can be harmful
for another. [K/U]
5. Most wolves look quite similar. Use the domestication of dogs to illustrate the genetic diversity that is contained
within the wolf population. [K/U]
6. How have modern genetic engineering methods changed the way that plant breeders develop plants with new and
potentially valuable traits? [K/U]
7. Using a specific example, outline a hypothesis and simple step by step procedure a breeder could use to create a breed
with a desired trait. [K/U, T/I]
8. How does the genetic diversity of a population and mutation rates limit the ability of breeders to create organisms
with desired traits? [K/U, A]
9. What characteristics of bacteria and insects enable them to evolve relatively quickly? [K/U]
10. All domestications of plants and animals begin with humans selecting a wild species living nearby. Do research to find
out where each of the follow domesticated species originated: [T/I, A]
(a) chicken
(b) pig
(c) cattle
(d) corn
(e) wheat
(f) rice
(g) chocolate
11. [research question about genetic mutations to cover C2.2]
12. [add question referencing single mutation leading to short legs in dog breeds.]
[END PAGE]
[BEGIN PAGE; 6 pages]
7.2
immutable something that cannot be changed
The Evolution of an Idea
Dating back at least as far as Aristotle (384-322 BCE) most Europeans
accepted the idea that the Earth and all living things had been created in their
present forms and were immutable – they could not change and had not
changed. The explanations for all natural phenomena proposed by Aristotle
and others were largely based on strongly held religious beliefs, philosophical
debate thoughtful conjecture. It was not until science began to come of age in
the 15th to 18th centuries, that European philosophers recognized the
importance of careful observation, experimentation, and deductive reasoning.
It was during this time that Copernicus, Galileo, and Newton demonstrated the
power of science to explain the laws of motion both on Earth and in the
heavens above.
The Seeds of an Idea
[catch C07-P14-OB11USB;
Size D; Research. Image of the
(vestigial toes of a pig)—
illustating that they do not touch
the ground.]
Figure 1 Many mammals, including pigs, have
toes that do not reach the ground. Buffon puzzled
over such useless features and considered them
strong evidence that these species had changed
over time.
A French scientist Comte (Count) Georges-Louis Leclerc de Buffon (17071788) applied scientific methods to the detailed study of anatomy. He closely
examined animal body structures, considered their functions, and tried to
account for his findings. Buffon was puzzled by anatomical features that
seemed to serve no purpose. For example, he wondered why pigs have extra
toes that do not reach the ground (Figure 1). Buffon believed the species had
been created in a more perfect form, but that they had changed over time.
At about the same time, other prominent scientists, including Carl
Linnaeus (1707-1778) and Erasmus Darwin (1731-1802), also proposed that
life changed over time. Erasmus Darwin, the grandfather of Charles Darwin,
even suggested that all life might have evolved from a single original source.
While the seeds of evolutionary thought had been sown, these scientists
could offer no explanation for how living things change. Without a plausible
mechanism to explain how a species could change, their ideas remained
speculative.
Adaptation and Heredity
[catch C07-P15-OB11USB; Size D; Research.
Photo of an athlete in training with obvious strong
muscles.]
Figure 2 Muscles increase in size in response to
vigorous exercise. Such an increase in size is
considered an acquired characteristic
A student of Buffon, Jean-Baptiste Pierre Antioine de Monet, Chevalier de
Lamarck (1744–1829), was the first scientist to offer a possible mechanism for
the evolution of species. Lamarck proposed that evolutionary change resulted
from two distinct principles.
Lamarck’s first principle was that of use and disuse. He believed that
structures an individual used became larger and stronger, while structures
that were not used became smaller and weaker. On the surface, this principle
seems to be supported by evidence from everyday observations. When
athletes train, their muscles respond by getting stronger and increasing in size
(Figure 2). Conversely, astronauts that return from space have reduced muscle
mass resulting from lack of use. It seems reasonable to think that similar
responses to use and disuse might occur among all organisms.
Lamarck’s second principle was the inheritance of acquired
characteristics. Lamarck believed that individuals could pass on to their
offspring characteristics they had acquired during their lifetime. He believed,
for example, that if adult giraffes stretched their neck during their lifetimes,
then their offspring would be born with slightly longer necks.
[END PAGE]
[BEGIN PAGE]
To Lamarck, these two principles could explained why species were so
adapted to their environment and how they could evolve if the environment
changed. If the climate gradually cooled, animals might respond by growing a
thicker coat of hair and would pass on this acquired characteristic to their
offspring. Their offspring would then be born better adapted to the changing
environment. The example of the giraffe’s neck is often used to illustrate
Lamarck’s theory (Figure 3).
[catch C07-F03-OB11USB; Size B; New. A series diagram showing Lamarck’s
theory of evolution by the inheritance of acquired characteristics.]
Figure 3 Lamarck’s theory of evolution by the inheritance of acquired characteristics.
Today we know that Lamarck’s theory was is flawed. Although organisms
can acquire many characteristics during their lifetime, many features do not
change in response to use and those features that do change are not normally
heritable. For example, your vision does not improve the more you use your
eyes. It is possible to stretch your neck slightly, but this will not alter your DNA
and your children will not be born with longer necks.
Despite Lamarck’s flawed theory, he did make a number of very
significant contributions to our understanding of evolution. Lamarck proposed
the following:
• All species evolve over time.
• Species evolve in response to their environment and become better adapted
to that environment.
• Changes are passed on from generation to generation.
Lamarck’s theory stimulated a great deal of scientific discussion and his
contributions provided a sound basis for the theory of evolution that would
follow.
Patterns of Change
Even scientists that did not accept the idea that species could change were
finding evidence that was extremely puzzling. They found some of this
evidence in the form of fossils, which are preserved ancient remains of dead
organisms. A minimum age of 10 000 years is sometimes used as a criteria for
being designated as a fossil.
[END PAGE]
[BEGIN PAGE]
fossil any ancient remains, impressions, or
traces of an organism or traces of its activity that
have been preserved in rocks or other mineral
deposits in the Earth’s crust. Hardened body
parts such as bone and shell are the most
common fossilized remains
Fossil Formation
Most fossils are in the form of hard impressions in solid rock Many leave little
doubt as to what they represent. No one could mistake a well-preserved fossil
of Knightia (Figure 4(a)) for anything other than a fish, or fail to recognize an
obvious fossilized leaf (Figure 4(b)). It seemed self evident to most scientists
that such fossils had been formed by once living organisms.
The next two images will be placed side by side in the text measure. Should
have the same orientation.
[catch C07-P16-OB11USB; Size B1; Image of Knightia.]
[catch C07-P17-OB11USB; Size B1; Research. Image of a leaf fossil.]
Figure 4 Fossils of both (a) Knightia and (b) leaves are extremely abundant in some from rock formations.
The most common and easily recognized fossils are of hard body parts
such as bones, teeth, and shells. Fossils are formed when the remains of a
buried organism are gradually replaced by mineral deposits (Figure 5). After
an organism dies, the body usually decomposes. However, if the body sinks to
the bottom of a body of water and is quickly buried by sediments, the resulting
lack of oxygen can prevent decomposition. As sediments accumulate over time,
the body becomes compressed, and very gradually chemical changes occur that result in the body being mineralized.
[Formatter: This 4-part image will go across text width in two rows of two (i.e. 2 * 2). It can go full page width if that works
better, but with minimal height—see notes in art ms.]
[catch C07-F04a-OB11USB; Size B1; New. Image showing how a fossil forms
underwater. Part a: a dead organism underwater]
[catch C07-F04b-OB11USB; Size B1; New. Image showing how a fossil forms
underwater. Part b: an organism becomes buried in thick sediments]
[catch C07-F04c-OB11USB; Size B1; New. Image showing how a fossil forms
underwater. Part c: the sediments and chemical action change the organism in
to a mineral form over time]
[catch C07-F04d-OB11USB; Size B1; New. Image showing how a fossil forms
underwater. Part d: the fossil is uncovered through erosion and excavation.]
Figure 5 Most fossils form underwater a) when an organism becomes buried in thick sediments b).The organisms does not
decay because of a lack of oxygen. Over time the pressure of the sediments and chemical action change the organism into
a mineralized form. c). Fossils dating back millions and even billions of year may be found when such deposits are
excavating
[END PAGE]
[START PAGE]
Organisms can also become trapped and preserved in amber – fossilized
tree sap (Figure 6). Some of the most well preserved fossils are formed when
entire organisms become trapped in materials that conserve the chemical
remains of the organism. Such can be the case when organisms are trapped in
volcanic ash, ice formations such as permafrost, or acidic bogs.
The necessary conditions for fossil formation are rare. When oxygen is
present, bodies usually decompose too quickly to fossilize. Therefore, only
organisms that die in low-oxygen locations will fossilize. Most often these are
aquatic organisms living in locations where sediment is continuously
deposited on the bottom. In addition, organisms with hard body parts are
much more likely to be preserved than soft bodied organisms. As a
consequence, fossils of marine organisms with hard body parts such as clams
and snails are very common, whereas fossils of land animals and plants are
much less common. Dinosaur fossils are extremely well known but are very
rare by comparison to fossils of marine organisms.
Fossils can also be formed from footprints, burrows, and even faecal
remains. Sediments may fill in a footprint or burrow and then harden over
time to create a fossil (Figure 7).
[formatter: place figures 6 & 7 next to each other in the text measure]
[Catch C07-P52-OB11USB; Size B1; Research. Photo of an insect in amber.]
[catch C07-P18-OB11USB; Size B1; Research. Photo of a fossilized footprint, preferably of a dinosaur such as sample
image.]
Figure 6 [t/k]
Figure 7 Under the right conditions, footprints can become fossilized.
Reading The Fossil Record
[C07-P19- OB11USB; Size D;
Research. Photo of a
triceratops skeleton at a
museum.]
Figure 8 Fossils of dinosaurs like this triceratops
leave little doubt that some fossil species are
dramatically different than any species alive
today.
At first scientists may have speculated that fossils were nothing more than
recently living organisms that had become trapped in muddy deposits and
then hardened over a relatively brief period of time. Perhaps fossils were just
preserved plants and animals that were no more than a few hundred or a few
thousand years old. This simple explanation was quickly contradicted by a
number of observations that are very difficult to account for:
• Many fossils appear to be of unusual and unknown organisms. There are
fossils of thousands of species that are no longer living (Figure 8).
• There are no fossils of most living species.
• Fossils are often buried very deep within rock formations. Some are more
than a kilometre below the Earth’s surface.
• Fossils are often found in unexpected locations. For example, fossils of sea
life are found high in mountain formations and in present-day deserts.
Such observations were of great interest to early scientists. They became
determined to develop a better understanding of how fossils formed and to
understand what they could tell us about life in the past. This emerging science
that studied fossil organisms to learn about prehistoric life was called
palaeontology. [END PAGE]
[START PAGE]Palaeontologists used fossils to provide evidence that life had been
very different in the past. Also, around this time, the field of geology, the study
of Earth’s surface features, was beginning to develop. Two prominent
scientists, a paleontologist named George Cuvier and a geologist named
Charles Lyell, began to provide a wealth of new evidence on how species and
Earth might change over time (Figure 9). <career link paleontologist>
Catastrophism and Uniformitarianism
palaeontology the scientific investigation of
prehistoric life through the study of fossils
The famous palaeontologist Georges Cuvier (1769-1832) conducted the first
detailed studies of fossils. Cuvier noted the following:
• Fossils of very simple organisms are found in all depths of fossil deposits.
