Although many scientists already suspected the human immunodeficiency virus originated in African primates, the natural lair of HIV has remained a mystery since the disease surfaced almost 20 years ago. Finding the ancestor of AIDS not only solves a long mystery, it may help guide researchers looking for a cure.

After analyzing the genetic make-up of a similar virus that infects chimpanzees, scientists from the University of Alabama at Birmingham say that one subspecies of chimpanzees harbors a virus that gave rise to the current epidemic.

Hahn and her colleagues believe that slaughtering the animals exposes the hunters to vast amounts of blood and allows the virus to slip into the human population. The chimps could have also transmitted the virus through bites. Her studies cannot determine when the jump occurred.