The PhET Natural Selection lab is one of the clearest ways to show students how evolution works over generations. In the free Natural Selection simulation from the University of Colorado Boulder, students watch a population of bunnies reproduce, add mutations such as brown fur or long teeth, and then switch on selection pressures like wolves or tough food. In a single class period they can see allele frequencies shift in a way a textbook diagram cannot show.
This guide gives you a ready-to-use PhET Natural Selection lab for middle school life science and high school biology: setup, a step-by-step procedure, a data table, analysis questions and common misconceptions to watch for. It runs in any web browser, so it works on Chromebooks, laptops and tablets.
In this guide11 sections
What the Natural Selection simulation does
The simulation has two screens. The Intro screen keeps things simple with one trait, fur color, so students can focus on the basic idea. The Lab screen adds three traits (fur color, ear shape and teeth length), lets students choose whether each new allele is dominant or recessive, and offers three selection agents: wolves, tough food and limited food.
Students can switch between an equator environment (brown, sandy background) and an arctic environment (white, snowy background). Graphs show population size and the proportion of each trait over time, and a pedigree view lets students trace how a trait passed from one bunny to its offspring.
Learning goals
- Explain that variation in a population comes from mutations and inheritance.
- Describe how a selection pressure changes which traits become more common.
- Show that the “best” trait depends on the environment.
- Interpret population and proportion graphs as evidence.
- Distinguish between dominant and recessive alleles in a population (Lab screen).
These goals line up well with middle and high school standards on natural selection and adaptation, such as NGSS MS-LS4-4 and HS-LS4-4.
Setup before class
- Open the Natural Selection simulation on the PhET website and check that it loads on student devices.
- Decide whether students will use the Intro screen only (about 30 minutes) or both screens (a full 50 to 60 minute period).
- Prepare the data table below on paper or in a shared document.
- Pair students up. One controls the simulation, one records data, then they swap for Part 2.
If you use several PhET labs during the year, our classroom simulations page keeps them all in one place.
Part 1: Fur color and wolves (Intro screen)
- Click Add a Mate to start the population with two bunnies.
- Let the population grow for a couple of generations with no mutation and no selection. Record the population size.
- Add the brown fur mutation. Let three generations pass and record the number of brown and white bunnies.
- Keep the equator environment and turn on wolves. Run several more generations and record the results.
- Switch to the arctic environment with wolves still on. Predict first, then run and record.
Ask students to write a prediction before every change. The prediction is where most of the learning happens, because students have to commit to an idea before they see the evidence.
Part 2: Multiple traits and selection agents (Lab screen)
- Start a new population and add the long teeth mutation.
- Turn on tough food. Predict which teeth trait will increase, then run several generations.
- Reset. Add the floppy ears mutation and choose whether it is dominant or recessive.
- Turn on limited food and observe what happens to the population size.
- Challenge round: combine two mutations and two selection agents. Groups write a short claim about which bunnies survive best and why.
Data table
| Trial | Environment | Mutation(s) | Selection agent | Prediction | Trait proportion after run | Population size |
|---|---|---|---|---|---|---|
| 1 | Equator | None | None | |||
| 2 | Equator | Brown fur | None | |||
| 3 | Equator | Brown fur | Wolves | |||
| 4 | Arctic | Brown fur | Wolves | |||
| 5 | Equator | Long teeth | Tough food | |||
| 6 | Your choice | Your choice | Limited food |
Because the simulation includes randomness, groups will get slightly different numbers. That is a feature, not a problem: compare results across the class and talk about why repeated trials matter.
Analysis questions
- Where did the brown fur trait come from? Did any bunny “decide” to change color?
- Why did brown fur become more common at the equator with wolves, but less common in the arctic?
- What happened to the population when there was no selection agent? Why?
- How did tough food affect the proportion of long-toothed bunnies?
- Did a dominant mutation spread faster or slower than a recessive one? Use your data.
- Write a claim-evidence-reasoning paragraph explaining natural selection using one of your trials.
For a quick end-of-lab check, use one of these exit ticket ideas, such as “Explain why the best trait depends on the environment.”
Misconceptions to watch for
- “The bunnies changed because they needed to.” Point out that mutations appear at random and the environment only affects who survives and reproduces.
- “Individuals evolve.” No single bunny changes during its life. The population changes across generations.
- “There is one best trait.” The arctic versus equator comparison shows that fitness depends on context.
- “Dominant means more common.” Students can test this directly on the Lab screen.
Extensions
- Have students graph the proportion data by hand and compare it with the simulation graph.
- Connect the lab to real examples, such as the peppered moth or antibiotic resistance in bacteria, and ask students to match each to a part of the simulation.
- Pair this lab with the Build a Molecule PhET lab or other simulations for a “virtual lab week.”
Frequently asked questions
Is the PhET Natural Selection simulation free?
Yes. PhET simulations are free to use and run in a web browser on most devices, including Chromebooks.
What grade level is this lab for?
The Intro screen works well for grades 6 to 8. The Lab screen, with dominant and recessive alleles and multiple selection agents, fits high school biology.
How long does the lab take?
Part 1 takes about 25 to 30 minutes. Both parts plus analysis fill a 50 to 60 minute class period.
Why do different groups get different results?
The simulation includes chance, just like real populations. Pooling class data gives a clearer pattern and opens a good discussion about sample size.
Wrap-up
The PhET Natural Selection lab turns an abstract idea into something students can watch, test and argue about with evidence. Keep the predictions, compare class results and finish with a written explanation. For more simulation-based lessons, try the PhET pH Scale lab or the Gravity and Orbits simulation lab.