• Fossils of more complex organisms are only found at shallower depths, in
[catch C07-P20-OB11USB; Size D; Research.
Photo of a paleontologist working with a large
fossil—either in a museum or in the field.]
Figure 9 A paleontologist works on a
Tyrannosaurus rex fossils at the Tyrell Museum in
Drumheller, Alberta.
younger rock.
• Fossils in the shallower depths are more likely to resemble living species.
• Rock layers contain fossils of many species that do not occur in layers above
or below them (Figure 10).
[catch C07-F05-OB11USB; Size B; New. Image of fossils in strata showing gradually increasing complexity from bottom to
top. ]
[Formatter: Place next to subhead,
Catastropism...]
CAREER LINK
Paleontologist
Paleontologists are scientists that study ancient
fossilized remains. Their work may require
expeditions to different parts of the world. To
learn more about becoming a paleontologist,
[catch web link banner]
catastrophism the theory that the pattern of
fossils could be accounted for by a series of
global catastrophes that wiped out most species
on Earth
uniformitarianism the theory that geological
changes are slow and gradual and that natural
laws and processes have not changed over time
Figure 10 Cuvier noticed that all fossils from deeper layers were simpler than the most complex fossils above.
Such observations offered strong support for the theory that life had
evolved from simple to more complex forms over time. The oldest fossil
deposits contain only simple life forms. More recent fossil deposits contain
species that are both more complex and more similar to present living species.
Although the fossils Cuvier found showed a clear pattern of change from
layer to layer, Cuvier believed that species themselves did not change. Instead,
he proposed a theory of catastrophism. According to the theory of
catastrophism, global catastrophes, such as floods, had caused the widespread
extinctions of species. These extinct species, some of which were fossilized,
were then replaced by a newly created set of species. Cuvier’s theory
accounted for the different groups of species in each layer but did not
adequately account for why each layer included progressively more complex
forms.
At about the same time that Cuvier was postulating catastrophism,
Charles Lyell (1797-1875) was studying rocks and fossils and coming to the
opposite conclusion. Considered the father of modern geology, Lyell
revolutionized geology with his theory of uniformitarianism. In 1830, Lyell put
forth the following principles of uniformitarianism in his now famous
Principles of Geology:
• Earth has been changed by the same processes in the past that are occurring
in the present.
• Geological change is slow and gradual rather than fast and catastrophic.
• Natural laws that influence these changes are constant and eternal and they
operated in the past with the same intensity as they do today.
[END PAGE]
[BEGIN PAGE]
Lyell’s ideas were radical. He was proposing that entire mountain ranges
might have formed by extremely slow processes, and that deep gorges were
the product of slow erosion. Lyell’s theories directly challenged the belief in a
very young Earth. If he was right, Earth was extremely old and life had had a
very long time to undergo evolutionary change (Figure 11).
[FORMAT HOWEVER WORKS BEST FOR THE PAGE] RESEARCH
THIS: PALAEONTOLOGY AND GEOLOGY
Skills: Researching, Communicating, Evaluating
The anatomist and palaeontologist Baron George Cuvier and the geologist Sir Charles Lyell made substantial
contributions to our early understanding of history of life on Earth. In this research activity, you will partner with a fellow
student and investigate the contributions of these individuals.
1. With your partner, research the lives of Cuvier and Lyell. When and where they were born? What was their social status,
upbringing, and education? Take note of any unusual aspects of their lives.
2. Document Cuvier’s and Lyell’s contributions to palaeontology and/or geography. Include their association with the
[catch C07-P21-OB11USB;
Size D; Research. Photo of the
Grand Canyon that accentuates
depth of the canyon and shows
layers of rock.]
Figure 11 [t/k]
following theories: catastrophism, actualism, and uniformitarianism.
A. Create a short “biographical sketch” of these two individuals.
B. Summarize their contributions to science. In what ways did they break new ground in our scientific understanding of
Earth and life on Earth?
The Stage is Set
By the 19th century, scientific thoughts regarding the history of Earth and its
life forms were undergoing substantial change. There was growing evidence
that Earth was ancient and that species might be evolving. However, a
mechanism for such change had yet to be adequately explained. Furthermore,
Lamarck’s contributions to thoughts on evolution were significant but his
explanation for how life evolves was unsatisfactory. However, unlike the
debate over the age of Earth, tThe search for a mechanism for evolution would
not have to wait for very long. It was to become the life’s work of a young man
named Charles Darwin.
7.2 SUMMARY
• By the 18th century scientists were beginning to gather evidence that
supported the theory that life had changed over time.
• Lamarck was the first scientist to recognize that species evolved in response
to their environment, but his hypothesis of how species evolved has proven to
be incorrect.
• Fossils provide compelling evidence that species living in the past were
different than those living in the present.
• Fossils show a progression of an increasing complexity of organisms over
time with the most complex organisms being found only more recent fossil
deposits.
• Lyell proposed that those of the Earth’s geologic features can be accounted
for by very slow changes occurring over very long periods of time.
• Cuvier proposed that species did not change but were eliminated by
catastrophic events only to be replaced by newly created forms.
7.2 QUESTIONS
1. (a) Why was Buffon puzzled by pig’s toes? [K/U]
(b) How did he explain them?
2. What explanation did Lamarck propose for how species had changed over time? [K/U]
3. What role did Lamarck believe the environment played in evolution? [K/U]
4. Use Lamarck’s theory to explain the evolution of running speed in Cheetahs. [K/U, A]
5. What do the following characteristics of fossils reveal about the history of life on Earth. [K/U, A]
(a) Some fossils of marine organisms are discovered at high elevations in mountains.
(b) Most fossils are of species that are no longer living.
(c) most living organisms are not found in the fossil record.
(d) Most fossils are of marine organisms.
(e) The oldest fossil deposits only contain simple organisms. More recent deposits contain both simple and complex
fossils.
6. How did the theory of catastrophism account for patterns seen in the fossil record? [K/U]
7. How did the theory of uniformitarianism account for patterns seen geology? [K/U]
8. Use labelled sketches to illustrate the process of fossil formation. [K/U, C]
9. How might it be possible for fossils to provide evidence about the behaviour of an organism? [A]
10. Imagine you were asked to excavate fossils from deposits near the top of the grand canyon and near the bottom.
Predict any pattern you would expect to find in the fossils. [T/I, A]
11. The most famous fossil deposit in Canada is the Burgess Shale. Do research to answer the following questions. [T/I,
A]
(a) Where are the Burgess Shale located?
(b) When and by whom were they discovered?
(c) What is the age of the fossils in the deposit?
(d) What makes the deposit of special interest?
[END PAGE]
[FORMATTER: Please format Journal as per Design (it is a Science Journal); 2pp total]
7.3 The Voyage of the Beagle
ABSTRACT
[FORMATTER: RUN FULL PAGE WIDTH, AS PER DESIGN]
Charles Darwin’s five-year voyage aboard the HMS Beagle stimulated his curiosity and set him on the path to great
discovery. Darwin’s keen powers of observation, exhaustive collections, and new findings provided a wealth of
evidence on the origin of species. Darwin was puzzled by many of his observations that could not be explained based
on his previously held beliefs. Darwin would devote much of his life to developing a theory that could account for his
many observations.
[Formatter: run the rest of the text in 2 columns, as per design]
Introduction
In December 1831, Charles Darwin set sail on the HMS
Beagle and began a five-year voyage of discovery (Figure
1). The young Darwin, age 22, had been recommended
for the voyage by his former Professor John Henslow,
who considered Darwin an exceptional naturalist.
[C07-P23-OB11USB; Size C3; Research. Photo of fossil
Glyptodon without much background detail.]
[catch C07-P24-OB11USB; Size C3; Research. Photo
of a present day armadillo.]
[catch C07-P22-OB11USB; Size C2; Research. Photo
of the young Charles Darwin.]
Figure 2 The (a) fossil Glyptodon resembled the (b) present day armadillo except that the
Glyptodon was almost 200 kg heavier.
Figure 1 [t/k]
Darwin also discovered fossils of marine organisms
high in the Andes Mountains. Later, following a severe
earthquake, he was informed that a section of coastline
had risen three metres out of the water as a result. This
evidence supported Lyell’s theory that such events could,
over millions of years, account for large-scale changes
like the formation of mountain ranges.
By the time Darwin left South America, he was
becoming increasingly convinced that the Earth was
indeed dynamic and changing.
Captain Robert Fitzroy’s, primary mission was to
survey and map the coastal waters of South America for
the British Navy. Darwin was to observe, record, and
collect specimens of rocks, minerals, plants, and animals.
His supplies included specimen jars and preservative, a
microscope, binoculars, a compass, many notebooks, a
pistol, a rifle, and a book given to him by Henslow – the
first volume of Lyell’s Principles of Geology.
What Darwin Saw
As the crew of the Beagle was conducting surveys
along the east and west coast of South America, Darwin
hired guides and porters and travelled inland to explore,
often for weeks at a time. Darwin was impressed by the
diversity of life he encountered, the grandeur of the rich
tropical rainforests, and the geographic features of the
landscape. He was keen to document everything he saw.
Darwin was a meticulous observer and painstaking
collector. During the voyage he gathered thousands of
specimens and filled notebooks with more than 4000
pages of detailed observations. At intervals Darwin
would ship his specimens back to England to be looked at
by experts. His many rock, mineral, and fossil specimens
were particularly heavy and in a 1932 letter to Henslow,
who had agreed to receive his specimens, Darwin wrote:
“I am afraid you will groan, or rather the floor of the
Lecture room will, when the casks arrive.”
While in Patagonia, Darwin made some important
discoveries including fossils of giant Glyptodon (Figure
2) and Megatherium. Darwin would later find out that
these specimens resembled the much smaller modern
armadillos and sloths, respectively. Darwin noted that
modern and extinct animals that resemble each other
seemed to share similar geographical distributions. In
this case, like their fossil relatives, modern-day
armadillos and sloths are both found in South America.
The Galapagos Islands
The most famous of Darwin’s observations and
conclusions were on the Galapagos Islands, lying
approximately 1000 km off the west coast of South
America (Figure 3). This small isolated archipelago is
comprised of 18 islands, which were formed from
volcanoes that rose up from the ocean floor.
Upon his arrival Darwin was immediately struck by
the harsh dry landscape and the unusual and unique
flora and fauna that inhabited the islands. Among the
most unusual species were tame birds, such as the
nesting boobies, that you could walk up to, an iguana that
dives underwater to feed on seaweed, and the giant land
tortoises (Figure 4).
[formatter: The next two photos will run side-by-side across column width. Should have
the same orientation.]
