H2 Biology Notes (9477, 2026): Core Idea 4 — Biological Evolution
17 Oct 2025, 00:00 Z
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Q: What does H2 Biology Notes (9477, 2026): Core Idea 4 - Biological Evolution cover?
A: Develop a rigorous understanding of variation, natural selection, speciation, and phylogenetics so you can write high-mark evolution essays and analyse unfamiliar data in the 2026 H2 Biology papers.
TL;DR
Use this guide to build evolution answers that stay population-focused: variation → selection → speciation, plus evidence lines and phylogeny/classification tools for Papers 2–3 and data-handling.
Status: Updated for SEAB H2 Biology (9477, first exam 2026); syllabus last checked 2026-01-12. [1]
Why evolution closes the core sequence
- Paper 1 (1 h, 15%): MCQs on variation sources, selection, and species concepts.
- Paper 2 (2 h, 30%) and Paper 3 (2 h, 35%): Data-based and essay prompts link genetics, variation, evidence for evolution, and classification.
- Paper 4 (2 h 30 min, 20% split across Planning/MMO/PDO/ACE): Evolution datasets can appear in data-handling tasks; population-level reasoning is expected.
- Core Idea 4 scope (SEAB 9477, first exam 2026): Variation from mutation/meiosis/sexual reproduction, natural selection as a population process, evidence lines, species concepts, allopatric/sympatric speciation, phylogeny and classification using molecular sequences. [1]
Core content highlights
- Variation sources and why populations-not individuals-evolve
- Natural selection driven by environmental factors
- Evidence lines: fossils, anatomical and molecular homologies, biogeography
- Species concepts and allopatric/sympatric speciation routes
- Phylogeny, classification, and use of genome sequences
- Preservation of genetic variation (including harmful recessive alleles)
Concept 1: Variation as evolution’s raw material
- Genetic mutation: Point mutations, insertions/deletions, and gene duplication generate new alleles. Mutation is random with respect to fitness; selection acts on the outcomes.
- Meiosis: Crossing-over and independent assortment create recombinant gametes.
- Sexual reproduction: Random fertilisation increases allele combinations.
- Environmental influence: Phenotypic differences can also arise from environmental effects (phenotypic plasticity) rather than heritable genetic changes-distinguish clearly in data-based questions. [2]
Harmful recessive alleles can persist in heterozygotes; balancing situations (e.g. heterozygote advantage) help maintain variation in populations. [2]
