Scientists believe they have found a "missing link" in the evolution of the virus that causes AIDS. It bridges the gap between the infection that does no harm to most monkeys and the one that kills millions of people.

That link is a virus that is killing chimpanzees in the wild at a disturbingly high rate, according to a study in Thursday's journal Nature. Chimpanzees are the first primate besides man shown to get sick in the wild in significant numbers from a virus related to HIV. Chimps are also man's closest relative among primates.

And chimps are already endangered.
http://www.msnbc.msn.com/id/32086366/ns/health-aids/