This guide covers IGCSE Biology topic 18: variation and selection. You will revise continuous and discontinuous variation, natural selection (mutations, competition, survival, reproduction), artificial selection (selective breeding), and evolution.

Key concepts to revise

• Variation – Continuous (e.g. height, mass; range of values) vs discontinuous (e.g. blood group; distinct categories). Caused by genes, environment, or both.
• Natural selection – Variation exists; competition for resources; better-adapted individuals survive and reproduce; alleles passed on; population changes over time.
• Artificial selection – Humans choose organisms with desired traits to breed; repeated over generations; e.g. crop yield, milk production.
• Evolution – Change in species over time; natural selection is the mechanism; evidence: fossils, comparative anatomy.

Exam tips and command words

• State – One example of continuous and one of discontinuous variation.
• Describe – The process of natural selection (variation → competition → survival → reproduction → allele frequency changes).
• Explain – Why antibiotic resistance is an example of natural selection (mutations; resistant bacteria survive; pass on resistance).
• Compare – Natural vs artificial selection (who selects; what is selected for).

Common mistakes

• Saying “organisms adapt” in order to survive (variation exists first; selection acts on it; individuals do not “choose” to adapt).
• Confusing natural selection (environment; survival of fittest) with artificial selection (humans choose).
• Not stating that mutation is the source of new variation (random; may be beneficial, harmful or neutral).

Revision checklist

• Give one example each of continuous and discontinuous variation and state causes (genes, environment).
• Describe natural selection in four steps (variation, competition, survival, reproduction).
• Explain antibiotic resistance or another example of natural selection.
• Describe artificial selection (selective breeding) with one example.

Next steps

Book a free trial with an IGCSE Biology tutor to practise variation and selection questions, or explore Tutopiya’s learning portal for more revision resources.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial