Download Chapter 8 Developing a Theory of Evolution

CHAPTER
8
Developing a Theory
of Evolution
Specific Expectations
In this chapter, you will learn how to . . .
• C2.1 use appropriate terminology
related to evolution (8.1, 8.2)
• C2.3 analyze, on the basis of research,
and report on the contributions of
various scientists to modern theories
of evolution (8.1)
• C3.1 explain the fundamental theory
of evolution, using the evolutionary
mechanism of natural selection to
illustrate the process of biological
change over time (8.1, 8.2)
• C3.2 explain the process of adaptation
of individual organisms to their
environment (8.2)
The word evolution is often used to describe a process of change
over time. Cars, fashion, language, and many other things are said
to “evolve.” Evolution in the biological sense is the process by which
hereditary changes occur in one or more characteristics within a
species over long periods of time, usually over many generations.
Evolution by natural selection is a scientific theory that explains
how Earth’s vast biodiversity developed in the past, continues to
develop in the present, and will continue to develop in the future.
Many theories have been developed through collaborative efforts, and
the theory of evolution is no different. As you will learn in this chapter,
the theory of evolution is built on the work of many contributors and
is based on different kinds of evidence, such as fossils.
The fossils shown here are trilobites. These fossils were found
in rock that is about 515 million years old. There were more
than 15 000 species of trilobites living in Earth’s oceans, but they
disappeared about 260 million years ago.
324 MHR • Unit 3 Evolution
Launch Activity
Forming a Hypothesis
Many theories are developed and refined as a result of collaborating with
team members and with other teams. In this activity, you will collaborate
with members in your group and with another group to try to identify an
animal from its paper fossil bones. You can assume that all the fossil bones
in your envelope are from the same animal.
Materials
• paper fossils
• printout of fossil remains of various animals
Procedure
1. Work in groups of four. Open your envelope of fossils, and remove
three fossil bones. Do not look at the other fossil bones in your
envelope. Try arranging the bones in different ways to help you form
a hypothesis about the identity of the animal. Record the group’s
hypothesis or hypotheses in a table like the one below.
Fossil Data
Step
Number of
Bones
Total Number
of Bones
1
3
3
2
3
6
3
4
10
Hypothesis
Notes
4
5
2. Remove three more bones from your envelope. If necessary, revise
your hypothesis and record your new hypothesis in your table.
3. Remove four more bones from your envelope. If necessary, revise your
hypothesis and record your new hypothesis in your table.
4. Compare your findings with those of another group. If necessary,
revise your hypothesis and record your final hypothesis in your table.
5. Compare your fossil assembly with the printout of fossil remains of
other animals. Note any similarities and differences.
6. Return your fossil bones to the envelope, and return the envelope to
your teacher.
Questions
1. Did your group reach an agreement on the identity of the animal?
Explain why or why not.
2. From looking at the fossil and the printout of fossil remains, what
could you say about how and where this animal lived?
3. What features of the nature of science do you think this activity
demonstrates?
Chapter 8 Developing a Theory of Evolution • MHR 325
SECTION
8.1
Key Terms
paleontology
catastrophism
uniformitarianism
inheritance of acquired
characteristics
theory of evolution by
natural selection
evolution
survival of the fittest
descent with modification
Scientific Contributions to a Theory of Evolution
Scientific knowledge develops as people observe the world around them, ask questions,
and seek answers to their questions. A scientific hypothesis is a statement that provides one
possible answer to a question, or one possible explanation for an observation. Hypotheses
are tested to determine their validity, mainly through experiments, observation,
developing models from data, or a combination of these activities. Hypotheses that
consistently lead to successful predictions and explanations are sometimes synthesized
into a general statement that explains and makes successful predictions about a broad
range of observations. Such a statement is called a scientific theory.
The question “Where did we come from?” has been asked and debated for
thousands of years. Many of the earliest ideas about the origins of life were strongly
influenced by religion and philosophy. These ideas suggested that all forms of life have
existed, unchanged, since their creation. In the 1600s, however, scholars in Europe
began to use a system of empirical studies to explain the natural world. Empirical
studies involve observation and experiment to form ideas and hypotheses about nature.
The first scientist to carry out empirical studies of the natural world was John Ray
(1627–1705), in England. He developed a classification system for plants and animals
based on anatomy and physiology. This system was later extended by the Swedish
naturalist Carolus Linnaeus (1707–1778). Both systems helped scientists of the time
recognize and think about similarities and differences between organisms.
Georges-Louis Leclerc, Comte de Buffon (1707–1788)
One of the first people to publicly challenge the idea that life forms are unchanging
was French naturalist Georges-Louis Leclerc, Comte de Buffon. His 44-volume Histoire
Naturelle compiled his understandings of the natural world. In this work, Buffon noted
the similarities between humans and apes, and speculated that they might have a
common ancestor, suggesting that species change over time. In other writings, Buffon
suggested that Earth was much older than 6000 years, as was commonly believed.
Buffon’s ideas were revolutionary for his time. By 1830, however, other scholars
from many other areas of inquiry—paleontology, geology, geography, and biology—
began to share their ideas to explain how life could change with the passage of time.
The Science of Paleontology
Figure 8.1 Mary Anning
was very skilled at
collecting fossils. As a
result, she made many
important contributions to
the field of paleontology.
paleontology the
study of ancient
life through the
examination of fossils
326 MHR • Unit 3 Evolution
Fossils are important to the study of evolution. A fossil is the preserved remains of a
once-living organism. Fossils include specimens preserved in amber, permafrost, dry
caves, and the more common fossils preserved as rock. Mary Anning (1799–1847),
shown in Figure 8.1, was a fossil hunter in England. Her most important discovery was
the first plesiosaur, an aquatic reptile. French naturalist Georges Cuvier (1769–1832)
was doing important work with fossils around Anning’s time. Cuvier examined
Anning’s drawing of the plesiosaur to see if it was genuine. Cuvier’s acknowledgment
of her work essentially made Anning respectable in the scientific world, a difficult
achievement for a young woman in a male-dominated field.
Georges Cuvier is largely credited with developing the science of paleontology—
the study of ancient life through the examination of fossils. Cuvier found that each
stratum (layer of rock) is characterized by a unique group of fossil species. He also
found that the deeper (older) the stratum, the more dissimilar the species are from
modern life (see Figure 8.2). As Cuvier worked from stratum to stratum, he found
evidence that new species appeared and others disappeared over the passage of time.
This evidence showed that species could become extinct.
A
B
C
younger stratum
with more recent
fossils
thicker layer
of sediment
A fossil is formed when an organism
falls into a body of water and settles in
the sediment. The sediments, brought
by rivers or streams to larger bodies of
water, keep the organism or parts of the
organism from decomposing.
More sediment is laid down on top of older
sediments and on top of remains of the
organism. These additional layers of
sediment compress lower strata, and then
these lower strata turn into rock. Over time,
many strata of rocks are formed. Sometimes,
each of the strata contains fossils.
Movements of the soil and
erosion of the rock can result
in fossil-laden rocks being
exposed above water level.
older stratum
with older fossils
Figure 8.2 Deep rock strata (layers of rock) are older than strata that are closer to the surface.
Different species of fossilized organisms can be found in different sedimentary rock strata.
This is evidence that not all life forms came into existence at the same time.
