Download Darwin`s Theory

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Section Summary
Darwin’s Theory
Key Concepts
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What important observations did Darwin make on his voyage?
What hypothesis did Darwin make to explain the differences
between similar species?
How does natural selection lead to evolution?
In 1831, Charles Darwin left England on board the HMS Beagle. Darwin’s
important observations included the diversity of living things, the
remains of ancient organisms, and the characteristics of organisms on the
Galápagos Islands. Darwin saw many different species. A species is a group
of similar organisms that can mate with each other and produce fertile
offspring. Darwin saw the fossil bones of animals that had died long ago. A
fossil is the preserved remains or traces of an organism that lived in the past.
In 1835, the Beagle reached the Galápagos Islands in the Pacific Ocean.
Darwin was surprised that many of the plants and animals on the Galápagos
Islands were similar to organisms on mainland South America. However,
there were also important differences. Darwin inferred that a small number of
different species had come to the islands from the mainland. Eventually, their
offspring became different from the mainland relatives. The finches on the
Galápagos Islands were noticeably different from one island to another. The
most obvious differences were the varied sizes and shapes of the birds’ beaks.
Beak shape is an example of an adaptation, a trait that helps an organism
survive and reproduce. Darwin reasoned that plants or animals that arrived
on the Galápagos Islands faced conditions that were different from those on
the mainland. Perhaps, Darwin hypothesized, the species gradually
changed over many generations and became better adapted to the new
conditions. The gradual change in a species over time is called evolution.
Darwin’s ideas are often referred to as the theory of evolution. A scientific
theory is a well-tested concept that explains a wide range of observations.
In his book The Origin of Species, Darwin proposed that evolution occurs by
means of natural selection. Natural selection is the process by which
individuals that are better adapted to their environment are more likely to
survive and reproduce than other members of the same species. A number of
factors affect the process of natural selection: overproduction, competition,
and variations. Any difference between individuals of the same species is
called a variation. Some variations make certain individuals better adapted to
their environment because of helpful traits they possess. Darwin proposed
that, over a long period of time, natural selection can lead to change.
Helpful variations may gradually accumulate in a species, while
unfavorable ones may disappear. Without variations, all members of a
species would have the same traits. Only traits that are inherited, or controlled
by genes, can be acted upon by natural selection.
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Guided Reading and Study
Darwin’s Theory
This section discusses Charles Darwin and his theories of evolution, which are based
on what he saw during his trip around the world.
Use Target Reading Skills
In the graphic organizer, identify factors that cause natural selection.
Causes
Overproduction: More offspring
than can survive
Effect
Darwin’s Observations
1.
Is the following sentence true or false? Charles Darwin was not surprised by the variety of living things he saw on his voyage around the
world. ________________________
2.
A group of similar organisms that can mate with each other and produce
fertile offspring is called a(n) ________________________.
3.
A(n) ________________________ is the preserved remains or traces of an
organism that lived in the past.
4.
Is the following sentence true or false? Darwin observed the greatest
diversity of organisms on the Galápagos Islands.
________________________
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Natural Selection
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Darwin’s Theory
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Guided Reading and Study
(continued)
Galápagos Organisms
5.
Circle the letter of each sentence that is true about Darwin’s
observations.
a. Many Galápagos organisms were similar to organisms on mainland South
America.
b. Iguanas on the Galápagos Islands had small claws for climbing trees.
c. Darwin thought the ancestors of Galápagos animals and plants came from mainland South America.
d. All tortoises living in the Galápagos Islands looked exactly the same.
6.
Darwin noticed many differences among similar
________________________ as he traveled from one Galápagos island to
the next.
Look at the bird beaks below. Match the bird beaks with the kind of food the
bird eats.
Kind of Food
Bird Beaks
____ 7. insects
____ 8. seeds
9.
a.
b.
A trait that helps an organism survive and reproduce is a(n)
________________________.
Evolution
10. Circle the letter of each sentence that is true about Darwin’s conclusions.
a. Darwin understood immediately why Galápagos organisms had many different
adaptations.
b. Darwin thought that Galápagos organisms gradually changed over many
generations.
c. Darwin believed that evolution had occurred on the Galápagos Islands.
d. Selective breeding helped Darwin understand how evolution might occur.
