Answer:
it can be explain in such a way that there might be a kind of likelihood of cross-species transmission when a person is exposed to one strain versus another.'
it was found through research with evidence that SIV strains mutate when they enter cells to overcome human-specific barriers to infection, something that had been suspected for a long time.
Step-by-step explanation:
The first strain of a virus considered the ancestor of HIV, the virus that causes AIDS, was passed to humans in the early 1900s, somewhere near a West African rainforest. Now a study has backed up this theory, by proving forms of HIV can cross between chimps and humans.