MYP Biology: Variation & Natural Selection — FAQ

Variation & natural selection is the MYP Biology unit explaining two linked ideas: why individuals within a species differ (variation), and why some of those differences help organisms survive and reproduce more successfully in a given environment (natural selection). Schools typically teach it in MYP 4 or MYP 5 as a Life Science unit.

Continuous variation is measured on a scale with no fixed categories — height, mass, or hand span — and produces a bell-shaped distribution when plotted. Discontinuous variation falls into distinct, separate categories with nothing in between, like blood group or the ability to roll your tongue, and is usually controlled by a single gene.

Variation comes from three sources: sexual reproduction shuffling parental alleles at fertilisation, random mutations altering DNA sequences, and environmental factors — diet, sunlight, exercise — affecting how a trait is expressed. Only genetically-caused variation gets passed to offspring, which is exactly why it matters for natural selection and not the environmentally-caused kind.

Natural selection works because populations produce more offspring than the environment can support, and individuals with an advantageous trait survive and reproduce more successfully than others. Over many generations, the allele for that trait becomes more common — the population changes, even though no single organism evolves during its own lifetime.

Variation is the observable difference between individuals; mutation is a random change in DNA that can create new variation; adaptation is a feature that becomes common in a population because it improves survival, or the process by which that happens over generations. Mutation is a cause, variation is the raw material, adaptation is the outcome.

A top-level answer names the specific selection pressure, identifies which allele or trait is advantageous and why, and traces the change in allele frequency across generations — not a vague 'the strongest survive.' MYP Criterion A rewards students who apply the theory to an unfamiliar scenario rather than reciting the peppered moth example word for word.

The mistake I mark down most is writing that an individual organism 'evolves' or 'adapts' during its own lifetime — natural selection acts on populations over generations, not on one animal changing by choice. A close second: language implying organisms 'need' or 'decide' to develop a trait, which suggests intention rather than pre-existing variation being selected for.

Natural selection is one mechanism that drives evolution; evolution itself is the broader, observable change in a population's inherited characteristics over time. Natural selection explains why certain traits spread through a population, but evolution can also occur through other mechanisms — genetic drift, gene flow between populations, or mutation rates alone.

This content is mainly assessed under MYP Sciences Criterion A: Knowing and understanding, where you explain scientific ideas and apply them to unfamiliar situations. If your unit includes a practical or simulation — a 'natural selection game' investigation, for example — Criteria B and C, Inquiring and designing, and Processing and evaluating, come into play too.

Yes — MYP eAssessment includes on-screen exams for Sciences, and content like natural selection can appear as short-answer or extended-response questions testing Criterion A knowledge. According to the IB, MYP Sciences on-screen exams combine multiple-choice and constructed-response items drawn from across the subject's taught content, not a single guaranteed topic every year.

Expect 'describe', 'explain' and 'outline' for core natural selection questions, with 'analyse' or 'evaluate' appearing when you're given unfamiliar data — say, a graph of antibiotic-resistant bacteria increasing over time. Each command term tells you exactly how much reasoning the marker expects, so matching your answer's depth to the verb genuinely affects your mark.

MYP Biology introduces natural selection conceptually — the story of why traits spread through a population — using accessible examples like peppered moths or antibiotic resistance. DP Biology revisits the same idea with more rigour: allele frequencies, the Hardy-Weinberg principle, and exam questions marked against specific criteria rather than open discussion.

Because DP Biology assumes natural selection is already familiar and builds straight into quantitative genetics — allele frequencies, Hardy-Weinberg calculations, and speciation — without re-teaching the basic mechanism first. A student who's shaky on the core idea at MYP level often struggles disproportionately once DP adds the maths on top of it.

The most useful resources pair a clear conceptual explanation with practice questions marked against real criteria — Revision Notes to nail the concept, then Topical Worksheets to apply it to an unfamiliar scenario, which is exactly what MYP Criterion A rewards. Past unit tests from your child's own school are worth more than a generic revision guide, if you can get hold of them.

It depends what your child's school already provides. If classroom materials are light on practice questions — common for content-heavy MYP units like this one — a structured question bank or worksheet set can genuinely close the gap; if the school already sets regular past-paper style homework, it's less essential to buy anything extra.