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Guided Reading and Study
11. Circle the letter of the term that means a well-tested concept that
explains many observations.
a. idea
b. evolution
c. scientific theory
d. hypothesis
Natural Selection
12. In his book The Origin of Species, Darwin explained that evolution occurs
by means of ________________________.
Definitions
____ 14. Effect caused by limited food
and other resources.
____ 15. Differences between
individuals of the same
species
Factors
a. overproduction
b. competition
c. variations
____ 16. Effect caused by species
producing more offspring
than can survive.
17. Is the following sentence true or false? Only traits that are controlled by
genes can be acted upon by natural selection.
________________________
18. Is the following sentence true or false? Darwin knew all about genes and
mutations. ________________________
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13. Is the following sentence true or false? Individuals with variations that
make them better adapted to their environment will not survive.
________________________
Match the factors that affect the process of natural selection with their
definitions.
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Review and Reinforce
Darwin’s Theory
Understanding Main Ideas
Answer the following questions on a separate sheet of paper.
Who was Charles Darwin, and what did he do on the Beagle’s voyage?
What is evolution?
Explain how the shape of a finch’s beak is an example of an adaptation.
When members of a species compete, what do they compete for?
What happens when species overproduce offspring?
Suppose a variation makes an individual member of a species better
adapted to its environment. How might that variation affect the
individual’s reproduction?
7. How does the environment “select” organisms?
8. How do helpful variations accumulate in a species over time?
9. Why can only traits controlled by genes be acted upon by natural
selection?
1.
2.
3.
4.
5.
6.
Building Vocabulary
Fill in the blank to complete each statement.
10. A(n) ________________________ is a group of similar organisms that can
mate with each other and produce fertile offspring.
11. A(n) ________________________ is a trait that helps an organism survive
and reproduce.
12. A scientific ________________________ is a well-tested concept that
explains a wide range of observations.
13. The process by which individuals that are better adapted to their
environment are more likely to survive and reproduce is called
________________________.
14. That some newly hatched turtles can swim faster than others of the same
species is evidence of ________________________ within the species.
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Enrich
Two Theories of Evolution
If you had been a biologist in the 1800s, you would have had to decide
between two main theories about how evolution occurred. Consider the
long neck of a giraffe. How did that evolve? Read the two explanations
below, and then answer the questions that follow.
Theory 2
The ancestors of giraffes had short necks, and there was great competition
for the plant food near the ground. Some of the ancestral giraffes naturally
had slightly longer necks than others. The individuals with longer necks
could reach leaves higher up in trees, and therefore could eat more food.
Because those ancestral giraffes ate more food, they survived to produce
offspring while the individuals with shorter necks did not. The offspring of
giraffes with longer necks inherited the longer necks. This process continued
for generation after generation. In this way, giraffes evolved with longer and
longer necks.
Answer the following questions on a separate sheet of paper.
1. In Theory 1, what caused the giraffe neck to become longer?
2. In Theory 2, what caused the giraffe neck to become longer?
3. According to what scientists now know about genes, could the giraffes’
offspring have inherited longer necks as described in Theory 1? As
described in Theory 2? Explain.
4. Which of the two theories matches Darwin’s theory of evolution?
Explain.
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Theory 1
The ancestors of giraffes had short necks, and there was great competition
for the plant food near the ground. Some of the giraffes kept trying to stretch
their necks to reach leaves higher in the trees. As they stretched and
stretched, their necks became longer. As their necks became longer, they
were able to reach more food. Those ancestral giraffes survived to
reproduce, while the giraffes that had not stretched their necks died. The
offspring of giraffes with stretched necks inherited the longer necks. This
process continued for generation after generation. In this way, giraffes
evolved with longer and longer necks.
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Skills Lab
Nature at Work
Problem
How do species change over time?
Skills Focus
predicting, making models
Materials
scissors
marking pen
construction paper, 2 colors
Procedure
1. Work on this lab with two other students. One student should choose
construction paper of one color and make the team’s 50 “mouse” cards,
as described in Table 1. The second student should choose a different
color construction paper and make the team’s 25 “event” cards, as
described in Table 2. The third student should record all the data.
PART 1 A White Sand Environment
2. Mix up the mouse cards.
3. Begin by using the cards to model what might happen to a group of mice
in an environment of white sand dunes. Choose two mouse cards. Allele
pairs WW and Ww produce a white mouse. Allele pair ww produces a
brown mouse. Record the color of the mouse with a tally mark in the data
table on the next page.
