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A4.2.8—EDGE of Existence programme

The EDGE programme prioritizes species that are both globally endangered and evolutionarily distinct, protecting disproportionate evolutionary history from permanent loss.

Syllabus
First assessment 2025
Objective
A4.2.8
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks2

Common command terms

  • Outline
  • Describe

Scoring notes

Common mistake
Explaining EDGE only by expanding the initials without linking distinctiveness to extinction risk.

Recent exam appearances

May 2025Paper2 ["HL"] · TZ26(c)(i)[ 2 ]A4.2.8—EDGE of Existence programme
Practice this objective

Coverage 2025–2025 · Updated 15 Jul 2026

EDGE Prioritizes Unique and Threatened Species

The EDGE of Existence approach prioritizes species that are both evolutionarily distinct and globally endangered.

Evolutionary distinctiveness estimates how much unique evolutionary history a species represents; global-endangerment status estimates extinction risk. Combining them directs limited conservation resources toward irreplaceable branches and urgent threats. Use the evidence scale and context before drawing a broad conclusion.

Interpret an EDGE priority:

  • distinct lineage contribution
  • evidence of high threat
  • feasible conservation action
  • local communities and governance

Protecting a highly distinct, critically endangered mammal can preserve more unique evolutionary history than protecting a common close relative.

EDGE ranking does not mean other species have no value; it is a prioritization tool under limited resources.

EDGE of Existence programme

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, multiple choice, commonly using Outline / Describe.

Command terms

Outline / Describe

What earns marks

Build the answer around this relationship: EDGE species are both evolutionarily distinct and globally endangered.

Watch for

Explaining EDGE only by expanding the initials without linking distinctiveness to extinction risk.

Representative question

Question 1

[Maximum number: 2]

Outline the importance of the EDGE of Existence programme.

Build A Conservation Argument

A strong conservation answer follows a chain: define biodiversity, measure evidence of decline, identify human drivers, then justify conservation action. Biodiversity includes ecosystem, species, and genetic diversity; species diversity uses richness and evenness. Evidence comes from estimates, fossils, repeated surveys, IPBES reports, and indices. Drivers include extinction pressure, ecosystem conversion, population-driven resource demand, pollution, and invasive species. Responses include in situ, ex situ, and EDGE prioritization.

  • Define biodiversity across ecosystem, species, and genetic levels.
  • Measure species diversity using richness, evenness, and Simpson’s reciprocal index.
  • Use evidence cautiously: modern estimates, fossil gaps, repeated surveys, IPBES reports, and reliability checks.
  • Explain drivers using named examples: moa, Caribbean monk seal, Borneo, Great Barrier Reef, lionfish, water hyacinth.
  • Choose conservation responses: in situ, ex situ, and EDGE priorities.

Concept essentials

  • EDGE species are both evolutionarily distinct and globally endangered.
  • Few close relatives means extinction would remove a large amount of unique evolutionary history.
  • EDGE rankings help set conservation priorities for irreplaceable lineages.
  • The programme links phylogenetic information with practical conservation action.