The model also traced the most recent common ancestor of both strains to 1908.
The team's findings appear today in the journal Nature.
"This confirms that this was a virus that was lurking around for many decades before it exploded into the human population to become a noticeable pandemic, as opposed to something that started in the '70s or '80s," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), in Maryland.
NIAID funded the study along with the National Institutes of Health.
"It solidifies our understanding of the timetable of how this virus emerged from the chimpanzees to establish itself as a human infection," Fauci added.
"[HIV-1] flew below the radar level for decades until social conditions such as the end of colonization, migration of people to cities, increase in prostitution, and promiscuous sexual activity made it much easier for the disease to explode into a pandemic," Fauci explained.
Robert Garry is a microbiologist at New Orleans's Tulane University who was not involved with the study.
In the late 1980s, Garry was the first scientist to examine tissues samples taken from the U.S.'s first confirmed AIDS patient, who died in 1969.
"This study is very important, and what they are finding here is when the human virus started circulating in people," he said. "We still don't know when exactly the virus jumped from chimpanzees to humans, but it may be pushed back even further with this study.
"There will be other emerging viruses in the future, and what we learn about the conditions that help viruses spread, be it social changes or changes within the virus itself, will make us better prepared for other epidemics," he said.
Garry also argues that, though the rapid growth of cities in west-central Africa may have sparked the spread of infections, the virus itself underwent some sort of genetic change to facilitate transmission.
"We have to figure out what that change was," he cautioned.
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