A new study suggests that AIDS originated 100 years ago, decades longer than scientists thought, The Associated Press reports. Scientists have reason to believe that HIV emanated in 1908 rather than 1930, the disease’s original discovery date.

The new result is “not a monumental shift, but it means the virus was circulating under our radar even longer than we knew,” says Michael Worobey of the University of Arizona, an author of the new work.

According to the article, the new dates correspond with the rise of cities in Africa, possibly linking urban development and the spread of AIDS. While scientists theorized that the virus passed from monkeys to humans, researchers are now examining the growth of African cities, which placed people close together, and the promotion of prostitution as primary catalysts for the epidemic.