Dr. David Whitehouse writes in BBC News Online that AIDS arose from a combination of two chimpanzee viruses. Chimps could have had one form of SIV (the simian form of HIV), then eaten smaller monkeys, and caught another form of SIV from them. When humans ate the chimps, they contracted HIV from the combination of the two SIV viruses.
Scientists now know that HIV was passed from chimpanzees to humans sometime after 1860 in the Guinea-Bissau region of Africa. The transfer may have happened more than once, because of the different strains of HIV. They know the date because no 19th century slave traders report cases of AIDS. The first U.S. case was discovered in 1981, although there may have been an earlier case here in 1969. In Africa, HIV was found in a blood plasma sample from a Congo man in 1959. The rate of genetic divergence between HIV-1 and HIV-2 suggests it jumped to humans around 1940.
Are humans going to make it here? We need to be able to look into the future in order to find out.
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