Explain how natural selection can lead to a change in the inherited characteristics of a population over many generations.

WJEC GCSE Biology (Wales) — 2.4.2 Evolution and natural selection · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A population of mice lives in a snowy environment. Some mice have white fur and some have brown fur. Predators find it easier to spot brown mice against the snow.

Model answer (4 marks)

White‑furred mice are better adapted to the snowy environment, so predators find them harder to spot. Consequently, white‑furred mice are more likely to survive and reproduce. Their offspring inherit the allele(s) for white fur, increasing the frequency of this advantageous allele in the population. Over many generations the proportion of white‑furred mice rises, so the population’s inherited characteristics change.

Examiner tips

Use the word "adapted" or "suited" to link the trait to the environment
Show the chain: better survival → more reproduction → allele frequency change → population change
Mention "over many generations" to satisfy the time element

Common mistakes

Failing to explain that the allele frequency increases, not just the number of white mice
Using vague terms like "more common" without linking to inheritance
Omitting the link between survival advantage and reproduction

Mark scheme (4 marks)

White fur mice are better adapted / suited to the snowy environment, so are less likely to be eaten by predators
White mice are more likely to survive and reproduce
The allele(s) for white fur are passed on to offspring, increasing the frequency of the advantageous allele in the population
Over many generations, the proportion of white-furred mice in the population increases / the population's inherited characteristics change

Key terms in this question

natural selection · inherited characteristics