4. Choose an event card. An “S” card means the mouse survives. A “D” or a
“P” card means the mouse dies. A “C” card means the mouse dies if its
color contrasts with the white sand dunes. (Only brown mice will die when
a “C” card is drawn.) Record each death with a tally mark in the data table.
5. If the mouse lives, put the two mouse cards in a “live mice” pile. If the
mouse dies, put the cards in a “dead mice” pile. Put the event card at the
bottom of its pack.
6. Repeat Steps 3 through 5 with the remaining mouse cards to study the
first generation of mice. Record your results.
7. Leave the dead mice cards untouched. Mix up the cards from the live
mice pile. Mix up the events cards.
8. Repeat Steps 3 through 7 for the second generation. Then repeat Steps 3
through 6 for the third generation.
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Skills Lab
Mouse Cards
Number
Label
Meaning
25
W
Dominant allele for white fur
25
w
Recessive allele for brown fur
Event Cards
Label
Meaning
5
S
Mouse survives.
1
D
Disease kills mouse.
1
P
Predator kills mice of all colors.
18
C
Predator kills mice that contrast with the environment.
Data Table—Part 1
Type of Environment:
Population
Generation
White Mice
Brown Mice
Deaths
White Mice
Brown Mice
1
2
3
Data Table—Part 2
Type of Environment:
Population
Generation
White Mice
Brown Mice
Deaths
White Mice
Brown Mice
1
2
3
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Number
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Nature at Work
Skills Lab
(continued)
PART 2 A Forest Floor Environment
9. How would the data differ if the mice in this model lived on a dark
brown forest floor? Record your prediction in the space provided.
________________________________________________________________________
________________________________________________________________________
10. Use the cards to test your prediction. Remember that a “C” card now
means that any mouse with white fur will die.
Analyze and Conclude
Write your answers on a separate sheet of paper.
1. Calculating In Part 1, how many white mice were there in each
generation? How many brown mice? In each generation, which color
mouse had the higher death rate? (Hint: To calculate the death rate for
white mice, divide the number of white mice that died by the total
number of white mice, then multiply by 100%.)
2. Predicting If the events in Part 1 occurred in nature, how would the
group of mice change over time?
3. Observing How did the results in Part 2 differ from those in Part 1?
4. Making Models How would it affect your model if you increased the
number of “C” cards? What would happen if you decreased the number
of “C” cards?
5. Communicating Imagine that you are trying to explain the point of this
lab to Charles Darwin. Write an explanation that you could give to him.
To prepare to write, answer the following questions: What are some ways
in which this investigation models natural selection? What are some
ways in which natural selection differs from this model?
Design an Experiment
Choose a different species with a trait that interests you. Make a set of cards
similar to these cards to investigate how natural selection might bring about
the evolution of that species. Obtain your teacher’s permission before carrying
out your investigation.
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Section Summary
Evidence of Evolution
Key Concepts
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What evidence supports the theory of evolution?
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How do scientists infer evolutionary relationships among organisms?
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How do new species form?
Modern-day organisms can provide clues about evolution. Fossils,
patterns of early development, and similar body structures all provide
evidence that organisms have changed over time. By comparing organisms,
scientists can infer how closely related the organisms are in an evolutionary
sense. Scientists compare body structures, development before birth, and
DNA sequences to determine the evolutionary relationships among
organisms.
Scientists make inferences about evolutionary relationships by
comparing the early development of organisms. An adult opossum, chicken,
salamander, and fish look quite different; however, during early
development these four organisms are similar. These similarities suggest
that these vertebrate species are related and share a common ancestor.
An organism’s body structure is its basic body plan, such as how its
bones are arranged. Fishes, amphibians, reptiles, birds, and mammals, for
example, all have a similar body structure—an internal skeleton with a
backbone. This is why scientists classify all five groups of animals together
as vertebrates. Presumably, these groups all inherited these similarities in
structure from an early vertebrate ancestor that they shared. Similar
structures that related species have inherited from a common ancestor are
called homologous structures. Sometimes scientists find fossil evidence that
supports the evidence provided by homologous structures.
Scientists infer that species with similar body structures and
development patterns inherited many of the same genes from a common
ancestor. Recall that genes are made of DNA. By comparing the sequences in
the DNA of different species, scientists can infer how closely related the
species are. The more similar the sequences, the more closely related the
species are. Recall also that the DNA bases along a gene specify what type of
protein will be produced. Therefore, scientists can also compare the order of
amino acids in a protein to see how closely related two species are.
