Scene: Those Poor Pigeons!

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Those Poor Pigeons!

The Amazing Story of the Peppered Moth

Fish Fence Crisis

Suited for Survival—Animal Adaptations

Science-Fiction Science—Planets X and Y

Scene: Those Poor Pigeons!

Duration: Approximately 50 minutes

In this Science Scene, a dialogue to read aloud as a class, students play the role of several friends who wonder about the acceptability of killing a bird that did not leave the roadway in time. With her friends, one girl, Erica, explores what her father meant by "if they weren't fast enough to get out of the way, they didn't deserve to survive." The father seems to imply that he had helped the species by doing in this particular bird. The children are rightfully skeptical, but is there a kernel of actual science in the father's comment?

LEARNING OBJECTIVES

Students will begin thinking through the mechanisms of natural selection with a real-life example.

Students will broaden their use of the term "fitness" to include an organism's ability to survive in an environment.

Students will compare "breeding" (artificial selection) with natural selection.

Teacher Tips

Think ahead about how best to have your students engage with a script with three roles (Will, Shawnte, Erica), perhaps in groups or by having volunteers read in front of the class. Note that students often willingly take on roles regardless of the gender of the characters.
While it is possible for the students to read the PDF of the script online, we suggest printing the script for the students so they can hold it in their hands and mark it as they read. Consider scaffolding the lesson for English language learners: you could let them preview the script before the lesson or read the dialogue silently once and ask questions to a partner.
Prior to the reading the script, explain to students that they will encounter new vocabulary terms and ideas that may not be familiar. Reassure them that this lack of familiarity is okay. The reading is meant to introduce the ideas, not explain them completely.
Review the focus words of the week. The focus word chart linked on the unit overview page should be used as a resource for students to review definitions and sample sentences.
This activity is intended only as an introduction to the concepts.

Teacher Tune-up

What are the common misconceptions related to evolution?

Set the context (10 minutes)

Engage with the script (20 minutes)

In this scene, three friends are discussing whether or not running over pigeons that are too slow to get out of the road is helping to create a smarter, faster pigeon. They find information about natural selection on the Internet and struggle to understand the concept.

Some teachers have several groups of students read at the same time. Other teachers select a few students to "perform" in front of the class.

You may want to read the entire passage out loud to the class once before assigning roles to students or dividing up into groups.

The Script:

Characters: Will, Shawnte, Erica

Setting: It’s early morning. Erica and Shawnte are sitting on the steps outside of school. Will walks up to them. Erica looks upset.

Will: What's wrong with Erica?

Shawnte: She's been quiet since I got here. Erica, what’s up?

Erica: My dad ran over some birds by the park.

Shawnte and Will: What?!

Shawnte: That's messed up. What happened?

Erica: There were lots of pigeons on the road and my dad just drove right through them. I thought they’d get out of the way, but it felt like we ran over something. There were feathers under the car when I got out. It made me feel terrible.

Will: Good for your dad. Pigeons are nasty birds. There are too many of them anyway.

Shawnte: It doesn't matter how many there are. It's still wrong to kill them!

Erica: My dad said that if they weren't fast enough to get out of the way, they didn't deserve to survive. He said he was helping the pigeon population by killing the slow and dumb ones. Which I think is kind of sick.

Will: How does killing pigeons help them? I don't get it.

Erica: Well, he said if you kill all the slow and stupid pigeons, only the smart and fast ones survive. You’re helping nature with natural selection.

Shawnte: It doesn’t sound natural; it sounds pretty messed up to me.

Shawnte, Will, and Erica keep talking. Erica pulls up an entry for natural selection on her phone, but it doesn’t make much sense to her. She doubts Shawnte will get it either, but she decides to read it out loud anyway.

Erica: I’m not sure, but I think this is the basic idea. Listen:

Natural selection is the gradual, nonrandom process by which biological traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution.

Shawnte: Oh, that probably just means there’s, like, a type of bird or fish and some are red and some are green. Say the red ones do better for some reason and the green ones bite the dust more often. Of course, you’d get more baby red ones going forward even if the color was just random before.

Erica: (shocked that Shawnte understood) Who ARE you? And what have you done with Shawnte?

Shawnte: (ignoring the insult) Maybe your dad thinks that since he killed the slow pigeons, the ones that are left will have babies that will be smarter or faster.

Will: Maybe after enough time we'll have pigeons with super powers! I saw this TV show a couple of weeks ago about how some pigeons have a GPS in their head. They can sense where they are and find their way home. That's like a super power.

