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 beings belong to two genera, "Pediculus" and "Pthirus": head lice ("Pediculus humanus capitis"), body lice ("Pediculus humanus humanus"), and pubic lice ("Pthirus pubis"). Human head and body lice (genus "Pediculus") share a common ancestor with chimpanzee lice, while pubic lice (genus "Pthirus") share a common ancestor with gorilla lice. Using phylogenetic and cophylogenetic analysis, Reed et al. hypothesized that "Pediculus" and "Pthirus" 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, hostparasite cospeciation events are likely.