 Its closest relatives are the Cuban iguana ( Cyclura nubila ) and the Northern Bahamian rock iguana ( Cyclura <unk> ) , the three species having diverged from a common ancestor some three million years ago . The species has a low genetic diversity but does not seem to suffer the same lack of vitality that afflicts other such species of rock iguana . One theory is that the species evolved from a single female Cuban iguana ( C. nubila nubila ) with eggs inside her who drifted across the sea , perhaps during a storm . It is distinct from the subspecies found on Little Cayman and Cayman Brac known as C. nubila caymanensis , although it can breed with this subspecies and produce fertile offspring . 
