Natural Selection: Simulating Kettlewell's Famous Peppered Moth Experiment

This is a classic simulation lab linking student prior knowledge about natural selection as a mechanism for evolution to our study of Kettlewell's moth experiment.  At the time, this experiment was essential to the discussion and debate about natural selection.  People wanted to hear examples of this happening in real time and not just explained through fossils…and here was one such example!  

In this simulation, students use newsprint, white paper, and tweezers to experience the predator-prey relationship against a changing background that shifts the camouflage adaptation from one paper type to the other.  This is also a great lab to use to reinforce basic graphing skills.  You will find that students are self directed during this activity both because it is highly engaging to them and due to their increased maturity and student skills at this time of the school year in our biology class together.  Student enjoy seeing theories that make sense to them play out in real life right in front of them and it is very satisfying for students to see the data for themselves. 

There are many versions of this lab, many of them online.  I continue to use this particular version in addition to the computer simulations we work with because each time we slow down and do handwork, both in terms of lab procedure and data presentation (graphing), I find that student conversations about the topic under investigation go deeper and provoke more clarifying questions that they feel confident enough to tackle as a team.

To give you a sense of what we've discussed throughout this unit, check out our evolution slide presentation as a reference.

1.  Tell students that today you are going to continue with yesterday's discussion about Kettlewell's moths and natural selection with a lab activity.

2. Remind students that the simulation will include a graph and that they should take out their graphing rules document as a reminder of our graphing guidelines and best practices.  

3.  Pass out the peppered moth survey document and ask students to read the procedure quietly to themselves.  Highlight the following information:

• Students will be using newsprint, white paper, forceps (tweezers), and a timer in this simulation of Kettlewell's famous experiment.
• Talk through the meaning of the phrase industrial melanism. Students may remember that melanin refers to skin coloring and that industrial may have something to do with the historical event known as the Industrial Revolution.  The class should come to the conclusion that industrial melanism refers to the coloring of the trees due to industrial pollution.
• Point out that there are two trials for each background and that this means that each member of the lab pair can take on each of the roles (time/data recorder and predator/data collector) twice out of four trials total.
• Refer students back to the introductory information and their experimental data as they discuss and respond to the analysis questions on the lab document.
• Remind students about the requirements for a well constructed graph.

4.  Review the materials they will be using by showing students the major variable of this simulation:the white background vs. the newsprint background.  Once they see the lab activity set up, they will be ready to get to work!

• Note:  The instructions here are straightforward and students will not typically have any deep conceptual questions.  If anything, you will find that they are ready to get to work and are eager to see if what they read about will actually happen in their simulation with their partners.  

5.  Tell students that they will be working in pairs at their lab tables to complete this activity. Remind them again of your expectation that each partner should have the opportunity to be the recorder as well as the predator with tweezers.  Show students where the lab materials are located for each table and ask students to have one lab table member come to pick up the materials for their table of two student pairs.

1.  As students move to their lab tables with their materials, remind them of the location of rulers, colored pencils, and graph paper in your classroom.  

• Note: I also like to put a half sheet graphing guidelines document copy on each lab table just in case students have forgotten their personal copy of basic graphing guidelines.  I keep a set of 8 of these in plastic sheet protectors for this purpose and I find that accessibility reminds students to refer to the rules as they discuss data and construct graphs and data tables.

2.  As students work to collect and record data, observe each group closely while hanging back as much as possible.  At this point in the year, they should be able to figure out most if not all issues on their own and giving them the opportunity to see if they can do so is a great chance to allow them to continue to stretch their collaboration and problem-solving abilities.

• Note:  In general, you will find that students are quite self sufficient and able to complete the activity on their own.  The most I find I need to do is to write up the graphing guidelines on the board and refer to them about halfway through the class period as students begin to shift from data collection to graph making.  

3.  You will see many positive collaboration behaviors happening during this class session:

• Students referring to their activity document, reading directions out loud to each other and asking clarifying questions.
• Students conferring with other lab pairs to reassure themselves of their data accuracy/trends and procedural interpretations.
• Students taking turns timing trials accurately, completing the task, and documenting their data/results.
• Students looking at their graphing guidelines for support as they construct their graphs.
• Students gathering supplies for graph creation.
• Students discussing analysis questions, referring to their textbook, notes, or Powerpoint slides.
• Students coming to the front to discuss specific questions with the instructor.

4.  If you see any group struggling to perform any of these types of tasks, that is when you can come over to their lab table and ask how things are going.  If they have a question, they will typically ask it then.  If they seem reluctant to do so, confused about what to ask, or that there is tension between the members of the team, suggest one of the behaviors above as a place to start.  Some students will still be working on their ability to break down an activity into smaller tasks and having specific things to suggest will help them choose what is the best one for them at that moment.

1.  As the class session comes to an end, announce that students should return their lab materials to the front and put rulers and colored pencils back in their designated storage location.

2.  Tell students that you will take clarifying questions the next day after they have had an evening at home to work on their graphs and look more closely at their analysis questions.

• Note:  Typically, students will feel very comfortable about the conceptual aspect of this activity.  However, they may still be struggling to attend to the basics of creating an effective graph.  Depending upon your students and the amount of time you have already devoted to graphing skills, taking some additional minutes to remind/review some of the major pitfall areas may be useful to you and your class.  

2.  Remind students of the assignment deadline before dismissing the class.

• Note:  As you can see from this typical student work sample, students are able to connect the work to our broader themes and concepts well.  The area that I find I may take off points on any given student work document involves graphing norms such as a descriptive title or labeled axes.