Scientists have combined the evidence from DNA, protein structure,
fossils, early development, and body structure to determine the evolutionary
relationships among species. In most cases, DNA and protein sequences have
confirmed conclusions based on earlier evidence. Scientists use such combined
evidence to construct branching trees. A branching tree is a diagram that shows
how scientists think different groups of organisms are related.
Isolation, or complete separation, occurs when some members of a
species become cut off from the rest of the species. A new species can form
when a group of individuals remains separated from the rest of its species
long enough to evolve different traits.
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Guided Reading and Study
Evidence of Evolution
This section tells how scientists decide which living things are related.
Use Target Reading Skills
As you read, identify the evidence that supports the theory of evolution. Write the
evidence in the graphic organizer.
Evidence
Fossils
Evolution
Interpreting the Evidence
1.
Similar body structures that related species have inherited from a
common ancestor are called ________________________.
2.
What similarities in development lead scientists to infer that opossums,
chickens, salamanders, and fish share a common ancestor?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
3.
Why do scientists classify fish, amphibians, reptiles, birds, and
mammals together in one group?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Theory
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Guided Reading and Study
Evidence of Evolution
(continued)
Inferring Species Relationships
4.
Is the following sentence true or false? The more closely related species
are, the more similar their DNA sequences. ________________________
5.
What have scientists learned about the elephant shrew based on DNA
evidence?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
6.
Circle the letter of each sentence that is true about evolutionary
relationships of organisms.
a. DNA comparisons show that dogs are more similar to coyotes than
to wolves.
b. Scientists can compare protein structure to determine how closely
two species are related.
c. A branching tree shows how scientists think different groups of
organisms are related.
d. DNA evidence shows that giant pandas are more closely related to
raccoons than to bears.
7.
Is the following sentence true or false? When a group of individuals
remains isolated from the rest of its species long enough to evolve
different traits, a new species can form. __________________________
8.
What are three ways that isolation can occur?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Review and Reinforce
Evidence of Evolution
Understanding Main Ideas
Use the figures below to answer the questions that follow. Write your answers on a
separate sheet of paper.
Seal
1. Compare and contrast the bones of a bird’s wing and a seal’s flipper.
2. What do scientists infer from the similarities between these two
structures?
3. What do scientists call such similar structures?
4. Describe how DNA evidence might be used to confirm scientists’
conclusions about any relationship between birds and seals.
Answer the following questions on a separate sheet of paper.
5. What types of evidence do scientists use to determine evolutionary
relationships among groups?
6. What do similarities in the early development of organisms suggest?
Building Vocabulary
Fill in the blank to complete each statement.
7. Similar structures that related species have inherited from a common
ancestor are called ________________________ structures.
8. A(n) ________________________ is a diagram that shows how scientists
think different groups of organisms are related.
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Bird
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Enrich
Species Relationships
Mammals
Birds
Amphibians
Bony fishes
Reptiles
Sharks and
their relatives
Jawless
fishes
Use the figure above to answer the following questions. Write your answers on a
separate sheet of paper.
1. What is this type of diagram called, and what is the purpose of such a
diagram?
2. What types of evidence did scientists use to make this diagram?
3. Did amphibians evolve from reptiles? Give evidence for your answer.
4. Are birds more closely related to mammals or to reptiles? Explain your
answer.
5. What could cause scientists to change the information on this diagram in
the future?
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Skills Lab
Telltale Molecules
Problem
What information can protein structure reveal about evolutionary
relationships among organisms?
Skills Focus
interpreting data, drawing conclusions
________________________________________________________________________
3. Compare the amino acid sequence of the horse to that of the donkey. How
many amino acids differ between the two species? Record that number in
your notebook.
4. Compare the amino acid sequences of each of the other animals to that of
the horse. Record the number of differences in your notebook.
Section of Cytochrome c Protein in Animals
Animal
Amino Acid Position
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
Horse
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
Donkey
A
B
C
D
E
F
G
H
Z
J
K
L
M
N
O
Rabbit
A
B
C
D
E
Y
G
H
Z
J
K
L
M
N
O
Snake
A
B
C
D
E
Y
G
H
Z
J
K
W
M
N
O
Turtle
A
B
C
D
E
V
G
H
Z
J
K
U
M
N
O
Whale
A
B
C
D
E
Y
G
H
Z
J
K
L
M
N
O
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Changes Over Time
Procedure
1. Examine the table below. It shows the sequence of amino acids in one
region of a protein, cytochrome c, for six different animals.
