 Lice have been the subject of significant DNA research in the 2000s that led to discoveries on human evolution . The three species of sucking lice that parasitize human being belong to two genera : Pediculus and Phthirus. head lice ( Pediculus humanus capitis ) , body lice ( Pediculus humanus corporis ) , and pubic lice ( Phthirus pubis ) . Human head and body lice ( genus Pediculus ) share a common ancestor with chimpanzee lice , while pubic lice ( genus Phthirus ) share a common ancestor with gorilla lice . Using phylogenetic and cophylogenetic analysis , Reed et al. hypothesized that Pediculus and Phthirus are sister taxa and monophyletic . In other words , the two genera descended from the same common ancestor . The age of divergence between Pediculus and its common ancestor is estimated to be 6 @-@ 7 million years ago , which matches the age predicted by chimpanzee @-@ hominid divergence . Because parasites rely on their hosts , host @-@ parasite cospeciation events are likely . 
