5,600,000 BC Based on (mtDNA) data, human head lice (Pediculus humanus) separated from Chimpanzee head lice (Pediculus schaeffi) about 5.6 million years Ago. At this time, ancient man separated from ancient Chimpanzee. [Anon., 2004] [Reed et al., 2004]
c. 1,180,000 BC Mankind split into two lineages, one leading to modern Homo sapiens and the other to now extinct Homo erectus, about 1.18 million years ago. Since Pediculus humanus pre-dates this split, it also formed two races, one (consisting eventually of both head lice and body lice [H+B]) was carried by ancestors of modern H. sapiens and eventually became distributed world wide; the other (currently consisting of head lice only [H only]) may have been carried by archaic H. erectus to Asia, transferred to H. sapiens and carried to the New World by early migrants from Siberia, according to a recent hypothesis. [Anon., 2004] [ Reed et al., 2004] This view has been challenged by a study which shows that [H only] is much more widely distributed than just in the New World. [Leo & Barker, 2005].
So, where did we pick up these unwanted blood suckers in the first place? All signs point to a human–ape connection, and "connection" may mean something more tangible than an evolutionary link. Some studies suggest interaction between earlyHomo species and gorillas, and also between early Homo species and us.
The lice we carry around are sucking lice. That’s pretty self explanatory. Two subspecies we harbor, head lice and body lice, belong to the Pediculus(picture left) genus (Pediculus humanus capitis andPediculus humanus humanus, respectively). The other species we harbor, you know, down there, is a member of the genus Phthirus. Our closest living relatives, the chimpanzees, harbor Pediculus, as well, while gorillas are home to another Phthirus species.
In other words, we share a genus with each of them.
Sucking lice have been sucking primate blood for at least 25 million years. The big story, though, is what happened about 6 to 7 million years ago, and in the case of the gorilla, even later. Humans and apes are supposed to have parted evolutionary ways at about the 6 million year mark. The Pediculus genus seems to have split at the same time, with Pediculus schaeffi hitching a ride with the chimp lineage, and Pediculus humanus sticking with what would become the Homo line. The gorillas split off a little earlier, maybe about 7 million years ago, and the Phthirus may have done the same, sending Phthirus gorillae with the gorillas (natch), while Phthirus pubis eventually became a human problem.
Things get a bit, well, sticky when it comes to thePhthirus line (Phthirus pubis - picture right), however. The split between the gorilla and human lice seems to have happened around 3 to 4 million years ago, millions of years after the gorilla and human branches parted ways. That means that at the 3 to 4 million year point, human ancestors and gorillas must have had some kind of…contact.
The authors who uncovered this finding note in their paper that "How we might have acquired our pubic lice from gorillas is not immediately apparent, however it would be interesting to know whether the switch was very recent (say less than 100,000 years old) or whether it was considerably