Biology · 40 minutes
Suggested grades 9–10 · Unit 3: Populations and Biological Evidence · Lesson 2 of 2
Explain a Population Shift Without Intent
Connect inherited variation, resource limits and reproductive success in an original model.
Mr. S Teaches · Original starter lesson · HS-BIO-06 · Grade range is planning guidance.Watch, notice, discuss
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Natural Selection
By Amoeba Sisters
Identify inherited variation, selection pressure and differential reproduction; revise explanations that give organisms intentions.
Open on YouTube: Natural Selection (opens a new tab) ↗Can wildlife adapt to climate change? - Erin Eastwood
By TED-Ed
Apply selection reasoning to climate-related examples; distinguish population change across generations from individual adjustment.
Open on YouTube: Can wildlife adapt to climate change? - Erin Eastwood (opens a new tab) ↗What idea from the video helps you construct a natural-selection explanation using four required factors and distinguish population change from individual intention? Identify one useful example and one limit of the video's model or explanation.
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Learning objective
Construct a natural-selection explanation using four required factors and distinguish population change from individual intention.
Before you begin
- Know inheritance and calculate a proportion.
Gather your materials
- Paper or notebook
- Pencil; calculator optional for numerical work; all task data supplied below
Language to know
- heritable variation
- Differences that can be transmitted through inherited information.
- reproductive success
- Contribution of surviving offspring to later generations.
- selection pressure
- A condition linked to differences in survival or reproduction.
Understand the concept
Original population model: A beetle population has inherited light and dark shell variants. More offspring are produced than local food can support. On a dark background, birds detect light beetles more often. Of 100 adults of each variant, dark beetles contribute 160 surviving offspring and light beetles 80. Assume shell variant is inherited and other conditions are comparable. The model suggests a frequency shift, not that beetles choose a needed color or that one short comparison proves every mechanism of evolution.
Teach it step by step
- Read the model and locate inherited variation, excess offspring, resource limits and unequal reproductive success.
- Calculate the fraction of surviving offspring contributed by each starting variant.
- Draw two generation bars and explain the changing population composition without making individual beetles change color.
- Write a qualified explanation naming the assumptions and one alternative influence requiring investigation.
Make the thinking visible
Worked example or model response
The offspring total is 240, with dark contribution 160/240 = 2/3. The initial adults were half dark, so the modeled contribution shifts toward dark variants. This assumes the relevant variant is inherited; a temporary noninherited color change would not support the same explanation.
Guided practice
Together revise “The beetles became dark because they wanted to survive” using variation already present before predation.
Independent practice
Write a six-sentence explanation including all four factors, numerical evidence, inheritance and a limit. Propose a comparison on a light background.
Quick assessment
Would natural selection necessarily favor the same shell variant in every environment?
Answer key & assessment criteria
Answers and teaching guidance
- Guided: Dark variants were already present; differential reproductive contribution changes frequencies over generations rather than fulfilling an individual wish.
- Independent: Require four factors, 2/3 offspring contribution, inheritance assumption and an appropriate background comparison or alternative cause.
- Quick check: No. Advantages depend on environmental conditions and tradeoffs; the model does not establish a universally best variant.
Look for: Assess the stated objective using the concrete criteria and explanations in the answer key. Invite an alternative supported solution; distinguish a model’s prediction from an established observation.
Make it work for your learner
More support
Offer four factor cards and a two-generation bar outline, then organize the explanation around those cards.
Extension challenge
Predict how migration or chance in a small sample could complicate this simple selection account without replacing the selection mechanism.
Verified references · Selected contributions
Standards connections
Selected NGSS high school-band contribution; full performance requires additional evidence and instruction.
Subject-content standards
These records identify the part of a subject standard practiced here. Course placement is instructional guidance; the source’s category or band remains authoritative.
Contributes to NGSS performance expectation
HS-LS4-2
NGSS · High school band
Explain natural selection using inherited variation and unequal reproductive success.
Read the official performance expectation ↗This selected model connects the four factors associated with natural selection. It lacks independent empirical sources and does not model all evolutionary mechanisms or long-term species change.
Verified 2026-11-04. Selected contribution, not full attainment.
Supporting literacy connections
These records apply to the specified reading, writing or communication task. They do not establish subject-content alignment.
Supporting Common Core literacy connection
RST.9-10.1
Common Core · Grades 9–10
Use precise textual details in scientific analysis.
Read the official standard ↗The activity explicitly analyzes the provided technical text, table or model. It contributes selected literacy practice rather than complete grade-band reading coverage or independent subject-content alignment.
Verified 2026-11-04. Selected contribution, not full attainment.