G8.C3.W3

Evolution & Natural Selection Synthesis

MS-LS4-4 · MS-LS4-6 · How does natural selection change populations over time?

Instructions

Driving Question: How do trait frequencies shift across generations under selection pressure?

1. Choose an environment (desert, forest, arctic) — this sets which colors survive best.

2. Set predation pressure — higher pressure means stronger selection.

3. Click Run Generation to simulate one cycle of selection and reproduction.

4. Watch the trait histogram shift over generations!

50%
5%
50
Population View
Trait Frequency Over Generations

Population Stats (Gen 0)

Light (tan):33%
Medium (green):34%
Dark (brown):33%
Avg Fitness:--
Pop Size:50

Synthesis Concepts

Variation: individuals differ in heritable traits (color)
Selection: environment determines which traits are advantageous
Reproduction: survivors pass traits to the next generation
Adaptation: over many generations, the population shifts toward advantageous traits
Data JournalTrial 0
# Gen Env Light% Med% Dark% AvgFit
Data Journal — Record & Analyze Your Experiments
#Predation pressure percentageMutation rate percentagePopulation sizeObservation
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Predict

In a desert environment, which color organisms will become most common after 20 generations? What about in an arctic environment?

Observe

Run the simulation with high vs. low predation pressure. How does selection strength affect the speed of trait change? Does the population ever become 100% one color?

Explain

Why does natural selection act on individuals but evolution happens to populations? How does mutation prevent a population from losing all variation?