# Explain why natural selection does not lead to the evolution of a population when a trait is determined entirely by the environment rather than by genes.

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

## Mark scheme (4 marks)

1. Natural selection requires heritable variation; environmentally determined traits are not encoded in the genotype and therefore cannot be inherited by offspring.
2. Natural selection acts on phenotype, but if phenotypic differences have no underlying allelic basis, differential survival/reproduction does not change allele frequencies in the next generation.
3. Evolution by natural selection requires a change in allele frequencies across generations; without a heritable genetic basis for the trait, no such change can occur.
4. Offspring will not inherit the favourable phenotype because its expression depends on the environment, not on genes transmitted from parents; each generation's phenotype is reset by environmental conditions.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-natural-selection-does-not-f976ba7c) · Published by Druglandscape Ltd.