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Lesson 5


Evaluating Evolutionary Explanations

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Evaluate


At a Glance

Overview

Students use what they have learned about evolution and medicine to review an article written for a school publication. The task is to identify errors, explain the incorrect statements, and correct the information. They then explain the process of natural selection by creating a labeled illustration using one of the examples from an earlier lesson.

Major Concepts

Because this is an Evaluate lesson, we do not present new concepts. Students should apply what they have learned in previous lessons to this new situation.

Objectives

After completing this lesson, students will

  • have evaluated explanations of evolution that are relevant for medicine,
  • have identified common misconceptions about evolution and medicine, and
  • have summarized their understandings of natural selection.

Teacher Background

Consult the following sections in Information about Evolution and Medicine:
4.0 Students’ Prior Conceptions about Evolution
5.0 Featured Examples of Evolution and Medicine

In Advance
Web-Based Activities
Activity Web Component?
1 No
Photocopies, Transparencies, Equipment, and Materials
Photocopies and Transparencies
1 copy of Master 5.1 for each student
1 transparency of Master 5.2
Equipment and Materials
Note or chart paper for each student
Different-colored pens or pencils
Preparation
Make the copies and the transparency for this activity and gather the paper and different-colored pens or pencils.

Procedure

Activity 1: Evaluating Evolutionary Explanations

Estimated time: 50 minutes

Note: This final lesson gives you an opportunity to assess students’ understandings of the major concepts the supplement addresses. It does not introduce new content.

1.

Introduce the activity by explaining that the school newspaper has decided to include a special section on evolution and medicine. The editor of the newspaper has asked for help. Students will use what they have learned about evolution and medicine to review an article written by a fictional fellow student. The task is to serve as a peer reviewer who identifies incorrect or misleading statements, corrects them, and explains why the corrections are necessary.

In this activity, students should use what they have learned throughout this supplement to review a short article and write a short summary. This task is not a research project—students should be able to analyze the information provided and apply it to a new situation.

2.

Give each student one copy of Master 5.1, Editing an Article about Vitamin C and Evolution. Briefly review the instructions with the class before asking students to work in groups of four. Explain that all group members should read the first paragraph together. Then two group members should review and comment on Paragraph 2, and the other two should review and comment on Paragraph 3.

Students should concentrate on the author’s explanations of the data rather than the accuracy of the data. For the purpose of this activity, the scientific facts are accurate. For example, L-gulonolactone oxidase (GULO) is one of the enzymes required for vitamin C biosynthesis. Vitamin C is not synthesized in humans, other primates, guinea pigs, and some bats, and the gene sequences and the evolutionary tree are scientifically accurate. The text contains some incorrect explanations of the data, based on common misconceptions. (For example, the information in the tree may be interpreted incorrectly.)

One strategy that students can use for the review is to place a number next to the piece of information they wish to rebut. Then, in their science notebooks, they can explain for each number what is incorrect, why it is incorrect, and how to correct it.

3.

After each pair of students within the group has completed the review, pairs should discuss their comments with the other two group members (who reviewed the other paragraph).

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Content Standard A: Scientific explanations must adhere to criteria such as: a proposed explanation must be logically consistent; it must abide by the rules of evidence; it must be open to questions and possible modification; and it must be based on historical and scientific knowledge.

4.

After groups finish, hold a class discussion to check students’ understandings. Ask for volunteers to identify one thing that they felt needed to be corrected and how they changed it. Check whether other class members agree with the volunteers’ ideas. If they disagree, they should be prepared to explain why and how they would (or would not) change a statement. Project Master 5.2, Editing an Article about Vitamin C and Evolution, Answer Key, at the end of the discussion. Point out any misconceptions or misinterpretations that students did not identify.

It will be important to resolve any discrepancies so students do not leave the class confused about an issue or accepting common misconceptions.

