To begin the lesson, have students complete the anticipation guide about natural selection, in order to gauge the students’ prior knowledge. Review the guide together as a class, making note of misconceptions that students hold; you will want to tweak this lesson in order to address the specific needs of your students. Let students know that we will be exploring these concepts in a few simulation activities.
Ask students if we all have the same color hair? Do we all have attached earlobes? (Allow them time to see if their earlobe is attached or free) Can we all roll our tongue? We are all the same species, so where do these differences come from? (The goal is for students to lead the answers and discussion to genetic variation and that we all are different because we have different traits, genes, or DNA, etc. There are different versions for each trait – for the earlobe trait, attached earlobe is one version & detached earlobe is another version.)
Discuss with students whether the trait to roll our tongue or the trait for our attached or detached earlobes affects our survival. Ask them if they can think of any examples in animals in which certain traits can affect their survival. Do these traits act independently in affecting an animal’s probability of survival or do they work together? Explain your reasoning. (If students are unable to come up with examples, ask students to think of predator/prey relationships. What traits may help an animal survive from a predator?)
Photo taken from https://en.wikipedia.org/wiki/Peppered_moth_evolution
Tell students about the peppered moths in England: Share the picture of the light peppered moth and the fact that in the mid-1800s, peppered moths were known to look like this, which is why it was notable when an English naturalist named RS Edleston recorded that he had seen a dark–colored peppered moth (and then share a picture of the second moth). Over the years following Edleston’s observation, dark-colored peppered moths increased significantly in number and were more commonly sighted. Scientists wanted to know why they were seeing so many more dark-colored peppered moths and they conducted many investigations to find the answer. Tell students that they will engage in several activities today, using birds as an example, to be able to explain what happened to the moth population and why there was a shift in the type of peppered moths.
Preparation for Activity Part 1:
- Timer or clock
- One cup per student
- Small seeds (ex: sunflower seeds, pumpkin seeds)
- Larger seeds or nuts
- One tray or plate for every group of four students
- A variety of “beaks” – some tweezers, tongs, clothespins, and binder clips
Note: these beaks can be substituted with other utensils or tools
- Place a few handfuls of seeds in each tray or plate
- Perform this activity ahead of time and decide on an appropriate number of seeds that can be collected in 30 seconds (basing it off of the tweezer beak) such that most students can survive.
Activity Part 1:
Introduction & Preparation:
- Tell students that they will participate in a simulation that will help answer the question: How might a genetic trait affect an organism’s chance of survival?
- Discuss the activity with the students so they understand the directions: Tell students that they will represent finches (birds) with different types of beaks, and will be competing to acquire food. Each student will receive a cup which will represent their (the finch’s) nest that they will hold in one hand. Each student will also receive a tool, which will represent the finch’s beak that will hold in their other hand. The goal of the activity is to pick up food from the food source table and place it in their nest. The students will pick up the food only by using their tools (no hands!), and the food will only count once it is placed in the cup using the tool. The goal is to bring as much food back to their nest as possible in the time allotted.
- Divide students into groups of four for the activity. Give each student a paper cup. Give the first student in each group a tweezers as the beak. Give the second student in each group tongs as the beak. Give the third student in each group a clothespin as the beak. Give the fourth student in each group a binder clip as the beak.
- Place a tray with some seeds at the center of each group for the food source (make sure the seeds are more easily picked up using the tweezers). Tell students that when you start the simulation, every student will have 30 seconds to pick up and put in their nest as many seeds as possible from their group’s food source.
- Ask students what data they think they should record from the simulation and why. (Students should record the number of seeds that successfully make it into the cup before the 30 second time is up.) Ask students if there are any rules that they want in place before they start the simulation. (For example, any food that falls down (outside of the cup) does not count. Students cannot use hands to pick up food.) Ask students how many trials they think they need to do in order to get a sufficient amount of data. Decide on a number.
- Have each student create a data table in which they can record their entire group’s data for all the trials. Make sure students have an average section, where they can average the trials for the number of seeds picked up by each bird. If students struggle creating their own data table, encourage them to work as groups to develop a table, or provide them with a starting point (i.e., they can put a type of beaks on top of each column, so how many columns do they need?).
- Once students are done creating their data table, tell the class that all four students in the group will have 30 seconds to bring as many seeds as possible from their group’s food source to their nest. After 30 seconds, they should stop collecting food, count the number of seeds in their nest, and record the total.
Activity & Recording Data:
- Start the timer for 30 seconds and tell students to begin picking up and depositing food. At the end of 30 seconds tell students to stop. They should count the number of seeds in their cup and record the number in the data table.
- After recording their data, all seeds should be returned to the tray for the next trial.
- Steps 8 and 9 should be repeated for each trial.
- After all trials have been completed, have students share their individual data with the group and fill in the rest of their table.
- Inform students that all birds that have procured at least __ seeds survived, while the others died. This will be based off of the average number of seeds procured by each bird. (Perform this activity ahead of time and decide on an appropriate number such that most groups will survive.) Have students place an “x” next to the birds that died in their group.
- Compile class data (including which birds died from each group), and then find the whole class average for each type of beak. (If technology is available, using a Google form to collect and compare data makes the process more seamless.)
Interpreting & Analyzing Data:
- Ask students to reflect on the results of Part 1:
- Do you notice any patterns or trends in the data?
