View Larger Version | One two of the four subspecies of chimpanzee, Pan troglodytes troglodytes and Pan troglodytes schweinfurthii, are known to harbor SIV. The eastern chimps in a new study may have acquired SIV from their western relatives. Previous work suggests the SIV version in the western chimps is a mix of versions from red-capped mangabeys and greater spot-nosed monkeys and relatives. Credit: Adapted from Weiss and Heeney/Nature