Catastrophism
To explain his observations, Cuvier proposed the idea that Earth experienced many
destructive natural events in the past, such as floods and volcanic eruptions. These
events, which he called revolutions, were violent enough to have killed numerous species
each time they occurred. Cuvier’s idea is now called catastrophism. Cuvier suggested
that these revolutions, or catastrophes, corresponded to the boundaries between the
strata he studied. He also thought they were limited to local geographical regions, and
that the area would be repopulated by species from nearby unaffected areas. This is how
Cuvier explained the appearance of fossils of species that did not exist anymore.
catastrophism the idea
that catastrophes such
as floods, diseases, and
droughts periodically
destroyed species living
in a particular region,
allowing species from
neighbouring regions to
repopulate the area
Charles Lyell (1797–1875)
Other scientists had ideas that differed from Cuvier’s theory. Scottish geologist Charles
Lyell rejected catastrophism. He proposed instead, based on the work of geologist
James Hutton, that geological processes operated at the same rates in the past as they do
today in a process called uniformitarianism. Lyell reasoned that, if geological changes
are slow and continuous rather than catastrophic, then Earth might be more than
6000 years old. He also theorized that slow, subtle processes could happen over a long
period of time and could result in substantial changes. The forces that build and erode
mountains, for example, and the rate at which such geological change happens, are no
different today than they were in the past. Floods in the past had no greater power than
floods that occur today. This idea inspired naturalist Charles Darwin and others. If Earth
is slowly changing, they wondered, could slow, subtle changes also occur in populations?
uniformitarianism
Charles Lyell’s theory
(based on Hutton’s
theory) that geological
processes operated at
the same rates in the
past as they do today
Learning Check
1. What is the empirical system?
2. Why were Buffon’s ideas revolutionary for his time?
3. Contrast uniformitarianism and catastrophism.
4. Georges Cuvier explained the appearance of fossils
of species that did not exist anymore. Why is this
an important contribution to science?
5. Do you think Cuvier’s ideas on catastrophism
suggest the idea that organisms change over time?
Explain your answer.
6. Do you think that the same geological processes
operate today as they did in the past, as Lyell suggests?
Is anything different today? Explain your answer.
Chapter 8 Developing a Theory of Evolution • MHR 327
Jean-Baptiste Lamarck (1744–1829)
inheritance of acquired
characteristics the
idea that characteristics
acquired during an
organism’s lifetime can
be passed on to
its offspring
In his book Philosophie Zoologique, French naturalist Jean-Baptiste Lamarck outlined
his ideas about changes in species over time. By comparing current species of animals
with fossil forms, Lamarck observed what he interpreted as a “line of descent,” or
progression, in which a series of fossils (from older to more recent) led to a modern
species. He thought that species increased in complexity over time, until they achieved
a level of perfection.
Lamarck hypothesized that the organisms would become progressively better
adapted to their environments. At the time, many thought that body parts that were
used extensively to cope with conditions in the environment would become larger
and stronger. Following this reasoning, giraffes stretched their necks to eat the foliage
from tall trees. Over time, they would pass on this stretched neck condition to their
offspring, resulting in tall giraffes that can eat from the tops of trees. (It is important to
note that giraffes did not develop their long necks in this way.) Lamarck called his idea
the inheritance of acquired characteristics. Lamarck also suggested that body parts
not used would eventually disappear. This idea is called use and disuse.
Lamarck provided a hypothesis for how the inheritance of characteristics from one
generation to the next might happen. More importantly, he noted that an organism’s
adaptations to the environment resulted in characteristics that could be inherited
by offspring. At the time, there was little understanding of cell biology and no
understanding of genetics. The idea of inheriting acquired characteristics was generally
accepted to explain observations that species are not static and could change. Even
Charles Darwin, who is credited with developing a comprehensive theory to explain
how change in populations can occur, accepted Lamarck’s idea of inheritance and
acknowledged Lamarck in his writing. But Lamarck’s ideas were controversial to the
many people who firmly believed that species never changed.
Charles Darwin (1809–1882)
theory of evolution
by natural selection
a theory explaining how
life has changed, and
continues to change,
during Earth’s history
evolution the process
of genetic change in a
population over time
In 1831, 22-year-old Charles Darwin left England on the HMS Beagle, a British survey
ship. The primary purpose of the expedition was to map the coast of South America.
The journey also provided Darwin with an opportunity to explore the natural history of
various countries and geographical locations. Figure 8.3 outlines the Beagle’s journey.
At first, Darwin did not always understand the significance of many of his
observations. Years later, however, many of these observations (as well as ideas and
observations resulting from new work by Darwin and others) became important to
his theory of evolution by natural selection. Darwin’s main observations, and the
questions he asked about these observations, are summarized in Table 8.1.
Figure 8.3 The five-year
voyage of the HMS Beagle
took Darwin around much
of the world. He spent most
of his time exploring the
coast and coastal islands
of South America.
England
Azores
C
Canary Is.
Cape Verde Is.
Galapagos Is.
Tahiti
Callao
Valparaiso
Tierra del Fuego
328 MHR • Unit 3 Evolution
Ascension Is.
St. Helena Is.
Bahia
Rio de
Janeiro
Montevideo
Falkland Is.
New
Zealand
Cocos Is.
M
Mauritius
Sydney
King
George
Sound
Hobart
Table 8.1 Darwin’s Observations and Questions Arising from Them
Observations
Questions
1. The flora and fauna of the different regions the Beagle visited were distinct from
those Darwin had studied in England and Europe. For example, the rodents in
South America were structurally similar to one another but were quite different
from the rodents Darwin had observed on other continents.
If all organisms originated in their
present forms during a single event,
Darwin wondered, why was there
a distinctive clustering of similar
organisms in different regions of the
world? Why were all types of organisms
not randomly distributed?
2. Darwin observed fossils of extinct animals, such as the armadillo-like glyptodont,
that looked very similar to living animals.
Why would living and fossilized
organisms that looked similar be
found in the same region?
A glyptodont, an ancient 4 m, 2 tonne
animal from South America
A modern armadillo from South America
(1.5 m)
3. The finches and other animals Darwin saw
on the Galapagos [guh-LA-pa-gos] Islands
closely resembled animals he had observed
on the west coast of South America.
The Galapagos Islands, shown in this
satellite image, include more than
20 small volcanic islands located
approximately 1000 km off the coast of
Ecuador, some of which are shown here.
They formed at approximately the same
time and have similar abiotic conditions.
Isabela
Santiago
Why did the Galapagos species so
closely resemble organisms on the
adjacent South American coastline?
Santa Cruz
Fernandina
4. Galapagos species (such as tortoises and finches) looked identical at first, but they
actually varied slightly between islands. Each type of Galapagos finch, for example,
was adapted to eating a different type of food based on the size and shape of its beak.
Ten finch species that occur on one of the islands, Santa Cruz, are shown here.
warbler finch
(Certhidea olivacea)
cactus ground finch
(Geospiza scandens)
woodpecker finch
(Cactospiza pallida)
sharp-beaked ground
finch (Geospiza difficilis)
small insectivorous tree finch
(Camarhynchus parvulus)
small ground finch
(Geospiza fuliginosa)
large insectivorous tree finch
(Camarhynchus psittacula)
medium ground finch
(Geospiza fortis)
vegetarian tree finch (Platyspiza
crassirostris)
large ground finch
(Geospiza magnirostris)
5. Through his experience with artificial selection (breeding pigeons and studying breeds
of dogs and varieties of flowers), Darwin knew that it was possible for traits to be passed
on from parent to offspring, and that sexual reproduction resulted in many variations
within a species.
Why was there such a diversity of
species in such a small area? Could
these species have been modified from
an ancestral form that arrived on the
Galapagos Islands shortly after the
islands were formed?
Could a process similar to artificial
selection also operate in nature?
Chapter 8 Developing a Theory of Evolution • MHR 329
Darwin, Wallace, and the Theory of Evolution by Natural Selection
survival of the fittest
the idea that the
organisms that are the
fittest leave the most
offspring, so those
organisms win the
struggle for survival;
phrase coined by John
Spencer
SuggestedInvestigation
ThoughtLab Investigation
8-A, Comparing the Ideas of
Lamarck and Darwin
descent with
modification Darwin’s
theory that natural
selection does not
demonstrate progress,
but merely results from
a species’ ability to
survive local conditions
at a specific time
Activity
8.1
After his trip on the Beagle, Charles Darwin began to propose answers to his questions,
and to organize his and others’ observations into a comprehensive theory to explain
how species change over time. Alfred Russel Wallace (1823–1913), another British
naturalist, reached conclusions that were similar to Darwin’s.