Although it’s beyond this supplement’s content, you may wish to discuss the role of evolutionary processes in the loss of the ability of make vitamin C — if your class seems to have a good understanding of the example. If the loss of the ability to make vitamin C were driven by natural selection, then individuals with a mutation that disabled the GULO gene would have an advantage in survival or reproduction. This scenario is unlikely, however. It is more likely that individuals that had mutations in the past that disrupted the GULO gene were not at a disadvantage for survival or reproduction, and the loss of the ability to make vitamin C was due to chance.

5.

Explain that the newspaper editor is concerned that readers may have misconceptions about natural selection. Along with the article about vitamin C and evolution, she wants to include some illustrations and explanatory text that describes the steps involved in the process of natural selection.

6.

Instruct students to take a few minutes to create an illustration that explains the process of evolution with an example from one of the earlier lessons. Have students count off by fours.

There are four examples from the earlier lessons, so this approach ensures that approximately equal numbers of students will illustrate each example.

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Content Standard A: Communicate and defend a scientific argument.


7.

Assign students to use the examples as follows:
  1. Selection for methicillin-resistance in Staphylococcus aureus (MRSA)
  2. Selection for lactase persistence in some human populations
  3. Selection for alleles associated with alpha-thalassemia in some human populations
  4. Selection among influenza viruses

8.

Outline on the board the elements of the task:

  • Students should create one or more simple illustrations that describe how the process of natural selection works.
  • Before making the illustrations, students should review the work in their notebooks from the previous lessons to help them reflect on natural selection and the major principles involved in the process.
  • Students should use the example they were assigned in Step 7 as the focus of the illustrations.
  • The illustrations should include labels and enough explanatory text that a reader unfamiliar with natural selection can understand how the trait of interest changed in a population over time.

9.

Collect students’ illustrations when they are complete. Ask for volunteers to explain the features of the illustrations. For each example, guide the discussion to bring out the five major principles of natural selection.

Box 1. Five Major Principles of Natural Selection

Throughout this curriculum supplement, students focused on five principles related to natural selection.

  1. Variation: Individuals within a population vary for many traits, including physical and biochemical traits.
  2. Inheritance: Some of the differences in traits among individuals can be passed from parents to offspring. (They are heritable.)
  3. Origin of variation: Some of the variation in traits among individuals has a genetic basis. This variation originated, often many generations ago, as mutations—changes in the genetic information that are random with respect to the needs of the organism.
  4. Fitness: Both the environment and the traits that individuals possess affect survival and reproduction. Individuals with heritable traits that enable them to better survive and reproduce in a particular environment will leave relatively more offspring.
  5. Evolutionary change in populations: The frequency of traits and the alleles that affect those traits change in a population over time.

10. Assess students’ understanding of natural selection as depicted in the illustrations. Use the following descriptions to help you identify the five major points of natural selection for each example. Logo1.eps

