6.MS-LS4-1LS4.A: Evidence of Common Ancestry — analyze and interpret data for patterns in the fossil record and other evidence documenting how life has changed over Earth's history.6.MS-LS4-2LS4.A: Anatomical Structures — apply concepts to explain how anatomical similarities and differences among organisms provide evidence of evolutionary relationships.SP2: ModellingScience Practice 2: Developing and using models — using a simulation to analyze how populations can change over time in response to environmental events.
Simulation & ModellingSimulations help students manipulate variables and connect causes to population-level outcomes.Pattern RecognitionStudents identify patterns in trait frequencies and connect those patterns to survival pressure.Invisible PressureThis model helps students understand that environmental pressure can be invisible, not just visual.
Extension
Chernobyl Tree Frogs
Explore how a frog population changed after a sudden environmental disaster. Run the model, track light, medium, and dark frogs, then use your graph to explain what the data shows about how the population shifted over generations.
Above-Grade Science Connection
This real-world case explores evidence that populations can change over time. The biological mechanism behind these changes is studied in greater detail in Grade 8 evolution units.
1. Read
2. Simulate
3. Graph
4. Reflect
Phase 1
Before You Investigate
Unlock all four concepts to understand how selection pressure changes a population, then make a prediction before the simulation begins.
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What is this simulation showing?
You are watching how a population can change over time in response to an environmental event. The frog population begins with different melanin levels; this is called variation. When radiation enters the environment, data shows that certain frog colors become more common across generations. Your job is to observe the pattern, record the evidence, and construct an explanation for what the data shows.
Click to read
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Why are there different frog colors to begin with?
Variation exists naturally in every population. Some frogs start lighter and some start darker because of inherited differences in melanin. Natural selection does not create that variation from nothing; it acts on the variation that is already there. Before the Chernobyl event, neither color has a strong advantage. Once radiation enters the environment, selection pressure begins to act on that existing variation.
Click to read
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What makes this different from the beetle simulation?
In the beetle simulation, selection pressure came from predators spotting beetles by sight. Here, the pressure is radiation, an invisible environmental change. Survival depends on protection from cellular damage, not camouflage. The Chernobyl disaster changed the environment suddenly, just as the Industrial Revolution changed the trees that peppered moths already lived on.
Click to read
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Why do some light frogs still survive?
Because natural selection is probabilistic, not guaranteed. A lighter frog can still survive by chance, and a darker frog can still die. What changes over generations is the probability of survival, not a guarantee. This is why lighter frogs never completely disappear from the population; they just become rarer as the better-adapted trait becomes more common.
Click to read
Key Insight
Make Your Prediction
Before running the simulation: what do you think most determines which frog type becomes more common after the Chernobyl event?
A
Melanin protection, darker frogs are more likely to survive after radiation enters the environment
B
Starting numbers, whichever frog type begins with more individuals will always stay dominant
C
Individual need, frogs become darker because they need protection from radiation
D
Pure chance, frog populations shift randomly with no connection to the environment
Ready to Investigate
Here is what you will be tracking:
Light frog percentage, at every even generation (G0, G2, G4...)
Medium frog percentage, at the same generations
Dark frog percentage, watch how the Chernobyl event changes the trend
Phase 2
The Simulation
Run the model and watch what happens before and after the Chernobyl event. The population starts with variation, then radiation changes which traits improve survival.
Controls
Model Note
Radiation affects many traits. This model focuses on melanin as one example of how a population can change over time.
Simulation Complete
Population
0
Generation
Light frogs
Medium frogs
Dark frogs
40% light35% medium25% dark
20
Light
18
Medium
12
Dark
50
Total
Light frogs
Medium frogs
Dark frogs
Phase 3
Plot Your Data
Select a frog type on the right, then click each even-numbered generation to plot that type's percentage. Plot all three types, check your graph, and then continue to reflection.
Your Graph
Progress 0 / 33
Your Data
Gen
% Light
% Medium
% Dark
Run simulation first...
Plotting color
Actions
Your light points
Your medium points
Your dark points
Actual light %
Actual medium %
Actual dark %
-
Graph Accuracy
Plot one point per frog type at G0, G2, G4... Click a filled slot to replace it.
Phase 4
Reflect
Reflection questions are hiddenComplete the graph and written reflection for your teacher
Student Information
Your Name *
Your Teacher *
Question 1
Describe the shape of your graph. Which frog type became more common, and when did the biggest change happen?
Question 2
A major environmental event occurred during the simulation. What effect did it have on the frog population?
Question 3
If the simulation continued for 10 more generations, what do you predict would happen to the population? Explain your reasoning using natural selection.
Question 4
Why was a line graph the correct type of graph to use for this data? What does a line graph show that a bar graph or pie chart could not?