Darwin and Wallace accepted that populations changed as time passed, but they
were unclear how populations changed. An essay by economist Thomas Malthus
(1766–1834), called Essay on the Principles of Population, provided them with a
key idea. Malthus proposed that populations produced far more offspring than
their environments (for example, their food supply) could support. He said that the
populations were eventually reduced by starvation or disease.
According to Darwin and Wallace, individuals with traits that helped them survive
in their local environments were more likely to survive to pass on these traits to
offspring. They reasoned that competition for limited resources between individuals
of the same species would select for individuals with favourable traits—traits that
increased their chances of surviving to reproduce. Thus, a growing proportion of
the population would have these traits in later generations and, as time passed, the
population as a whole would have them. This is the idea of survival of the fittest, and
Darwin called this process natural selection. He published his ideas in 1859 in a book
whose title is often shortened, for convenience, to The Origin of Species.
He proposed that all life descended from some unknown organism. As descendants
of this organism spread out over different habitats during the millennia, they developed
adaptations that helped them better survive in their local environments. Darwin’s
theory of natural selection showed how populations of individual species became better
adapted to their local environments over time. His ideas are summarized as follows:
• Organisms produce more offspring than can survive. Therefore, organisms compete
for limited resources.
• Individuals of a population vary extensively, and much of this variation is heritable.
• Individuals that are better suited to local conditions survive to produce more offspring.
• Processes for change are slow and gradual.
Descent with Modification
Darwin did not use the word evolution in the original edition of The Origin of Species.
Instead, he spoke of descent with modification. Darwin felt the word evolution
implied progress, the notion that each generation was somehow improving in some
way. Natural selection does not demonstrate progress; it has no set direction. It results
from the ability of certain individuals in any population to survive local environmental
conditions and to pass on the traits that helped them survive in the first place.
Building a Theory
In this activity, you will research the work of several scholars
whose work influenced Darwin.
Materials
• computer with Internet access
• print resources
Procedure
1. Using print or Internet resources, research how the
following contributed to Darwin’s theory of evolution:
Comte de Buffon, Charles Lyell, Thomas Malthus,
Jean-Baptiste Lamarck, and Alfred Russel Wallace.
330 MHR • Unit 3 Evolution
2. Create a presentation that includes the following:
• one contribution from each that is not mentioned in
this textbook, and the evidence that supports it
• societal influences at the time of each contributor
• how Darwin was influenced by their work
Question
In your opinion, which contributor was the most influential
to the development of Darwin’s theory of evolution by
natural selection? Explain your answer.
Section 8.1
RE V I E W
Section Summary
• Scientific theories explain facts and connect them
in a comprehensive way, enabling scientists to make
predictions about new situations and experimental
outcomes.
• The question of whether living things have changed over
the course of Earth’s history has been considered by many
different philosophers and scholars.
• In Histoire Naturelle, Buffon challenged the idea that life
forms are unchanging and that Earth was 6000 years old.
Cuvier founded the science of paleontology and proposed
catastrophism as an explanation for fossil history.
• Geologist Charles Lyell noted that Earth’s geological
features were in a slow, continuous cycle of change,
which he called uniformitarianism. Lamarck proposed
the idea of inheritance of acquired characteristics, which
suggested that parents passed on learned adaptations to
the environment, which resulted in evolution.
• Darwin brought together his own observations from
his journey on the HMS Beagle, his observations from
his selective breeding, and the work of many other great
thinkers to develop his theory of evolution. His theory
proposes natural selection as the mechanism for how new
species arise from ancestral species in response to the
local environment.
Review Questions
1.
2.
3.
K/U Explain how the diagram shown below is
evidence that not all life forms came into existence
at the same time.
Imagine yourself to be Cuvier, examining fossils.
You find the fossil of a species of fish in one stratum
but not in the next highest stratum. Write a brief letter
to a peer that proposes an explanation for your
observations.
C
C
Using a graphic organizer, show the difference
between catastrophism and uniformitarianism, and
how these ideas relate to the development of the theory
of evolution.
4.
K/U How did Lyell’s observations about changes in
Earth’s geological features inspire naturalists’ ideas
about changes in life forms on Earth?
5.
A
How might Lamarck have explained an
elephant’s long trunk?
6.
An athlete breaks her leg. Years later she has
a child who walks with a limp. Is this an example of
evolution? Explain your answer.
7.
How is the work of Malthus related to the
concept of survival of the fittest?
8.
K/U Describe the contributions of the following
people to the understanding of evolution.
a. Cuvier
c. Wallace
e. Lamarck
b. Malthus
d. Lyell
9.
Create a concept map showing the individuals
from this section whose contributions led to the
development of the theory of evolution by natural
selection. State their contributions.
10.
A
Nature writer Wallace Stegner once wrote of a
population of trout in a mountain lake that were in a
“Malthusian dilemma.” Explain what Stegner meant.
11.
T/I Explain why Darwin used the phrase descent
with modification rather than evolution.
12.
K/U Describe, using two examples, how Charles
Darwin used observations of the world around him to
develop his hypothesis about how species might
change with the passage of time.
13.
C
Draw a concept map that summarizes Darwin’s
four main ideas related to evolution.
14.
T/I Much of the theory of evolution has been
developed by interpreting certain observations or by
making logical inferences about these observations.
Outline the inferences that Darwin and other scientists
made from each of the following observations.
a. Some species found on islands are very similar to
species found on neighbouring continents.
b. No two individuals are exactly alike.
c. Resources, such as food, are limited.
15.
A
Explain how breeding dogs would provide you
with observations that would support Darwin’s theory
of evolution by natural selection.
A
K/U
C
Chapter 8 Developing a Theory of Evolution • MHR 331
SECTION
8.2
Key Terms
fossil record
transitional fossil
vestigial structure
biogeography
homologous structures
analogous structures
embryology
Sources of Evidence for Evolution
In The Origin of Species, Darwin assembled a group of facts that had previously
seemed unrelated. Darwin certainly was not the only person to conclude that life had
changed over long periods of time, but he was the first person to publish these ideas
in a comprehensive manner. Darwin’s ideas were developed, for the most part, by his
observations of the distribution of organisms throughout the world (as outlined in
Table 8.1 on page 329). Before and after publication of The Origin of Species, biologists,
geologists, geographers, and paleontologists provided a wealth of information that
supported and strengthened what Darwin called—and today’s scientists also call—the
theory of evolution by natural selection.
Fossils: Evidence for the History of Life
fossil record the
remains and traces of
past life that are found
in sedimentary rock; it
reveals the history of life
on Earth and the kinds
of organisms that were
alive in the past
Sedimentary rock with fossils provides a fossil record of the history of life by showing
the kinds of species that were alive in the past, such as those shown in Figure 8.4.
For instance, when people examined the Burgess Shale fossil beds in British Columbia,
they found fossils of animals that lived in an ancient ocean during the Cambrian
period, over 500 million years ago. In addition to micro-organisms and soft-bodied
animals, the Burgess Shale fossil beds also preserved some of the earliest animals with
hard parts to be seen in the fossil record. Some of the fossilized animals found in the
Burgess Shale are ancestors of animals that are common today. Others have long been
extinct and are unlike anything in our modern oceans. The geological time scale in
Figure 8.5 shows approximately when organisms first appear in the fossil record.
Opabinia
Pikaia
trilobites
Figure 8.4 The animals unearthed in the Burgess Shale lived over 500 million years ago during
a period called the Cambrian explosion, when there was a sudden increase (on a geological scale)
in the diversity of animal species.
