ESEB Descent with Modification UnitVanderbilt University Inclusivity in the Biosciences Association

Introductory Lesson 1-2Learning objectives 2

Evidence of learning 3

Learning outline 3-4

Materials list 4

Step-by-step protocol 5-6

Guided Follow-Up Discussion 6-8

Troubleshooting 8-9

Modifications 9-11

Introductory Lesson1) How are organisms related?

a) Lesson plan: Ask students to draw out their family tree and describe how closely some people in the tree are related. Ask students to describe which characteristics are shared by all members of the family, and which are specific to only a few. Ask them what the word “related” means- does it have different degrees of relatedness in different cases?

b) Sample answers: Family tree, all have black hair except a cousin with red hair. The aunts and uncles are more closely related than the students are to their grandparents. Related can be anything from distant cousins to twins because it is a relative term that only means that at some point in evolutionary history, there was a common ancestor/shared ancestral node in a family tree.

2) How are shared traits passed on, and how do they change over time? a) Lesson plan: Ask students to discuss the concept of heritability and what might make

those traits in their family change over time.b) Sample answers: The black hair is inherited from their grandparents. However, the

cousin with red hair has a parent from another country that gave him a new color. He might pass this new color on to his kids someday.

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3) What other kinds of traits (physical or behavioral) exist in animals? Why might they have these traits?

a) Lesson plan: Ask each student to pick an animal and describe what traits help it survive.b) Sample answers: Bears have claws and sharp teeth to hunt, fur to keep them warm, and

hibernate so they don’t need to eat much during the winter when food is scarce.4) How long do adaptations/trait changes take?

a) Lesson plan: Show two examples: development of birds from dinosaurs and development of antibiotic resistance in bacteria. Ask which occurred faster and why.

b) Sample answers: Depending on the change, it can take little time or a long time. Development of birds took a long time because so many changes were needed. Generation times also matter a great deal. A fly can develop pass on new traits faster than elephants because their lives are much shorter. Development of antibiotic resistance happens quickly in bacteria because sometimes it only takes a single mutation. Bacteria also have extremely fast generation times (~1 hour or less) to accumulate changes, and they have huge populations which makes it more likely for a mutation to occur to help develop resistance.

Learning ObjectivesEstablished goals: Teach students the concepts of descent with modification and common ancestry.

Students will understand that…a. Evolution occurs through descent with modificationb. Organisms develop traits to help them survive in their environmentsc. Development of new traits can happen over very long or very short timescalesd. All organisms have a common ancestor and some have more recent shared ancestors than

others making them more similar

Students will know…a. How to describe relationships in an evolutionary treeb. The concepts of common ancestry and descent with modificationc. Evolution occurs at the population leveld. Some reasons changes occur in organisms over timee. That traits that are selected over time in a population are inheritedf. Many traits take a very long time to develop, even thousands or millions of years, depending on

the starting point, the complexity of the trait, and the impact of the potential fitness benefit

Students will be able to…a. Accurately discuss and describe relationships among organisms, past and present

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Evidence of LearningPerformance tasks: [What do we want the students to do to allow the teacher to assess if they understand the content?] We want students to be able to construct a phylogeny/evolutionary tree (as a group) and to describe relationships among various organisms in the tree accurately. Teachers will be able to assess this through discussion and the assessments outlined below. Also, ask the same questions before and after the exercise to assess learning.

Pre- and post-assessment (ask students these questions before the lesson and afterwards): Correct answers in bold.

1) What is a common ancestor? a. An ancestor of every animal on Earthb. The previous generation in a familyc. An ancestor that descendant species have in commond. The species that all current living things came from

2) What is an adaptation in the evolutionary sense? a. A change that affects the ability of an organism to survive in its environmentb. A behavioral change in response to a predatorc. A change in the environment to help the animal survived. A change that does not affect the ability of an organism to survive in its environment

3) Adaptations always mean that the animal gains a new trait. (True or False?)

4) Animals can be closely related, but still look very different from each other. (True or False?)

5) Adaptations cannot be passed down to the next generation. (True or False?)

