Cambridge IGCSE Biology 0610 · Topic 18
Variation and Selection
No individual is an exact copy of another member of its species, and that simple fact carries this entire chapter. Where that variation comes from, which of it is inherited, and what happens when an environment starts favouring one version over another — that is the whole of Topic 18, and every question in it is really testing whether you can keep those three ideas in the right order.
Cambridge builds this chapter around three syllabus points: 18.1 Variation, 18.2 Adaptive features and 18.3 Selection. They are not three unrelated topics stacked together. Variation supplies the raw differences between individuals; adaptive features are the inherited differences that happen to help an organism survive and reproduce in a particular environment; and selection — whether the environment is doing the choosing, or a farmer is — is the process that changes how common those differences become across generations. Read in that order, the chapter tells one continuous story rather than three separate ones.
Most of the marks lost in this topic come from one specific error: writing about an organism as though it changed itself on purpose because it needed to survive. A mutation happens first, for no purpose at all; whether it turns out to be useful is decided afterwards, by the environment, not by the organism’s needs. Every page below keeps that causal order explicit, because it is exactly the distinction a Cambridge mark scheme is built to check for.
What’s in this chapter
| Page | Level | What it covers |
|---|---|---|
| Continuous and discontinuous variation | Core | Why body mass and blood group are tested as opposite patterns of variation, and how to investigate each one properly. |
| Mutation and genetic variation | Core + Supplement | What a mutation actually is, why it is the only source of a genuinely new allele, and the other three sources that shuffle existing ones. |
| Adaptive features | Core | The feature-to-advantage chain examiners want, and how to reason about an organism you have never seen before. |
| Hydrophytes and xerophytes | Supplement | Opposite water problems, opposite solutions — why a floating leaf and a desert leaf are built to solve nothing alike. |
| Natural selection | Core + Supplement | The full six-step sequence, why adaptation is a process and not a feature, and antibiotic resistance as a worked example. |
| Selective breeding and artificial selection | Core + Supplement | The repeated cycle behind every improved crop or livestock breed, and how it differs from what the environment does on its own. |
Core or Supplement?
Two pages here are Core-only: continuous and discontinuous variation, and adaptive features. Every candidate needs those regardless of tier. Hydrophytes and xerophytes is Supplement-only, required for the Extended paper and not for Core candidates. The remaining three pages — mutation and genetic variation, natural selection, and selective breeding — carry both: each has a Core layer every candidate needs, and a Supplement layer built on top of it (gene mutation and the four sources of variation; adaptation as a long-term process and antibiotic resistance; and the formal comparison of natural against artificial selection). If you are not sure which tier you are sitting, that is worth checking before you spend time on the Supplement sections, since none of the Core content depends on them.