332 MHR • Unit 3 Evolution
135 million years ago
Flowering plants first
appear in the fossil record
0
1.8
Periods
Eons
Cenozoic Eras
Millions of
Years ago
7 million years ago
Hominids first appear
in the fossil record
Mesozoic
Late
Paleozoic
Phanerozoic
65
144
225 million years ago
Dinosaurs and
mammals first appear
in the fossil record
206
248
290
354
417
400 million years ago
Seed plants first appear
in the fossil record; tetrapods
and insects first appear
in the fossil record
443
490
543
Quaternary
Tertiary
Cretaceous
160 million years ago
Birds first appear in the
fossil record
Jurassic
Triassic
Permian
300 million years ago
Reptiles first appear
in the fossil record
Carboniferous
Devonian
Silurian
450 million years ago
Large terrestrial colonization
by plants and animals
Ordovician
Cambrian
533–525 million years ago
Cambrian explosion creates diverse animal life
520 million years ago
First vertebrates; first
land plants
Middle
590 million years ago
Bilateral invertebrate animals
first appear in the fossil record
1600
Precambrian
Early
Proterozoic
900
543 million years ago
Shelled animals first
appear in the fossil record
1.5 billion years ago
Multicellular eukaryotic
organisms first appear
in the fossil record
2.5–2.0 billion years ago
Eukaryotic cells first appear
in the fossil record
Middle
3000
Early
Archaean
Late
2500
3.5 billion years ago
Fossils of primitive
cyanobacteria first appear
in the fossil record
3400
3.8–3.5 billion years ago
Prokaryotic cells first appear
in the fossil record
Hadean
3800
4500
Figure 8.5 This geological time scale illustrates the approximate appearance in the fossil record of
various organisms during Earth’s 4.6 billion year history. Note that this illustration is not to scale.
Chapter 8 Developing a Theory of Evolution • MHR 333
Evidence from the Fossil Record
The fossil record provides the following evidence:
• Fossils found in young layers of rock (from recent geological periods and usually
closer to the surface) are much more similar to species alive today than fossils found
in older, deeper layers of rock. For example, paleontologists have used fossils to trace
the evolution of the modern camel. As you can see in Figure 8.6, the camel ancestor
from the Miocene epoch is more similar to the modern camel than the ancestors
from the more distant epochs.
• Fossils appear in chronological order in the rock layers. So, probable ancestors for a
species are found in older rocks, which usually lie beneath the rock in which the later
species is found.
• Not all organisms appear in the fossil record at the same time. For example, the fossil
history of vertebrates shows that fish are the oldest vertebrates. In subsequent layers,
the fossils of other vertebrates—amphibians, reptiles, mammals, and birds—appear.
This reinforces scientific evidence that amphibians evolved from ancestral fish,
reptiles evolved from ancestral amphibians, and both mammals and birds evolved
from different groups of reptiles (mammals first, and then birds). It is important to
remember that these changes were slow and took millions of years.
Figure 8.6 Paleontologists
have used fossils to
trace the evolution of
the modern camel. The
Paleocene, Eocene,
Oligocene, and Miocene
epochs are subdivisions of
the Cenozoic era.
Paleocene
Eocene
tooth
66 million years ago
Oligocene
Miocene
Present
leg bone
skull
54 million years ago
37 million years ago
26 million years ago
transitional fossil
a fossil that shows
intermediary links
between groups of
organisms and shares
characteristics common
to two now separate
groups
vestigial structure
a structure that is a
reduced version of
a structure that was
functional in the
organism’s ancestors
334 MHR • Unit 3 Evolution
Evidence from Transitional Fossils
The original fossil record gave only scattered “snapshots” of ancestral forms. Scientists
wondered about the gaps between these snapshots. The ongoing discovery of hundreds
of transitional fossils—fossils that show intermediary links between groups of
organisms—has helped scientists better understand the evolutionary process and
relationships between groups of organisms. Transitional fossils link the past with
the present.
For example, scientists have found fossilized whales that lived 36 to 55 million
years ago. These fossils link present-day whales to terrestrial ancestors. Basilosaurus
and Dorudon were ancient whales that had tiny hind limbs but led an entirely aquatic
life. Dorudon was about the size of a large dolphin, about 5 m long. It had a tiny pelvis
(located near the end of its tail) and legs about 10 cm long. These characteristics would
have been useless to an animal that lived an aquatic life. Structures that are the reduced
forms of structures that were functional in the organism’s ancestors are called vestigial
structures. The pelvic bone in the Dorudon whale—and in some modern whales, such
as baleen whales—is called a vestigial pelvic bone.
Ambulocetus, a transitional form that was discovered more recently (announced
in 1994), had heavier leg bones. Scientists hypothesize that it lived both on land and
in water. In Figure 8.7, compare Ambulocetus with a modern toothed whale, as well as
two other ancestors of present-day whales, Pakicetus and Rodhocetus. The discovery of
Pakicetus and Rodhocetus has filled gaps in the fossil record of whales.
Pakicetus attocki lived on
land, but its skull had
already evolved features
characteristic of whales.
Ambulocetus natans
likely walked on land
(as modern sea lions do)
and swam by flexing its
backbone and paddling
with its hind limbs (as
modern otters do).
Rodhocetus kasrani’s
small hind limbs would
not have helped it swim,
much less walk.
Figure 8.7 Fossil evidence
suggests that modern
toothed whales evolved
from a terrestrial ancestor,
Pakicetus attocki. Basilosaurus
and Dorudon, not shown
in this illustration, appear
more recently in the fossil
record, after the appearance
of Rodhocetus.
Modern toothed whale
Archaeopteryx: A Transitional Fossil
In 1995, the fossil of a previously unknown dinosaur called Atrociraptor (savage
robber) was discovered near Drumheller, Alberta. Atrociraptor was a small meat-eating
dinosaur, about the size of a 10-year-old child. It is thought to be a close non-birdlike
relative of Archaeopteryx. Fossils of Archaeopteryx show a transitional stage in the fossil
record because this species had characteristics of both reptiles (dinosaurs) and birds.
Archaeopteryx had feathers, but, unlike any modern bird, it also had teeth, claws on its
wings, and a bony tail.
Evidence from Biogeography
Biogeography is the study of the past and present geographical distribution of
organisms. Many of the observations that Darwin and Wallace used to develop their
theories were based on biogeography. Darwin and Wallace hypothesized that species
evolve in one location and then spread out to other regions. Biogeography supports
this hypothesis with examples such as the following:
biogeography the
study of the past and
present geographical
distribution of species
populations
• Geographically close environments (for example, desert and forest habitats in South
America) are more likely to be populated by related species than are locations that
are geographically separate but environmentally similar (for example, a desert in
Africa and a desert in Australia). So, for instance, cacti are native only to the deserts
of North, Central, and South America. They are not found naturally in other deserts
in the world, such as those in Australia and Africa.
• Animals found on islands often closely resemble animals
found on the closest continent. This suggests that animals
on islands have evolved from mainland migrants, with
populations becoming adapted over time as they adjust to the
environmental conditions of their new home. For example, the
lizards found on the Canary Islands, off the northwest coast of
Africa, are very similar to the lizards found in west Africa.
• Fossils of the same species can be found on the coastline of
neighbouring continents. For example, fossils of the reptile
Cynognathus have been found in Africa and South America.
How can this be explained? The location of continents is not
fixed; continents are slowly moving away from one another.
About 510 million years ago, the continents of Africa and
South America were joined in one supercontinent, called
Gondwana, as shown in Figure 8.8.
• Closely related species are almost never found in exactly
the same location or habitat.
Gondwana
Africa
South
America
India
Australia
Antarctica
Figure 8.8 As the southern supercontinent Gondwana
broke apart about 150 million years ago, the land
masses that became the current continents of Africa,
Australia, South America, and Antarctica were isolated
from each other.
Chapter 8 Developing a Theory of Evolution • MHR
335
Learning Check
7. What is the fossil record?
11. Compare each drawing in Figure 8.6 and
describe the changes that you see from one
epoch to the next.
