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# Why did the beetles change?

Year 10 Biology · Evolution

<!-- Speaker note: Students model natural selection as predators, explain it in steps, reject the idea that individuals change because they need to, and connect it to common ancestry and the tree of life (AC9S10U02, node 2, a hinge node). About 26 minutes (Engage and Explore 9 min · Explain 11 min · Evaluate 3 min · Typical adds 4 min, Wider about 1 min). -->

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## Today

**We are learning to** natural selection: individuals vary; more are born than survive; those best suited to the environment are more likely to survive and reproduce, passing on their alleles. Over generations the population changes. Individuals don't change to suit the environment.

- I can explain natural selection in steps.
- I can explain that populations change, not individuals.
- I can explain why "fittest" depends on the environment.
- I can explain that all living things are related in a branching tree, and why features alone can mislead about relatedness.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it pairs well with the classic peppered moth story and a paper-dots predation game. Set the width with `?width=minimum`, `typical` (default) or `wider`. The hinge misconception is need-driven change ("the beetles turned dark to hide"). The Engage question puts it directly, and the board never changes a beetle's colour. Closing the loop with Year 7: the last three Explain questions take natural selection to common ancestry (a branching tree, not a ladder; DNA similarity tracks how recently species shared an ancestor) and back to the Year 7 Kingdoms lesson, where students met the idea that kingdoms sort by features, not relatedness. This supports the descriptor's "explain past and present diversity" and prepares the evidence for evolution. Board notes: half the beetles are eaten each generation; survivors breed back to the full number, and each offspring gets the average of two parents' colours plus a small random change (a stand-in for many genes and mutation). The automatic birds favour beetles that contrast with the ground but also eat some at random. Results vary from run to run; with student hunting, a student who clicks randomly sees little change, which is a good discussion point. -->

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## Why it matters

> After a bushfire, the ground is black. A few years later, a beetle population on it is darker than before. No beetle changed colour.

<!-- Speaker note: Individuals vary. This lesson: what happens to that variation when some individuals are more likely to survive. -->

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## Engage: predict

**Birds eat the beetles they can see most easily. Over many generations the population becomes better camouflaged. How?**

- Beetles that blend in survive more often and have more offspring, so the population's colours shift
- Beetles choose a ground that matches
- The birds teach the beetles
- Each beetle changes colour to hide, because it needs to

<!-- Speaker note: What happens: Beetles that blend in survive and breed more, so their offspring (with similar colours) make up more of the next generation. Individuals never change; the population does. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: count how many chose 'each beetle changes colour'. -->

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## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fbiology-10%2Fnatural-selection%2Fstep-2&code=widget%3A+selection%0Aground%3A+light%0Ahunter%3A+student%0Aneed%3A+3%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-10/natural-selection/?full=step-2#step-2)

<!-- Speaker note: You are a bird. Click beetles to eat them (as fast as you can, like a hungry bird). Then press **Survivors breed**. Compare the bar charts: the start and the latest generation. -->

<!-- Speaker note: Teacher: collect the class's starting and final averages; most should have moved towards the ground colour. -->

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## What happened?

* Beetles that blend in survive and breed more, so their offspring (with similar colours) make up more of the next generation. Individuals never change; the population does.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

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## The steps

**Put the steps of natural selection in order.**

Groups: 1st · 2nd · 3rd · 4th · 5th

Beetles in the population vary in colour · Birds eat the beetles that stand out most · Beetles that blend in are more likely to survive · Survivors breed, passing on the alleles for their colour · Over generations, the population's average colour shifts

* Answer: Beetles in the population vary in colour → 1st; Birds eat the beetles that stand out most → 2nd; Beetles that blend in are more likely to survive → 3rd; Survivors breed, passing on the alleles for their colour → 4th; Over generations, the population's average colour shifts → 5th

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: 'did any beetle change?' is the checkpoint. -->

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## Who changed

**Did any single beetle on the board change its colour?**

- Yes, the survivors got paler
- No: each beetle kept its colour; the population changed because of who survived and bred
- Yes, the eaten ones got darker
- Only the babies changed

* Answer: No: each beetle kept its colour; the population changed because of who survived and bred

