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Detailed notes on Variation and Selection for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
How populations evolve. Natural selection (environment) + artificial selection (humans). Both shape life over generations.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Variation, competition, selection, inheritance. Repeat for many generations. Population evolves.
The four-step argument Cambridge expects:
1. Variation.
2. Competition.
3. Selection (survival of the fittest).
4. Inheritance.
Result: EVOLUTION — change in the population's genetic makeup over time.
Famous example: peppered moths.
Worked qualitative. A geneticist suggests that giraffes' long necks evolved because their ancestors 'stretched their necks to reach high leaves'. Why is this WRONG?
Cambridge tip. Memorise the four steps. Cambridge often gives a scenario (peppered moths, antibiotic resistance) and asks 'explain in terms of natural selection'.
Antibiotic resistance, pesticide resistance — happening now.
Antibiotic resistance.
Insecticide resistance.
Heavy metal tolerance in plants.
Sickle-cell allele in malaria regions.
Worked qualitative. Why does antibiotic resistance evolve so FAST in bacteria but slowly in mammals?
Cambridge tip. Cambridge's modern examples mostly come from medicine + agriculture. Memorise antibiotic resistance + pesticide resistance.
Humans choose which individuals breed. Faster than nature.
The process:
Examples:
| Crop / animal | Trait selected | Result |
|---|---|---|
| Wheat | High yield, disease resistance | Modern wheat varieties yield 4-5× more than ancient wheat |
| Maize | Larger cobs, more rows of kernels | Modern corn vs ancient teosinte |
| Cattle | High milk yield | Holstein cows ~25 litres/day |
| Sheep | Lots of fine wool | Merino sheep |
| Dogs | Various traits — size, behaviour, looks | Hundreds of breeds from one wolf ancestor |
Worked qualitative. Why are domesticated dogs SO MUCH more variable than wolves?
Problems with selective breeding:
Cambridge tip. Selective breeding is NOT genetic modification. Selective breeding uses NATURAL reproduction; GM directly changes DNA.
Verbatim phrases and definitions Cambridge mark schemes credit.
Selection appears every Paper 4 (8-10 marks: explain natural selection, give examples, describe selective breeding). Examiner reports flag students saying individuals 'try to evolve' and missing the four-step structure.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (18.3); 0610/42 May/Jun 2024 — Q22 (selection); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on selection, written exactly the way a tutor would explain them at the board.
Question
State the key differences between natural selection and artificial selection (selective breeding).
Step-by-step solution
Step 1
In natural selection, the environment decides which individuals survive and reproduce.
Step 2
In artificial selection, humans decide which individuals are allowed to breed.
Step 3
Natural selection produces features that help the organism survive in the wild; artificial selection produces features that are useful to humans.
Answer
Natural selection: the environment selects, producing features for survival. Artificial selection: humans select, producing features useful to people.
Question
State whether each is natural or artificial selection: (a) farmers breeding cows that give the most milk; (b) faster gazelles surviving to escape predators; (c) breeding wheat plants with the highest grain yield.
Step-by-step solution
Step 1
(a) Humans choosing which cows breed → artificial selection.
Step 2
(b) The environment (predators) deciding which gazelles survive → natural selection.
Step 3
(c) Humans choosing which wheat plants breed → artificial selection.
Answer
(a) Artificial; (b) natural; (c) artificial.
Examiner tip
If humans choose who breeds, it is artificial selection; if the environment does, it is natural selection.
Question
Explain natural selection as a clear sequence of steps.
Step-by-step solution
Step 1
Variation: individuals in a population vary, because they have different alleles.
Step 2
Competition / struggle to survive: more offspring are produced than can survive, so there is competition for resources.
Step 3
Survival of the fittest: individuals with the most useful (advantageous) features are more likely to survive and reproduce.
Step 4
Inheritance: these survivors pass on their alleles to their offspring, so over many generations the advantageous alleles become more common — the population becomes better adapted.
Answer
Variation → competition → individuals with advantageous features survive and reproduce → they pass on their alleles → the advantageous features become more common over generations.
Examiner tip
Cambridge marks the full argument: variation; competition/over-production; advantageous individuals survive and reproduce; pass on alleles.
Question
Describe how a farmer could use selective breeding to produce cattle that give a high milk yield.
Step-by-step solution
Step 1
Choose the cattle that produce the most milk as the parents.
Step 2
Breed these chosen individuals together.
Step 3
From the offspring, again select those that give the most milk and breed them.
Step 4
Repeat this over many generations, so that the milk yield gradually increases and the desired feature becomes well established in the herd.
Answer
Choose the highest-yielding cattle, breed them together, select the best offspring, and repeat over many generations until high milk yield is well established.
Question
Explain how the development of antibiotic-resistant bacteria is an example of natural selection.
Step-by-step solution
Step 1
Bacteria show variation: a random mutation makes some bacteria resistant to an antibiotic.
Step 2
When the antibiotic is used, it acts as the selection pressure: the non-resistant bacteria are killed, but the resistant ones survive.
Step 3
The surviving resistant bacteria reproduce and pass on the resistance allele to their offspring.
Step 4
Over many generations, the proportion of resistant bacteria increases, so the population becomes resistant — exactly the process of natural selection.
Answer
A mutation gives some bacteria resistance (variation); the antibiotic kills the non-resistant ones but the resistant survive and reproduce, passing on the allele; over generations resistance spreads — natural selection.
Examiner tip
Map onto the steps: variation (mutation); selection pressure (antibiotic); survival and reproduction of the resistant; inheritance of the resistance allele.