8. Explain two ways in which the fossil record has
helped scientists understand that organisms
change over time.
9. Why are transitional fossils important?
10. How does the existence of vestigial pelvic bones
in whales refute Lamarck’s idea of use and disuse?
12. Explain the following sentence: Islands have
many unique species of animals and plants that
are found nowhere else in the world.
Evidence from Anatomy
homologous structures
structures that have
similar structural
elements and origin but
may have a different
function
Vertebrate forelimbs can be used for various functions, such as flying (birds and bats),
running (horses and dogs), and swimming (whales and seals). Despite their different
functions, however, all vertebrate forelimbs contain the same set of bones, organized
in similar ways. How is this possible? The most plausible explanation is that the basic
vertebrate forelimb originated with a common ancestor.
Homologous structures are those that have similar structural elements and
origin but may have a different function. The limbs shown in Figure 8.9 have similar
structures, such as number of bones, muscles, ligaments, tendons, and blood vessels.
These structural elements are arranged, however, to be best suited for different
functions: walking, flying, or swimming. Homologous structures are similar because
they were inherited from a common ancestor. As you can see in Figure 8.9, homologous
structures differ in their anatomy based on an organism’s lifestyle and environment. For
example, the bones in a horse’s leg are larger and heavier than the bones in a bat’s wing.
Human
Frog
Bat
Porpoise
Horse
Figure 8.9 These vertebrates have the same basic arrangement of bones (as indicated by the
colours), but the bones have different uses.
analogous structures
structures of organisms
that do not have a
common evolutionary
origin but perform
similar functions
336 MHR • Unit 3 Evolution
Homologous structures can be similar in structure, function, or both. The limbs
in Figure 8.9 are structurally similar. The lower limbs of the human, frog, and horse
perform the same function: movement on land. Functional similarity in anatomy,
however, does not necessarily mean that species are closely related. The wings of
insects, birds, bats, and pterosaurs (extinct flying reptiles) are similar in function but
not in structure. For example, bones support bird wings, whereas a tough material
called chitin [KYE-ten] makes up insect wings. All of these organisms evolved
independently of one another, and they do not share a common ancestor with wings.
Body parts that perform similar functions, even though the organisms do not
have a close common evolutionary origin, are called analogous structures. Analogous
structures evolve in species of different origin who live in similar ecological units.
Homologous Hair
In mammals, hair is homologous. Compare variations in the functions of mammalian
hair by completing Activity 8.2 below.
Activity
8.2
Homologies of Hair
Mammals are the only animals that have hair. Among
mammalian species, hair can vary in length, density, texture,
and colour. The basic structure of hair, however, is the same
in all mammals. Each hair has a central medulla that is
surrounded by a dense cortex, which contains most of the
pigment granules that give each strand of hair its colour.
A layer called the cuticle covers the cortex. The scales of
the cuticle are specific to a particular genus or even species
of mammals. Thus, mammalian hair has a common origin,
yet may serve different functions. In this activity, you will
investigate variations in the functions of mammalian hair.
Cross Section of a Hair
cuticle
pigment
granules
cuticular
scale
medulla
cortex
Materials
• computer with Internet access
• print resources
Procedure
1. Work in a group of three or four.
2. Each person in your group should choose a different
type of mammalian hair from the following list:
• stout, strong hairs of a porcupine
• dense underfur, or underhairs, of a sea otter
• whiskers (vibrissae) of a cat
• long, thick hair of a woolly mammoth
• horn of a rhinoceros, which is made of densely
packed hair
• thick mane of a lion
• “scales” of a pangolin, which are modified hairs
• soft, fluffy underfur (qiviut) of a musk-ox
3. Using print and Internet sources, research the structure
of the hair you have chosen. Research how the animal’s
lifestyle and habitat might explain the particular
function(s) of its hair.
Questions
1. Based on the information you collected and your
understanding of natural selection, hypothesize how
the structure of the hair is related to abiotic conditions
in an animal’s environment. Write a hypothesis stating
how the variations might have arisen from the basic
hair structure of a common mammalian ancestor.
2. Present your findings to the others in your group in
a written or oral report, a computer presentation, or
another form that is easily shared.
3. In a graphic organizer, describe one similarity and one
difference in the adaptation of the hair studied by the
members of your group.
porcupine
sea otter
cat
woolly mammoth
rhinoceros
lion
pangolin
musk-ox
Chapter 8 Developing a Theory of Evolution • MHR 337
Evidence from Embryology
embryology the study
of early, pre-birth
stages of an organism’s
development
Embryology is the study of early, pre-birth stages of an organism’s development.
Embryology has also been used to determine evolutionary relationships between animals.
The embryos of different organisms exhibit similar stages of embryonic development.
For example, all vertebrate embryos have paired pouches, or out-pocketings, of the
throat. In fish and some amphibians, the pouches develop into gills. In humans, the
pouches become parts of the ears and throat. At certain stages in the development of
the embryo, the similarities between vertebrates are more apparent than the differences,
as you can see in Figure 8.10.
The similarities between embryos in related groups (such as vertebrates) point to
a common ancestral origin. It follows that related species share both adult features
(such as basic arm-bone arrangements, as discussed earlier) and embryonic features
(such as the presence of paired pouches in the throat).
Fish
Chicken
Pig
Human
Figure 8.10 Similarities in the embryos of fish, birds, and mammals provide evidence of
evolution of species from a common ancestor.
Describe the differences and similarities between the fish and the chicken embryos.
Evidence from DNA
As you learned in Section 1.2, the evolutionary relationships between species are
reflected in their DNA. Since DNA carries genetic information, scientists can determine
how closely related two organisms are by comparing their DNA. If two species have
similar patterns in their DNA, this indicates that these DNA sequences must have been
inherited from a common ancestor. For example, by studying gene sequences, scientists
have determined that dogs are related to bears and that whales and dolphins are related
to ungulates [UN-gya-lets] (hoofed animals such as cows and deer).
The use of modern technology has led to many discoveries that support Darwin’s
theory. Scientists now know how species pass on their traits to their offspring, and
how the genes for these traits could change by mutation, as you learned in Section 7.1.
Current evolutionary theory connects genetics with the theory of natural selection,
and how natural selection operates on populations. Thus, genetic evidence and our
understanding of heredity and mutations lend support to hypotheses that stem from
observations of fossils, anatomy, biogeography, embryology, and DNA relationships.
338 MHR • Unit 3 Evolution
STSE
BIOLOGY Connections
T. rex and chickens share
a common ancestor?
After excavating a T. rex fossil in 2003,
scientists found it was too big to transport
by helicopter. The scientists carefully broke
the thigh bone in half to ship the bone. The
results of later tests on the broken bone were
surprising—the bone held preserved soft
tissues! These tissues, shown in the photograph
below, included connective tissue, blood vessels,
and possibly even blood cells.
SOFT TISSUE In 2007, the fossil of the
68-million-year-old T. rex was tested for the
first time to see if dinosaurs could be shown to
share genetic markers with modern animals.
The examination of dinosaur fossils allows
scientists to understand how life on Earth has
changed over time. The discovery of soft tissue
allows new tests to be performed. It is possible
that many more dinosaur bones contain soft
tissue samples.
Molecular evidence suggests that the Tyrannosaurus rex and the
chicken are related. (These images are not to scale.)
In previous studies, physical similarities between early
bird fossils and dinosaur fossils supported this link. For
example, some fossils showed that the earliest birds had feet
very similar to dinosaur feet. Several dinosaur fossils also
show evidence of feathers.
A group of scientists at North Carolina State
University introduced a protein to chicken and the T. rex
soft tissue. The protein reacted strongly in the presence of
the collagen found in chickens. (Collagen is a protein found
in the connective tissue of animals.) A similar reaction was
observed when the protein was administered to the dinosaur
tissue. This indicates a molecular similarity between chicken
tissues and dinosaur tissues.
