Evolutionarily Distinct and Globally Endangered (EDGE) species are threatened species that have few or no close relatives on the tree of life. EDGE species are usually extremely distinct in the way they look, live and behave as well as in their genetic make-up. If they disappear, there will be nothing like them left on the planet.
How to Identify an EDGE Species
Every species in a particular taxonomic group (e.g. mammals or amphibians) is scored according to the amount of unique evolutionary history it represents (Evolutionary Distinctiveness, or ED), and its conservation status (Global Endangerment, or GE). These scores are used to identify EDGE species.
Evolutionarily Distinct
Some species are more distinct than others because they represent a larger amount of unique evolution. Species like the aardvark have few close relatives and have been evolving independently for many millions of years. Others, like the dog originated only recently and have many close relatives. Species uniqueness’ can be measured as an 'Evolutionary Distinctiveness' (ED) score, using a phylogeny, or evolutionary tree. A phylogeny is a diagram showing how all the species in a particular taxonomic group are related to one another.
In the example phylogeny below, species A would have a higher ED score than either species B or C - it represents a branch rather than a twig on the tree of life. If species A were to go extinct, there would be no similar species left on the planet and a disproportionate amount of unique evolutionary history would be lost forever. Assuming that resources are limited and each species is equally threatened, it therefore seems reasonable to give priority to species A.
The world’s most Evolutionarily Distinct mammal is the duck-billed platypus. The most distinct amphibian is the Mexican burrowing toad.
Follow the links to view the world’s most Evolutionarily Distinct mammals and amphibians.
Globally Endangered
Globally Endangered (GE) scores for each species are based on the IUCN Red List Categories (Critically Endangered, Endangered, Vulnerable, Near Threatened and Least Concern). The IUCN Red List of Threatened Species is the world's most comprehensive assessment of the conservation status of plant and animal species. Species which are Critically Endangered receive a higher score than less threatened species, which in turn, receive a higher score than those not currently in danger of extinction.
Download the EDGE scientific paper to find out more about how EDGE scores are calculated.
EDGE Scores
The two scores are then combined to produce an overall EDGE score for each species. EDGE scores are calculated by multiplying ED and GE together. In mathematical terms, EDGE scores are an estimate of the expected loss of evolutionary history per unit time.
Follow the links to find out more about the top 100 EDGE mammals and amphibians
EDGE Species
EDGE species are species which have an above average ED score and are threatened with extinction (Critically Endangered, Endangered or Vulnerable on the IUCN Red List). There are currently 521 EDGE mammal species (~12% of the total) and 799 EDGE amphibian species (~%14 of the total). Potential EDGE species are those with high ED scores but whose conservation status is unclear.Follow the links to view potential EDGE mammals and amphibians.
Focal Species
Many EDGE species are not being adequately protected by existing conservation measures. This suggests that a disproportionate amount of evolutionary history is likely to be lost in the near future. To redress this balance, we have selected 10 Focal Species from each top 100 list for which little or no conservation is currently taking place.
Follow the links to view the Focal EDGE mammals and amphibians.
Download the EDGE scientific paper to find out more about how EDGE scores are calculated.
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Learn more about:
EDGE Mammals
EDGE Amphibians
