Scientists now say that the simian immunodeficiency virus (SIV) in chimpanzees (Pan troglodytes), which is believed to have been transmitted to humans to become HIV-1—the virus that causes AIDS—didn't start its life in chimps.

Instead, it was a product of separate viruses jumping from different monkey species into chimps, where they recombined to form a hybrid virus, according to a new study.

Researchers believe the chimpanzee virus is a hybrid of the SIVs naturally infecting two different monkeys, the red-capped mangabey (Cercocebus torquatus) and the greater spot-nosed monkey (Cercopithecus nictitans). Chimps eat monkeys, which is likely how they acquired the monkey viruses. The hybrid virus then spread through the chimpanzee species, and was later transmitted to humans to become HIV-1.

The study suggests