An improved metric has been developed for prioritising the conservation of ‘evolutionarily distinctive’ species

The new metric, EDGE2, adds measures of scientific uncertainty and status of related species to the existing metric, say scientists.

An updated metric for prioritising species’ conservation that incorporates scientific uncertainty and complementarity between species, in addition to extinction risk and evolutionary distinctiveness, has been published by author Rikki Gumbs from the Zoological Society of London (ZSL), UK, and colleagues.

In 2007, ZSL established the Evolutionarily Distinct and Globally Endangered (EDGE) metric to prioritise species for conservation based on preserving evolutionary history embodied within endangered species.

The approach allocates each species a score based on the evolutionary distance, measured in millions of years, that separates a species from its closest living relatives, and its conservation status in the IUCN Red List.

EDGE has since been applied to mammals, amphibians, birds, sharks and rays, corals, and flowering plants, and is used to allocate conservation funding.

To update the EDGE metric to incorporate recent advances in evolutionary biology and conservation, ZSL hosted a workshop for conservation scientists and practitioners, who reached a consensus on EDGE2 – an updated metric that includes the extinction risk of closely related species and uncertainty in species’ relationships and conservation status.

See also: Planet’s most unique birds at higher risk of extinction



Limited conservation funds


Applying the EDGE2 methodology to 6,253 mammal species, the researchers found that the Mountain Pygmy Possum (Burramys parvus) scored highest, representing 25 million years of evolution at critical risk of extinction.

They identified 645 priority species that together account for 81% of the evolutionary diversity at risk. Protecting the 100 highest ranking species from this list – representing 1.6% of all mammal species – would preserve over 700 million years of evolutionary history.

EDGE2 lists can help guide the effective and practical prioritisation of limited conservation funds to preserve distinctive evolutionary features and ecological functions, the authors say.

They also propose an EDGE2 research list, calling for further research on species that are evolutionarily distinct, but whose conservation status is unknown.

Gumbs said: “The variety of life at which we marvel is the product of the shared and unique evolutionary histories of species past and present, yet many of the most evolutionarily distinct species on Earth today are at risk of extinction.

“We brought together experts in conservation science and practice to create a robust and coherent framework to prioritise the world’s most evolutionarily distinct species for conservation action, and applied the framework to produce an updated prioritisation of the world’s mammals.”

The research is published in PLOS Biology.


Image 1: The Pygmy Sloth (Bradypus pygmaeus) is endemic to the island of Escudo, Panama, and is both evolutionarily distinct and threatened with extinction. © ZSL (CC-BY 4.0,

Image 2: The Red-bellied lemur (Eulemur rubriventer) is one of many threatened mammals now recognised as EDGE species following the improved approach to identifying robust priorities. © Rikki Gumbs (CC-BY 4.0,

Image 3: The Red Panda (Ailurus fulgens) is the only extant member of its family, Ailuridae, and is one of the highest priority EDGE mammals. © ZSL (CC-BY 4.0,