# Explain how the concept of a changing environment contributes to natural selection acting on a population over successive generations.

> IB DP Biology Higher Level (2023 syllabus) — D4.1 Natural selection · Explain · 4 marks

> A population of ground-dwelling beetles lives in a habitat where the soil colour shifts gradually from pale sandy loam to darker clay over several decades due to changing drainage patterns.

## Mark scheme (4 marks)

1. Variation exists within the beetle population in traits such as body colouration, arising from random mutations and genetic recombination.
2. As soil darkens, darker-coloured beetles have greater camouflage and are less likely to be detected and eaten by predators, giving them a selective advantage / higher relative fitness.
3. Individuals with the advantageous phenotype survive longer and reproduce more, passing the alleles for darker colouration to offspring at a higher frequency — this is differential reproductive success.
4. Over successive generations, the allele frequency of darker-colouration alleles increases in the population, shifting the population's mean phenotype — illustrating evolution by natural selection.

## Key terms

- [natural selection](https://www.gradenine.co.uk/glossary/natural-selection)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-concept-of-a-4793a611) · Published by Druglandscape Ltd.