Selection — Cambridge IGCSE Biology
Natural selection and adaptation, antibiotic-resistant bacteria, selective breeding and how natural and artificial selection differ.
Revision notes
3 short notes, in the order of the specification. Each one in short:
Natural selection is the process by which individuals that are better adapted to their environment survive and pass on their alleles. There is genetic variation, more offspring than the environment can support, and a struggle for survival. Better adapted individuals survive and reproduce, so helpful alleles become more common. Over many generations this causes adaptation.
Antibiotic-resistant bacteria
SupplementAntibiotic-resistant bacteria are an example of natural selection. A random mutation produces an allele that makes a bacterium resistant. When the antibiotic is used, it kills the non-resistant bacteria, but the resistant bacterium survives, reproduces and passes on the resistance allele. Bacteria reproduce very quickly, so a resistant strain can become common in a short time.
Selective breeding, or artificial selection, is when humans choose which organisms breed so the next generation has desirable features. Individuals with the features are selected and crossed, then offspring showing the features are selected, and this is repeated over many generations. It improves crops such as wheat and rice, and animals such as dairy cattle.
Exam questions
7 exam-style questions (23 marks), each with its mark scheme.
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Quick check questions
Give two things organisms compete for.
Show answer
Any two from food, water, light, space, mates.
What happens to the alleles of better-adapted individuals?
Show answer
They are passed on to the next generation.
Name the three stages of selective breeding.
Show answer
Select individuals with desirable features; cross them; select offspring showing the desirable features.
Supplement Define adaptation.
Show answer
The process, resulting from natural selection, by which populations become more suited to their environment over many generations.
Supplement Who or what selects in natural selection and in artificial selection?
Show answer
The environment selects in natural selection; humans select in artificial selection.
Frequently asked questions
How does natural selection lead to evolution?
Supplement Natural selection leads to adaptation of a population over many generations. There is genetic variation, and more offspring are produced than the environment can support, so there is a struggle for survival. Better adapted individuals survive and reproduce, passing on their alleles. The helpful alleles become more common, so the population becomes more suited to its environment.
What are the stages of natural selection?
Natural selection has five stages. There is genetic variation within populations. Organisms produce more offspring than the environment can support. There is a struggle for survival, including competition for food, water and mates. Better adapted individuals have a greater chance of surviving and reproducing. They pass on their alleles, so helpful alleles become more common.
How does antibiotic resistance show natural selection?
Supplement Antibiotic resistance shows natural selection because the antibiotic selects bacteria that already have a resistance allele. A random mutation makes one bacterium resistant. The antibiotic kills the non-resistant bacteria, and the resistant one survives, reproduces and passes on the allele. Over time most of the population is resistant and the antibiotic no longer works.
What is selective breeding in plants?
Selective breeding in plants is when humans choose crop plants with desirable features, such as higher yield, disease resistance or larger seeds, and cross them. Offspring showing the desirable features are selected and bred again, and this is repeated over many generations. Each generation has more of the desirable features, for example in wheat and rice.
What is the difference between natural and artificial selection?
Supplement In natural selection the environment selects, while in artificial selection humans select. Natural selection favours features that help survival and reproduction, so organisms become better adapted. Artificial selection favours features humans want, to improve crops and domesticated animals. Artificial selection is usually faster, because humans choose every breeding pair in each generation.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026