In another study performed by a team of researchers
from Harvard Medical School, scientists obtained protein
sequences from the T. rex soft tissue. The amino acid sequence
in the proteins was similar to the amino acid sequence in
chickens, showing clear support for an ancestral link between
chickens and dinosaurs. (Amino acids are compounds that
form proteins.)
THE TEST
soft
tissue
The soft tissue from the T. rex was almost perfectly preserved.
Two independent tests on the soft tissue found in
the fossil indicate that the T. rex is likely related to the
present-day chicken. This new research provides molecular
evidence that supports hypotheses that a common ancestor
linked birds and dinosaurs.
Connect to Scientific Inquiry
Before researchers tested the reaction of protein and collagen
in the soft tissue of chickens and dinosaurs, they had to
formulate a hypothesis. Write a hypothesis that they might
have tested.
Chapter 8 Developing a Theory of Evolution • MHR 339
Section 8.2
RE V I E W
Section Summary
• The theory of evolution connects facts to provide a logical
framework that explains how life on Earth has changed
and is still changing.
• Charles Darwin and Alfred Russel Wallace both
developed hypotheses to explain natural selection.
• New discoveries of fossils, called transitional fossils, help
fill in the gaps in the fossil record.
• Homologous structures have similar structural elements
and origin but may have a different function. Analogous
structures perform similar functions, even though the
organisms do not share a recent common ancestor.
• The fossil record, biogeography, anatomy, embryology,
and relationships in DNA all provide evidence for
evolution.
Review Questions
1.
K/U Charles Darwin was not the only person to
discuss the idea of evolution. Why is his name often
synonymous with the idea of evolution?
8.
K/U Describe how comparing the anatomy of
animals is used to support the theory of evolution by
natural selection.
2.
T/I Evolutionary biologist John Haldane once said,
“I’d give up my belief in evolution if someone found a
fossil rabbit in the Precambrian.” Explain this quote.
9.
K/U What kinds of structures are the arm of a
human and the forelimb of a horse?
10.
3.
How does the discovery of transitional fossils in
the fossil record help you understand the evolutionary
events of the past?
K/U Explain the difference between analogous
structures and homologous structures.
11.
K/U Are bird wings and bat wings homologous
structures or analogous structures? Explain your
answer.
4.
K/U
C
Choose a fossil (either one described in this
textbook or another one you have researched) and
describe what information it provides that helps you
understand evolution.
5.
A scientist finds a rare organism—a whale
with hind legs. Explain how this finding is evidence
for evolution.
6.
A
The island of Madagascar is thought to
have split from Africa about 150 million years ago.
Discuss the types of organisms you would expect
to find on this island. Explain your reasoning.
12.
T/I Scientists discover that the pharyngeal (gill)
pouches are similar in the early embryological stages
of vertebrates such as snakes, cats, bats, and human
embryos. Yet, the later stages of development show
many more differences between these organisms.
Explain why the early stages are so similar.
14.
C
Create a concept map that shows how different
types of scientific evidence support the theory of
evolution. Go to Using Graphic Organizers in Appendix A
to learn more about making a concept map.
15.
T/I A person tells you that evolution, like the big
bang, is “just a theory.” Explain to the person what a
theory means in a scientific sense, and provide four
facts that support the theory of evolution.
16.
Baleen whales, such as grey and humpback
whales, have teeth and body hair while they are
embryos, but they lack these features as adults. What
does this tell you about the evolutionary history of
these animals?
17.
Use a diagram such as a flowchart to illustrate
the process of evolution by natural selection in a giraffe
population competing for leaves in the high canopy of
trees. Go to Using Graphic Organizers in Appendix A
to learn more about making a flowchart.
Africa
Madagascar
7.
Make a hypothesis about what species changes
and environmental changes you would expect to see
on Madagascar, after a long period of time, if it were
somehow reconnected to mainland Africa today. How
might a scientist test your hypothesis?
T/I
340 MHR • Unit 3 Evolution
Define vestigial structure. Provide an example.
13.
K/U
The island of Madagascar is just east of Africa.
K/U
T/I
C
ThoughtLab
INVESTIGATION
8-A
Skill Check
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Comparing the Ideas of Lamarck and Darwin
Darwin and Lamarck both developed ideas about the inheritance of
characteristics. Although Darwin read Lamarck’s work and learned from his
ideas, Darwin eventually proposed an alternative hypothesis that gave a different
explanation for the mechanism that resulted in biological change. Read the
quotations from the writings of Lamarck and Darwin on the left.
Pre-Lab Questions
1. List two ideas proposed by Lamarck’s theory of evolution.
This is an artist’s
impression of
Jean-Baptise Lamarck.
2. List two ideas proposed by Darwin’s theory of evolution.
Question
What is the key difference between the ideas of Lamarck and Darwin?
“The environment exercises a great
influence over the activities of animals,
and as a result of this influence the
increased and sustained use or disuse of
any organ are causes of modification of
the organization and shape of animals
and give rise to the anomalies observed
in the progress of the complexity of
animal organization.”
—Jean-Baptiste Lamarck in
Philosophie Zoologique, 1809
Organize the Data
1. Rewrite each quotation in your own words.
Analyze and Interpret
1. How does Lamarck’s idea of “use or disuse” differ from Darwin’s idea, which
was later called “descent with modification”?
2. Flying fish (Exocoetus volitans) use large pectoral fins to glide in air to
escape predators. Explain how Lamarck and Darwin might account for the
origin of these large pectoral fins and the ability to glide.
Conclude and Communicate
3. A farmer spends much of her time outdoors. As a result, her skin has
become very tanned. What would Lamarck predict about her children?
What would Darwin predict about her children? How does this reflect the
key difference in their theories?
This is an artist’s
impression of
Charles Darwin.
Extend Further
“[N]atural selection, or survival of the
fittest, does not necessarily include
progressive development—it only takes
advantage of such variations as arise and
are beneficial to each creature under its
complex relations of life. And it may be
asked what advantage, as far as we can
see, would it be to an … intestinal worm
… to be highly organised. If it were no
advantage, these forms would be left, by
natural selection, unimproved or but little
improved, and might remain for indefinite
ages in their present lowly condition.”
4. INQUIRY According to Lamarck’s ideas, “functions create organs.” What
does this statement mean? Do you agree or disagree with this statement?
Explain your answer.
5. RESEARCH In his book Philosophie Zoologique, Lamarck describes organic
beings as existing on a ladder of life. Research the Great Chain of Being.
Explain how this idea fit into Lamarck’s view of species change over time.
—Charles Darwin in
The Origin of Species, 1859
Chapter 8 Developing a Theory of Evolution • MHR 341
Chapter 8
Section 8.1
SUMMARY
Scientific Contributions to a Theory of Evolution
The work of many great thinkers supported Darwin’s
direct observations and led to Darwin’s formulation of
the theory of evolution by natural selection.
KEY TERMS
catastrophism
descent with modification
evolution
inheritance of acquired characteristics
paleontology
survival of the fittest
theory of evolution by natural selection
uniformitarianism
KEY CONCEPTS
• Scientific theories explain facts and connect them in a
comprehensive way, enabling scientists to make predictions
about new situations and experimental outcomes.
• In Histoire Naturelle, Buffon challenged the idea that life
forms are unchanging and that Earth was 6000 years old.
Cuvier founded the science of paleontology and proposed
catastrophism as an explanation for fossil history.
• Geologist Charles Lyell noted that Earth’s geological
features were in a slow, continuous cycle of change, which
he called uniformitarianism. Lamarck proposed the idea of
inheritance of acquired characteristics, which suggested
that parents passed on learned adaptations to the
environment, which resulted in evolution.
• Darwin brought together his own observations from his
journey on the HMS Beagle, his observations from his
selective breeding, and the work of many other great
thinkers to develop his theory of evolution. His theory
proposes natural selection as the mechanism for how
new species arise from ancestral species in response
to the local environment.