[catch C07-P26-OB11USB; Size C3; Permission. Photo
of a Galapagos marine iguana.]
[catch C07-P27-OB11USB; Size C3; Permission. Photo
of a species of Galapagos tortoise.]
Figure 4 The (a) Galapagos marine iguana and (b) a species of Galapagos tortoise
Formatter: Place map at top of second page and make it full page (2 column) width.
[catch C07-F06-OB11USB; Size A; New. Map showing Darwin’s voyage.]
[formatter: The next two photos will run side-by-side across column width.Should have
the same orientation.]
Investigation X.X.X 21
resembled species in mainland South America; they did
not live there.
Darwin’s Return
[Formatter: place C07-P25 as an inset photo on top of C07-F06.]
[catch C07-P25-OB11USB; Size E; Research. Photo of the HMS beagle.]
igure 3 Darwin spent 5 years on the HMS Beagle. The HMS Beagle was 27.5 m in length
and carried 74 people. Darwin’s cabin was so small that to lie down he had to remove a
draw from the end of his bunk to make room for his feet.
Oddly, these species bore a striking resemblance to
species he had observed on the continent of South
America even though they lived in entirely different
habitats. Moreover they were very unlike the species he
had observed on the Cape Verde islands off the coast of
Africa although the habitat was similar to the Galapagos.
As he went about collecting specimens, it did not
occur to Darwin that neighbouring islands, often within
sight of each other, might be home to entirely different
species. Only later would he learn from experts that
many of the specimens he had assumed were just
varieties of a single species, were different species
entirely, including the 13 species of Darwin’s finches that
are now famous.
Perhaps as surprising were the species that were
absent from the Galapagos. There was not a single native
species of amphibian or large land mammal in the entire
Galapagos, even though some of these islands were over
a 100 km in length. Darwin realized that the only types of
species that did live in the Galapagos were those that
could have arrived by air or water. Insects, birds, plants
(seeds), and reptiles, which can go weeks without eating
or drinking, could have arrived by air or water.
Amphibians perish in salt water and no large mammal
can survive without fresh water for long. It seemed the
islands had been populated by species that had arrived
from elsewhere. However, most of these species only
Darwin had left England believing that species were
immutable, but returned five years later with many
doubts. Darwin was an individual of extraordinary
determination. He would spend the next 20 years of his
life formulating his theory of evolution and unravelling
what he referred to as “that mystery of mysteries." The
influence of the Beagle voyage is captured in Darwin’s
own journal entry of 1837 “... Had been greatly struck ...
on character of S. American fossils—& species on
Galapagos Archipelago. — These facts origin (especially
latter) of all my views.”
Further Reading
Darwin, Charles. (1839). The Voyage of the Beagle.
Available online.
Darwin, Charles. (1835). Galapagos Notebook. Available
online as part of The Complete Work of Charles Darwin.
Stewart, P.D. (2007). Galapagos: The Islands that
Changed the World. New Haven: Yale University Press.
7.3 QUESTIONS
1.
What qualities of a good scientist did Darwin display on the voyage? [K/U]
2.
Describe Darwin’s key observations regarding the distribution of fossils. [K/U]
3.
Darwin was surprised by the species he found on the Galapagos Islands. [K/U,
T/I, A]
(a) Of what other species did they remind him?
(b) Why had Darwin expected to find species similar to those on the Cape Verde
islands?
(c) What is the connection between the types of native animals on the
Galapagos and their ability to cross the open ocean?
4.
Form a small group of two or three students, and conduct online research to
complete the following: [T/I, A]
(a) Examine Darwin’s childhood and formal education.
(b) Find out the circumstances that lead to Darwin’s selection and his
acceptance for participation in the voyage.
(c) Describe the life history of at least one species of Galapagos wildlife.
(d) Outline some of Darwin’s other scientific findings on the voyage, including
his investigation of coral reefs.
(e) Describe Darwin’s work ethic and approach to science. Did Darwin conduct
any experiments of his own? Did he rely on the opinions of others?
(f) Explore the relationship between Darwin and Captain Fitzroy.
5.
Select and present in the form of a skit one piece of biographical information you
gathered in Question 4. [C]
Investigation X.X.X 22
[begin page; 8pp]
7.4
The Preponderance of Evidence
Charles Darwin returned to England in 1836, ending his voyage on the HMS
Beagle. Darwin had spent five years making countless observation and
gathering thousands of specimens. He was now filled with new ideas and
questions about species.
In July of 1837 Darwin began writing his first notebook on what he called
the “transmutation of species.” It would mark the beginning of Darwin’s farreaching investigations on the evolution of species. In a letter to his friend J.D.
Hooker in 1844, Darwin described his approach: “I was so struck ... that I
determined to collect blindly every sort of fact, which could bear any way on
what are species. I have read heaps of agricultural and horticultural books, and
have never ceased collecting facts.” In the years that followed, Darwin stayed
true to his words, continuing to consult experts, conduct numerous
experiments, and spend long hours contemplating his findings.
This section will present the many forms of evidence that convinced
Darwin of the evolution of species and enabled him to formulate his theory.
Biogeography
biogeography the scientific study of the
geographic distribution of organisms based on
both living species and fossils
Some of the most compelling evidence for evolution comes from biogeography,
the observed geographic patterns of distribution of species. Darwin’s
observations of both living and fossilized species during the voyage of the
Beagle laid the foundation for this new science. Darwin was particularly
surprised by the unusual assortment of species he found on the Galapagos
Islands. Though not witnessed by Darwin, other remote islands, including New
Zealand and Hawaii, held similarly odd collections of species (Figure 1).
The next two images will be placed side by side in the text measure. Should
have the same orientation.
[catch C07-P28-OB11USB; Size B1; Research. Photo of the New Zealand
Kakapo in natural habitat.]
[catch C07-P29-OB11USB; Size B1; Research. Photo of a Sifaka lemur in its
natural habitat]
Figure 1 (a) The New Zealand Kakapo is a giant nocturnal parrot and the world’s largest and only flightless parrot. It is
critically endangered. (b) Sifaka lemurs are found only on the island of Madagascar but there are fossils in India.
[catch C07-P30-OB11USB;
Size D; Research. Photo of
humans interacting with tame
species on Galapagos or other.]
Remote islands are also associated with unusual examples of animal
behaviour. Many species are unusually tame (Figure 2). Such behaviour
surprised Darwin and is immediately apparent to any present-day tourist
visiting these remote environments. Birds may land on your head, iguanas will
allow themselves to be picked up, and sea lions are content to have you sit next
to them on the beach. Darwin believed that this lack of fear of people could
also be accounted for by evolution. Perhaps these species, living and evolving
in a location with no natural predators had lost their instinctive fear.
Darwin’s Hypotheses
Figure 2 Many species that live on remote
islands show little or no fear of humans.
Darwin realized that the patterns he had observed regarding the distribution
of species, both living and extinct, was evidence that species might have
evolved. He hypothesized that remote oceanic islands became populated by
species that arrived by water or air, and then many had evolved into new
species over time.
[END PAGE]
[BEGIN PAGE]
Darwin considered this the best explanation for why such islands had
many species that were found nowhere else, but that bore a resemblance to
Investigation X.X.X 23
species on the nearest continental land mass. Table 1 lists some key
observations regarding the species inhabiting the Galapagos Islands. Each
observation is matched with Darwin’s corresponding hypothesis for all remote
islands based on the theory that species evolve.
Table 1 Species on Remote Islands
Observations from the Galapagos Islands
Darwin’s hypotheses regarding remote islands
Many species of plants, birds, insects, and, in some
cases, reptiles
Only these kinds of organisms are able to reach remote
islands by crossing large expanses of open ocean.
No native amphibians and very few land mammals
Amphibians and most mammals are unable to cross open
ocean and will not occur on remote islands.
Many unique species, found nowhere else on Earth
Over time ancestral species will have evolved into new
geographically isolated species.
Unique species most closely resemble species on the
nearest continental land mass
Unique species are descendents of ancestral species from
the nearest continental land masses and will exhibit some
similarities.
Testing Darwin’s Hypotheses
[catch C07-P31-OB11USB; Size D; Permissions.
Photo of the Galapagos or Hawaian islands
showing volcanic nature/origin.]
Figure 3 The Galapagos and Hawaiian islands
were formed by volcanoes that rose from the
bottom of the Pacific ocean. To learn more about
the formation of these islands go to <catch web
link>
<CATCH: web link To learn more about the
fascinating species that live on the Galapagos
and other remote islands go to . . . .>
[catch C07-P32-OB11USB; Size D; Research.
Photo of an extinct bird species from Hawaii, e.g.
the Black Mamo (Drepanis funera).]
Figure 4 The Black Mamo (Drepanis funera), a
species of honeycreeper, went extinct in about
1907. Of the original 41 species of Hawaiian
honeycreeper, 17 are probably extinct, 14 are
endangered, and only 3 species continue to have
large healthy populations.
Darwin’s hypotheses were tentative explanations for his observations. If
correct, these hypotheses would apply to similar situations. The strength of
any hypothesis is determined by how well it is supported by future tests and
observations. In this case, the Hawaiian islands provide an excellent test case
of Darwin’s hypotheses. Like the Galapagos, the Hawaiian islands were formed
from volcanoes that rose directly from the ocean floor (Figure 3). They have a
wide range of habitats and have never been connected to any other land mass.
An examination of the native species of Hawaii supports Darwin’s
hypotheses. There are no native amphibians or mammals with the exception of
bats and sea lions. There are many species of unique plants, birds, and insects.
Unlike the Galapagos, there are no native terrestrial reptiles. The only
Hawaiian reptiles are marine species: a sea snake and five species of sea turtle.
This difference can be accounted for by the fact that the Galapagos lie within
1000 km of the coast of South America, whereas the Hawaiian islands are
much more remote – more than 4000 km from the coast of North America. No
land reptile could be expected to survive such a long ocean crossing. <CATCH:
web link>
In testing a hypothesis, it is important to consider alternative
explanations that might account for your findings. What if remote islands lack
certain groups of organisms simply because these species are not able to live in
such settings? Perhaps mammals and amphibians, for example, simply cannot
survive on large oceanic islands. This alternative hypothesis has been put to
the test when non-native species are introduced to islands. Introduced species
have not only thrived in these new environments, but also have had a
devastating impact on many native species. Rats, dogs, and pigs have wreaked
havoc on native bird and tortoise populations. They eat the eggs and young of
tortoises and ground-nesting bird species, which exhibit no fear or defensive
behaviours. The impacts have been particularly damaging in Hawaii where an
estimated 271 species have gone extinct since the arrival of Europeans in 1778
(Figure 4). Therefore, mammals and amphibians are, indeed, able to survive on
remote islands once they are introduced and we cannot accept the alternative
hypothesis.
To date, Darwin’s hypotheses have been supported by the observations of
life on all remote islands.