2. Predict which of the five other animals is most closely related to the horse.
Which animal do you think is most distantly related?
________________________________________________________________________
Name ____________________________ Date ____________________ Class ____________
Changes Over Time
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Skills Lab
Telltale Molecules
(continued)
Analyze and Conclude
Write your answers in the spaces provided.
1. Interpreting Data Which animal’s amino acid sequence was most
similar to that of the horse? What similarities and difference(s) did
you observe?
________________________________________________________________________
________________________________________________________________________
2. Drawing Conclusions Based on these data, which species is most closely
related to the horse? Which is most distantly related?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
3. Interpreting Data For the entire protein, the horse’s amino acid sequence
differs from the other animals’ as follows: donkey, 1 difference; rabbit, 6;
snake, 22; turtle, 11; and whale, 5. How do the relationships indicated by
the entire protein compare with those for the region you examined?
________________________________________________________________________
________________________________________________________________________
4. Communicating Write a paragraph explaining why data about amino
acid sequences can provide information about evolutionary relationships
among organisms.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
More to Explore
Use the amino acid data to construct a branching tree that includes horses,
donkeys, and snakes. The tree should show one way that the three species
could have evolved from a common ancestor.
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Section Summary
The Fossil Record
Key Concepts
■
How do most fossils form?
■
How can scientists determine a fossil’s age?
■
What is the Geologic Time Scale?
■
What are some unanswered questions about evolution?
Most fossils form when organisms that die become buried in sediments.
Sediments are particles of soil and rock. Layers of sediments cover the dead
organism. Over millions of years, the layers harden to become sedimentary
rock. Some remains that become buried in sediments are actually changed to
rock. These fossils are called petrified fossils. Sometimes shells or other hard
parts buried by sediments are gradually dissolved. A hollow space in
sediment in the shape of an organism or part of an organism is called a mold.
Sometimes a mold becomes filled in with hardened minerals, forming a cast.
Organisms can also be preserved in ice.
Scientists can determine a fossil’s age in two ways: relative dating and
radioactive dating. Scientists use relative dating to determine which of two
fossils is older. In a sequence of rock layers, the top layers are usually younger
than the lower layers. Therefore, fossils found in top layers are younger than
fossils found in bottom layers. Another technique, called radioactive dating,
allows scientists to determine the actual age of fossils. Rocks near fossils
contain radioactive elements, unstable elements that decay, or break down,
into different elements. The half-life of a radioactive element is the time it
takes for half of the atoms in a sample to decay. Scientists can compare the
amount of a radioactive element in a sample to the amount of the element into
which it breaks down to calculate the age of the rock.
The millions of fossils that scientists have collected are called the fossil
record. Despite gaps in the fossil record, it has given scientists a lot of important
information about past life on Earth. Almost all of the species preserved as
fossils are now extinct. A species is extinct if no members of that species are still
alive. Scientists have calculated the ages of many different fossils and rocks.
From this information, they have created a “calendar” of Earth’s history that
spans more than 4.6 billion years. This calendar of Earth’s history is sometimes
called the Geologic Time Scale.
Two unanswered questions about evolution involve the causes of mass
extinctions and the rate at which evolution occurs. A mass extinction occurs
when many species become extinct at the same time. Scientists are not sure
what causes mass extinctions. There are two theories about the rate of
evolution. According to one theory, called gradualism, evolution occurs
slowly but steadily. Tiny changes in a species gradually add up to major
changes over very long periods of time. According to another theory, called
punctuated equilibria, species evolve during short periods of rapid change.
Species evolve quickly when groups become isolated and adapt to new
environments. Most scientists think that evolution can occur gradually at
some times and fairly rapidly at others.
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Changes Over Time
■
Guided Reading and Study
The Fossil Record
This section explains what fossils are and how fossils give clues about evolution. It
also describes the Geologic Time Scale, a calendar of Earth's history.
Use Target Reading Skills
After you read the section, reread the paragraphs that contain definitions of key
terms. Use all the information you have learned to write a definition of each key term
in your own words.
How Do Fossils Form?
Circle the letter of each item that can form a fossil.
a. bone
b. shell
c. stone
2.