• The question of whether living things have changed over
the course of Earth’s history had been considered by
many different philosophers and scholars.
Section 8.2
Sources of Evidence for Evolution
Many different lines of scientific evidence from before,
during, and after Darwin’s time all support the theory
of evolution by natural selection.
KEY TERMS
analogous structures
biogeography
embryology
fossil record
homologous structures
transitional fossil
vestigial structure
KEY CONCEPTS
• The theory of evolution connects facts to provide a logical
framework that explains how life on Earth has changed and
is still changing.
• Charles Darwin and Alfred Russel Wallace both developed
hypotheses to explain natural selection.
• New discoveries of fossils, called transitional fossils, help fill
in the gaps in the fossil record.
• Homologous structures have similar structural elements
and origin but may have a different function. Analogous
structures perform similar functions, even though the
organisms do not share a recent common ancestor.
• The fossil record, biogeography, anatomy, embryology, and
relationships in DNA all provide evidence for evolution.
342 MHR • Unit 3 Evolution
Chapter 8
REVIEW
Knowledge and Understanding
Select the letter of the best answer below.
1. Which of the following sources of evidence of
evolution is used to establish genetic relationships
between organisms?
a. the fossil record
d. embryology
b. transitional fossils
e. DNA
c. biogeography
2. How do vestigial structures provide evidence for
evolution?
a. They show direction of change.
b. They show shared ancestry.
c. They show genetic relationships.
d. They show how new structures evolve.
e. They show geographical relationships.
3. Which of the following is a main point of Lamarck’s
idea of biological change over time?
a. Organisms produce more offspring than can
survive, so they compete for limited resources.
b. Individuals of a population vary extensively, and
some of this variation is heritable.
c. All body parts not used will eventually disappear.
d. Individuals that are better suited to local conditions
survive to produce offspring.
e. Processes for change are slow and gradual, and
Earth is much older than 6000 years.
4. Lamarck and Darwin proposed different explanations
for how characteristics are passed from parent to
offspring, but their theories had some similarities.
Which of the following points is true?
a. The men disagreed that there was a line of descent
in organisms.
b. Both believed that organisms adapt to their
environments.
c. Both believed in catastrophism and the idea that if a
body part were not used, it would simply disappear
over time.
d. Both believed that characteristics were acquired in
each generation.
e. Both believed that giraffes acquired their long necks
by stretching to reach leaves high in trees.
5. Which of the following are homologous structures?
a. the wings of a sparrow and the wings of an owl
b. the wings of a sparrow and the wings of a dragonfly
c. the legs of an ant and the legs of a horse
d. the jaws of a Venus’s-flytrap and the jaws of a clam
e. the wings of a moth and the wings of a hummingbird
6. Which of the following scientists influenced Darwin’s
views on the nature of population growth?
a. Cuvier
b. Malthus
c. Lyell
d. Wallace
e. Buffon
7. Which of the following scientists influenced Darwin’s
views on slow, subtle changes in populations?
a. Cuvier
b. Malthus
c. Lyell
d. Wallace
e. Buffon
8. In support of evolution, Archaeopteryx is known to be
a transitional form between
a. birds and mammals
b. mammals and reptiles
c. fish and amphibians
d. dinosaurs and birds
e. amphibians and reptiles
Answer the questions below.
9. After The Origin of Species was published, many
scientists accepted the concept of evolution but not
the mechanism of natural selection. Explain why.
10. Why do homologous structures demonstrate evidence
of evolution?
11. Summarize the observations that Darwin made
while on the voyage of the Beagle, which he later
incorporated into his theory of evolution by natural
selection.
12. Some caves contain fish that are blind. These fish have
eye sockets and vestigial eyes. How would Lamarck
account for the origin of sightlessness in these fish
and other blind cave-dwellers? How would Darwin
account for it?
This southern cave fish (Typhlichthys subterraneus) is blind
but still has vestigial eye sockets.
Chapter 8 Developing a Theory of Evolution • MHR
343
Chapter 8
REVIEW
13. How does the study of embryology support evolution?
14. Insects reproduce fast enough that they could quickly
populate and overrun Earth.
a. Explain why this does not occur.
b. How was this significant to Darwin?
15. Explain how scientists can use DNA to determine the
evolutionary relationships between two organisms.
16. What is the significance of a vestigial structure as
evidence of evolution?
Thinking and Investigation
17. Examine the fossils found in the sedimentary rocks
shown in the diagram below. Explain what these
rock strata and the fossils in them can tell you about
evolution.
These sedimentary rock layers contain
various fossils.
18. Lamarck proposed an incorrect inheritance
mechanism for how evolution can occur, but his ideas
were instrumental for Darwin’s future work. Which
aspect of Lamarck’s work did Darwin build upon?
19. Red Island and Blue Island are hypothetical islands
500 km off the coast of South America. Red Island is
volcanic in origin and is only 5 million years old. Blue
Island separated from South America more than 80
million years ago. Predict the origins of the animals on
both islands, and explain how they may be similar to
or different from the animals of South America.
22. Malthus pointed out that all populations eventually
face limits to their population because of limited
resources. Compare a micro-organism (such as the
bacterium Staphylococcus aureus), a plant species (such
as a tree), and a mammal (such as a deer) with respect
to the types of factors that might limit the growth of
their populations.
23. Darwin applied Malthus’s ideas to various organisms.
For example, Darwin calculated that a single pair
of elephants could have 19 million descendants in
750 years. He knew that population explosions of this
kind do not happen, and he began to think about the
mechanism that must be controlling the populations
of all species on Earth. The largest possible number
of offspring produced by one individual is called the
biotic potential of a species.
a. Calculate the maximum biotic potential of a
pumpkin. Assume that there are 70 seeds in one
pumpkin. These 70 seeds are planted, and each
seed grows into plants that produce two pumpkins.
Calculate the number of seeds produced by this
generation.
b. If you plant all the seeds from part (a), how many
seeds are available at the end of the next generation?
c. Why is the maximum biotic potential impossible to
reach in nature?
24. If the science of genetics had been established in
Darwin’s time, would it have been easier or more
difficult for him to reach his conclusions about
evolution? Explain your answer.
25. Adult chickens and other birds have four digits in their
feet. A research study in the field of embryology reveals
that during early development of the chicken, there is
a fifth digit that later disappears.
As embryos, chickens
have five digits, but they
only grow four digits.
20. Many organisms found in tidal pools along the west
coast of Vancouver Island look almost identical to
organisms found in tidal pools along the east coast of
New Brunswick. Would you expect these species to be
closely related? Explain your answer.
21. Suppose you find two identical fossils in two adjacent
sedimentary strata. What can you conclude?
344 MHR • Unit 3 Evolution
a. How do you interpret this scientific finding?
b. How does this finding provide evidence for evolution?
Communication
26.
27.
Evolution is the process of biological
change over time based on the relationships
between species and their environments. Does
evolution mean that organisms are becoming
progressively better with each generation? Explain
your answer in one or two paragraphs.
The theory of evolution is a scientific
explanation based on a large accumulation
of evidence. Use a graphic organizer to summarize the
different kinds of evidence for evolution. Go to Using
Graphic Organizers in Appendix A to learn more
about which graphic organizer to choose.
28. Use a Venn diagram to show the differences between
homologous and analogous structures.
29. Explain the theory of evolution by natural selection
in a presentation format of your choice, such as a
poster, a computer slide presentation, or a wiki page.
30. Two populations of flowers of the same species are
found in nearby meadows. There are slight differences
in the plants between the two populations, such as
flower colour and leaf shape. In a diagram, express how
Darwin might have interpreted these observations.
31. Compare and contrast Darwin’s and Lamarck’s views
on the importance of variation and how variation is
inherited. Write your answer as a brief dialogue between
the two men if they were to meet and have a debate.
32. You have your own web page that explains the theory
of evolution by natural selection. List the points you
would include on the site, as well as links to other sites.
