Two million years ago, chimpanzees experienced a drastic loss of variability in certain genes that help them fight viruses, a new study reports. Widespread infection with an HIV-like virus may have pruned from the species individual chimps with some of these immunity genes, the study's authors hypothesize. Ironically, the change could have conferred AIDS resistance on modern chimpanzees.
Chimpanzees are more genetically diverse than people (SN: 11/06/99, p. 295). That is, specieswide, they tend to have more polymorphisms–or different versions of a given gene–than humans do. But this trend is unexpectedly reversed for the immunity genes known as class I of the major histocompatibility complex (MHC), Ronald E. Bontrop of the Biomedical Primate Research Center in Rijswijk, the Netherlands, and his colleagues report in the Sept. 3 Proceedings of the National Academy of Sciences.