Is the following sentence true or false? Most fossils form when
organisms that die become buried in sediments.
________________________
3.
Particles of soil and rock are called ________________________.
4.
Remains of organisms that are actually changed to rock are called
________________________ fossils.
5.
Circle the letter of each sentence that is true about molds and casts.
a. A mold forms when hard parts of an organism buried by sediments are
gradually dissolved.
b. A cast is a hollow space in sediment in the shape of an organism.
c. A mold that becomes filled in with hardened materials forms a cast.
d. A cast is a copy of the shape of an organism.
6.
Is the following sentence true or false? The formation of any fossil is a
common event. ________________________
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Changes Over Time
1.
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Changes Over Time
■
The Fossil Record
Guided Reading and Study
(continued)
Determining a Fossil’s Age
7.
Is the following sentence true or false? By determining the age of fossils,
scientists can reconstruct the history of life on Earth.
________________________
8.
In what two ways can scientists determine the ages of fossils?
a.________________________ b.________________________
9.
In layers of sedimentary rock, the ________________________ layer is
usually at the bottom. Each higher layer is ________________________
than the layers below it.
10. Is the following sentence true or false? Relative dating can only help
scientists determine whether one fossil is older than another.
________________________
11. Scientists use unstable elements that decay, called
________________________ elements, to determine the actual age
of a fossil.
12. What is the half-life of a radioactive element?
________________________________________________________________________
________________________________________________________________________
13. Potassium-40 breaks down into ________________________ over time.
14. How do scientists use radioactive dating to determine the age of a fossil?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
What Do Fossils Reveal?
15. The millions of fossils that scientists have collected are called the
________________________.
16. Is the following sentence true or false? The remains of all organisms
have become fossils. ________________________
17. How have scientists learned about extinct species?
________________________________________________________________________
________________________________________________________________________
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Changes Over Time
■
Guided Reading and Study
18. Circle the letter of the largest span of time in the Geologic Time Scale.
a. Precambrian Time
b. eras
c. periods
d. years
19. Look at the illustration of the Geologic Time Scale in your text. What are
the names of the three eras?
________________________________________________________________________
________________________________________________________________________
Unanswered Questions
20. What are mass extinctions?
________________________________________________________________________
21. Complete the table below about the two theories of evolution.
How Fast Does Evolution Occur?
Theory of Evolution
What the
Theory Says
Intermediate
Forms of Species?
Gradualism
Punctuated Equilibria
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Changes Over Time
________________________________________________________________________
Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Review and Reinforce
The Fossil Record
Understanding Main Ideas
Use the figure below to answer questions 1 and 2. Write your answers on a separate
sheet of paper.
Cenozoic Era
Precambrian
Time
Paleozoic Mesozoic
Era
Era
1. What is shown in the figure above?
2. What evidence do scientists use to place events on this timeline?
Answer the following questions on a separate sheet of paper.
3. Describe the process by which most fossils form.
4. Which is probably older, a fossil in a sedimentary rock layer at the bottom
of a canyon or a fossil in a sedimentary rock layer at the top of a canyon?
Explain.
5. How do scientists use radioactive elements to determine the actual age of
fossils?
6. What is the fossil record, and why is it incomplete?
Building Vocabulary
Match each term with its definition by writing the letter of the correct definition on
the line beside the term.
____ 7. relative dating
a. a species that has no living members
____ 8. half-life
b. the preserved remains or traces of an
organism that lived in the past
____ 9. gradualism
____ 10. radioactive dating
____ 11. extinct
c. the theory that species evolve during
short periods of rapid change
____ 12. sedimentary rock
d. a way to determine the actual age of
fossils
____ 13. fossil
e. rock made of hardened sediment
____ 14. punctuated equilibria
f. the time it takes for half of a radioactive
sample to decay
g. the theory that evolution occurs slowly
but steadily
h. a way to determine which of two fossils
is older
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Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Enrich
Evolution of Horses
Fossil evidence indecates that Hyracotherium is a small animal that lived over
50 million years ago. It is the ancestor of the modern horse, Equus, and many
other horselike species that are now extinct. Fossils of these species show
differences in body structures. Refer to the table below to answer the
following questions.