Question
Before industrial pollution, most peppered moths were pale, with a few dark ones. In polluted areas the tree bark became dark with soot, and over time the dark moths became the most common. Explain this change using natural selection.
Step-by-step solution
Step 1
There was variation: most moths were pale and a few were dark (a dark form had arisen by mutation).
Step 2
On the soot-darkened bark, the dark moths were now better camouflaged from birds, while the pale moths stood out and were easily seen.
Step 3
So birds ate more of the pale moths, and more dark moths survived to reproduce (the selection pressure was predation).
Step 4
The surviving dark moths passed on the allele for dark colour, so over many generations the dark moths became the most common form in the polluted areas.
Answer
Dark and pale moths varied. On sooty bark the dark moths were better camouflaged, so fewer were eaten by birds; they survived, reproduced and passed on the dark allele, so dark moths became common — by natural selection.
Examiner tip
Identify the variation, the selection pressure (bird predation on the more visible moths), and the inheritance of the advantageous allele.
High-scoring sample answers for selection on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State what is meant by natural selection. (1 mark)
Model answer
Natural selection is the process by which individuals with features best suited to their environment are more likely to survive and reproduce, passing on their alleles.
Why this scores
One mark for the idea of the best-suited individuals surviving and reproducing (and passing on alleles).
State two differences between natural selection and artificial selection. (2 marks)
Model answer
In natural selection the environment selects which individuals survive and reproduce, whereas in artificial selection humans choose which individuals breed. Natural selection produces features that aid survival in the wild, whereas artificial selection produces features that are useful to humans.
Why this scores
Two genuine contrasts: who/what selects; what kind of features are produced.
Describe how a plant breeder could use selective breeding to produce a wheat variety with a high grain yield. (3 marks)
Model answer
The breeder selects the wheat plants that produce the highest grain yield and breeds them together. From the resulting offspring, the plants with the highest yield are again selected and bred, and this process is repeated over many generations until a high-yielding variety is produced.
Why this scores
Three marks: select the highest-yielding plants; breed them together; repeat over many generations (selecting the best each time).
Explain how the development of antibiotic-resistant bacteria is an example of natural selection. (4 marks)
Model answer
A random mutation makes some bacteria in the population resistant to the antibiotic — this is the variation. When the antibiotic is used, it kills the non-resistant bacteria, but the resistant bacteria survive. The surviving resistant bacteria then reproduce and pass on the resistance allele to their offspring. Over many generations, the proportion of resistant bacteria increases until the whole population is resistant — the same steps as natural selection.
Why this scores
Four marks: mutation gives resistance (variation); antibiotic kills non-resistant; resistant survive and reproduce; pass on the resistance allele / population becomes resistant.
Explain the process of natural selection. (5 marks)
Model answer
Within a population there is genetic variation, because individuals have different alleles. Organisms produce more offspring than can survive, so there is competition for resources such as food. The individuals with the most advantageous features (best suited to the environment) are more likely to survive this competition. Because they survive, they are more likely to reproduce and so pass on the alleles for their advantageous features to their offspring. Over many generations, these advantageous alleles become more common in the population, so the population becomes better adapted to its environment.
Why this scores
Five marks: variation (different alleles); over-production/competition; advantageous individuals survive; they reproduce and pass on alleles; advantageous alleles become more common over generations.
Originally, pale peppered moths were far more common than dark ones. After an area became polluted and the tree bark turned dark with soot, the dark moths became the more common form. Explain how this change happened. (6 marks)
Model answer
There was variation in the moth population: most moths were pale and a small number were dark, the dark form having arisen by mutation. Before the pollution, the pale moths were well camouflaged on the pale, lichen-covered bark, so birds found them hard to see, while the dark moths stood out and were eaten — so pale moths were the more common. After the area became polluted, the bark became dark with soot. Now the dark moths were better camouflaged against the dark bark, while the pale moths stood out and were easily seen by birds. As a result, birds ate more of the pale moths, so more dark moths survived to reproduce (predation by birds was the selection pressure). The surviving dark moths reproduced and passed on the allele for dark colour to their offspring. Over many generations, the proportion of dark moths increased until they became the more common form in the polluted area — a clear example of natural selection.
Why this scores
Up to 6 marks: variation (pale and dark, dark from mutation); selection pressure (bird predation); on sooty bark dark moths better camouflaged / pale moths eaten more; dark moths survive and reproduce; pass on the dark allele; over generations dark form becomes common.
Definitions to memorise and the exact keywords mark schemes credit for selection answers — sharpened from recent examiner reports for the 2026 0610 sitting.
The process by which individuals with features best suited to their environment are more likely to survive and reproduce, passing on their alleles to the next generation.
The change in the inherited features of a population over many generations, brought about by natural selection.
The process in which humans choose individuals with desired features to breed together, over many generations, to enhance those features.
An environmental factor (such as predation, disease or an antibiotic) that affects which individuals survive and reproduce.
The traps other students keep falling into on selection questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
It is easier to picture.
How to avoid it
Individuals do not evolve; POPULATIONS evolve over generations as the frequencies of alleles change. Individuals simply survive (and reproduce) or not.
Why it happens
It sounds active.
How to avoid it
Selection acts on variation that already exists. New variation (new alleles) comes from MUTATION; selection only decides which existing alleles spread.
Why it happens
Both involve human intervention.
How to avoid it
Selective breeding uses SEXUAL reproduction over many generations and produces variation. Cloning produces identical copies in one generation (asexual).
The things students keep getting wrong in this sub-topic, answered.