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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
HL

Exam analysis

Chance of appearing6%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks2–7

Common command terms

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  • Outline
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  • Explain
  • Describe

Scoring notes

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

Recent exam appearances

May 2025Paper1A ["HL"] · TZ221[ 1 ]A4.1.6—Speciation by splitting of pre-existing species
May 2022Paper2 ["HL"] · TZ27(c)[ 7 ]A4.1.6—Speciation by splitting of pre-existing species
November 2020Paper2 ["HL"] · TZ08(b)[ 5 ]A4.1.6—Speciation by splitting of pre-existing species
May 2019Paper2 ["HL"] · TZ17(b)[ 7 ]A4.1.6—Speciation by splitting of pre-existing species
May 2017Paper2 ["HL"] · TZ17(b)[ 4 ]A4.1.6—Speciation by splitting of pre-existing species
Practice this objective

Coverage 2013–2025 · 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 HL