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.

🔬 Learning Science Focus Simulation & Modelling Pattern Recognition Invisible Pressure
📋 MA STE Standards · Grade 6 6.MS-LS4-1 6.MS-LS4-2 SP2: Modelling
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.
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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.
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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.
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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.
Key Insight