Explain how natural selection acts on variation within a population to bring about evolutionary change over successive generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Heritable variation exists within a population because of mutation and sexual reproduction, which introduces new alleles and recombines them.
Individuals possessing favourable phenotypic variants survive and reproduce more successfully than others.
These advantageous alleles are therefore transmitted to a larger proportion of the next generation, raising their frequency in the gene pool.
Over many successive generations the cumulative shift in allele frequencies produces evolutionary change, giving rise to new adaptations or even new species.
Individuals possessing favourable phenotypic variants survive and reproduce more successfully than others.
These advantageous alleles are therefore transmitted to a larger proportion of the next generation, raising their frequency in the gene pool.
Over many successive generations the cumulative shift in allele frequencies produces evolutionary change, giving rise to new adaptations or even new species.
Examiner tips
- Use the word "heritable" to link variation to selection. Show the causal chain: variation → differential survival → allele frequency change → evolution. Keep each point brief but include the key terms: mutation, recombination, differential reproductive success, allele frequency, evolutionary change.
Common mistakes
- Confusing mutation with natural selection; forgetting to mention heritability. Using vague phrases like "changes over time" without linking to allele frequencies. Omitting the step that favourable alleles increase in frequency due to differential reproduction.
Mark scheme (4 marks)
- Heritable variation exists within a population due to mutation and/or sexual reproduction (recombination / random fertilisation).
- Individuals with favourable/advantageous phenotypic variants have a greater chance of survival and reproduction (differential reproductive success).
- Favourable alleles are passed on to offspring at a higher frequency, so allele frequencies in the population change over generations.
- Accumulated changes in allele frequencies over many generations result in evolutionary change, potentially producing new adaptations or new species.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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