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3. Follow your teacher’s instructions and post your display for the class. If you
were a textbook editor, which display would you choose to use in the book and
why? Record your answer in your journal.
Elaborate
Explaining the Zebra’s Stripes
In the last activity, you examined the process of biological classification. Biologists
use this as a tool to organize and express the structural and evolutionary relationships
that exist among all living things. Think about that idea more closely. Might we
expect classification schemes to contain some areas of controversy and question?
Certainly, when scientists are classifying an organism about which little is known, you
would expect to hear arguments about where to place it in the classification scheme.
Perhaps your team encountered such controversies when you created a classification
scheme in the last activity. Would you also expect classification schemes to change
over time? What happens as scientists discover new information that increases or
modifies their understanding of particular relationships and adaptations?
An important characteristic of scientific knowledge is an openness to change and
modification. Scientific knowledge is not static. Scientists continuously discover new
information and test and reevaluate existing understandings. Usually, changes in
scientific knowledge are not so great that we must discard all of our previous
explanations in favor of
new ideas. Nevertheless,
as we gain more detailed
information about the
natural world, our
explanations grow and
change to reflect it.
Your next activity
illustrates this
Chapman’s zebra
Grant’s zebra
characteristic of growth
in scientific knowledge.
You will participate in a
process to learn about the
difficulties that scientists
face as they sort through
what might appear to be
easily answered questions.
Can you tell a zebra by its
stripes? Is one zebra just
Grevy’s zebra
mountain zebra
like the next?
Figure 3.7 What similarities and differences do you observe among these
four zebras?
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Figure 3.8
Sample table. Record your observations in a table similar to this one.
Materials
(per team of 4)
DVD and player
PROCESS AND PROCEDURES
Part A Looking Closely at the Concept of Species
1. Work with the other members of your team to compare the physical
characteristics of the 4 zebras shown in the DVD segment “Zebras” and in
Figure 3.7.
These zebras represent 4 populations that live in Africa; each population has a
different common name. Record your observations about these animals in your
journal in a table similar to the one in Figure 3.8.
2. Examine the map in Figure 3.9. Compare the ranges of each of these
4 populations of zebras. Add this information to the observations that you
recorded in step 1.
3. Discuss with your teammates how you might categorize the 4 zebras into
species. Record your answer in your journal.
The fundamental question here is whether each of these populations of zebras represents
a separate species or whether some of them are members of the same species. Develop
and support your answer using the information that you collected in steps 1 and 2.
4. Examine the additional information on Copymaster African Zebras to make
further comparisons among the 4 populations of zebras. How might you
categorize these zebras? Support your answer using all of the information you
have available to you. Record your answer in your journal.
5. Contribute your ideas to a class discussion about the zebras and about the
difficulties involved in assigning species distinctions.
ELABORATE: Explaining the Zebra’s Stripes
N S TA
Topic: species/speciation
Go to: www.scilinks.org
Code: human3E79
Unit 1: Chapter 3
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Africa
Grant’s and Chapman’s
mountain
Equator
Grevy’s
South
Atlantic
Ocean
Indian
Ocean
1000 Km
overlapping areas
1000 Mi
Figure 3.9
How do the ranges of the four zebras compare?
Part B Explaining the Adaptive Significance of Structural Characteristics
One of the most important relationships that you have encountered in this
chapter is the relationship between the particular adaptations that a species displays
and its environment. In the activity Adaptation, Diversity, and Evolution, for example,
you looked at some of the different adaptations that various types of marine
organisms possess. You then matched these adaptations to the challenges that these
organisms face in their particular environments. In the same activity, you looked at
the history of the evolution of plants. You noted how the appearance of new
adaptations correlated with movements onto land.
How far can we extend this statement: Biological diversity results from random
genetic change combined with natural selection? Is all variation among different
species the result of selection for adaptive characteristics? Alternatively, are there
limitations to the explanations that we can offer about some characteristics?
1. Hold a brainstorming session with the other members of your team about the
significance of a zebra’s stripes. How might these stripes be adaptations? List
your ideas in your journal.
2. Read the 2 explanations on Copymaster Ideas about the Zebra’s Stripes for the
appearance and perpetuation of the zebra’s stripes.
3. Work with the other members of your team to analyze the data that relate to
each explanation.
As you read and discuss each explanation, identify and record each bit of evidence,
each inference, and all of the assumptions that you recognize. Then decide whether
each piece of information supports, does not support, or contradicts each explanation.
Take notes in your journal about the results of your discussion. View the DVD
segment again if you think it will help you.
4. Discuss the strengths and weaknesses of each of the 2 explanations.
Summarize this discussion with a list of the evidence that supports, or fails to
support, each explanation.
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5. Work with the other members of your team to determine which explanation
best accounts for the data presented. Record your answer in your journal.
Weigh the data that you have collected by asking yourself questions such as, What
pieces of information are most relevant to each explanation? What are the most
serious flaws of each explanation? Might there be more than 1 explanation to account
for the stripes?
6. Participate in a discussion and evaluation of the explanations.
Analysis
Answer the following questions in your journal:
1. Do new species appear on earth because two individuals from separate species
mate and their offspring is a new and different species? Explain your answer.
2. Have you ever heard people say, “I don’t pay much attention to reports about
new scientific findings. After all, scientists say one thing about x, y, or z this
year. But they said something else last year, and something different the year
before. It’s clear that they don’t know what’s going on”?
Analyze those statements in light of what you have learned in this activity
about the nature of science. In your answer, refer to your experiences in both
Part A and Part B of this activity. Record your critique in your journal. Be
prepared to share it as your teacher directs.
3. In the essay Five Kingdoms, you read about the history of the classification
scheme that biologists use to group all living systems into five large kingdoms.
a. How does that history illustrate this statement: Classification is not an end
in itself, but is a means, or a tool, that biologists use to express their
understanding about biological diversity?
b. How does it illustrate this statement: Science is characterized by its
openness to change and modification?
c. What role does the discovery or development of new evidence play in the
modification of scientific ideas?
First Encounter with the Critter
Figure 3.10
U.S. researcher Karla
MacEwan collecting
plant samples in
Costa Rica.
Evaluate
Throughout the activities and essays in this chapter, you have focused on how
evolution has produced the tremendous diversity of living systems that exist (and
have existed) on earth. You also have seen that, in addition to explaining the
diversity of life, evolution accounts for its unity. Evolution has produced organisms
that are very different from one another, adapted to life in different habitats, and
even adapted differently to the same habitat. Evolution from a common ancestor,
however, also has resulted in organisms that show important similarities to
each other.
EVALUATE: First Encounter with the Critter
Unit 1: Chapter 3
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