The study investigates the origin of HIV-1 in chimpanzees, specifically focusing on the subspecies *Pan troglodytes troglodytes*. The researchers found that all known HIV-1 strains, including groups M, N, and O, are closely related to SIVcpz (Simian Immunodeficiency Virus of chimpanzees) strains infecting *P. t. troglodytes*. They identified a unique SIVcpz strain, SIVcpzUS, which is distinct from other SIVcpz strains and is closely related to HIV-1 groups M and N. The phylogenetic analysis showed that HIV-1 groups M and N are equidistantly related to SIVcpzGAB1 and SIVcpzUS, while HIV-1 group O is slightly more divergent. The geographic range of *P. t. troglodytes* coincides with areas of HIV-1 group M, N, and O endemicity, suggesting that this subspecies is the primary reservoir for HIV-1. Additionally, the study found evidence of recombination among divergent SIVcpz lineages, indicating that SIVcpz infection rates in wild chimpanzees may have been substantial. The authors conclude that *P. t. troglodytes* is the natural host and reservoir for HIV-1, and further research is needed to understand the full extent of natural SIVcpz infection and zoonotic transmission to humans.The study investigates the origin of HIV-1 in chimpanzees, specifically focusing on the subspecies *Pan troglodytes troglodytes*. The researchers found that all known HIV-1 strains, including groups M, N, and O, are closely related to SIVcpz (Simian Immunodeficiency Virus of chimpanzees) strains infecting *P. t. troglodytes*. They identified a unique SIVcpz strain, SIVcpzUS, which is distinct from other SIVcpz strains and is closely related to HIV-1 groups M and N. The phylogenetic analysis showed that HIV-1 groups M and N are equidistantly related to SIVcpzGAB1 and SIVcpzUS, while HIV-1 group O is slightly more divergent. The geographic range of *P. t. troglodytes* coincides with areas of HIV-1 group M, N, and O endemicity, suggesting that this subspecies is the primary reservoir for HIV-1. Additionally, the study found evidence of recombination among divergent SIVcpz lineages, indicating that SIVcpz infection rates in wild chimpanzees may have been substantial. The authors conclude that *P. t. troglodytes* is the natural host and reservoir for HIV-1, and further research is needed to understand the full extent of natural SIVcpz infection and zoonotic transmission to humans.