Cophylogeny (cospeciation) has been documented repeatedly in pocket gophers and chewing lice, largely resulting from the asociality and patchy distribution of the hosts and the low vagility of the parasites. This island-like distribution of lice restricts host-to-host transfer to gopher mating events and maternal rearing of young. Fossil and molecular dating of the pocket gopher phylogeny shows that the gopher-louse symbiosis has persisted for at least 25 million years. The long term stability of this relationship, coupled with several other life-history traits of gophers and lice, suggest that the relationship between gophers and lice may actually be commensalism, or even mutualism, rather than parasitism. There is no evidence that chewing lice harm pocket gophers in any way, but there is evidence that they may, in fact, be protecting their hosts from truly harmful ectoparasites.