Whale lice, parasitic cyamid crustaceans that live off skin debris, offer further information through their own genetics. Because these lice reproduce much more quickly than whales, their genetic diversity is greater. Marine biologists at the University of Utah examined these louse genes and determined their hosts split into three species 5–6 million years ago, and these species were all equally abundant before whaling began in the 11th century. The communities first split because of the joining of North and South America. The rising temperatures of the equator then created a second split, into northern and southern groups, preventing them from interbreeding. "This puts an end to the long debate about whether there are three "Eubalaena" species of right whale. They really are separate beyond a doubt", Jon Seger, the project's leader, told BBC News.