Grade 10 · Evolution and Natural Selection · Natural Selection
Variation and Natural Selection
Why some individuals survive, reproduce and pass on their traits.
Learning objectives
- Distinguish inherited from environmental variation.
- Explain natural selection using a worked example.
- Use data to justify a claim about selection pressure.
NGSS alignment
MS-LS4-6
Use mathematical representations to support explanations of how natural selection may lead to increases and decreases of specific traits in populations over time.
HS-LS4-2
Construct an explanation based on evidence that the process of evolution primarily results from four factors: potential for a species to increase in number, heritable genetic variation, competition for resources, and proliferation of those organisms better able to survive and reproduce.
MS-LS4-4
Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals' probability of surviving and reproducing in a specific environment.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion B — Inquiring and Designing
- Criterion C — Processing and Evaluating
ENGAGE
Peppered moths on soot-blackened bark
In industrial England, dark peppered moths went from rare to common in a few decades, then became rare again after clean air laws.
Think about it
- What advantage did dark moths have on soot-covered trees?
- Why did the pattern reverse when the air became cleaner?
EXPLAIN
How natural selection works
| Type of variation | Cause | Example |
|---|---|---|
| Inherited | Alleles from parents | Blood group, fur colour |
| Environmental | Surroundings and lifestyle | Scars, language, plant height in poor soil |
| Both | Genes and environment | Human height, body mass |
The four steps
- Variation — individuals in a population differ
- Selection pressure — competition, predators or disease mean not all survive
- Survival and reproduction — better adapted individuals leave more offspring
- Inheritance — helpful alleles become more common over generations
Common misconception
Individuals do not evolve to suit their environment. Populations change because some individuals already carried useful alleles.
Antibiotic resistance in bacteria is natural selection happening fast enough to observe in a laboratory.
INVESTIGATION
Modelling a selection pressure
research question
How does background colour affect the survival of paper prey in a timed predation model?
hypothesis
Prey that match the background will survive longer than prey that contrast with it.
variables
Independent: background colour. Dependent: number of each prey colour collected in 20 seconds. Controlled: number of prey, time, collecting rules.
method
Scatter 50 dark and 50 light paper discs on a dark sheet. A collector picks up discs for 20 seconds. Count survivors, then repeat on a light sheet.
safety
Clear the working area to avoid slips.
analysis
Draw a bar chart of survivors and explain the results using selection pressure. Identify two limitations of the model.
Watch
Natural Selection
Amoeba Sisters · 8 min
Walks through the mechanism with clear examples.
Before you watch: What has to already exist in a population for selection to act?
- List the four steps of natural selection.
- Explain antibiotic resistance using these steps.
Interactive simulation · PhET
Natural Selection
Add a mutation, then add wolves as a selection pressure and watch the population change.
While you explore
- Which trait became more common, and why?
- What happens if you remove the selection pressure?
Key vocabulary
- Adaptation
- A feature that helps an organism survive where it lives.
- Natural selection
- Better suited individuals survive and pass on their traits.
Practice questions
0/2 correct
Level 1 · Criterion A
Which is an example of inherited variation?
Level 2 · Criterion A
Natural selection can only act if a population already has:
MYP criterion tasks
Level 3 · Criterion B
A bacterial population survives a course of antibiotics. Explain this using natural selection, and suggest how a hospital could test whether resistance is spreading.
Reflect & track
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