50 million
years ago
35 million
years ago
26 million
years ago
3 million
years ago
Hyracotherium
Mesohippus
Merychippus
Equus
Skull
Skull
Changes Over Time
Forefoot
Skull
Forefoot
Skull
Forefoot
Forefoot
• 38 cm at shoulders
• padded feet
• lived in dense-forest
environment
• 52 cm at shoulders
• padded feet
• lived in mixed
woods-and-fields
environment
• 100 cm at shoulders
• hoofed feet
• lived in high-grass
(savanna) environment
• 135 cm at shoulders
• hoofed feet
• lived in short-grass
(prairie) environment
Use the table above to answer the following questions. Write your answers on a
separate sheet of paper.
1. Use the figure, The Geologic Time Scale, in your textbook to determine the
era and period in which Hyracotherium lived.
2. When did Equus first appear in the fossil record?
3. How do the forefeet structures differ among the fossils?
4. How do the skulls differ among the fossils?
5. How might the environment in which each of these species lived have
affected the evolutionary history of the horse?
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Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Key Terms
Key Terms
Answer the clues to solve this crossword puzzle.
1
2
3
4
6
5
7
8
9
10
11
Clues down
Clues across
1. The gradual change in a species over
time
4. A trait that helps an organism
survive and reproduce
6. The process by which individuals
that are better adapted to their
environment are more likely to
survive is called natural
________________________.
8. A fossil formed when an organism
buried in sediment dissolves,
leaving a hollow area
2. Any difference between individuals of
the same species
3. The theory that evolution occurs slowly
but steadily
5. Similar structures that related species
inherited from a common ancestor are
________________________ structures.
7. The theory that evolution occurs during
short periods of rapid change is
punctuated _______________________.
9. The preserved remains of an organism
10. A group of similar organisms that can
mate and produce fertile offspring
11. No members of a species are still alive
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Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Connecting Concepts
Connecting Concepts
which are
longer
which are
shorter
eras
which is
due to
adaptations
casts
petrified
fossils
homologous
structures
which can be
viewed by
comparing
which can be
viewed by
comparing
variation
which selects
individuals with
factors that
affect it include
developed by
scientific theory
is a
overproduction
similarities
in early
development
Evolution
occurs by means of
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Changes Over Time
is supported by
evidence such as
which
include
fossils
which allow
us to
understand
which can be
broken into
Develop a concept map that uses the Key Concepts and Key Terms from this
chapter. Keep in mind the big idea of this chapter. The concept map shown
is one way to organize how the information in this chapter is related. You
may use an extra sheet of paper.
Changes Over Time
Laboratory Investigation
TEACHER NOTES
Variation in a Population
Key Concept
Teaching Tips
Variations occur in all species.
■
Skills Focus
observing, inferring, measuring, graphing
Time
40 minutes
Possible Materials (per group)
■
(More to Explore) Students with severe allergies to peanuts should not participate in this
activity.
(More to Explore) The results for peanuts
should be similar to the variations found in
the lima bean, leaf, and hand studies. Sample
size will influence results. All organisms of
the same species show variations in different
traits. Heredity and environment both affect
how traits vary.
10 large lima beans
10 leaves of the same species
metric ruler
graph paper
3 colored pencils
Alternate Materials: Other large seeds, such as
kidney beans, pumpkin seeds, and pinto beans,
may be used instead of the lima beans. Leaves
can be from a variety of trees or house plants.
Advance Preparation
Have students collect leaves before the
experiment.
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Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Laboratory Investigation
Variation in a Population
Pre–Lab Discussion
Are you and your friends all exactly alike? Of course not. Although you are
all members of one species, you are different in many ways. These
differences are called variations and exist in all species.
Some variations are inherited by the offspring of an organism. Most
inherited variations are neutral, that is, they do not affect the organism’s
survival. Helpful inherited variations are called adaptations. Harmful
inherited variations make the organism less suited to its environment.
Better-adapted organisms are more likely to reproduce and pass beneficial
traits to their offspring. This process is called natural selection.
In this investigation, you will observe variations in two types of plants and
in your class population.
________________________________________________________________________
2. What variations exist among members of your class?
________________________________________________________________________
________________________________________________________________________
Problem
How can you measure the variation in plant and animal populations?
Materials (per group)
10 large lima beans
10 leaves of the same species
metric ruler
graph paper
3 colored pencils
Safety
Review the safety guidelines in Appendix A of your textbook.
Do not eat the lima beans.
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Changes Over Time
1. What does variations mean?
________________________________________________________________________
Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Laboratory Investigation
Variation in a Population (continued)
Procedure
Part A: Variation in Plant Species
1. Obtain 10 large lima beans and 10 leaves of the
same species of tree.