<!-- Speaker note:  -->

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## No variation

**What would happen if every beetle started exactly the same colour?**

- Selection couldn't change the population: there would be no variation to select from
- They would all be eaten
- They would turn the ground's colour
- They would still evolve the same way

* Answer: Selection couldn't change the population: there would be no variation to select from

<!-- Speaker note:  -->

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## A branching tree

**Over millions of years, populations split apart and natural selection changes each part differently. What does that mean for living things today?**

- Each species began separately, so they aren't related
- They are all related, in a branching family tree: close relatives share a recent common ancestor
- They form a ladder, with humans at the top as the most evolved

* Answer: They are all related, in a branching family tree: close relatives share a recent common ancestor

<!-- Speaker note: Splitting and selection, repeated over millions of years, give a branching tree of life. Every living thing is related; the question is how closely. -->

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## Closest DNA

**If relatives share ancestors, which pair would you expect to have the most similar DNA?**

- A human and a mushroom
- A human and a mouse
- A human and a chimpanzee

* Answer: A human and a chimpanzee

<!-- Speaker note: The more recently two species shared an ancestor, the more similar their DNA. Comparing DNA is how biologists now draw the tree of life. -->

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## Back to the kingdoms

**In Year 7, kingdoms put mushrooms in their own group, and many people think of them as plant-like. DNA shows fungi share a more recent ancestor with animals than with plants. Why don't features alone show this?**

- Similar features can evolve in unrelated groups, and close relatives can come to look very different
- Fungi evolved from plants
- DNA tests are unreliable

* Answer: Similar features can evolve in unrelated groups, and close relatives can come to look very different

<!-- Speaker note: Natural selection shapes features to suit each environment, so features can mislead about family. That is why classification moved from kingdoms by features to groups by shared ancestry, and changes as evidence improves. -->

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## Elaborate: after the bushfire

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fbiology-10%2Fnatural-selection%2Fstep-4&code=widget%3A+selection%0Aground%3A+light%0Ahunter%3A+birds%0Achange%3A+on%0Aneed%3A+6%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-10/natural-selection/?full=step-4#step-4)

<!-- Speaker note: What this step is for: Changing the environment and watching the direction of selection reverse shows 'fittest' depends on the environment. -->

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## Fittest

**Before the fire, paler beetles survived best. After it, darker ones did. What does that tell you about 'survival of the fittest'?**

- Fittest means strongest
- Fittest means best suited to the current environment, which can change
- The darker beetles were always fitter
- Fitness doesn't depend on the environment

* Answer: Fittest means best suited to the current environment, which can change

<!-- Speaker note:  -->

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## Elaborate: antibiotic resistance

**Why does using antibiotics more often make resistant bacteria more common?**

- Each use kills the bacteria that aren't resistant; any that happen to be resistant survive and multiply
- Bacteria learn to resist
- Antibiotics make bacteria resistant
- It doesn't make a difference

* Answer: Each use kills the bacteria that aren't resistant; any that happen to be resistant survive and multiply

<!-- Speaker note: What this step is for: Applying natural selection to bacteria and antibiotics transfers the steps to a medical context. -->

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## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- **Natural selection:** individuals **vary**; more are born than survive; those **best suited** to the environment are more likely to **survive and reproduce**; they pass on their **alleles**; over **generations**, the population changes.
- **Individuals don't change** to suit the environment; the population does.
- "Fittest" means best suited to the **current** environment. Selection needs **variation**.
- Over millions of years, populations split and diverge: all living things are related in a **branching tree of life**, not a ladder. The more recent the **common ancestor**, the more similar the DNA.
- Features can mislead about relatedness (fungi are closer to animals than to plants), so modern classification uses shared ancestry, and changes as evidence improves.

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**Explain why the beetle population got paler on pale ground.**

* Beetles varied in colour; birds ate the darker, more visible ones; paler beetles survived and bred, passing on their colour; over generations, the average colour got paler.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this leads: Later: evidence for evolution (fossils, comparative anatomy, DNA) in more depth, and speciation, if your program covers them. Year 7 Kingdoms is the earlier half of the classification thread. In class: the paper-dots predation game on newspaper and plain paper; antibiotic resistance as a case study. -->