Human acquired immunodeficiency syndrome (AIDS) is a retrovirus found in two forms HIV-1 and HIV-2. The AIDS virus is a relatively new virus that received attention in the 1980s. Just as quickly as it spread across the world, it reached epidemic proportions just as quickly. Acquired immunodeficiency syndrome is a virus that enters and infects the body through sexual activity with an infected party. AIDS is a very contagious and dangerous virus that causes the death of many human beings. AIDS is characterized by two single-stranded RNAs and uses reverse transcription of the enzyme to integrate into the host's DNA. The AIDS virus is transmitted through sexual activity with someone who is infected with the virus. HIV has the greatest genetic diversity observed in viruses. HIV enters the immune system through the body fluids of an infected party. Upon entering the body, the virus (two strands of single-stranded RNA) replicates using reverse transcription to enter the DNA. HIV promotes the entry of the CD4+ receptor into cells, which allows binding. While simply not getting the receptor does not make a person 100% less susceptible to the virus, it still allows the person to contract the virus. The lack of receptors comes from ancestors who survived the Black Death in Europe. Their adaptation was passed on to their children and also created greater resistance to AIDS. After attachment to the cell, preferably with CD4+, HIV must now enter viral transcription. HIV-1 and HIV-2 are two distinct forms of the virus, which arise from different origins in the evolutionary tree. The split between the two forms occurred over 150 years ago. Both forms of the HIV virus come from the simian immunodeficiency virus (SIV) found in other primates. The two forms arrive... at the center of the card... they could begin to infect humans. While the origins of the HIV-1 form of HIV are disputed and hypothesized through scientific research, the origin of HIV-2 is more concrete. The evolutionary history of HIV-2 originates from the 〖SIV〗_sm strain found in Sooty Mangabey monkeys. It is very likely that HIV-2 originated in West Africa and remains prevalent there as well. HIV-2 can be separated into six distinct phylogenic lineages. Each of the six distinct lineages is equally related to each other and to 〖SIV〗_sm. The AIDS virus has the gift of replicative powers. The virus replicates at a very fast rate and also has a very high mutation rate. Together defeating the virus is very difficult, because it is constantly evolving to combat the drugs launched against the virus. Each strain of AIDS within each infected human is distinct from them.