L01 — The War Zone

Module: M07 — The Arms Race Periods: 1 NGSS: HS-LS4-2 Lesson Type: Launch / Explore

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Learning Objective

• By the end of this lesson, students will be able to explain the four conditions required for natural selection (variation, inheritance, selection pressure, differential reproduction) by simulating a population under environmental stress.

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Phenomenon / Hook

MRSA Story, Part 1: Read aloud the opening of Addie’s story: “Addie was a healthy 17-year-old who scraped her knee at volleyball practice. Two days later, she was in the ER with a 104°F fever. The infection wasn’t responding to any antibiotics. Doctors told her parents she might not survive. The bacteria in her blood had evolved resistance — and it was winning.”

Pose the question: “How can bacteria ‘beat’ medicine that used to kill them? What does it mean to evolve?”

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Materials

• Projector for Addie story
• Colored tokens or dried beans: 30 red, 30 blue, 30 yellow (per group of 4)
• Paper cups (one per group)
• “Environment” cards (predator: students pick by sight — color matters)
• Data recording sheet: [[handouts/L01-selection-simulation-data]]
• Chart paper and markers

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Agenda

Opening (8 min)

• Read Addie MRSA story, Part 1 (3 min)
• Think-Pair-Share: “What does it mean for something to ‘evolve’? Have you heard the phrase ‘survival of the fittest’? What does ‘fittest’ actually mean?” (3 min)
• Collect ideas on board — don’t correct yet (2 min)

Explore (18 min)

• Selection Pressure Simulation
  • Each group of 4 gets 90 tokens (30 red, 30 blue, 30 yellow) in a cup representing a population with variation
  • Round 1 — Random Environment: Students spread tokens on desk. Teacher says “scramble!” Students have 10 seconds to grab as many tokens as possible (simulating random predation). Record survivors by color. Survivors “reproduce” — add one same-color token per survivor.
  • Round 2 — Selective Environment: Teacher announces “blue background!” (place blue paper under tokens). Now blue tokens are camouflaged. Predators (students) can only pick tokens they can see. Record survivors. Reproduce.
  • Round 3 — Environment Shift: Teacher announces “red background!” Repeat. Record. Reproduce.
  • Round 4 — Repeat red. Record. Reproduce.
  • Groups graph their population data: x-axis = round, y-axis = count by color
  • Guiding questions:
    1. Which color had the most survivors each round? Why?
    2. Did the population choose to change, or did the environment change which individuals survived?
    3. What happened when the environment shifted from blue to red?

Explain (10 min)

• Teacher-led synthesis on board:

• Over time: Population shifts toward the trait favored by the environment
• Students annotate their data sheet with these four terms and definitions
• Connect to MRSA: “In Addie’s body, the ‘environment’ was full of antibiotics. Bacteria with resistance survived. They reproduced. The population shifted.”

Elaborate (7 min)

• Quick Write: “If the environment shifted back to a neutral (no background) in Round 5, what would happen to your population? Would it return to equal numbers of all three colors? Why or why not?”
• Share 2–3 responses — emphasize that evolution isn’t reversible in a simple “undo” way

Closing (5 min)

• Exit Ticket: [[exit-tickets/L01-exit-ticket]]
  1. List the four conditions needed for natural selection to occur.
  2. In the simulation, why did the blue population increase when the background was blue? What “pressure” was acting on the population?

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Differentiation

Support	Extension
Provide a vocabulary anchor chart with the four conditions pre-printed — students fill in examples from the simulation	Ask: What if there were TWO predators with different abilities (e.g., one picks by sight, one picks by speed)? How would that change the outcome?
Pre-assign roles in groups: data recorder, graph maker, materials manager, reporter	Challenge students to calculate the rate of change per round for each color — which trait changed fastest?

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Assessment

• Formative: Circulate during simulation — check that groups are recording data accurately and can articulate why certain colors survive
• Exit Ticket: Four conditions identification + application to simulation

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Teacher Notes

• Pre-count tokens into cups before class. This saves 3+ minutes.
• The “predator” mechanic is just students grabbing tokens quickly — keep it fast and chaotic. That randomness is the point.
• If a group’s data looks weird (e.g., all one color by Round 3), that’s actually a great teaching moment — it shows how quickly selection can shift a population when the pressure is strong.
• The simulation is deliberately simple. Resist the urge to add complexity. The goal is to internalize the mechanism, not model every variable.
• Start the MRSA thread here and reference it in L02: “Remember Addie? Tomorrow we see exactly how her bacteria evolved.”