Learning OutlineHook their interest: Introduce evolution, survival of the fittest, the concept of heritability, and natural selection. Bring up the example of a family tree and ask them to think of phylogenies this way. The introductory lesson is advised at this point.

Introduce essential question(s): What contributes to the diversity in life we see today? How can all animals be related to each other? How long does it take for this diversity to develop?

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Equip students with ideas/vocabulary (tailor to difficulty level desired): Fitness, evolution, heritability, biome, adaptation/trait, natural selection, common ancestor, descendants, lineage, convergent vs divergent evolution, subpopulation, and speciation

Run simulation exercise: Protocol below

Assessment: i. Standard/simple assessment: Use included pre and post assessment questions. Use

discussion questions in the protocol below. ii. Homework assessment: Give them homework where they are given a scenario with

Figure 1, where population 1 is a dinosaur and populations 8-15 are modern birds (or any other real or imaginary lineage), and ask them to draw major intermediary steps in between and answer similar questions to those in the discussion about the relation between different individuals and the timelines. To make it simpler for younger students, you can start with a simple shape (like a triangle) and end with multiple complex shapes, and ask them to draw intermediary shapes, allowing for only one change per step. Ask them which shapes are more closely related/similar (ask them to compare specific shapes that are listed in the question).

iii. Challenging assessment: Ask them questions if something changed, for example, what would the animals look like if the timeline really only was a few generations? Or, what would they look like if the environment changed halfway through from a jungle to a savannah due to trees dying over time? Or, what if some of these animals interbred (hybridization)?

Materials ListIncluded

Paper plates (pack of xx plates)Glue (2 bottles)

Environment cards (2 sets)Markers, crayons, or colored pencils (2 boxes)

Craft items: feathers, pipe cleaners, beads, felt, googly eyes, glitter, etc. (assorted)Yarn/string or popsicle sticks (1 yarn ball)

Not IncludedScissors (optional)

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Step-by-Step Protocol

Before you play:

1. Group students: We recommend groups of about 15 students each, although this can be changed if needed. Assign each student a number, 1-15. Each student assigned a 1 will be the common ancestor for their group, and each person assigned to another number represents a later generation. Each generation, mutations occur that change that individual. Many of these changes are to help them better survive in the environment. See the chart below to understand the sequence of the game.

Figure 1. Example tree of generations for a group of 15 students. Each group starts with a single common ancestor. The ancestor has two branching offspring that each evolve different traits. Each of these then have two of their offspring, etc.

2. Pass out the materials: Each person should be given a plate and each group should sit in a circle so that they can see the plates of all others in their groups. Place other materials in the middle of the circle.

Playing the game:

1. Each person starts with a plate, which is a mask that they will make of whatever imaginary animal they are. Explain that each person represents a population of the animal, each of which share a certain trait. Everyone draws basic features on the plate: eyes, nose, and mouth. The group will vote on or be given an environment to survive in (for example, desert or jungle). The instructor may decide to hand out the environments randomly, and if so, the included environment cards can be used to assign biomes to each group.

2. Explain to each group that the first person is their ancestor in their assigned biome. Show them the chart from Figure 1 (or one adapted to the number of students).

3. Explain the turns they will take. The first person makes an alteration to their plate that everyone else then has to make (adding a feather, adding big ears, adding a tail, etc.). They may add

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whatever adaptation they want, the only rule is that each adaptation has to have a purpose that affects the fitness of their animal in its environment (feathers to fly, big ears to hear prey, tail for balance while climbing, etc.). Everyone else (students 2-15) immediately makes the same adaptation on their plate. The adaptations are made by gluing/cutting craft items or drawing in traits, etc.

4. Participants 2 and 3 then work simultaneously and each makes a different adaptation. This can be either an addition, an alteration of an existing feature, or removing a previous feature. We recommend removal of a feature only be allowed once per game, and only when students have the maturity to not be too competitive if their adaptation is removed by a subsequent person. Therefore, it may be good to reserve this for older students. Whatever is done, however, must be for a reason (such as losing a tail because the creature adapted to food on the ground, for example). People 4, 5, 8-11 copy person 2 and people 6, 7, and 12-15 copy person 3 (see Figure 1).

