Natural selection

Overview

This lesson introduces natural selection as a mechanism for evolution, building towards later lessons that examine fossil evidence and more detailed evolutionary patterns. Students will connect variation within a species to survival and reproduction, and use fossil ideas to explain why change over long time periods is expected.

Learning intentions

Students will:

• understand that individuals of the same species show variation
• explain natural selection as a process where advantageous traits become more common over generations
• describe how fossils can provide evidence that species change over time
• use scientific modelling (simple population changes) to justify explanations

Success criteria

Students can:

• explain natural selection using the terms variation, inheritance, and survival/reproduction
• give at least one example of a trait becoming more common due to environmental conditions
• link fossil evidence to the idea that organisms evolved over long periods
• describe why natural selection is driven by competition for limited resources

Curriculum links

• Inheritance, chromosomes, DNA and genes: connects variation between individuals with how traits can be passed on and become more common
• Science – key stage 3: encourages modelling and abstract ideas to evaluate explanations
• Science – key stage 3: relates scientific explanations to phenomena in the world (e.g. changing environments and survival)
• Science – key stage 3: builds foundational knowledge about how variation and selection drive change over time

Lesson structure (60 minutes)

1. 0–5 min · Hook. Teacher shows two pictures of the “same species” in different habitats (e.g. beaks in different food types) and asks: “Why might one kind survive better than another?” Students quick-write 1–2 predictions about what determines who survives.

2. 5–15 min · Activate prior knowledge + define key ideas. Teacher leads a short discussion on variation (differences within a species) and introduces the idea that some variation is inherited from parents (kept conceptually simple). Students complete a “Variation → Advantage?” think-pair-share, choosing which trait might help in a given environment and why.

3. 15–25 min · Direct teach: natural selection model. Teacher explains the cycle: variation exists → environment creates a challenge → some traits help survival and reproduction → those traits become more common over generations. Students annotate a class diagram of the process and answer two teacher prompts: “What changes over generations?” and “What does not need to be aimed or planned?”

4. 25–40 min · Activity: population simulation (paper or cards). Teacher sets up a simple “population” using cards representing individuals with different traits (e.g. Trait A or Trait B), plus an “environment” condition card for this round (e.g. scarce food type). Students run 3 generations: in each, they select which individuals “survive” based on the environment, then “reproduce” by adding offspring cards from survivors (keeping the setup consistent). Teacher prompts: “Record the proportion of each trait after each generation.”

5. 40–50 min · Fossil evidence mini-lesson (bridge to unit). Teacher introduces fossils as evidence that helps scientists reconstruct how organisms have changed, using examples of “older vs newer” layers and observable differences over time (no detailed dating required). Students create a short “Claim–Evidence–Reasoning” statement: “Fossils suggest change over time because…”.

6. 50–58 min · Whole-class synthesis. Teacher leads a structured recap: connect simulation results to natural selection, then connect fossil patterns to the idea of evolutionary change across long periods. Students answer: “How does natural selection explain what we see in fossils?” using sentence starters displayed.

7. 58–60 min · Exit ticket. Teacher collects one quick response: “Explain natural selection in 4 steps” and “Give one example of how an environmental change could shift which trait becomes more common.” Students submit on paper or a worksheet.

Resources

• Image slides or printed pictures showing similar species in different environments
• Trait cards (e.g. A/B) for 30 students (or group sets)
• Environment cards (one for this lesson) describing a survival challenge
• Recording sheet with tables for Generation 1–3 trait proportions
• Fossil picture set (a few printed examples of older/newer comparisons)
• Claim–Evidence–Reasoning template (one per student)
• Exit ticket slips

Assessment

• During hook and discussions: teacher checks misconceptions (e.g. “traits appear by choice”) through targeted questions
• During simulation: teacher listens for correct use of “variation” and evidence from recorded proportions
• Exit ticket: assesses ability to explain natural selection and link fossil evidence to change over time

Differentiation

• Support: provide sentence starters for explanation (e.g. “Because individuals vary…, in this environment…, therefore…”) and a completed example diagram partially filled in
• Support: give a simplified recording sheet with prompts (“Count Trait A”, “Count Trait B”, “Which increased?”)
• Extension: ask students to propose a different environment for a second run and predict the new direction of change before simulating
• EAL/SEN: allow use of first language for planning on rough paper, then scaffold into UK English using provided frames; check understanding of key terms (variation, inherited, generations) with quick teacher questioning