Example 1: Selection for methicillin-resistance in Staphylococcus aureus (MRSA)
  1. Variation. Some individuals within a population of S. aureus are able to live in the presence of methicillin, whereas others cannot.
  2. Inheritance. Resistance to methicillin in S. aureus is caused by specific alleles. Therefore, resistance can be inherited.
  3. Origin of variation. Mutations occur randomly. Some mutations to genes enable some individual bacteria to become resistant to methicillin.
  4. Fitness. In the presence of methicillin, individual bacteria that have inherited the alleles for methicillin resistance will survive and leave relatively more offspring in the next generation.
  5. Evolutionary change in populations. The frequency of the alleles that cause resistance to methicillin increases in the S. aureus population over time. As a result, the frequency of methicillin resistance in the population also increases.
Example 2: Selection for lactase persistence in some human populations
  1. Variation. Some individuals can digest lactose as adults, whereas others cannot.
  2. Inheritance. Lactase persistence in humans is caused by specific mutations in a DNA control region. Therefore, lactase persistence or lactase nonpersistence can be inherited.
  3. Origin of variation. Lactase persistence has a genetic basis. Mutations occur randomly. Mutations to a DNA control region enable some individuals to make lactase as adults.
  4. Fitness. In certain cultural or environmental contexts, individuals who are lactase persistent left relatively more offspring. The culture-historical hypothesis says that individuals who are lactase persistent had a selective advantage in pastoralist populations. The calcium absorption hypothesis suggests that individuals who drank milk had a selective advantage in areas with low amounts of UV light.
  5. Evolutionary change in populations. The frequency of the alleles that cause lactase persistence increased in some human populations over time. As a result, the frequency of lactase persistence in the population also increased.
Example 3: Selection for genes associated with alpha-thalassemia in some human populations
  1. Variation. Some individuals have the traits associated with alpha-thalassemia, whereas other individuals do not have alpha-thalassemia.
  2. Inheritance. Alpha-thalassemia in humans is caused by specific alleles. Therefore, the disease can be passed from parents to offspring.
  3. Origin of variation. Alpha-thalassemia has a genetic basis. Mutations occur randomly. Mutations to a gene cause the disease.
  4. Fitness. In certain cultural or environmental contexts, individuals who have alpha-thalassemia had relatively higher survival rates and left relatively more offspring. Alpha-thalassemia offers some protection against malaria. In areas with high rates of malaria, individuals with alpha-thalassemia have a lower chance of developing severe malarial anemia or dying from malaria.
  5. Evolutionary change in populations. The frequency of the alleles that cause alpha-thalassemia increased in some human populations over time. As a result, the frequency of alpha-thalassemia in the population also increased.
Example 4: Selection within the influenza virus
  1. Variation. Some individual viruses are able to avoid recognition by the human immune system, whereas other individual viruses are initially recognized by the immune system.
  2. Inheritance. The hemagglutinin region is coded for by a gene in influenza. This gene can be passed from one generation of viruses to the next.
  3. Origin of variation. Mutations occur randomly within the genome of influenza viruses. Mutations to a gene that codes for a protein that is important for immune recognition enable some individual viruses to escape detection.
  4. Fitness. Individual influenza viruses that avoid initial detection by the immune system are able to enter human cells and produce relatively more offspring.
  5. Evolutionary change in populations. The frequency of the alleles that allow influenza viruses to avoid initial detection by the immune system increases in the population over time. As a result, the population of influenza viruses changes rapidly.

Lesson 5 Organizer

Activity 1: Evaluating Evolutionary Explanations
Estimated time: 50 minutes
Page and Step

Explain that that the school newspaper will include a section on evolution and medicine and that students will serve as peer reviewers for a newspaper article.

Page 156
Step 1
Give each student one copy of Master 5.1.
  • Form groups of four students.
  • Ask all group members to read the first paragraph together.
  • Have two group members read and comment on Paragraph 2.
  • Have two group members read and comment on Paragraph 3.
  • Ask student pairs to discuss their comments with the other pair in the group.
Page 156–157
Steps 2
and 3
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Hold a class discussion to assess students’ understandings.

  • Project Master 5.2.
  • Point out anything students did not identify.

Page 157
Step 4
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Instruct students to create an illustration that explains natural section with an example from an earlier lesson.

  • Have students count off by fours.
  • Assign examples as follows:
  1. selection for methicillin resistance in S. aureus
  2. selection for lactase persistence in some human populations
  3. selection for alleles associated with alpha-thalassemia in some human populations
  4. selection among influenza viruses

Page 158
Steps 5–7

Outline the task on the board:

  • Create one or more simple illustrations that describe how the process of natural selection works.
  • Review the work in your notebooks to help you reflect on natural selection and the steps involved in the process.
  • Use your assigned example as the focus of the illustrations.
  • Create illustrations with labels and enough explanatory text that a reader unfamiliar with natural selection can understand how the trait of interest changed in a population over time.

Page 158
Step 8

Collect the illustrations.

  • Ask for volunteers to explain the features of their illustrations.
  • Relate each example to the five major principles of natural selection.

Page 158
Step 9

Assess students’ understanding of natural selection as depicted in the illustrations. Page 159
Step 10

= Involves copying a master.        Logo7.eps = Involves making a transparency.

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