Doctors Find AIDS' 'Lucy'

Scientists have found the earliest known appearance of HIV in humans--in the blood sample of a Bantu man from Central Africa who died in 1959. The study, co-authored by Dr. David Ho and to be published in this week's Nature, holds little promise for the HIV sufferer of today. But its findings may shed important light on the virus' murky origins.

"It's known that HIV crossed over to humans from non-human primates," says TIME Medical correspondent Christine Gorman, "What's not yet explained is whether it began in humans as a single, distinct virus or as the family of viruses it is now." The 1959 virus seems to be an ancestor of two modern strains, suggesting that HIV had already infected humans before it began to mutate.

The discovery also gives a helpful glimpse at HIV's future. "HIV is very mutable," says Gorman. "If you know how much it's changed since 1959, you can better predict the rate of mutation into the future." Giving vaccine-hunting scientists a better idea of what, if anything, can keep up with a shape-shifting enemy.