The article by Paul M. Sharp and Beatrice H. Hahn provides a comprehensive overview of the origins and evolution of HIV-1 and HIV-2, the viruses responsible for the AIDS pandemic. The authors trace the transmission of simian immunodeficiency viruses (SIVs) from African primates to humans, highlighting the critical role of cross-species transmissions. They discuss the genetic changes that occurred during these transmissions, which allowed SIVs to adapt to new hosts and become more pathogenic. The article also explores the impact of host restriction factors, such as tetherin, on the ability of SIVs to infect humans. The authors conclude by discussing the geographic distribution and epidemiology of HIV-1 and HIV-2, emphasizing the importance of understanding the evolutionary history and host-specific adaptations of these viruses to predict future zoonotic risks.The article by Paul M. Sharp and Beatrice H. Hahn provides a comprehensive overview of the origins and evolution of HIV-1 and HIV-2, the viruses responsible for the AIDS pandemic. The authors trace the transmission of simian immunodeficiency viruses (SIVs) from African primates to humans, highlighting the critical role of cross-species transmissions. They discuss the genetic changes that occurred during these transmissions, which allowed SIVs to adapt to new hosts and become more pathogenic. The article also explores the impact of host restriction factors, such as tetherin, on the ability of SIVs to infect humans. The authors conclude by discussing the geographic distribution and epidemiology of HIV-1 and HIV-2, emphasizing the importance of understanding the evolutionary history and host-specific adaptations of these viruses to predict future zoonotic risks.