The world’s most extra­or­di­nary species are also some of the most threatened


he Thy­lacine or Tas­man­ian Tiger (Thy­lac­i­nus cyno­cephalus) is one of the sad­dest exam­ples of how a species can become extinct due to irre­spon­si­ble human behaviour.

The thy­lacine was the largest mar­su­pial car­ni­vore and the last remain­ing rep­re­sen­ta­tive of an entire mam­mal fam­ily. Thy­lacines were once wide­spread across the Aus­tralian main­land, but became extinct there and sur­vived only on Tas­ma­nia. The rea­sons for its dis­ap­pear­ance in main­land Aus­tralia and its con­tin­ued sur­vival in Tas­ma­nia remain a mys­tery, although cli­mate change (Jour­nal of Bio­geog­ra­phy, 27.09.2017), an increase in human activ­ity and the pres­ence of din­goes are high on the list of cul­prits. Only when dri­ven to the brink of extinc­tion by human per­se­cu­tion in Tas­ma­nia as well, the species was finally awarded legal pro­tec­tion in 1936. Sadly, this action came too late for the thy­lacine. Hunted out of exis­tence by Aus­tralian farm­ers who feared that the striped, canine-​like mar­su­pi­als would kill their sheep, the last thy­lacine died in cap­tiv­ity in Hobart Zoo 75 years ago next week, on Sep­tem­ber 7, 1936 (although the species was not offi­cially declared extinct by inter­na­tional stan­dards in 1986). Even more sadly a recent study revealed that the preda­tor was prob­a­bly not a threat to sheep after all. Its notably long jaw, one of the animal’s most dis­tinc­tive fea­tures, could open to an amaz­ing 120 degrees but was too weak to kill sheep (Jour­nal of Zool­ogy, 31.08.2011)

Footage of the last known thy­lacine, and its strik­ing jaw, shot before its death in captivity:

EDGE of Exis­tence programme

The EDGE of Exis­tence pro­gramme is a con­ser­va­tion pro­gramme of the Zoo­log­i­cal Soci­ety of Lon­don (launched in Jan­u­ary 2007), and is the only global con­ser­va­tion ini­tia­tive to focus specif­i­cally on threat­ened species that rep­re­sent a sig­nif­i­cant amount of unique evo­lu­tion­ary his­tory. Using a sci­en­tific frame­work to iden­tify the world’s most Evo­lu­tion­ar­ily Dis­tinct and Glob­ally Endan­gered (EDGE) species, the EDGE of Exis­tence pro­gramme high­lights and pro­tects some of the weird­est and most won­der­ful species on the planet. EDGE species have few close rel­a­tives on the tree of life and are often extremely unusual in the way they look, live and behave, as well as in their genetic make-​up. They rep­re­sent a unique and irre­place­able part of the world’s nat­ural her­itage, yet an alarm­ing pro­por­tion are cur­rently slid­ing silently towards extinc­tion unnoticed.

Whether or not this par­tic­u­lar loss of unique evo­lu­tion­ar­ily his­tor­i­cal genes, will decrease Planet Earth’s resilience to human over­ex­ploita­tion, we will never know if we do not stop this loss of diversity


The EDGE of Exis­tence pro­gramme seeks to:
  • Raise aware­ness of the world’s most Evo­lu­tion­ar­ily Dis­tinct and Glob­ally Endan­gered (EDGE) species
  • Iden­tify the cur­rent sta­tus of poorly known and pos­si­bly extinct EDGE species
  • Develop and imple­ment con­ser­va­tion strate­gies for all EDGE species not cur­rently being protected
  • Increase con­ser­va­tion capac­ity in the coun­tries in which EDGE species occur, through sup­port­ing and train­ing local sci­en­tists and con­ser­va­tion pro­fes­sion­als to under­take research into the focal EDGE species
  • Sup­port all ongo­ing con­ser­va­tion activ­i­ties for EDGE species
Each year a num­ber of the most poorly known and neglected EDGE species are selected for con­ser­va­tion atten­tion. The top one hun­dred EDGE ani­mals are pre­sented on a com­pre­hen­sive inter­ac­tive web­site which high­lights the actions nec­es­sary to save them from extinction.
So, the aim of the EDGE pro­gramme is to put these species on the map and catal­yse con­ser­va­tion action to secure their future

EDGE mammals button EDGE amphibians button EDGE coral reefs button EDGE birds button

The method­ol­ogy of iden­ti­fy­ing and rank­ing the EDGE animals

Every species in a par­tic­u­lar tax­o­nomic group (e.g. mam­mals or amphib­ians) has been given a score based on the amount of unique evo­lu­tion­ary his­tory it rep­re­sents, and its con­ser­va­tion sta­tus accord­ing to the IUCN Red List of Threat­ened Species, the world’s most com­pre­hen­sive assess­ment of the con­ser­va­tion sta­tus of plant and ani­mal species. These scores are used to iden­tify and rank EDGE species.

EDGE phylogeny
Each species is given an ‘Evo­lu­tion­ary Dis­tinc­tive­ness’ (ED) score, which is cal­cu­lated from a fam­ily tree or phy­logeny. In this phy­logeny (see fig­ure A), 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.

A ‘Glob­ally Endan­gered’ (GE) score is then cal­cu­lated for each species based on the 2006 IUCN Red List. 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. The two scores are then com­bined to pro­duce an EDGE score for each species. EDGE species are species which have an above-​average ED score and are threat­ened with extinc­tion (Crit­i­cally Endan­gered, Endan­gered or Vulnerable).

EDGE photos buttonEDGE map button

A selec­tion of videos fea­tur­ing Evo­lu­tion­ar­ily Dis­tinct & Glob­ally Endan­gered species

Jonathan Bail­lie intro­duces the EDGE of Exis­tence con­ser­va­tion programme

An intro­duc­tion to the EDGE of Exis­tence con­ser­va­tion pro­gramme by Pro­fes­sor Jonathan Bail­lie, who is a global author­ity on the sta­tus and trends of threat­ened species. He is Con­ser­va­tion Pro­grammes Direc­tor at the Zoo­log­i­cal Soci­ety of Lon­don and works on a large num­ber of projects which focus on mon­i­tor­ing the sta­tus of rare and threat­ened species.

Please go to the EDGE pages for fur­ther infor­ma­tion and donation.

Most of the above text is reprinted from mate­ri­als avail­able at EDGE. Orig­i­nal text may be edited for con­tent and length.

Goal: 7000 tigers in the wild

Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

about zoos and their mis­sion regard­ing breed­ing endan­gered species, nature con­ser­va­tion, bio­di­ver­sity and edu­ca­tion, which of course relates to the evo­lu­tion of species.
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