[END PAGE]
[BEGIN PAGE]
RESEARCH THIS: INVESTIGATE DARWINS RESEARCH
Investigation X.X.X 24
Skills: Researching, Predicting, Planning, Controlling Variables, Performing, Observing, Analyzing, Evaluating
[catch Skills Handbook icon: t/k]
Darwin was aware that not all seeds could have been carried to remote islands by the wind or birds. He hypothesized that
some must have reached the islands by floating in ocean currents. If his hypothesis was correct, the seeds must have been
able to withstand exposure to salt water for days or weeks on end.
1.t/k
2.
3.
4.
A.
B.
C.
Homologous and Analogous Features
homologous features structures that share a
common evolutionary origin but may serve
different functions in modern species (e.g., bat
wings and human hands)
If all living things are related to each other, as the theory of evolution suggests,
then we should expect to find evidence for such relationships by examining
their anatomy. Darwin and others were struck by the numerous instances in
which similar structures of two organisms could have entirely different
functions (Figure 7). These homologous features puzzled Darwin who wrote:
“What can be more curious than that the hand of a man, formed for grasping,
that of a mole for digging, the leg of the horse, the paddle of the porpoise, and
the wing of the bat, should all be constructed on the same pattern, and should
include the same bones, in the same relative positions?” Imagine an engineer
being asked to design a robotic hand, a canoe paddle, and an aircraft wing, and
choosing the same internal frame design for each device!
[catch C07-F07-OB11USB; Size B; New. Image showing the forelimbs of
different organisms that are each adapted to carry out very different functions
yet they all possess very similar bone structures.]
Figure 7 The forelimbs of these organisms are each adapted to carry out very different functions, yet they all possess very
similar bone structure.
It struck Darwin as unreasonable to think that finger bones would serve
any useful purpose inside the stiff flipper of a whale. He also wondered why
almost all mammals would have precisely 28 skull bones and 7 neck bones,
regardless of the size of their skull or length of their necks. If species had been
created in their present forms, why would the skull of a whale have the same
number of bones as the skull of a mouse, and why would the giraffe not be
given more neck bones than mammals with the shortest of necks? Indeed, why
were the bones in all mammals, including bats, whales, horses and humans, so
similar in number and arrangement (Figure 8, next page)?
[END PAGE]
[BEGIN PAGE]
The next two images will be placed side by side in the text measure. Should
have the same orientation.
[catch C07-P33-OB11USB; Size B1; Research. Photo of a bat skeleton with
outstretched limbs]
[catch C07-P34-OB11USB; Size B1; Research. Photo of a human skeleton
with limbs outstretched]
Investigation X.X.X 25
Figure 8 All mammals have an almost identical number and arrangement of bones. This (a) tiny bat skeleton is very similar
in many respects to that of (b) a human.
Although Darwin had no understanding of chromosomes and genes, he
knew that many traits were inherited from generation to generation. Darwin
was also aware that artificial breeding of animals and plants could, over many
generations, produce dramatic results. For example, he knew that dog
skeletons had changed through the efforts of breeders. Darwin concluded that
the homologous features he observed could be explained by evolution. Closely
related species had homologous features because they shared a common
ancestor. Over time original structures were modified as each species evolved.
Closely related species share homologous developmental processes and
patterns as well. In early developmental stages, the embryos of all vertebrates
including humans, chickens, and fish possess a short bony tail (Figure 9).
Human embryos also have gill slits even though, as adults, we do not have gills.
[catch C07-F08-OB11USB; Size B; New. Illustration of embryo comparison
between a fish, a salamander, a tortoise, a chick, a rabbit, and a human]
Figure 9 The embryos of all vertebrates share many homologous features including tails and gill slits.
[END PAGE]
[BEGIN PAGE]
Evolutionary relationships can also account for the observed differences
in the structure of analogous features – features that perform similar functions.
For example, the eyes and wings of flying insects serve the same function as
the eyes and wings of flying birds yet are completely different in structure.
Insects and birds are only distantly related and have evolved these features
quite independently of each other.
Vestigial Features and Anatomical Oddities
What would you say if you discovered a fish with eye sockets but no eyes, or a
running animal with toes that never touch the ground? These species would be
displaying vestigial features – features that no longer serve the function they
do in similar species. Several species of cave fish in the family Amblyopsidae
Investigation X.X.X 26
analogous features structures that perform the
same function but are not similar in origin or
anatomical structures For example bird and
insect wings
live in perpetual darkness (Figure 10). They have no eyes or tiny vestigial eye.
A number of mammals, including pigs, horses, and dogs, possess vestigial toes
that serve no useful purpose (Figure 11).
[catch C07-F09-OB11USB; Size B; New. Diagram comparing the toes of a
dog, pig, and a horse showing their vestigial toes in blue]
vestigial features rudimentary and nonfunctioning, or only marginally functioning
structures that are homologous to fully
functioning structures in closely related species
[catch C07-P35-OB11USB; Size D; Research.
Photo of a blind cave fish showing its empty eye
socket. Photo must be of the family
Ambylopsideae]
Figure 10 t/k
Figure 11 Dogs have a vestigial toe or “dew claw” on each front limb. The toe serves no useful function. Pigs have two welldeveloped toes and two vestigial toes that hang behind them. Horses have one greatly enlarged toe. The others are
vestigial or missing entirely. Vestigial toes are shown in blue.
There are many striking examples of vestigial features and anatomical
oddities. For example, the upland goose and frigate bird have webbed feet but
never enter the water. Some large snakes and whales have vestigial hip bones,
which are homologous to the hip bones that support the hind limbs of other
vertebrates (Figure 12).
[catch C07-F10-OB11USB; Size B; New. Image of a silhouette of a whale
showing the internal bone structure clearly. ]
Figure 12 Many species of large whale have vestigial hip bones.
[END PAGE]
[START PAGE]
A fascinating example of an anatomical oddity is found in the nervous
system of vertebrates. In fish, a particular nerve exits the brain and follows a
short and direct pathway to a gill located close to the heart. In all mammals,
the same nerve exits the brain but it follows an indirect path. The nerve passes
close to the heart, but then travels back up the neck and enters the larynx, or
voice box. In giraffes, the trip is quite lengthy: the nerve leaves the brain,
travels the full length of the neck down to the heart and back again before
entering the larynx. The distance from a giraffe’s brain to its larynx is a few
centimetres, but the pathway travelled is more than four meters!
Darwin recognized that such features were highly suggestive of an
evolutionary past. Vestigial features could be explained as evolutionary
baggage – features that, in an ancestor, had served a useful purpose, but had
become useless or greatly distorted as the species had evolved.
Humans also possess numerous vestigial features. You may have
experienced goose bumps in a cool breeze or when you were watching a scary
movie. Humans, like most mammals, have body hair. Each hair is attached
below the surface of the skin to a tiny muscle. Goose bumps are the result of
Investigation X.X.X 27
these tiny muscles contracting and lifting up the hair. For mammals with thick
hair, this action serves two functions: in response to cold temperatures, it
increases the insulation value of the hair making the animal warmer; and, in
response to a threat, it makes the mammal look larger. For a deer on a cold
winter day, this is a way of staying warm. For a cat confronted by a large dog,
this is a way of looking large and menacing. For humans, raising our hair does
nothing to keep us warm and certainly does not make us look any
larger.<catch web link icon>
Competition within Populations
To learn more about human vestigial features, go
to [catch Nelson web link banner]
The anatomical features of different species, biogeography, and the fossil
record provided Darwin with evidence that species had changed over time and
that species appeared to share a common ancestry. Breeders of domesticated
animals and plants repeatedly demonstrated that species could change by
selecting individuals with favoured traits to be the parents of each new
generation. Darwin wondered if nature, like human breeders, might be able to
favour certain individuals in a population over others. He found the answer in
October of 1838 while reading a mathematics paper on populations written by
the Reverend Thomas Malthus, Essay on the Principle of Population.
In his essay, Malthus showed that all populations were limited in size by
their environment – and in particular their food supply. Whatever the
conditions, populations could not continue to grow indefinitely. Darwin was
struck by the implications this had for individuals within populations. Many
species produced large numbers of offspring but not all will survive (Figure
13). There was a limit to the size of the population that the environment could
support. The result would be competition for survival between members of the
same species.
The next two images will be placed side by side in the text measure. Should have the same orientation.
[catch C07-P36-OB11USB; Size B1; Research. Photo of a pond with hundreds of frog or toad eggs]
[catch C07-P37-OB11USB; Size B1; Research. Photo of a flower (goldenrod for example) with seeds still attached but
ready to disperse.]
Figure 13 Frogs and toads produce hundreds of eggs, but few will reach maturity. Similarly many plants produce thousand
of seeds.
[END PAGE]
[BEGIN PAGE]
Competition between individuals of the same species is intense because
they are vying for the same resources. Consider a population of 1000 robins
that returns to Ontario in the spring. These 1000 robins form breeding pairs
that may lay two or three batches of eggs each summer. If they all hatched and
survived, the robin population would jump from 1000 in the spring to more
than 5000 by the end of the summer. Of these 5000 robins, only about 1000
will return the next spring. Under these conditions, only one out of every five
robins survives each year.
Darwin wondered if the environment might be favouring certain
individuals in this struggle for survival.
FORMATTER: PLEASE SET AS 2 COLUMNS USING FULL PAGE
WIDTH MINI INVESTIGATION: THE ELEPHANT PROBLEM
Skills: [t/k]
[catch Skills Handbook icon: t/k]
Species that produce large numbers of offspring experience intense competition. Darwin wondered if this applied to even
the slowest breeding populations like that of the elephant. His question is known as “the elephant problem.” In this
activity you will compare the breeding potential of different species and populations sizes that would result if there was
unlimited growth.
Table 1 includes sample estimates of changes in population size for two different situations: a) under natural conditions
and b) based on the assumption that all offspring live and reproduce under ideal conditions with no competition. For
example, in the case of elephants, the latter value is based on the assumption that all elephants live to be 90 years old
and each female has 6 offspring in her lifetime.
Investigation X.X.X 28
1. Examine Table 1 and compare the initial population sizes with the estimated final population sizes. Note that under
natural conditions populations often remain relatively stable over modest periods of time. (a) Calculate the percentage
change in the population size.
2. Compare the initial population sizes with the final population size if there was no competition (b). Calculate the
percentage change in the population sizes.
A. What might cause a change in population size under natural conditions?
B. How do these data provide evidence that species do not live under ideal conditions?
C. Choose one species from Table 1 and conduct online research to determine some of the resources they require in order
to survive (such as types of food, space, shelter). Which of these resources do you think would cause the greatest degree
of competition between individuals of the same species?
D. Imagine a dog breeder that makes a living selling champion show dogs. Do think the breeder would attempt to produce
the maximum number of pups each year? What might be the disadvantages and advantages of doing so?
