HIV-1 is more virulent, more easily transmitted, and the cause of the vast majority of HIV infections globally. Research in this area is conducted using molecular phylogenetics , comparing viral genomic sequences to determine relatedness.
Scientists generally accept that the known strains or groups of HIV-1 are most closely related to the simian immunodeficiency viruses SIVs endemic in wild ape populations of West Central African forests. Using HIV-1 sequences preserved in human biological samples along with estimates of viral mutation rates, scientists calculate that the jump from chimpanzee to human probably happened during the late 19th or early 20th century, a time of rapid urbanisation and colonisation in equatorial Africa.
Exactly when the zoonosis occurred is not known. Some molecular dating studies suggest that HIV-1 group M had its most recent common ancestor MRCA that is, started to spread in the human population in the early 20th century, probably between and Sample analyses resulted in little data due to the rarity of experimental material.
The researchers, however, were able to hypothesize a phylogeny from the gathered data. They were also able to use the molecular clock of a specific strain of HIV to determine the initial date of transmission, which is estimated to be around β There are six additional known HIV-2 groups, each having been found in just one person.
They all seem to derive from independent transmissions from sooty mangabeys to humans. Groups C and D have been found in two people from Liberia , groups E and F have been discovered in two people from Sierra Leone , and groups G and H have been detected in two people from the Ivory Coast.
