Lego Cladograms

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Objective

SWBAT explain how species evolve from common ancestors.

Big Idea

Students create their own cladogram model that demonstrates how life evolves from a common ancestor.

Warm-up

5 minutes

NOTE: This activity requires Legos, K'NEX, Magnetix, or other connectable toys.  If nothing else is available, pipe cleaners and creativity will work.

In the prior lesson, students learned how to read cladograms using an online interactive tutorial.  The purpose of this lesson is to give student some hands-on practice creating a cladogram that applies the information gained previously.

To begin this lesson I show students the following two images using Why Compare Cladograms With Family Trees PowerPoint slide and have students develop an explanation on why they think we use the comparison to family trees to help them understand cladograms.  I give the students two minutes to discuss this as a lab group. During the discussion I use a guided elaboration strategy to help students elaborate on their answers and help them to put thir thoughts into words. The video clip Classroom Video: Guided Elaboration explains this strategy in more detail.  Once students have their answers documented, I then conduct a whip around in which student group must share their answer without directly repeating any prior answer.  This encourages students to not only listen to what the other groups answer, but it also encourages students to be creative and thoughtful while developing their answer so they are less likely to have their answer "stolen" by another group (which would put them in the position of having to develop a different answer).  The video Classroom Video: Whip Around or Quick Share describes this strategy in more detail.

To wrap up this activity, I lead a small discussion that explains how students can use analogies to help with understanding new ideas. The video Classroom Video: Using Anthologies explains this strategy

Activity

25 minutes

This lesson is based off The Lego Tree of Life, as modified by the Concord Consortium. Prior to teaching this lesson copy, cut and laminate a set of SPLIT Cards and Mutation - Replication Cards for each group of students.  Also, organize your building materials and toothpicks into kits for each group.

Yesterday you learned how to read cladograms and use them to answer questions and make hypotheses.  Today, you are going to make and use a model that better illustrates how characteristics change over time showing how the diversity of life can stem from a single common ancestor.

On your table, you have some Lego bricks, toothpicks and a set of cards.  You will also need to have some colored pencils and paper to document this process.

Create a simple animal using 2-3 Lego bricks to represent the head, body, etc.  This is "Time 0"; draw and label this on the paper using your colored pencils.

You are going to pick a card from the deck and follow the instructions.  If the card says "mutation", make a copy of your animal and then create a mutation by adding, subtracting or changing a body part on your animal.  If the card says "replication", just make an exact copy of your animal.  If the card says "SPLIT" (mountain/river), duplicate your animal and place one copy on each side of the mountain or river.  Each time you draw a card the "Time" counts up by 1 and the toothpicks link the different generations.

I use the Student Directions PowerPoint slide and provide a demonstration to give the students visual examples of the directions.  Also, depending on the background of your students, you may need to discuss what "mutation" means with your students (random changes rather than deformities) and that mutations can help, hurt or have no impact on an organism.  This should be a quick explanation, just enough to clarify misconceptions of the word as this idea will be developed later on in the unit.

You are going to continue this process until you get to "Time 10" or I call time.  You may need to scavenge pieces from earlier generations so be sure that your group continually documents your activity on the paper where you recorded your Time 0 animal.  Remember that each animal in your model represents an entire population (or species) of animal at that time.  Remember that this is a scientific model and that models simplify complex ideas to make them easy to understand.

It is important to model these directions for the students as you are giving them or the students will be confused on what exactly they should do. The video Classroom Video: Modeling Complicated Directions shows how I did this with my students.

I cannot overstate the importance of discussing with students how to read the model they are creating to determine a variety of information about the species the model represents and the ecosystems that they inhabit.  This is a great time to really work with the students to develop their ability to create and use models (which is my favorite SEP!) The Classroom Video: Reading Models  and Classroom Video: Using Model to Draw Inferences each demonstrate how this can be done.

Wrap-up

15 minutes

Now that you have completed your cladogram, discuss the following questions with your lab group to develop a strong group response.  Write this answer on the back side of your documentation sheet.

This is a group discussion activity which means I need to actually hear you discussing your ideas and working together to formulate an answer that represents all of you.  Each of  you have unique  perspectives to offer, don't be afraid to speak your thoughts.  Groups: go out of your way to include everyone - even the shy kids!

QUESTIONS:

  1. Looking at only the species in the last generation, describe the variation that you see and explain why this variation is present.
  2. Which animal is the original common ancestor?
  3. How different are the end animals from the common ancestor? (Be specific)
  4. Pick a branch of your evolutionary tree (cladogram) and describe the patter in the animal traits.  It may be helpful to compare them to a species that are not part of that branch (who decended from a different ancestor).
  5. Why would it be good to have different features, such as tails, wings, long necks, or legs?
  6. Why might an animal on your evolutionary tree gone extinct?
  7. How long do you think it would take to go from the top to the bottom of this evolutionary tree?

I project the Analysis Questions on the front screen so all students can see all of the questions.