- How many birds survived? Are there any trends (and similarities or differences) in the type of birds that survived and/or died?
- If some birds died, why do you think that was the case? Are there any similarities as to the type of birds that died? Why do you think so?
- What determines the type of beak that the birds have?
- How does the genetic trait affect the birds’ beak shape? How does the beak shape affect the bird’s ability to access food?
- What versions of the beak traits are most beneficial for life on this island? Why?
- Based upon the data from the activity, how can a genetic trait affect an organism’s survival?
- How accurate/precise is the data we collected?
- What are the limitations of the data?
- Are there any anomalies?
Activity Part 2:
- Inform the students that hurricane winds (or another form of natural disaster) have disturbed the finch population and forced the birds to relocate to another island where their original food is no longer available. They therefore have to resort to a secondary food source.
- Place a tray with some larger seeds (make sure the seeds are more easily picked up using the tongs) at the center of each group for the food source.
- Repeat the same procedures and data collection as from Part 1.
- Inform students that all birds that have procured at least __ seeds survive, while the rest have died of starvation. (Again, perform this activity ahead of time and decide on an appropriate number, but this time make sure the number is difficult to reach).
- Ask students to reflect on the results of Part 2.
- Do you notice any patterns or trends in the data?
- How many birds survived? Are there are any trends in the type of birds that survived and/or died?
- Why do you think a lot of the birds died? Describe any patterns or similarities/differences as to the type of birds that died.
- Compare your data for the two islands with different food sources. What similarities are there in the types of birds that were able to acquire the most food and survive? What differences are there? Why do these similarities and differences exist?
- How does beak shape influence the bird’s ability to access food?
- Based on your data, what is happening to the bird population at the new island? Why - what are the causes?
- What versions of the beak trait are most beneficial for life on the new island?
- Do environments and available resources change in real life? Can those situations affect a population’s stability? How? Are these changes sudden, gradual or both?
- Does the activity represent a realistic situation? Why or why not? Is the change that disturbed the finch population in this activity a sudden change or a gradual change? Why?
- How accurate/precise is the data we collected?
- Are there any anomalies?
- What are some examples in our local ecosystem of living things that have characteristics that help them survive?
Have students construct a written explanation in which they develop a claim that explains the relationship between a bird’s beak type and its survival in a specific environment. Students should use the class data as evidence in their explanation to support their claim, including why the evidence is adequate for their explanation.
(Students will come back to revise this explanation after watching the video and the class discussion on natural selection. This can be used as a formative assessment opportunity to see how students are currently explaining the activity in terms of genetic variation and the environment. It also allows students to demonstrate if they can identify appropriate evidence from the activities for their explanation.
Depending on the abilities of your student, you may need to provide more details as to what an explanation should include. For students that are struggling with constructing explanations, you can have them work in pairs to brainstorm ideas or you can have them check in with you at various stages of writing the explanation.)
As a class, watch the following video: www.youtube.com/watch?v=0SCjhI86grU
Afterwards, have a class discussion about natural selection:
- What is natural selection?
- Is natural selection an immediate change or a gradual process? Why?
- Where did we see genetic variation in our activity?
- How does this genetic variation affect a bird’s ability to acquire food? How does a bird’s ability to acquire food affect its survival?
- If birds with a certain type of beak are able to survive and reproduce more successfully than other birds, what type of beaks do you think will be more common in the next generation in the population? Why?
- Is this genetic trait (the type of beak) the only factor that can affect a bird’s survival in the real world? Describe other factors that can affect a bird’s probability of survival.
- Why were some birds able to acquire more food on the first island than the second island? Why were some birds able to acquire more food on the second island than the first island?
- What do you predict will happen to the bird population over time (many decades) on the new island? Include your reasoning. What genetic variations for the bird beak do you think will be passed on? Why? What genetic variations of the bird beak will you see less of? Why? Do you think the shifts in the types of beaks visible in the population will be gradual or sudden? Why?
After the class discussion, have students revisit the explanation that they wrote. Students should revise their explanation by applying scientific reasoning that describes the relationship between natural selection and the evidence from the activities.
Inform students they will now take their understanding of genetic traits and natural selection to answer explain what happened in the peppered moth case. Describe the peppered moth case to students again. Tell students that during the mid-1800s when the shift in the color of peppered moths was seen, the industrial revolution was going on in England. The industrial revolution raised the pollution levels in many parts of England, as smoke was released by the factories. The pollution killed off lichens on trees and also settled on the trees’ barks, causing them to darken. Tell students to construct an explanation in which they develop a claim between the color of the peppered moths and their survival in their specific environments. Students should use the data from their activities to support their claim and include natural selection’s role in their reasoning.
Assessment: Students’ understanding of natural selection will be gauged on their anticipation guide, classroom discussion, and writing pieces in which they apply their knowledge of natural selection and genetic traits.
Adaptations: You may want to select organisms ahead of time that adapted or went extinct and allow students to choose from that list. You may also compile a list of resources for students to use to research their selected organism.
- After further studying natural selection, have students complete their anticipation guide (true/false) and discuss it together as a class.
- Have students research the effects of invasive species on native populations to show a connection to an environment changing and the organism having/not having the genotype for survival.
- Introduce artificial selection and compare it to natural selection.
- Have students model phenotypes/genotypes with Punnett squares to illustrate pattern of traits becoming more common over successive generations.