Shawnte: Yeah, right. I’m looking that up. What were those pigeons called?

Will: Homing pigeons, I think.

Shawnte: Hang on...whoa! This says that pigeons can find their way home from a thousand miles away! Some people even have racing pigeons and breed their own pigeons.

Erica: Is pigeon breeding like dog breeding? My friend’s mom breeds dogs. She finds dogs that have traits like soft fur and cute faces and has them make puppies.

Shawnte: Hey, it says here that Charles Darwin did sort of the same thing as your friend's mom. But he bred pigeons, not dogs.

Will: We learned about Darwin earlier. He was that evolution guy. So breeding is a kind of evolution?

Shawnte: That makes sense! By mating certain dogs together, you can get puppies with the traits you want. The dog population changes over the generations.

Erica: But I thought evolution was all about survival of the strongest. My friend's mom breeds dogs to be cute and fuzzy. Those dogs are pretty weak.

Will: Evolution is just living things changing over time. It doesn't say that they have to get stronger or faster. If that was true, everything would be super buff.

Shawnte: (pointing to phone) It says here that breeding animals is a kind of evolution called artificial selection. People select what survives and reproduces.

Erica: But humans don't go around breeding everything. How does evolution happen in nature?

Will: I guess things like weather and predators select who survives and reproduces. If you have traits that don’t help you succeed in your environment, you don't stick around to make babies.

Erica: But isn't that survival of the strongest?

Will: No. You don't have to be strong to survive.

Shawnte: Yeah, you could be hard to see, or have a good sense of smell, or have protective poison or something. This website says that most plants and animals evolve through natural selection. Natural selection is when some groups of plants or animals are better adapted to their environment than others and so they survive and reproduce. Being a good fit for your environment is called “fitness.”

Erica: Wait, I thought fitness meant being in good shape, like you’ve worked out a lot?

Shawnte: Fitness does mean that in P.E. class, but the meaning is a little different in science.

Will: Okay, so when your dad ran over pigeons with his car, was it artificial selection or natural selection?

Erica: Well, we didn’t breed them, we just ran over the slow ones according to my dad. So it must be natural selection.

Shawnte: Yeah, but because your dad ran them over, humans did it. It must be artificial selection.

Erica: Either way, I still say it’s messed up. I wish my dad taught me about evolution some other way.

Review the script (20 minutes)

When finished with the script, ask students to turn and talk to address the three questions on the slide.

Sample responses:

Humans have bred corn and soybeans to make them easier to grow and use in the production of other foods. Humans have also bred horses for various kinds of work and transportation. Some horse breeds are good for riding, while draft horses are bred big and strong to haul heavy loads.
I agree with Erica that running over pigeons by accident is natural selection because it doesn’t involve any human intention to breed smarter, faster pigeons. Or: I agree with Shawnte that this is artificial selection because cars are not part of the natural environment, so running over pigeons is a kind of human interference in evolution.
I don’t think it makes sense because I don’t think that being able to avoid cars is necessarily the most important survival skill for pigeons. Or: I think it does make sense because traffic is a fact of life for urban pigeons, so they need to adapt to it.
1) Erica and her father drove through the pigeons on the road. 2) It felt like they ran over something. 3) There were feathers under the car when she got out of the car.
(b) humans are selecting who reproduces.
Shawnte gave the example of an animal being hard to see; camouflage can help an animal hunt, or avoid hunters. Some animals, like skunks, use bad smells to defend themselves.

You may project the questions or distribute the PDF that includes both the "Turn and Talk" prompts and the "Refer back to the script" questions.

With a partner, read and discuss the three questions below:

Make a list of animals or plants that humans have bred. What traits do they have that make them valuable to humans?
Erica thinks her father running over pigeons is an example of natural selection. Shawnte thinks it’s an example of artificial selection. In what way does this example of selection seem natural, artificial, or both to you? Why?
Do you think that Erica’s father’s argument that he was helping nature by killing some pigeons makes sense?

Refer back to the script to answer the following questions:

4. List the evidence that caused Erica to conclude that her father ran over some pigeons.

5. Dog breeding is not natural selection because:

the effect is not permanent.
humans are selecting who reproduces.
certain traits are passed on to the next generation.
nature plays a larger role than humans.

6. Will and Shawnte pointed out that there are more traits than “being strong” that might help an animal or plant to survive. Restate one of their examples and then propose some more.

Natural Selection