Blade length
2. Measure the length of each lima bean and leaf
blade in millimeters. See Figure 1. Record your
measurements, rounded to the nearest millimeter,
in Data Table 1.
3. Notice in Figure 1 the petiole of the leaf. Measure the
Petiole length
length of the petiole of each leaf. Record your
measurements, rounded to the nearest millimeter,
Figure 1
in Data Table 1.
4. Record on the chalkboard your measurements for
each of the plants so that all groups’ data can be seen.
5. Using data from the entire class, record the range in lengths for the lima
beans, leaf blades, and petioles. Record the class findings in Data Tables
2, 3, and 4. Fill in the first row of each table with the lengths, from shortest
to longest, using increments of one millimeter. Add more columns to the
data tables if necessary.
6. Record the class’s total number of each size of lima bean, leaf blade, and
petiole in the second row of Data Tables 2, 3, and 4.
7. Using the data in Data Table 2, construct a line graph for the lima bean
lengths on a sheet of graph paper. Label the x-axis “Lima bean length
(mm)” and the y-axis “Number of beans.”
8. Using the data in Data Tables 3 and 4, construct line graphs for the leafblade lengths and the petiole lengths on your graph paper. Label the
x-axis “Leaf blade and petiole length (mm)” and the y-axis “Number of
leaves.” Use a different colored pencil to graph each set of data and
include a key for each graph.
Part B: Variation in Hand Spans
1. Measure your hand span. The measurement should
be made from the top of the thumb to the tip of the
little finger, as shown in Figure 2. Round off the
measurement to the nearest centimeter. Record
your hand span in a class chart on the chalkboard.
2. After all your classmates have recorded their hand
spans in the class chart, transfer the results to Data
Table 5. Your results will show the total number of
hands having the same hand span.
3. Construct a line graph of the results on a sheet of
graph paper. Label the x-axis “Hand-span length
(cm)” and the y-axis “Number of students.”
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Hand span
Figure 2
Name ____________________________ Date ____________________ Class ____________
Changes Over Time
Laboratory Investigation
■
Observations
Data Table 1
Length (mm) (Group Data)
1
2
3
4
5
6
7
8
9
10
Lima beans
Leaf blades
Petioles
Data Table 2
Class Data for Lima Bean Lengths
Total number of beans of
this size
Data Table 3
Class Data for Leaf Blade Lengths
Length of leaf blade (mm)
Total number of leaf
blades of this size
Data Table 4
Class Data for Petiole Lengths
Length of petiole (mm)
Total number of petioles
of this size
Data Table 5
Class Data for Hand-Span Lengths
Length of hand span (cm)
15 16 17 18 19 20 21 22 23 24 25 26 27 28
Total number of hand
spans of this size
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Changes Over Time
Length of lima bean (mm)
Name ____________________________ Date ____________________ Class ____________
Changes Over Time
■
Laboratory Investigation
Variation in a Population (continued)
Analyze and Conclude
1. In what length range are most of the lima beans? Most of the leaf blades?
Most of the petioles?
________________________________________________________________________
2. In what length range are the fewest beans? The fewest blades? The fewest petioles?
________________________________________________________________________
________________________________________________________________________
3. What is the general shape of the graphs of the lengths of the lima beans,
leaf blades, and petioles? What does the shape of the graphs indicate
about these lengths?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. Which hand-span length occurs most often? Least often?
________________________________________________________________________
5. What is the general shape of the graph of hand spans? What does the shape of the
graph indicate about the hand spans of students in your class?
________________________________________________________________________
________________________________________________________________________
Critical Thinking and Applications
6. List two ways in which a large hand span might be a useful human adaptation.
________________________________________________________________________
________________________________________________________________________
7. Do you think having many seeds in a pod would be a more useful
adaptation for a bean plant than having only a few seeds? Give a reason
for your answer.
________________________________________________________________________
________________________________________________________________________
8. Why might having large leaves be a harmful characteristic for a desert plant?
________________________________________________________________________
________________________________________________________________________
More to Explore
Investigate variations that occur in the lengths of peanut shells. Make your
measurements and graph the results as you did in the previous part of this
lab. Do you think that all organisms of the same species show variation in all
of their traits? Give a reason for your answer. CAUTION: Do not eat the
peanuts.
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