Table 1 Population Potential
Species
Initial population
Generations and
a) Final population
b) Final population
elapsed time
under natural
under ideal
conditions
conditions
Elephant
100
5 generations
84
24 300
300 years
Robin
100
5 generations
10 years
120
3.3 million
Deer Mouse
100
5 generations
10 years
96
320 million
Starfish*
2
1 generation
5 years
2
10 billion
*female starfish of some species can produce 2 billion eggs per year
Assessing the Evidence
Darwin spent more than twenty years gathering and examining every shred of
evidence he had on the question of whether species had evolved or had been
created in their present forms. In the end he was convinced that the
preponderance of evidence was undeniably in support of the evolution of
species but he also knew that his ideas would be controversial and conflict the
most commonly held religious beliefs of society. Many other scientitists,
including Linnaeus, Lamarck, and his own grandfather, believed species were
not immutable. What set Darwin apart was the great insights he had gained
while amassing the evidence. Darwin not only believed that species had
evolved but believed he had theory that could explain how they evolved. In the
next section you will learn the circumstances leading up to Darwin’s
publication of On the Origin of Species and be introduced to his famous and
elegant theory
[END PAGE]
[BEGIN PAGE]
7.4 SUMMARY
• Evidence from biogeography provides compelling evidence that remote
islands are populated by species that evolved from species that arrived there
from the closest major land mass.
• Patterns in embryonic development provide evidence of the evolutionary
relationships between species.
• The structures of numerous anatomical features provide strong evidence that
they have evolved from an original, homologous structure.
• Vestigial features are rudimentary structures that once performed important
functions in ancestral species.
• All species produce far more offspring than can survive to reproduce. This
results in competition for resources between members of the same species.
7.4 QUESTIONS
1. Which of the following would you expect to find on remote islands? Explain your reasoning: [K/U, T/I]
(a) a variety of hummingbirds OR a variety of larger seed eating birds
Investigation X.X.X 29
(b) large lizards OR large mammals
(c) some species that are genetically similar OR most species that are genetically very distinct.
(d) species found now where else on Earth OR species that are also found on other remote islands.
2. The coqui frog was accidentally introduced to Hawaii in 1988 where it has no natural enemies. The population has
risen dramatically and the frogs now pose a threat to native species, particularly insects and spiders. If these frogs are so
successful why are there no native frog species on these large islands? [T/I, A]
3. Which of the following pairs represent homologous features and which represent analogous features? Explain your
answers. [A]
(a) a lobsters claw and the hand of an ape
(b) the wing of a bat and the wing of a bird
(c) the eyes of a fly and the eyes of a hawk
(d) the tusks of an elephant and the teeth of a mouse
(e) the webbed feet of an otter and the fins of a fish
4. Explain how the bones, arranged in a pattern of five toes, within dolphin flippers provide evidence of evolutionary
change. [K/U, A]
5. The brown tree snake, Boiga irregularis, was introduced to the remote Pacific island of Guam sometime shortly after
World War II. Do research to answer the following: [T/I, A]
(a) What native species have been lost or threatened by this snake?
(b) How might the loss of these species influence the entire ecosystem on the island?
(c) How might an understanding of evolution enable scientists to predict which species might be most vulnerable to
invasive species?
6. For each of the following vestigial features state the likely original function of the structure and suggest a reason that it
may be become vestigial: [K/U, A]
(a) the muscles and hairs that cause goosebumps in humans
(b) short wing “stubs” in some insects like earwigs
(c) webbed feet in frigate birds that never enter the water
(d) rudimentary hip bones in some whales and in some large snake species
7. Describe the evidence of evolution revealed by the embryonic development of different species. [K/U]
8. Explain how Darwin knew that competition always occurs between individuals of the same species. Include a
numerical example to illustrate your answer. [K/U T/I]
[end page]
Investigation X.X.X 30
[BEGIN PAGE; 4 pages]
7.5
[catch C07-P38-OB11USB;
Size D; Research. Photo of the
cover page of the first edition of
Darwin’s On the Origin of
Species]
Figure 1 The cover page of the first edition of
Darwin’s On the Origin of Species.
To learn more about Alfred Russell Wallace and
his many contributions, go to <catch Nelson web
link banner>
natural selection the way in which nature favours
the reproductive success of some individuals
within a population over others; the “Theory of
Evolution by Natural Selection” explains how the
process of natural selection results in the
evolution of species
On the Origin of Species
Darwin’s On the Origin of Species was published in 1859. This book not only
described convincing evidence that species had evolved, but it also proposed a
theory of how species evolve. Darwin had formulated his theory much earlier.
In 1844, Darwin wrote to his friend, Sir Joseph Hooker, declaring: “At last
gleams of light have come, and I am almost convinced (quite contrary to
opinion I started with) that species are not (it is like confessing a murder)
immutable. ... I think I have found out ... the simple way by which species
become exquisitely adapted to various ends.” In the same year, Darwin
prepared a 231-page outline of his theory and gave it to his wife with
instructions that it be published should he die unexpectedly.
Aware that any theory of evolution would be controversial and rigorously
challenged, Darwin continued to gather evidence and look for flaws and
weaknesses in his own reasoning. His intention was to publish what he
referred to as his “Big Book” on evolution. By June 1858, when he had written a
quarter of a million words, he received a fateful letter from a brilliant young
biologist working in Malaysia. In the letter, Alfred Russell Wallace outlined his
own theory of how species evolved. His theory was almost a perfect match to
Darwin’s.
The young Wallace, with little evidence, was anxious to publish a theory
that he had thought about for only a few days. Darwin, having spent twenty
years amassing evidence and developing the same theory, had been unwilling
to publish. Lyell and Hooker convinced Darwin to submit a paper along with
Wallace’s at a meeting of the Linnean Society on July 1, 1858. The papers were
of interest to scientists of the Linnean Society but went unnoticed by the
public. A year and half later Darwin published a detailed account of his theory
in a 502-page book entitled On the Origin of Species by Means of Natural
Selection or The Preservation of Favoured Races in the Struggle for Life
(Figure 1).The book sold out on the first day.
<catch web icon>
The Theory of Evolution by Natural Selection
Although Darwin had been hesitant to publish, he was extremely confident in
his theory that species had evolved by a process he called natural selection.
Darwin described natural selection as the way in which the environment, or
nature, favours the reproductive success of certain individuals over others.
Evolution was simply the result of natural selection occurring over many
generations. Darwin’s reasoning is illustrated in Figure 2.
Formatter flow chart should be entire page width
[catch C07-F11-OB11USB; Size B; New. Art of a flowchart showing how
observations led to inferences which led to the Theory of Natural Selection for
Darwin.]
Figure 2 Darwin’s theory of evolution by natural selection was powerful because it was based on five key observations
which were well established and undeniable. Darwin realized that together, they gave rise to two logical inferences and
provided a mechanism for evolution. [END PAGE]
[BEGIN PAGE]
Darwin’s key observations were undeniable: all healthy populations
produced far more offspring than could survive and reproduce; and,
Investigation X.X.X 31
survival of the fittest a phrase that has been used
to describe the process of natural selection;
considered misleading and no longer used by
biologists
adaptation a characteristic or feature of a
species that makes it well suited for survival and
or reproductive success in its environment.
individuals exhibited heritable variability. Darwin believed that, under these
conditions, some individuals would have a better chance of success than
others. A faster cheetah would surely be more likely to catch prey than a
slower cheetah and a stronger male lion would be more likely to defend and
mate with a pride of females. If this were true and these differences were
inherited, then the traits of the favoured individuals would become more
common in the next generation. Faster cheetahs and stronger lions would have
more offspring than slower and weaker individuals of the same species.
Indeed, Darwin’s theory was so simple and elegant that his friend and eminent
zoologist Thomas Huxley exclaimed, “How extremely stupid not to have
thought of if myself!”
A contemporary of Darwin, Herbert Spencer, used the phrase “survival of
the fittest” to describe the process of natural selection. Although Darwin
himself thought the expression could be a useful synonym, it can be quite
misleading. You might consider an individual that lives a long life but is unable
to reproduce as physically “fit,” but the individual would pass on no genes to
the next generation. Such an individual would not be fit with respect to
Darwin’s theory of natural selection, or Spencer’s definition. As you will learn
in Chapter 8, the key to natural selection lies in its ability to favour
reproductive success.
The theory of evolution by natural selection could be extended to virtually
every biological characteristic or adaptation. Figure 3 shows a number of
adaptations and the selective advantage they represent. Darwin understood
that with a diversity of environments, the process of natural selection acting
over thousands of generations could produce an unlimited variety of species.
The next 7 images will go side-by-side across entire page width. Place text with each photo. Arrange however works best.
Photos should have the same orientation.
[catch C07-P39-OB11USB; Size C3; Research; Photo of a polar bear with ice/snow background.]
catch C07-P40-OB11USB; Size C3; Research. Photo of Galapagos finch, any species, showing their large bill.]
[catch C07-P41-OB11USB; Size C3; Research. Photo of an anteater with tongue visible of digging in termite/ant mound.]
[catch C07-P42-OB11USB; Size C3; Research. Photo of male moose with antlers.]
[catch C07-P43-OB11USB; Size C3; Research. Photo of elephant seal in water if possible.]
[catch C07-P44-OB11USB; Size C3; Research. Photo of cacti, any species, showing thick stem with sharp needles.]
[catch C07-P45-OB11USB; Size C3; Research. Photo of pine tree bark.]
Figure 3 Individual organisms possess traits that give them a selective advantage. or [t/k]
Evaluating the Theory
Darwin had proposed a revolutionary theory in biology that challenged not
only the established science of the day, but also currently held beliefs and
teachings of a large fraction of society. Darwin knew that all scientific theories
must be explanatory, have predictive powers, and be testable. We will examine
these below.
EXPLANATORY POWER
As you learned in previous sections, Darwin had amassed a great deal of
evidence from biogeography, the fossil record, the anatomical features of
different species, and artificial breeding. Consider how Darwin might have
applied his theory of natural selection to explain the evolution of large-billed
finches on the Galapagos Islands (Figure 4, next page).
[END PAGE]
[BEGIN PAGE]
[Formatter: This will be a 2x2 frame piece of art. Should take about ½ page or
slightly more.]
[catch C07-F12-OB11USB;Size A; New. Description of art to come.
Captions to be placed below each frame, include:
(a) An ancestral population of finches with medium-sized bills are the first seed-eating birds to arrive on the Galapagos
Investigation X.X.X 32
[catch C07-P46-OB11USB;
Size D; Research. Photo of a
large ground finch of the
Galapagos.]
Islands. They specialize in eating medium-sized seeds. With no initial competition, the finches establish a growing
population on a small island with a variety of plants, some with medium seeds but most with larger seeds.
(b) The population grows to a size where the number of finches has reached the limit of their food supply. Each year many
eggs are laid and hatched, but the island cannot support all the birds. The birds are not all alike – like any species, they
exhibit variation. Some birds have slightly larger, and some slightly smaller than average bills.
(c) Most of the birds must compete for the same medium-sized seeds, but any bird born with an unusually large bill is able
to also feed on the larger seeds. These particular birds have little or no competition have ample food available to them.
Darwin would say that the environment favours, or selects, these larger-billed birds. These larger-billed birds, being
healthier, lay more eggs on average. Their young are more likely to be born with larger bills.
(d) As this process is repeated generation after generation, the average bill size of the birds continues to increase (Figure
5). This is evolution by natural selection. Had medium-sized seeds been more common than larger seeds, the advantage
of the larger bill might have been offset by the energy needed to grow the bill and or disadvantages in reaching and
manipulating the medium sized seeds.
