The Social Tuco-tuco (Ctenomys sociabilis)

"A Patagonian rodent known as colonial tuco-tuco, has fascinated biologists because it seems to defy all odds. This threatened species has so little genetic diversity that the slightest breath of climate change or disease ought to have removed from the face of the earth long ago. Yet this vigorous creature not only managed to survive for thousands of years amid the harsh climate of Patagonia Argentina but evolved into a complex social structure, unique among the more than 50 species of tuco-tuco interrelated." 

Source: http://edant.clarin.com/diario/2006/04/27/sociedad/s-03615.htm