Explain why variation within a population is important for natural selection to occur.

Cambridge International IGCSE Biology (0610) — 18.3 Selection · Explain · 4 marks · View as Markdown

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

A population of Arctic foxes living in a snowy environment includes individuals with varying fur thickness. Over many generations, the population comes to consist almost entirely of foxes with very thick fur.

Model answer (4 marks)

Variation means individuals within the population have different inherited features, such as fur thickness.
Competition for resources and mates means not all individuals survive.
Individuals with advantageous features, like thicker fur, are better suited to the snowy environment and therefore survive and reproduce.
The favourable alleles are passed on to offspring, so over many generations the frequency of thick fur increases in the population.

Examiner tips

Use the exact terms from the mark scheme – ‘variation’, ‘competition’, ‘advantageous features’, ‘favourable alleles’. Show the causal chain: variation → competition → differential survival → inheritance → change in frequency. Keep the answer concise – 4 short points will earn full marks.

Common mistakes

Failing to mention that the variation is inherited. Confusing natural selection with artificial selection. Using vague phrases like ‘better adapted’ without linking to survival and reproduction.

Mark scheme (4 marks)

Variation means individuals within the population have different inherited features / alleles / traits
There is competition for resources / mates within the population, so not all individuals survive
Individuals with advantageous / favourable features are better suited to survive and reproduce in their environment
The favourable alleles are passed on to offspring, so over many generations the frequency of the advantageous feature increases in the population

Key terms in this question

variation · natural selection