Describe adaptation across many generations
Adaptation through natural selection is a population process, not a short-term individual change.
Section 18.3 · Selection
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Use the stated case, sample and assumptions. Diagrams and numerical records in this pathway are original teaching models; written answers are self-checked.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
In this syllabus, adaptation by natural selection describes what?
What you will learn
- Define adaptation as population change over generations
- Separate evolution from an individual response
Original selection schematic. Population counts and scenarios are supplied teaching models; they are not field observations.
| Stage or record | Meaning |
|---|---|
| Generation 1 | 20% stated phenotype |
| Generation 2 | 35% |
| Generation 3 | 52% |
| Interpretation | Trend only; inheritance and reproductive evidence needed |
Define adaptation as population change over generations
Cambridge defines adaptation here as the process resulting from natural selection by which populations become more suited to their environment over many generations. Begin with variation in a population; environmental conditions affect which individuals reproduce; inherited features can become more common among descendants over time.
An individual may acclimatise or change behaviour during its lifetime, such as moving into shade. That response can help the individual but is not the same as a population becoming more suited through inherited changes over generations. Do not describe a single organism “evolving” a needed feature during its life.
Separate evolution from an individual response
“More suited” is relative to a particular environment and timescale. A feature associated with greater reproduction in one condition might be neutral or disadvantageous when conditions change. Adaptation does not mean perfection, intention or guaranteed survival; populations continue to face changing constraints and chance events.
Use records from several generations and keep cohort membership clear. A changing fraction of a phenotype can be consistent with selection if inheritance and reproductive differences are supported. It is not automatically an allele-frequency measurement. Name the evidence, the environmental context and the limits before concluding that a population has adapted.
Pause and explain
Which evidence best supports a natural-selection account of adaptation?
Worked example
In an invented population, the share of a stated inherited drought-tolerant phenotype is 20%, 35% and 52% in three comparable generations. What trend is shown and what additional link supports adaptation by natural selection?
Show the worked solution
- Describe the recorded phenotype trend across the three generations.
- Look for evidence of differential reproduction and transmission of the inherited feature.
Answer The phenotype share rises across the three recorded generations. Evidence that the feature is inherited and associated with greater reproduction in the drought context would support adaptation by natural selection; the proportions alone do not prove cause.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A cold-island population has a rising share of an inherited insulating feature over five generations, and carriers produce more offspring in that setting. Give a bounded adaptation explanation.
Give me a hint
Link inherited variation, relative reproduction and multiple generations.
Compare my reasoning
- The feature is stated as inherited and exists in the population.
- Greater offspring contribution can make it more common in later generations.
The repeated pattern is consistent with adaptation by natural selection in the cold-island environment; it does not mean every carrier survives or the feature is best elsewhere.
Look for these in your work
- Inheritance and reproduction linked
- Context and limit retained
A lizard moves under a rock during hot weather. Does this alone show adaptation under S18.3.4?
Give me a hint
The observation concerns one individual and one lifetime.
Compare my reasoning
- Moving is an individual behaviour.
- No population trend over generations or inherited change is measured.
No. It may be an immediate response that helps that lizard, but it does not establish population adaptation through natural selection over many generations.
Look for these in your work
- Individual response distinguished
- Population evidence named
A phenotype rises from 15% to 40% over three samples, but each sample is from a different location and genotype data are absent. State what can and cannot be concluded.
Give me a hint
Keep the recorded percentage separate from inheritance and location.
Compare my reasoning
- The samples have different phenotype proportions.
- Location and genotype differences prevent a single selection explanation.
The recorded phenotype share is higher in the later sample, but the records do not establish a generational population trend, allele frequency or natural-selection cause.
Look for these in your work
- Observation accurately described
- Missing evidence
Common mistakes
- Saying one plant adapted its genes in a drought
- Calling every phenotype proportion an allele frequency
- Treating adaptation as perfection or intent
What can you explain now?
Which evidence best supports a natural-selection account of adaptation?
Compare with the explanation
Repeated population records with inherited variation and reproductive differences
The evidence connects inheritance, reproduction and generations.
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Make it stick
Without your notes, define adaptation as population change over generations and separate evolution from an individual response. Explain the mechanism, use the given population or breeding records and state what the evidence does not establish.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.