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A4.1.6—Speciation by splitting of pre-existing species

Speciation occurs when a pre-existing species splits into isolated gene pools that diverge until successful interbreeding is no longer possible.

Syllabus
First assessment 2025
Objective
A4.1.6
Level
SL

Exam analysis

Chance of appearing6%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks1–4

Common command terms

  • Discuss
  • Outline
  • Suggest
  • Explain
  • Describe

Scoring notes

Common mistake
Naming geographic separation without explaining gene-pool divergence or reproductive isolation.

Recent exam appearances

May 2025Paper2 ["SL"] · TZ28(b)[ 4 ]A4.1.6—Speciation by splitting of pre-existing species
May 2021Paper1 ["SL"] · TZ125[ 1 ]A4.1.6—Speciation by splitting of pre-existing species
May 2021Paper1 ["SL"] · TZ220[ 1 ]A4.1.6—Speciation by splitting of pre-existing species
November 2019Paper2 ["SL"] · TZ01(g)[ 4 ]A4.1.6—Speciation by splitting of pre-existing species
May 2019Paper2 ["SL"] · TZ17(c)[ 7 ]A4.1.6—Speciation by splitting of pre-existing species
Practice this objective

Coverage 2011–2025 · Updated 15 Jul 2026

Concept essentials

  • Speciation forms new species by splitting a pre-existing species into diverging populations.
  • Separated gene pools can diverge through mutation, drift and different selection pressures.
  • Reproductive isolation means gene flow is reduced or absent between populations.
  • A biological species boundary exists when fertile offspring cannot be produced by interbreeding.
ConceptIB Biology SL