Evolution
MYP Year 5 Biology — Evolution unit
Evolution is the one topic where exam answers fail not because students don't know the facts, but because they explain it like Lamarck did. Every 'explain' question here is testing whether you can describe a change in a population's allele frequency across generations — never an individual 'evolving' or 'trying' to adapt. Get that framing right and the four ideas below — mechanism (natural selection), outcome (adaptation), proof (evidence), and history (Darwin) — basically write themselves.
Overview: How the Topic Fits Together
What 'evolution' actually means
Evolution is the change in the inherited (heritable) characteristics of a population across successive generations. Notice what's missing from that definition: individuals. An individual mouse, moth, or bacterium does not evolve during its own lifetime — a population does, and only because the proportion of individuals carrying certain alleles shifts over time.
- Natural selection is the mechanism — the process by which some heritable traits become more common because they improve survival or reproduction.
- Adaptation is the outcome — a heritable trait that currently fits an organism to its environment, built up by selection acting over many generations.
- Evidence of evolution (fossils, anatomy, molecular data, biogeography) is what convinces scientists the process actually happened and is still happening.
- Darwin's theory is the historical framework that first tied variation + selection + inheritance together into a testable scientific explanation — published in 1859, still the backbone of modern biology.
The shape of the chapter
Command terms examiners actually use in this unit
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Describe | State the trend/pattern in data — direction, size, timeframe — with no reasoning attached. | Data handling | Mark goes to the number/direction (e.g. 'beak depth rose 0.9 mm between 1976 and 1978'); reasoning earns zero here because it wasn't asked for. |
| Explain | Build the full causal chain: variation exists → environment applies a selection pressure → some phenotypes survive/reproduce more → trait is heritable → allele frequency shifts across generations. | Reasoning | Missing any link in that chain (especially 'heritable' or 'over generations') caps the mark even if the rest is correct. |
| Identify | Name one specific feature, condition, or example — a phrase, not a paragraph. | Recall/application | 1 mark per named item; writing an explanation here wastes time and earns nothing extra. |
| Distinguish | Give the point of difference between two named terms, stated as a direct comparison. | Comparison | Defining each term separately without a comparative link ('whereas', 'unlike') loses the mark even if both definitions are correct. |
| Discuss | Present more than one side — e.g. a benefit and a limitation — with some weighing up. | Evaluation | A one-sided answer (all pros, no cons) is capped at roughly half marks. |
| Suggest | Propose a plausible, reasoned explanation for a novel scenario not directly taught. | Application | Credit is given for sound biological logic even if it isn't the exact model answer — as long as it's consistent with selection theory. |
Key point
Overview