Understanding the coevolution of humans, simians, and the H.I.V. virus

You might already know that scientific types are in agreement that H.I.V. was originally spread to humans from monkeys and apes in Africa. The disease S.I.V. (Simian immunodeficiency virus) is prevalent in non-human primates, but unlike the human form of the disease, the mortality rate from S.I.V. is very low - only very weak primates die from this virus.

The theory goes that somewhere along the line, the virus passed from monkey to human, probably via some hunter that cut himself while butchering a monkey, and contaminated his (or her) self with infected blood. In the process, the virus mutated into H.I.V. and became much deadlier as a result.

The questions remain: when did the transmission/mutation event occur? And why are humans so vulnerable to a virus that other primates cope easily with?

New research suggests that African monkeys have been coevolving with the S.I.V. virus for much longer than previously thought, over 32,000 years. And even more primitive strains of the virus have been found in Madagascar lemurs (which we know from lecture are more similar to ancestral primates than old world monkeys and apes) suggesting that this virus may have been evolving with primates for millions of years.

Since H.I.V. crossed over from monkeys to humans relatively recently, our tragic susceptibility to this disease makes sense evolutionarily. However, understanding the evolutionary ecology and history of the virus may assist future efforts in treatment. (ARTICLE AT NY TIMES)