How does a nuclear disaster change a frog population over time? Run the simulation and watch how melanin affects survival before and after the Chernobyl event.
This page is a three-step scientific investigation. Complete each step in order.
Individual frogs do not darken because they need to. Frogs are born with their traits. It is the population that changes over time — because some traits help survival more than others.
Read the four questions and answers before touching the controls. They explain what the simulation is modeling.
Press Run and watch what happens. The population stays stable at first, then a major environmental event changes survival conditions.
Switch to Graph Mode to plot your results, then answer the reflection questions and submit.
You are watching natural selection happen over time. The frog population begins with different melanin levels — this is called variation. When radiation is present, frogs with traits that better protect their cells have a greater chance of surviving and reproducing. As generations pass, those heritable traits can become more common in the population. This is adaptation through natural selection.
Variation exists naturally in every population — no two individuals are exactly identical. 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.
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. This models a key idea: selection pressure doesn't have to be visible to be powerful. The Chernobyl disaster changed the environment suddenly, just as the Industrial Revolution changed the trees that peppered moths already lived on.
Because natural selection is probabilistic, not guaranteed. A lighter frog can still survive by chance. 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. Chance is always part of the process.
Select a frog type on the right, then click on each even-numbered generation (G0, G2, G4…) to plot that type's percentage. One point per type per generation.
| Gen | % Light | % Medium | % Dark |
|---|---|---|---|
| Run simulation first… | |||
Plot one point per frog type at G0, G2, G4… Click a filled slot to replace it.