Figure 5 The large-billed ground finch of the
Galapagos islands evolved from an ancestral
species that possessed a much smaller bill.
Figure 4 Evolution of large-billed finches on the Galapagos Islands. or [t/k]
Critics of Darwin questioned the source of variability in characteristics.
Although small increases in bill size seemed possible, they wondered how an
ancestral giraffe with a short neck could ever evolve into a modern longnecked giraffe. Although Darwin could not have foreseen the discovery of DNA
and the role that mutations play in producing variation, he did have evidence
from animal breeding that suggested such dramatic changes were possible.
Although the source of the variation was a mystery, Darwin argued that if dogs
could be so altered in a few hundred years of artificial selection, why could
nature not accomplish even greater change in thousands and even millions of
years of natural selection.
PREDICTION
The theory of evolution by natural selection enables scientist to make
predictions about how species may change over time. Many of these
predictions are associated with changing environments. For example, the
theory of evolution predicts that species will evolve in response to climate
change because different environmental conditions will favour different traits.
Over time, bird species may change the timing of their migration and plants
may adapt to warmer or drier conditions. Such changes are already being
documented.
The theory of natural selection also predicted the evolution of antibiotic
resistance in bacteria and pesticide resistance in insects. Darwin made
predictions regarding the fossil record of humans. Based on the distribution of
the living great apes, he predicted that fossils of the most primitive human
ancestors would be found on the African continent. Darwin’s predictions have
come true.
[END PAGE]
BEGN PAGE]
TESTING AND FALSIFICATION
Darwin also knew that to be scientific, a theory must have the potential to be
falsified. This means that a scientific theory must be testable — there must at
least be the possibility of it being proven wrong. For example, the theory of
gravity meets this scientific standard because it could be falsified by observing
apples “falling up.” The fact that we never find such evidence adds strength to
Investigation X.X.X 33
Formatter: Place next to Testing & Falsification
heading.
INVESTIGATION 7.6.1
Natural Selection (p. XXX)
You will design and conduct a controlled
experiment to test Darwin’s theory in a simulated
predator-prey relationship.
the theory of gravity. Table 2 illustrates a few of the kinds of evidence that
could falsify the theory of evolution as well as the evidence that currently
exists.
Table 2 The Potential for Falsification
Hypothetical observations with the potential to falsify
Darwin’s theory
Actual observations and evidence
Amphibians and large land mammals on remote
oceanic islands
No native amphibians or large land mammals have
ever been discovered on remote oceanic islands.
Fossils of complex organisms found in the oldest
fossil deposits
Of millions of fossils, none contradict the predicted
pattern of increasing complexity over time.
Complex organisms with no vestigial features
All organisms that have been studied in detail exhibit
many vestigial features.
Species thought to be closely related that share no
homologous features with each other
All organisms that have been studied in detail exhibit
many homologous features with other closely-related
species.
Darwin knew that if evolution had not occurred, if species had not
changed over time, it should be easy to find falsifying evidence. His confidence
in the theory was greatly strengthened by the complete absence of falsifying
evidence.
7.5 SUMMARY
• Darwin’s theory of evolution by means of natural selection explains how the environment acts to favour the reproductive
success of individuals with certain heritable traits over others.
• Darwin’s theory of evolution by means of natural selection is able to explain how an adaptation can arise.
• Darwin’s theory of evolution by means of natural selection can be used to make predictions about the future evolution of
species.
• Darwin’s theory of evolution by means of natural selection is a testable scientific theory.
7.5 QUESTIONS
1. (a) What evidence from Darwin’s personal life suggest he did had developed his theory but was very hesitant to make
it public? [A]
(b) Why do you think Darwin might not have wanted to publish his ideas?
2. (a) How did Wallace influence Darwin’s decision to publish? [K/U, A]
(b) Do you think Wallace should be given as much credit as Darwin for the theory of evolution by natural selection?
Why or why not?
3. Match Darwin’s inferences, on the left, with his observations, on the right. [K/U]
[formatter: DO NOT format this in a table; format as you would a matching Q in the chapter review]
I. Some individuals will inherit characteristics
A. Populations produce more offspring than can
that are of benefit and increase their chance of
survive to adulthood
reproductive success
B. Individuals of all species show variability
II. Individuals of all species are in competition for C. Resources for any species is limited
resources
D. Populations do not continue to grow forever
E. Some variability is heritable
4. Use one or two examples to explain what Darwin meant by the term “selection.” [K/U]
5. A male walrus lives to be 20 years old and successfully mates with 18 females during its life. A second male only lives
to be 10 years old but mates successfully with 44 females. Which male has natural selection “favoured?” Explain your
reasoning. [K/U, A]
6. Suggest a probable selective advantage for each of the following traits: [A]
(a) the clear wings of many flying insects
(b) long tongue of a chameleon
(c) the tendrils of climbing plants
(d) sweet-tasting and brightly coloured fruits
(e) eel body shape
(f) dramatic colouration of the non-venomous false coral snake
7. Outline a set of hypothetic steps that might take place as a species of bird evolves a smaller bill after reaching a
remote island. [K/U, A]
8. How did the absence of falsifying evidence increase Darwin’s confidence in his theory? [K/U]
9. When he published On the Origin of Species, Darwin was still planning to write a much more detailed “Big Book” on
evolution, Darwin had originally titled his book An Abstract On the Origin of Species . . . His editor convinced him to
remove “An Abstract.” An abstract is a short summary of a larger scientific document. [T/I, A]
(a) What does this suggest about Darwin’s approach to science?
(b) Darwin never completed his “Big Book.” Go online and to learn about books that Darwin did write in the years
following the Origin.
10.
[a RT related to curriculum 2.3 in the section questions.]
[END PAGE]
Investigation X.X.X 34
Investigation X.X.X 35
[BEGIN PAGE; 6 pages]
7.6
The Modern Theory of Evolution
Evolutionary biology has made tremendous advances since Darwin. The
science of genetics has allowed scientists to uncover the mechanism of
heredity and the actual source of biological variation. The fossil record is now
extensive, and our ability to interpret fossil data has been greatly enhanced by
remarkable advances in the science of geology. These and other advances in
science have not only confirmed Darwin’s theory, but have greatly enhanced
our understanding of the fundamental biology of all living things. Among these
advances are: our ability to accurately date the age of Earth; our discovery of
the source of variations within species; and new sources of powerful evidence
in support of evolution.
The Age of Earth
Formatter: Place this beside Age of Hearth
heading
INVESTIGATION 7.7.1
A Walk Through Time (p. XXX)
You will investigate the timing of major events in
Earth and Human history using a physical time
scale model.
Until well into the 19th century many people, including some scientists,
believed that Earth was less than 6000 years old, and that it had not changed
significantly during that time. The mountains, coastlines, and rivers had always
been the way they were at the present time. They believed that in a few
thousand years, processes like erosion had not had enough time to
significantly alter the physical surface of Earth. This belief was extended to
living organisms. They believed that species never changed and that species
that are present today had always been present. These widely held beliefs
began to change early in the 20th century when the emerging sciences of
palaeontology and geology started to cast serious doubt on the belief in a
young Earth.
Today there is a wide scientific consensus that Earth is extremely old.
Modern geology, physics, and astronomy provide compelling evidence that
Earth and our solar system are more than 4.5 billion years old, and that the
universe is approximately 13 billion years old. Evidence for these values comes
from many different sources, all of which are in close agreement. The evidence
is largely a product of recent advances in technology and understanding.
Radiometric Dating
radioisotope atoms with an unstable nucleus that
are capable of undergoing radioactive decay
parent isotope changes into a daughter isotope
as radioactive decay occurs
daughter isotope an isotope formed as a result
of radioactive decay
Paleontologists are able to use radioisotopes to obtain very precise estimates
of the ages of the rocks that contain them. Radioisotopes are atoms that
undergo radioactive decay – a process in which the nucleus of an atom changes
and releases a subatomic particle. The nuclei of these atoms are unstable and
release subatomic particles changing from one form, the parent isotope, into
another, the daughter isotope. For example, most carbon atoms have six
protons and six neutrons and are not radioactive. However, a small fraction of
carbon atoms are radioactive. They have a nucleus containing six protons and
eight neutrons. When these radioactive carbon 14 (14 C) isotopes undergo
decay, they release a high energy particle and one of the protons changes to a
neutron. The daughter isotopes are now nitrogen atoms (14 N), each containing
seven protons and seven neutrons.
The technique of radiometric dating is complicated but is based on a
comparison of the ratio of parent to daughter isotopes in rock formations.
Radioisotopes undergo decay in a very precise way. The length of time that it
takes for half of any amount of a particular radioisotope to decay is a constant.
[END PAGE]
[BEGIN PAGE] [not a new para; just the same para continued on the next
page]This value, called the half-life, is the time it takes for exactly 50% of a
parent isotope to decay into a daughter isotope (Figure 1). It then takes an
Investigation X.X.X 36
half-life the time required for half the quantity of
a radioactive substance to undergo decay; the
half-life is a constant for any given isotope
additional half-life for the remaining amount to be reduced by half again, and
so on. Physicists have determined the half-life of all naturally occurring
radioisotopes.
[formatter: please centre art in text measure]
[catch C07-F13-OB11USB; Size C2; New. Graph showing the half-life of
radioactive decay.]
Figure 1 During each half-life of radioactive decay, 50% of a parent isotope decays into a daughter isotope. The result is a
quantitative, predictable relationship between the ratio of parent-to-daughter isotopes and elapsed time.
The Modern Synthesis
modern synthesis the modern theory of evolution
that takes into account all branches of biology
gene pool the complete set of all alleles
contained within a species or population
[catch C07-P47-OB11USB;
Size D; Research. Photo of a
curly haired poodle]
Figure 2 Perhaps hundreds of generations ago a
dog was born with a single base mutation in a
gene coding for a hair protein. The mutation
resulted in very curly hair - a trait that was
selected for by breeders and is now common in
number of breeds including poodles and many
terriers.
Darwin’s theory of evolution by natural selection could account for how
species evolve but could not explain the actual source of variation. The modern
synthesis in evolutionary biology resolved this weakness in the theory by
combining the principles of Darwin’s theory of natural selection with the new
science of genetics and other fields of biology.
We now know that inheritance involves the passing on of genes from
parents to offspring. Genes are sequences of DNA that code for heritable traits
and different forms of the same gene are called alleles. Individuals vary in their
traits because they inherit different combinations of these alleles. Natural
selection acts to favour some genetic combinations over others.
Darwin defined evolution as changes in the inherited traits of a species
over time. Today, biologists define evolution as changes in the gene pool of a
species over time. A gene pool consists of all the alleles of all individuals that
are currently present in a particular species or population.
Mutations: The Source of Variation
All species exhibit genetic variation. Different individuals have different
combinations of the many alleles that are already present in the population.