5. People 4-7 then simultaneously make changes and people 8-9 copy person 4, 10-11 copy person 5, 12-13 copy person 6, and 14-15 copy person 7.

6. People 8-15 then make their own changes.7. Add strings or popsicle sticks to the masks so that they can wear them by tying them around

their heads or hold them in front of themselves like a masquerade mask.8. Put all the masks together in a pyramid, as shown in Figure 1, and talk about what patterns are

seen.

Guided Follow-Up Discussion

The following are some suggested questions to help the class understand the concepts from additional angles and so that they think more critically about the evolutionary tree they made. Teachers may elect to use any, all, or none of these or to add or modify them however they see fit.

1. Can you see common features throughout the tree? Why?2. Does each student represent a single living organism or a population?

a. Explain that changes may start at the individual level, but that the traits spread through a population if they help the animal survive because that animal’s offspring will have a helpful ability/trait, while others without it are less likely to survive. This fitness boost allows the offspring of a successfully adapted animal to represent more of the population as time goes on.

b. Each student, therefore, represents a whole population that shares this trait among individuals because it is less likely for a trait to be maintained over time with few individuals.

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3. What is the relationship between individuals within a generation/level of the pyramid in Figure 1? What is the best way to describe how numbers 2 and 3 are related?

4. What is the relationship between individuals in different generations/levels of the pyramid in Figure 1? What is the best way to describe how numbers 10 and 6 are related?

5. How are the answers between b and c different or similar?6. How is this similar to a family tree? 7. Were there any cases where different branches developed the same characteristic? Explain the

concept of convergent vs. divergent evolution.8. How much time does it take to develop these different characteristics? Does each level

represent a single generation, or do you think it takes a lot longer to develop these new traits? Based on the answer, how closely related are individuals higher up in the tree versus those lower down? Which pair is most closely related: 2 and 3 or 8 and 12? Why? Do all ancestor generations necessarily die off, or is it possible that some subpopulations survived and did not make the same changes that the altered offspring generations did (i.e., speciation)? For example, are all representatives of population 7 necessarily gone by the time populations 14 and 15 develop?

a. Explain to students that this is a simplified version where they represent only certain, distant generations, and that the actual time between person 1 and people 2 and 3, for example, would likely be hundreds or thousands of years. Therefore, person 1 represents an animal that lived long before any others, and person 3 represents an animal that lived long before people 4-15, for example. Explain that the traits slowly develop over time (i.e., feathers do not appear spontaneously in a generation, it takes many generations to first develop a hollow cylinder-like protrusion, then over subsequent generations, these protrusions would branch, multiply, and hook together, as seen in Figure 2.

b. Explain that not all individuals necessarily need to change for another, new population to come from them. For example, some individuals of population 7 may have had offspring with mutations that give rise to populations 14 and 15, but not all individuals necessarily had offspring with that change, and those lineages may still exist.

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Figure 2. Evolution of the feather. This figure shows a few snapshots of how feathers develop over many generations. It begins with a hollow cylinder that appears as a spike in an ancestor, and these cylinders will eventually become branched and filamentous, and will finally multiply and form barbs to connect each branch together over the course of many generations of offspring. Each lettered picture represents a different stage in the evolution of the appendage, and each one is separated by many generations that incrementally change in the overall shown direction of a to d over time. Figure from Wikimedia, by Matt Martyniuk.

Troubleshooting

Problem Solutions

Students are not understanding the concepts or are unable to answer questions.

This indicates that they may be missing some background or may be too unfamiliar with the subject. Consider using one of the modifications below to simplify the activity. If desired, they could work up to a more complicated version by repeating the game with more complex rules after finishing a simpler trial first. This may also help if the issue is simply that the rules/steps are not clear.

Students are going through it without any challenge or difficulty.

This indicates that they may need more challenging material. Consider using the modifications to add difficulty listed below or ask them to come up with their own scenarios and build their own tree to fit the scenario. Alternatively, give them an ancient animal (like a dinosaur) for person 1 and more modern animals like birds for the bottom generations, and ask them what adaptations had to happen in between to get from dinosaur to each kind of bird. Ask them to draw in some intermediate animals representing the important changes to become each bird species from the same starting point. Compare and contrast the lineages.

