Salam Academy
Sign inCreate account
Learn4BI1Paper 2B · Paper 2 (all content)Reproduction and inheritanceVariation, mutation and selection
Reproduction and inheritance · Subtopic 5 of 5

Variation, Mutation and Selection

Variation is the differences between individuals. Continuous variation has a range of values (height, mass) and is affected by many genes and the environment; discontinuous variation falls into distinct groups (blood group) and is mainly genetic. Mutations are random changes in DNA that create new alleles. In natural selection, individuals with features better suited to the environment survive, reproduce and pass on their alleles, so populations change over time: evolution. Artificial selection (selective breeding) is when humans choose which individuals breed.

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 40 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Distinguish continuous and discontinuous variation.
  • Describe mutation and its causes.
  • Explain natural selection and evolution.
  • Describe selective breeding.
Pause and think

In polluted 19th-century Manchester, dark peppered moths became far more common than pale ones. Why?

Section 2 of 14

Core idea

Start hereEvolution in a few years

Bacteria can evolve resistance to an antibiotic within months. Evolution isn't only about the distant past; it's happening now.

The big idea

Variation exists in every population. Mutations add new alleles. The environment selects individuals with useful features, which survive and pass on their alleles.

1. Natural selection

How natural selection works

Repeated over many generations.

Worked examplePeppered moths

Dark moths became common in sooty industrial areas.

Goal
Explain using natural selection.
Strategy
Five steps.
  1. variation: pale and dark moths\text{variation: pale and dark moths}
    Colour is inherited.
  2. dark camouflaged on soot\text{dark camouflaged on soot}
    Birds eat fewer dark moths.
  3. dark moths reproduce more\text{dark moths reproduce more}
    Dark allele passed on and becomes more common.
AnswerSelection by bird predators increased the dark allele.
✓ CheckPale moths became common again after clean-air laws ✓.
Key takeawayTwo types of variation Continuous (range, many genes + environment, histogram) vs discontinuous (categories, usually one gene, bar chart).
Pause and think

Is selective breeding faster or slower than natural selection? Why?

Summary

  • Variation and mutation.
  • Natural selection changes allele frequency.
  • Selective breeding is human-directed.
Key words
Mutation
A random change in DNA.
Natural selection
Better-adapted individuals survive and reproduce more.
Adaptive feature
Inherited feature that helps survival.
HistoryDarwin and Wallace. Charles Darwin and Alfred Russel Wallace independently came up with natural selection; their ideas were presented together in 1858. Darwin's On the Origin of Species followed in 1859.
Fun factEvery dog is a wolf. From chihuahuas to Great Danes, all domestic dogs descend from wolves, shaped by thousands of years of selective breeding.
Keep reading for free

Create a free account to read the rest of this lesson: key formulae, worked examples, explore the graph, common mistakes, exam tip, guided practice and more. Your answers are checked and your progress is saved.

Create free accountSign in