Explain how natural selection can lead to evolution in a population of organisms over many generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A population of beetles lives on dark-coloured tree bark. Some beetles have dark colouring and others have pale colouring. Birds hunt the beetles by sight.
Model answer (4 marks)
Variation exists within the population – some beetles are dark‑coloured and others are pale.
Dark‑coloured beetles are better suited to the dark bark, so they are less likely to be eaten by birds.
Because they survive longer, dark‑coloured beetles are more likely to reproduce and pass the allele for dark colour to their offspring.
Over many generations the frequency of the dark‑colour allele rises, producing a gradual change in the population – evolution.
Dark‑coloured beetles are better suited to the dark bark, so they are less likely to be eaten by birds.
Because they survive longer, dark‑coloured beetles are more likely to reproduce and pass the allele for dark colour to their offspring.
Over many generations the frequency of the dark‑colour allele rises, producing a gradual change in the population – evolution.
Examiner tips
- Show the four stages in the correct order: variation, advantage, survival/reproduction, change in allele frequency.
- Use the words "variation", "advantageous", "survive", "reproduce", "allele frequency" – these are key terms.
- Explain that the change is gradual over many generations – not instant.
- Mention that the trait is inherited – the allele is passed on.
Common mistakes
- Forgetting to mention that the trait is inherited.
- Using vague terms like "better" without linking to camouflage. Not stating that the change occurs over many generations.
Mark scheme (4 marks)
- Variation exists within the population / beetles show variation in colour
- Dark-coloured beetles are better suited / have an advantageous phenotype as they are camouflaged on dark bark and are less likely to be eaten by birds
- Dark-coloured beetles are more likely to survive and reproduce, passing on the advantageous allele(s) to offspring
- Over many generations the frequency of the advantageous allele increases in the population, leading to a gradual change in inherited characteristics / evolution
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Evolution and natural selection questions
- Explain how variation within a population of organisms can lead to some individu…
- Describe how the fossil record provides evidence for evolution.
- Explain how a mutation could lead to a change in the characteristics of an organ…
- Antibiotic resistance in bacteria is an example of natural selection in action. …