 The five populations living on the largest island , Isabela , are the ones that are the subject of the most debate as to whether they are true subspecies or just distinct populations . It is widely accepted that the population living on the northernmost volcano , Volcan Wolf , is genetically independent from the four populations to the south and is therefore a separate subspecies . It is thought to be derived from a different colonization event than the others . A colonization from the island of Santiago apparently gave rise to the Volcan Wolf subspecies ( C. n. becki ) while the four southern populations are believed to be descended from a second colonization from the more southerly island of Santa Cruz . Tortoises from Santa Cruz are thought to have first colonized the Sierra Negra volcano , which was the first of the island 's volcanoes to form . The tortoises then spread north to each newly created volcano , resulting in the populations living on Volcan Alcedo and then Volcan Darwin . Recent genetic evidence shows that these two populations are genetically distinct from each other and from the population living on Sierra Negra ( C. n. guentheri ) and therefore form the subspecies C. n. vandenburghi ( Alcedo ) and C. n. microphyes ( Darwin ) . The fifth population living on the southernmost volcano ( C. n. vicina ) is thought to have split off from the Sierra Negra population more recently and is therefore not as genetically different as the other two . Isabela is the most recently formed island tortoises inhabit , so its populations have had less time to evolve independently than populations on other islands , but according to some researchers , they are all genetically different and should each be considered as separate subspecies . 