Sexual reproduction recombines, or shuffles, these alleles and produces an
almost unlimited number of combinations. New or altered traits arise when
new alleles and genes are produced by mutation and acted upon by natural
selection. A genetic mutation is a change in DNA. The bases that make up DNA
may be switched or lost, and or new bases may are be inserted (Figure 2).
Mutation events can also result in an individual having duplicate copies of
genes. Duplication events are usually the result of mismatches during
crossover in meiosis. A misalignment of the chromosomes during crossover
causes an unequal exchange – transferring a portion of one chromosome to
another (Figure 3). The transferred portion of the chromosome is likely to
contain many genes.
[formatter: please centre art in text measure]
[catch C07-F14-OB11USB; Size C2; New. Illustration of a mismatched
crossover event showing the duplication of genes.]
Figure 3 Cross over errors, a form of mutation, can result in one sister chromatid having a duplicated portion of a
chromosome, while the other chromatid will be missing a portion of the chromosome.
[END PAGE]
[BEGIN PAGE]
A gamete that receives a chromosome that is missing a section will have a
low chance of survival, while the gametes that receive a chromosome with
duplicated genes are often viable. In fact, having extra copies of genes can be
beneficial. For example, a recent study compared the number of copies of a
certain gene among people of Japanese descent having a diet that is
Investigation X.X.X 37
traditionally high in starch, with those of Amazon rainforest dwellers that have
a low-starch diet. This gene is responsible for the production of amylase, which
is the enzyme that breaks down starch. The people of Japanese descent had
multiple copies of the amylase gene – enabling their cells to produce more of
the digestive enzyme.
Gene duplication is an important type of mutation because it is a source of
new genes. The extra copy of the gene is free to mutate and potentially gain a
new function. The gene copies resulting from duplications can also be altered
through further mutation. Many genes code for vitally important proteins. If a
mutation in a gene results in a new protein that can no longer perform a vital
function, the organism may die – even if the new protein might be beneficial in
some other way. However, the same mutation occurring in an extra” copy of
the gene might result in the creation of a new and potentially beneficial
protein. The duplication and mutation of gene copies can result in entire
“families” of closely related genes. For example, four human genes – three
involved in colour vision and one for night vision – are all thought to have been
produced from a single ancestral gene.
The Effects of Mutations
[TOP ALIGN WITH “THE
EFFECTS OF MUTATIONS”]
LEARNING TIP
Consider the Numbers
Natural populations are often extremely large. A
small section of forest can be home to millions of
black flies while a soccer field is home to millions
of grass plants. Even if the mutation rates for
individuals are relatively low, the number of
mutations within a population is very large.
Table 1 Mutation and Evolution
Factor
Influence on
Evolution
Beneficial mutations Relatively rare but
are favoured by
natural selection
and tend to
accumulate in
populations over
time
Harmful mutations
More common than
beneficial mutations
but are selected
against and
therefore have no
influence of
populations
Duplication
Often neutral and so
mutations
do not immediately
benefit the
individual but
provide a source of
new genetic material
with the potential to
evolve into new
genes
Mutation rates
Relatively low for
As you learned in Section 7.1, mutations can be neutral, beneficial, or harmful.
Most mutations are neutral because they occur in non-coding portions of DNA
and therefore produce no visible change in an individual. The environment
does not favour or select against individuals with neutral mutations.
Beneficial mutations, which give the individual an advantage, are selected
for by the environment. Therefore we would expect beneficial mutations to
accumulate over time because they increase the reproductive success of
individuals. For example, mutations that have allowed some plants to produce
colourful flowers and attract pollinators have been beneficial to those species
and these new genes have become widespread.
Harmful mutations may make an organism less able to resist disease or
avoid predators, or less efficient at obtaining food. Regardless of the reason,
individuals with harmful mutations are less successful at reproducing and
therefore harmful mutations will tend to disappear.
MUTATION RATES
A common misconception is that mutations are rare. There is a very good
reason for this. When chromosomes, consisting of strings of DNA bases, are
replicated, the error rate is typically less than one mutation in a million bases.
Duplications, inversions, deletions, and other mutations are also relatively
uncommon events. However, organisms have genomes comprised of millions
and often billions of DNA bases. In addition, populations often consist of
millions of individuals.
Individual mutation rates are very difficult to estimate, but recent studies
suggest that species with large genomes are likely to have mutation rates
averaging more than one per individual. The same studies suggest that
humans, with genomes consisting of billions of bases, may average 20 or more
mutations per individual. Even if these are almost always neutral, the numbers
are staggering: the human population – approaching 7 billion people – is
carrying around well over 100 billion genetic mutations. A similar high
incidence of mutation occurs in all species with large populations. Table 1
summarizes key relationships between mutations and evolution.
[END PAGE]
[BEGIN PAGE]
Homologous Genes and Pseudogenes
Investigation X.X.X 38
individuals but can
be numerous in
populations over all
[END PAGE]
In Section 7.5 you observed that closely related species share many
homologous features. All mammals, for example, have similar numbers and
arrangements of bones because they have inherited this pattern from a
common ancestor to all mammals. Similarly, closely related species inherit
homologous genes. These genes, inherited from a common ancestor, mutate
and evolve over time. The degree of similarity between homologous genes
provides good evidence for the degree of relatedness between species. The
more closely related two species are, the more similar we would expect their
homologous genes to be. Figure 4 compares a very small portion of a DNA
sequence from a number of species.
[formatter: please centre art in text measure]
[catch C07-F15-OB11USB; Size C2; New. Figure showing the sequences of
bases on the DNA of a cow, deer, whale, hippo, pig, and rat.]
Figure 4 The letters represent the sequence of bases on the DNA of these species. All sequences code for a short portion
of a homologous gene. The more closely related the species the greater the similarity. Coloured letters highlight the
differences from those of the Rat sequence – the least closely related mammal.
pseudogenes vestigial genes that no code for a
functioning protein; most species have many
pseudogenes
Species also have pseudogenes –genes that have undergone mutations
and no longer serve a useful purpose. Like vestigial anatomical features,
pseudogenes represent what is remaining of a gene that once served a useful
purpose. For example, dolphins, like all mammals, breathe through their nose,
but unlike most mammals, have no need for a sense of smell in the air (Figure
5(a)). Dolphins are thought to have evolved from land mammals. Most land
mammals have an excellent sense of smell. Mammals have approximately 1000
functioning olfactory receptor (OR) genes that code for the receptors that
detect airborne chemicals. Dolphins have these same 1000 genes but only
about 200 of them are functional. The remaining 800 or so are pseudogenes.
Biologists suspect that after dolphins had evolved an aquatic lifestyle, their OR
genes were of no value. Any mutations that made the genes dysfunctional
would have been neutral and not been selected for or against. Over millions of
years most of the dolphins OR genes have become pseudogenes.
Pseudogenes, like vestigial features, are found in virtually all species. For
example, the stomach of the duck-billed platypus has no chemical digestive
function yet the platypus has three defective genes that code for the
production of digestive enzymes normally produced by the stomach. This
provides evidence that platypuses evolved from an ancestor with a stomach
that released digestive enzymes coded for by properly functioning genes
(Figure 5(b)).
The next two images will be placed side by side across the text measure.
Should have the same orientation.
[catch C07-P48-OB11USB; Size B1; Research. Photo of a dolphin head shot
in water]
[catch C07-P49-OB11USB; Size B1; Research. Photo of a platypus]
Figure 5 (a) Dolphins have many pseudogenes that are homologous to genes they no longer have a need for. They have
hundreds of pseudogenes that once coded for a keen sense of smell. (b) The platypus has pseudogenes for the
production of stomach enzymes – useful in ancestors that had a stomach.
[END PAGE]
Investigation X.X.X 39
[BEGIN PAGE]
Modern Paleontology
The last 100 years have witnessed many important fossil discoveries, which
have enhanced and enriched our understanding of evolution. These have
included fossils of early human ancestors, dinosaurs in western Canada, and
primitive whales in Pakistan. In recent decades, paleontologists have
unearthed spectacular fossils of feathered dinosaurs in China and have even
been able to determine the colour of some their feathers.
The distribution of fossils provided Darwin with important evidence for
his theory of evolution. He discovered fossil remains of giant prehistoric
mammals that were similar in form to present-day armadillos and sloths living
in the same region. Such a pattern has now been documented in many
locations around the world. Australia for example, is home to many fossils of
primitive kangaroos, but has no fossils of mammals typical of other continents.
Until the 1960s, the location of some fossils were quite puzzling.
Particularly surprising was the discovery of fossils of the same species in
Africa, India, and Antarctica – but nowhere else on Earth. Today the study of
biogeography has been complemented by great advances in the study of plate
tectonics and continental drift. Plate tectonics describes the movements of the
Earth’s crust and accounts for many large surface features, such as mountains,
as well as volcano and earthquake activity. Figure 6 illustrates the
arrangement of some of Earth’s major land masses approximately 200 million
years ago. Species’ distributions at that time were permanently captured in the
fossil record. <CATCH: Web link>
[catch C07-F17-OB11USB; Size B; New. Map of fossil location in Pangea.]
plate tectonics the scientific theory that
describes the large scale movements and
features of the Earth’s crust
WEB LINK
Fossil Discovery
To learn more about how fossils are discovered,
extracted, and preserved, go to <catch Nelson
web link banner>
Figure 6 Fossil distributions of these four species match the arrangements of the Earths land masses at the time the
species were alive.
Fossils also show distinct patterns in time. The oldest fossil deposits
contain only simple life forms. More recent fossil deposits contain species that
are both more complex and more similar to present living species (Figure 7).
Of the millions of fossils that have been recovered and carefully documented,
not a single fossil has been found to contradict this underlying pattern.
[END PAGE]
[BEGIN PAGE]
[FORMAT TWO COLUMNS; FULL PAGE MEASURE, INCLUDE 2 PHOTOS IN BOX]
RESEARCH THIS: PUIJILA, THE YOUNG SEAL
Canada has been home to many remarkable fossil finds. One of the most recent is that of Puijila darwini - a missing link
Investigation X.X.X 40
[catch C07-F16-OB11USB;
Size D; New. Illustration
showing horse evolution and
toes, based on sample below]
Figure 7 [t/k]
between prehistoric land mammals and modern seals (Figure 8). Puijila was discovered in Canada’s high Arctic by a team
led by Natalia Rybczynski, a paleontologist with the Canadian Museum of Nature in Ottawa. Dr. Rybczynski ‘s efforts and
success highlight the challenges and rewards of scientific discovery. In this activity you will have the opportunity to
research this important fossil discovery and see how paleontologists literally put pieces of evidence together. and gain a
rich understanding of life’s evolutionary past.
The next two images will be placed side by side in the margin. Should have the same orientation.
[catch C07-P50-OB11USB; Size C1; Research. Image of the Pujila fossil. Any “interesting” image from the Puijila web site
would be good.]
[catch C07-P51-OB11USB; Size C1; Research. Photo of the Haughton crater, Devon Island, Nunavut.]
Figure 8 (a) The Puijila fossil and (b) the Haughton crater, Devon Island, Nunavut.
