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# How different are individuals?

Year 10 Biology · Evolution

<!-- Speaker note: Students measure variation in a population, distinguish continuous from discontinuous and inherited from environmental variation, and explain why inherited variation matters for evolution (AC9S10U02, node 1, a hinge node). About 20 minutes (Engage and Explore 7 min · Explain 8 min · Evaluate 3 min · Typical adds 1 min, Wider about 1 min). -->

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## Today

**We are learning to** individuals in a population vary. Measuring one characteristic across a population gives a spread of values, often most near the middle. Some variation is inherited (genes) and some comes from the environment; inherited variation is what natural selection acts on.

- I can describe the variation in a measured population.
- I can classify variation as continuous or discontinuous, inherited or environmental.
- I can explain why only inherited variation is passed on.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it pairs well with measuring hand spans or heights in class. Set the width with `?width=minimum`, `typical` (default) or `wider`. The hinge misconception is that a species is uniform. The board's population is spread around a middle colour. Board notes: beetle colour runs from 0 (palest) to 1 (darkest); the starting population is spread around 0.5. Measuring doesn't change the population. The next lesson uses the same beetles under selection. -->

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## Why it matters

> Look closely at a patch of grass beetles, a school of fish or a class of Year 10s. No two are quite the same. That spread is the raw material of evolution.

<!-- Speaker note: Meiosis and fertilisation make every offspring different. This lesson: what that variation looks like across a whole population. -->

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## Engage: predict

**You measure the colour of 20 beetles of one species from the same field. What do you predict?**

- Completely random: no pattern
- A spread of colours, with most near the middle and a few very pale or very dark
- They're all the same colour: same species
- Two colours only

<!-- Speaker note: What happens: A spread, with most near the middle and fewer at the extremes. A characteristic controlled by many genes usually varies continuously like this. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: count how many chose 'all the same'. -->

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## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fbiology-10%2Fvariation%2Fstep-2&code=widget%3A+selection%0Agoal%3A+measure%0Aneed%3A+20%0An%3A+40%0A}}

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

<!-- Speaker note: Click beetles to measure their colour (0 is palest, 1 darkest). Watch the bar chart under the board as it fills. -->

<!-- Speaker note: Teacher: compare bar charts between students: similar shape, different details. -->

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## What happened?

* A spread, with most near the middle and fewer at the extremes. A characteristic controlled by many genes usually varies continuously like this.

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

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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>

## Continuous or not

**Continuous (any value in a range) or discontinuous (a few distinct groups)?**

Groups: Continuous · Discontinuous

Height · Blood group (A, B, AB, O) · The beetles' colour · Pea flower colour (purple or white) · Hand span

* Answer: Height → Continuous; Blood group (A, B, AB, O) → Discontinuous; The beetles' colour → Continuous; Pea flower colour (purple or white) → Discontinuous; Hand span → Continuous

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: the 'why only inherited' question is the checkpoint. -->

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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>

## Where it comes from

**Mainly inherited, mainly environmental, or both?**

Groups: Inherited · Environmental · Both

Blood group · A scar · Height · Natural eye colour · Speaking French

* Answer: Blood group → Inherited; A scar → Environmental; Height → Both; Natural eye colour → Inherited; Speaking French → Environmental

<!-- Speaker note:  -->

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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>

## What gets passed on

**Why does only inherited variation matter for evolution?**

- Environmental variation isn't real
- Environmental variation only happens in humans
- Only inherited characteristics are passed to offspring through genes
- Inherited variation is bigger

* Answer: Only inherited characteristics are passed to offspring through genes

<!-- Speaker note:  -->

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## Elaborate: where variation comes from

**Which of these makes new inherited variation in a population?**

- The environment changing an animal's genes to suit it
- Animals trying hard to change
- Eating different food
- Mutations, plus new combinations of alleles from meiosis and fertilisation

* Answer: Mutations, plus new combinations of alleles from meiosis and fertilisation

<!-- Speaker note: What this step is for: Naming the sources of new inherited variation links the genetics unit to this one. -->

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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>

## Elaborate: sampling

**Someone measures only the 5 easiest-to-spot beetles and says the population is mostly dark. What's wrong?**

- Beetles can't be measured
- They should have measured only pale beetles
- Nothing: 5 is enough
- The sample is small and biased: the easiest beetles to spot aren't typical

* Answer: The sample is small and biased: the easiest beetles to spot aren't typical

<!-- Speaker note: What this step is for: Questioning a sample's size and fairness uses the board's measurements as data. -->

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## Evaluate: look back

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

**Revision summary**

- Individuals in a population **vary**; measuring a characteristic gives a **spread**.
- **Continuous** variation takes any value (height); **discontinuous** falls into groups (blood group).
- Variation can be **inherited**, **environmental** or both; only inherited variation is passed on, so only it matters for evolution.
- New inherited variation comes from **mutations** and from **meiosis and fertilisation**.

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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

**Give an example of inherited variation and one of environmental variation in humans.**

* For example: blood group (inherited); a scar or a language spoken (environmental).

<!-- 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: Next: natural selection (node 2) with the same beetles. In class: measure and graph hand spans; compare with blood groups or earlobes. -->