scientists have found evidence that the ancestor to the virus that causes the disease has been in monkeys and apes for at least 32,000 years — not just a few hundred years, as had been previously thought.
That means humans have presumably been exposed many times to S.I.V., the simian immunodeficiency virus, since people have been hunting monkeys for millennia, risking infection every time they butcher one for food.
And that assumption in turn complicates a question that has bedeviled AIDS scientists for years: What happened in Africa in the early 20th century that let a mild monkey disease move into humans, mutate to become highly transmissible and then explode into one of history’s great killers, one that has claimed 25 million lives so far? [My emphasis]
I will recall the reader's attention to this