Skills: Researching, Communicating, Observing, Analyzing, Evaluating
1. Go online to learn the details of the Puijila fossil discovery and analysis.
2. Research the details of Rybczynski’s field work including the particular challenges associated with working in the Arctic.
3. Research the scientific publication of the discovery. In which journal was the research published?
A. Why was this particular fossil find so important? Why was this “missing link” of interest? [A]
B. What anatomical features of Puijila indicate it was semi-aquatic? [T/I, A]
C. New fossil species are given new names. How did Rybczynski’s team decide on a suitable name? [A]
D. Describe the formation of the Haughton crater and why it is a good location for finding fossils. [T/I, A]
E. Describe the events leading up to the discovery of the initial fossil and the later discovery of the skull fragment. [T/I]
F. In which science journal was this discovery reported? There are thousands of different journals. What makes this one
special? [T/I, A]
G. Report your findings to the class. Consider putting on a short skit to reenact the fossil discovery. [C]
Modern evolutionary biology is supported by the most recent advances
and discoveries in molecular genetics, geology, and paleontology. This has
enable scientists to understand the source of new variations within species,
account for the unusual distribution of some fossils, and confirm predictions of
the theory. As you will soon discover, the modern theory of evolution also has
the power to explain the evolution of complex adaptations and structures and
the evolution of entirely new species.
7.6 SUMMARY
- the Modern Synthesis of evolutionary biology combined Darwin’s theory of evolution by natural selection with the science
of genetics.
- genetic mutation events provide a continuous supply of all new inheritable information and variation within a species.
- Beneficial mutations are favoured by natural selection.
- neutral mutations have no immediate influence on the success of an individual
- harmful mutations are selected against – reducing their frequencies within a population
- pseudogenes provide compelling evidence for evolution
- the science of plate tectonics and paleontology have greatly enhanced our understanding of evolution
7.6 QUESTIONS
1. How might the daily experiences of people contributed to their belief in an Earth and species that don’t change? [A]
2. Approximately how old is Earth? What types of scientific evidence were used to arrive at this date? [K/U, A]
3. Describe the relationship between the following terms: [K/U, A]
(a) parent isotope, daughter isotope, half life
(b) evolution, gene pool, species
(c) duplication, crossover, gene family
4. E. coli bacteria are extremely numerous (billions of E. coli cells are living inside you!) and reproduce extremely quickly.
Geneticists estimate that every part of their DNA undergoes a mutation somewhere on Earth every day. What might this
suggest about the ability of E. coli to evolve? [A]
5. Humans are one of a small number of mammals that is unable to synthesize vitamin C. Instead we obtain vitamin C in
our diet. Humans have a pseudogene that is homologous to a gene involved in vitamin C synthesis in other mammals. [T/I,
A]
(a) Is the presence of this gene surprising? Why or why not?
(b) What does it suggest about human evolution?
6. Modern lemurs are only found on Madagascar Island off the coast of southern Africa. However, fossils of ancient lemurs
have been found thousands of kilometres away in India where there are no lemurs. Consult Figure X and provide a possible
explanation for this finding. [T/I, A]
7. Copy the following DNA base sequences into your notebook. They are all short samples taken from appear to be
matching chromosomes in closely related species. Compare the sequence in species A with that of Species B, and then
compare the sequence of species A with that of species C. [T/I, A]
Species A . . . . . GGTAA AACAG CCTTA AGCGCC . . . . .
Species B . . . . . GGTAA CAACA GCCTT AAGCGC . . . . .
Investigation X.X.X 41
Species C . . . . . GCTAA AACAG CCCCA AGCGGC . . . . .
(a) Is there any evidence that one species experienced a single base “insertion” mutation? Explain.
(b) Considering your answer in (a), which two species are probably more closely related?
[END PAGE]
Investigation X.X.X 42
[FORMATTER: Please format Inv in 2 columns, as per Design]
[2pp total]
7.6.1
Controlled Experiment
Natural Selection
Some prey species are extremely well camouflaged. Darwin believed
that the evolution of this trait was influenced by natural selection. If
this is true, better camouflaged individuals should be “favoured” over
less well camouflaged individuals and become more common in the
population over time. In this investigation, you will design and
conduct a controlled experiment to test Darwin’s theory in a
simulated predator-prey relationship over a number of
“generations”.
SKILLS MENU
Questioning
Researching
Hypothesizing
Predicting
Planning
Controlling Variables
Performing
Observing
Analyzing
Evaluating
Communicating
Investigation X.X.X 43
Testable Question
Can an environment favour the success of better camouflaged individuals in a predator-prey relationship?
Hypothesis
Formulate a hypothesis based on the testable question after considering options for your experimental design.
Variables
As you design your experiment, carefully choose your independent and dependent variables and decide which
variables will need to be control.
Experimental Design
Your experiment must simulate a predator-prey relationship in which prey exhibit varying degrees of camouflage.
There are many ways of designing and conducting such an experiment. Consider the following suggestions in your
experimental design process:
•
Use simple objects with different colours or patterns as your prey items (such as pieces of paper or coloured
candies,).
•
Use different coloured or patterned backgrounds for your environment (such as paper backgrounds or natural
ground covers).
•
Use a student as the predator and give him or her a limited time interval in which to hunt prey.
•
Use the ratio of camouflaged versus non-camouflaged individuals that survive predation to determine the ratios of
the following generation. For example, if there are 6 camouflaged individuals and 4 non-camouflaged individuals
surviving from an initial population of 20 individuals of each, then the next generation should begin with a ratio of 6:4
(or 3:2) camouflaged to non-camouflaged individuals.
•
Go online to find more ideas on how to design your experiment.
•
Be sure to carefully consider how you will collect and record you data. How will you design your data tables?
Equipment and Materials
•
Obtain materials as required for your design
[Caution, DO NOT consume any food items used in your experiment]
Procedure
1. Research and plan your controlled experiment.
2. Obtain teacher approval of your design and gather your needed equipment and materials.
3. Conduct your experiment.
4. Record your observations in an appropriate format. Consider graphing your results.
Analyze and Evaluate
(a) Identify the major variables that you measured and/or controlled in this investigation. Which variables were
manipulated (independent) and which were responding (dependent)?
(b) Prepare a formal lab report on this investigation.
(c) Share your findings with other students in the class. How did your results compare with theirs?
Apply and Extend
(d) Real-world experiments of natural selection involving predator-prey relationships have been conducted on small
islands in the Bahamas. Research and summarize the findings of these large-scale controlled experiments.
(e) Do an internet search for extremely well camouflaged species. Share your findings with the class.
(f) Try one or more online computer simulations of natural selection and or artificial selection. Explain how natural
selection differs from artificial selection. [CATCH weblink]
[catch web link banner]
Investigation X.X.X 44
[FORMATTER: Please format Inv in 2 columns, as per Design]
7.7.1
Observational Study
A Walk Through Time
In this activity you will gain perspective on important events in both
human history and the history of life on Earth. One timeline will be
used to represent events in the past 12 000 years of human
civilization while the other will represent major events during the
past 4.6 billion years of Earth history. The data used in this
investigation are based on historical references and the fossil record.
SKILLS MENU
Questioning
Researching
Hypothesizing
Predicting
Planning
Controlling Variables
Performing
Observing
Analyzing
Evaluating
Communicating
Investigation X.X.X 45
Purpose
To investigate the timing of major events in Earth and Human history using a physical time scale model.
Equipment and Materials
•
•
•
•
50 m measuring tape (one per class)
Human Civilization Event Cards (handout)
Life on Earth Event Cards (handout)
Data Table (handout)
Procedure
1. When instructed to do so, all student groups will place their Human Civilization Event Card(s) at the appropriate
positions along the same side of the tape measure according to the distance values indicated on the backs of the cards.
2. After all the cards have been placed on this scale, the entire class will “take a walk back through time” beginning at 0
m, which represents the present. Read and record the information from the events cards on your data table.
3. Next, place your Life on Earth Event Card(s) at the appropriate positions along the opposite side of the tape
measure.
4. After all the cards have been placed on this scale, the entire class will “take a walk forward through time” beginning
at the end of the tape (50 m). Read and record the information from the events cards in your data table.
Observations
Record all observation in the Data Table provided.
Analyze and Evaluate
(a) Did the historic timing of any of the Human Civilization events surprise you? Explain.
(b) Did any events demonstrate civilization made rapid progress from 1400–1900?
(c) Did any events suggest civilization made very slow progress between 1400–1900?
(d) Did the historic timing of any of the major Life on Earth events surprise you? Explain.
(e) For approximately how long did prokaryotes inhabit the Earth before any eukaryotes were present?
(f) Approximately how long did life exist on Earth before multi-cellular life arose?
(g) Based on these models, would you consider the following events to be “ancient” or “recent?”
i) first evidence of photosynthesis
ii) presence of life on land
iii) appearance of dinosaurs
iv) extinction of dinosaurs
v) appearance of apes
vi) first humans
(h) Do any of the events demonstrate or suggest that major change in life on Earth is slow?
(j) Do any of the events demonstrate or suggest that such change is fast?
Apply and Extend
(h) In this investigation you used a linear model to represent time. Research and report on other ways of depicting the
timing of events in Earth’s history. [CATCH weblink]
[catch web link banner]
[END 2pp]
7.1 Biological Change Over Time 46
[new page]
[Formatter: place the following features in 2 columns, as per design]
Chapter 7 Summary
Summary Questions
1. Create a study guide based on the Key Concepts listed at the beginning of the chapter on page XXX. For each point,
create three or four sub-points that provide further information, relevant examples, explanatory diagrams, or general
equations.
2. Return to the Starting Points questions at the beginning of the chapter on page XXX. Answer these questions using
what you have learned in this chapter. Compare your answers with those that you gave at the beginning of the chapter.
How has your understanding changed? What new knowledge and skills do you have?
Vocabulary
artificial selection
fossil
amber
paleontology
radioisotope
parent isotope
daughter isotope
half life
immutable
catastrophism
uniformitarianism
biogeography
homologous feature
analagous feature
vestigial feature
natural selection
survival of the fittest
modern synthesis
gene pool
neutral mutations
beneficial mutations
harmful mutations
pseudogenes
Career Pathways
Grade 11 Biology can lead to a wide range of careers. Some require a college diploma or a B.Sc. degree. Others require
specialized or post-graduate degrees. This graphic organizer shows a few pathways to careers mentioned in this
chapter.
1. Select two careers, related to Evolution that you find interesting. Research the educational pathways that you would
need to follow to pursue these careers. What is involved in the required educational programs? Prepare a brief report
of your findings.
2. For one of the two careers that you chose above, describe the career, main duties and responsibilities, working
conditions, and setting. Also outline how the career benefits society and the environment.
[catch C07-F18-OB11USB; Size A; MPU. Careers graphic organizer. MPU C04-F21-OB11USB.]
[end page]
7.1 Biological Change Over Time 47
[new page]
Chapter 7 Self-Quiz
[QUESTIONS TO COME]
[end page]
[new page – 6 pages begin]
Chapter 7 Review
[QUESTIONS TO COME]
[end 6 pages]
7.1 Biological Change Over Time 48