Older students do not want to do crafts. Older students may not want to do crafts. This is

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easily done simply by drawing as well, so a printed version of the outline of an animal’s body or face can be given to everyone instead and they can be asked to draw in the traits. This will help it seem less crafty.

Students disagree over changes. If they are likely to (or do) fight over some of the adaptations made by others in their group, make sure to not allow them to remove or alter a previous trait (this will cause problems). Also make sure to tell them that everyone gets to make their own change and no one can complain about another person’s change during the exercise, but that when they take their masks home with them, they can do whatever they want with them.

Running out of materials and no funds to get more.

If you are a teacher in Tennessee, please contact our group (iba@vanderbilt.edu) to ask if we have funds available to help your class (we sometimes do). If not, students can be asked to bring in their own supplies, or it can be completely drawn on paper (it doesn’t need to be a mask in this case, it can just be a drawing of an animal, where they all start with the same animal outline).

Modifications

Modifications to add difficulty (for older students, such as high schoolers, or those who want a challenge)

Solutions

Include lineages that do not change over large amounts of time.

Include one person in the second level of the pyramid (i.e., a person 4 at the same level as people 2 and 3) with one representative offspring at the lowest level of the pyramid and a much longer branch with no other representatives in between. Have the offspring person add no changes or only a very small adaptation. Ask students to discuss what this means. Discuss that changes do not always occur because they are not always needed. Sometimes an animal is

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already well adapted to its environment and there is no pressure or reason for it to change. Some kinds of animals, such as sharks, have largely maintained their adaptations over time because they are so successful.

Include lineages that have no existing offspring. Include one person (who isn’t in the bottom level of the pyramid) who does not have offspring. Talk about what that means (an extinct lineage) and why that might have happened. Discuss how common this might be (very common, most ancient lineages have no existing descendants).

Allow some lineages to have more or fewer offspring (i.e., not just two per generation).

Ask students why more lineages might come from a certain ancestor than another. What might encourage greater diversity in some cases than others?

Give each group the same biome to see if they develop the same or similar traits.

Talk about convergent evolution. For example, whales and sharks both have fins, but whales are mammals and sharks are fish. They have the same trait because by chance, both lineages developed similar adaptations for the same environment even though they’re not related.

Make the entire class one large group rather than smaller ones and add in more than one component listed above.

This will allow for multiple levels of complexity, which may be good for students who are older or more familiar with the material.

Modifications to simplify (for younger students, such as elementary schoolers, or students less familiar with the subject)

Solutions

Make the entire class one large group rather than smaller ones so that the instructor can go through each step with the students together.

Students may feel lost without more structure or instruction. For students in this situation, it may be good to have this be a largely teacher led assignment, where the teacher will instruct person 1 to make a change, all others to copy, and then person 1 can explain their change to the class while each person is listening. Then, the teacher can guide each subsequent generation and the class can hear from their peers. This will help them by discussing everything together and having the teacher there to lead.

Remove the ability to take away a previous student’s trait.

While in nature, some adaptations are lost, this will help with the younger students to avoid

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arguments over losing their creation. In addition, it will take away a layer of complexity so that the focus can just be on descent with modification.

Only have one offspring per individual after the second generation.

Have 2 and 3 still branch from 1, but after that, each subsequent generation will only have one offspring each. This will remove the complex network of the tree and allow students to focus on comparing two single, direct lineages.

Have the students play more than once. To reinforce the concepts, allow the students to play a second time with the other side of the plate, this time with another biome. This will give them a second chance to see the process.

Modifications for different class sizes Solutions

Groups of 1-10 Have each student represent multiple generations, so they are creating more than one mask. They can alternate with other students or some can draw numbers to see who will do multiples and who will do single masks.

Groups of 10-20 This is the ideal size for Figure 1. If fewer are present, remove either a generation level or change the number of offspring per generation (some generations may have more than others).

Groups of 20 or more This is ideal for more than one group, unless the group is younger or unfamiliar with the subject or older and in need of more challenges added. Based on the instructor’s judgment, classes this size can be broken into multiple groups or a larger class with modifications applied as described above for each scenario.

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