Biology & life sciences · 10 / 12
Evolution: populations and selection
Final-year concepts · Worked example and 4 exercises with solutions, at your pace.
The principle, simply
Evolution changes allele frequencies in populations across generations. Mutation creates variation; selection, genetic drift and gene flow may alter frequencies. Selection depends on reproductive success in an environment, not a wish to adapt or progress towards perfection.
- 01Heritable variation
- 02Reproduction
- 03Selection or chance
- 04Population frequencies
WORKED EXAMPLE
From principle to reasoning
A heritable variant may improve reproductive success after environmental change, increasing its frequency without individuals intentionally transforming.
Solve a problem in this subject
- Frame a question
State the relationship to explain and its scale: molecule, cell, organism, population or geological time.
- Describe evidence
Give a measurable observation, unit, comparison and conditions before explaining it. Observation and inference do different jobs.
- Connect a mechanism
Use a precise concept and label arrows as production, transfer, action or transformation. Sequence alone does not prove causation.
- Answer with a limit
Connect evidence and knowledge to the question. Distinguish the simplified model from living systems and identify a missing condition.
YOUR TURN
01 · Try before checking
A tiny population changes allele frequencies without an identified advantage. What mechanism should you consider?
One hint
Think of random sampling between generations.
Reveal and understand the solution
Genetic drift may change frequencies by chance, especially in small populations. Examine evidence for other mechanisms too.
Compare method, conditions and answer; identify the exact part to revisit.
IMPROVE THROUGH PRACTICE
Three additional challenges with solutions
Start with the first challenge. Write your method before opening a hint; use the solution to find the first step that needs work.
Does increased resistance mean organisms created a mutation because they needed it?
A hint to get started
Separate variation from selection.
Step-by-step solution
- Variants can pre-exist or arise without direction toward need.
- Treatment favours those surviving and reproducing.
- Selection changes frequencies; need does not direct mutation.
Which step did you miss? Retry without help, then explain why the method works.
A neutral allele changes frequency randomly in a small population. Which mechanism is this?
A hint to get started
The question specifies no selective advantage.
Step-by-step solution
- This is genetic drift.
- Random sampling during reproduction changes frequencies.
- The effect is often stronger in small populations.
Which step did you miss? Retry without help, then explain why the method works.
If two species share a recent ancestor, must one descend from the other?
A hint to get started
A node represents a common ancestor.
Step-by-step solution
- Both branches derive from that ancestor.
- Neither living species is automatically ancestral to the other.
- The tree represents relationships, not a ladder of perfection.
Which step did you miss? Retry without help, then explain why the method works.
The trap to avoid
Individuals do not genetically evolve to meet a need; selection and drift differ.
Without notes, can you…
- Explain the principle in your own words?
- Rebuild the diagram and its connections?
- Solve the exercise and justify the method?
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