33. Use a graphic organizer to distinguish between fact
and theory. Go to Using Graphic Organizers in
Appendix A to learn more about which graphic
organizer to choose.
37. Birds and dinosaurs are very different organisms.
In the past, scientists who proposed that birds were
descended from ancestors of dinosaurs were ridiculed.
What evidence is there to support the idea that birds
and dinosaurs have a common ancestor?
38. Richard Dawkins, a world-renowned evolutionary
biologist, refers to natural selection as the “blind
watchmaker,” meaning that natural selection is totally
blind to the future. Explain what Dawkins means by
this statement.
39. Dolphins and sharks share many similarities and
differences. Use Internet or print resources to research
dolphins and sharks. Create and complete a table like
the one below, and include an image of each animal.
Are the similarities analogous or homologous?
Comparison of Dolphins and Sharks
Question
Dolphin
Shark
How does each animal breathe?
Does the animal nurse its
young?
What is its skeleton made of?
Is the animal a mammal?
Does the animal have a fin on
the top of its body?
Is the body shape streamlined?
Does the animal have teeth?
40. A hoatzin is a tropical bird about the size of a chicken.
It lives in swampy areas near the Amazon River in
South America. Hoatzin chicks have claws on their
wings. The chicks use the claws to cling to branches, to
keep them from falling.
34. Explain to a younger sibling what the following
statement means: The fossil record gives us a
“snapshot” of ancestral forms.
35. Summarize your learning in this chapter using a graphic
organizer. To help you, the Chapter 8 Summary lists
the Key Terms and Key Concepts. Refer to Using
Graphic Organizers in Appendix A to help you decide
which graphic organizer to use.
Application
36. Your friend shows you a snake skeleton and points out
tiny bones that would make up the pelvis in an animal
with legs. Your friend tells you this was a mutant snake.
Do you agree or disagree? Explain your answer.
As the hoatzin chick matures, its claws disappear.
a. What other (extinct) bird has claws on its wings?
b. What might you conclude about bird ancestors?
41. You discover the remains of an extinct animal that has
a small amount of brain tissue preserved in its skull.
Outline the scientific techniques you might use to learn
more about the evolutionary history of this animal.
Chapter 8 Developing a Theory of Evolution • MHR 345
Chapter 8
SELF-ASSESSMENT
Select the letter of the best answer below.
1.
K/U Why was Lamarck’s work important to Darwin’s
development of his theory of evolution by natural
selection?
a. He supported a fixed, static view of life.
b. He established the principle of uniformitarianism.
c. He emphasized organisms adapting to their
environment.
d. He wrote about unchecked human population
growth.
e. He suggested a longer time period on Earth for
evolution to occur.
2.
K/U How did Lyell’s work contribute to evolutionary
thought?
a. He devised a classification system that is still used
today.
b. He suggested that constant geological processes
have shaped Earth over a long period of time.
c. He proposed that species are related by descent
from a common ancestor.
d. He proposed the theory of acquired characteristics
and the idea of “use and disuse.”
e. He viewed nature as fixed along a progressive scale.
3.
What is evolution?
a. Organisms adapt to their environment.
b. Species go extinct and thus are no longer on Earth.
c. Populations vary in their traits.
d. Organisms produce more offspring than can survive.
e. Genetic changes in characteristics of species over
time.
4.
K/U How does the idea of catastrophism relate
directly to observations in the fossil record?
a. Species suddenly disappear, while new species
appear, in the fossil record.
b. There are transitional species that link different
groups of organisms.
c. Older species are found in lower strata of the fossil
record.
d. Recently evolved species are found in the most
recent layers of the fossil record.
e. Fossils are very similar throughout the fossil record.
5.
6.
K/U What was the widely accepted view about life on
Earth prior to Darwin’s publication of The Origin of
Species in 1859?
a. Earth is 6000 years old, and the natural world does
not change.
b. Earth is 6000 years old, and populations change
over time.
c. Earth is millions of years old, and populations
rapidly change.
d. Earth is billions of years old, and populations are
unchanging.
e. Earth is millions of years old, and the natural world
gradually changes.
7.
K/U Which of the following is an intermediate fossil
illustrating the evolution of whales?
a. Pakicetus
b. Archaeopteryx
c. Atrociraptor
d. Gondwana
e. Pikaia
8.
K/U Which of these conditions favours the evolution
of traits in a population according to Darwin’s theory
of natural selection?
a. Some of the variation between individuals is
heritable.
b. Organisms produce only a few offspring in each
generation.
c. Resources are unlimited in the population, and
there is no competition for those resources.
d. The population lives in a habitat where there is
no competition for resources.
e. Individuals acquire traits from the environment and
pass on those acquired traits to offspring.
9.
K/U Which is an idea that Darwin used from the
work of Malthus?
a. Populations do not change and life is static.
b. Populations produce far more offspring than can
survive.
c. Earth has changed through a series of catastrophic
revolutions.
d. The fittest individuals survive due to favourable
adaptations.
e. Earth is more than 6000 years old, and life forms
are unchanging.
K/U
K/U Which scientist developed a theory of evolution
by natural selection at the same time as Darwin?
a. Malthus
d. Cuvier
b. Lyell
e. Wallace
c. Buffon
346 MHR • Unit 3 Evolution
10.
K/U Which is a plausible question that came from
Darwin’s observations during the voyage of the Beagle?
a. Are organisms becoming perfect over time?
b. Why do living species and fossilized organisms
look so different within the same country in South
America?
c. Why is there so much species diversity on small,
isolated islands?
d. Could all species have been created at the same
time?
e. Why did the Galapagos finch species look just like
the European finches?
15.
K/U What was important about the discovery of the
transitional fossil Archaeopteryx?
16.
T/I Explain Lamarck’s idea of the inheritance of
acquired traits. Explain why the idea is not a theory
and why it is incorrect.
17.
K/U How can embryo development reveal clues
about evolutionary history?
18.
T/I You are doing research on birds and you
discover that certain birds possess reptile-like scales on
the lower parts of their legs and feet. Another research
lab you are working with reports that these “scales” are
chemically identical to feathers.
a. How do you interpret this finding?
b. Assuming reptiles are older than birds in the fossil
record, what does this tell you about the origin of
feathers?
19.
Would Darwin support the statement “No
species is really more primitive or advanced than any
other”? Explain your answer.
20.
A
When entering Canada from abroad, you are
asked if you are bringing in any live specimens. Why
do countries try to avoid non-indegenous species being
brought in?
21.
T/I Infer how a functionless gene could be
considered a vestigial trait.
22.
C
Use a graphic organizer such as a Venn diagram
to compare and contrast homologous structures,
analogous structures, and vestigial structures. Go to
Using Graphic Organizers in Appendix A to learn
more about Venn diagrams.
23.
C
Use a graphic organizer to summarize the
similarities and differences between catastrophism and
uniformitarianism. Go to Using Graphic Organizers in
Appendix A to learn more about which graphic
organizer to choose.
24.
K/U What important contribution did Charles Lyell
make to science?
25.
K/U Define biogeography in your own words. In your
definition, include an example.
12
13
Use sentences and diagrams as appropriate to answer the
questions below.
11.
K/U What is a homologous structure? Include an
example in your answer.
12.
Use the diagram below to answer the following
questions.
T/I
Surface
A
B
C
D
a. Which layer of rock contains the youngest fossils?
b. Which layer of rock contains fossils most similar to
species alive today?
c. In which layer are the oldest fossils found?
13.
Design a brochure to explain to Grade 5
students two sources of evidence for evolution. Be sure
to use visuals in your brochure.
14.
K/U If you teach children to look both ways before
they cross the street, this action will help them survive.
a. How would Lamarck intrepret this behaviour?
b. Do you agree with this interpretation? Explain your
answer.
C
K/U
Self-Check
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Chapter 8 Developing a Theory of Evolution • MHR 347