"[B]efore researchers can develop new drugs" to "stave off the worst that viruses" -- such as HIV -- and "bacteria can produce, ... they must understand the evolutionary nature of individual diseases and how viruses and bacteria, in turn, shape the evolution of humans and other animals," Boston Globe columnist Stephen Smith writes in an opinion piece. Researchers believe that HIV derived from the simian immunodeficiency virus, which has "ceased to harm [primates], in part to allow its own survival," according to Smith. Researchers also have found that a lack of CCR5 receptors on human cells might prevent HIV from entering the cells, Smith writes, adding that a lack of such receptors appears not to have damaging effects. Smith says that some researchers have theorized the lack of CCR5 receptors is due to a regional evolutionary "artifact of the bubonic plague" that allowed people to survive the disease, adding that about 5% to 10% of people living in northern Europe are estimated to be living without CCR5 receptors. Because being without CCR5 receptors causes no harmful effects, drug companies currently are developing drugs to inhibit CCR5 receptors to prevent HIV transmission into cells, Smith writes. He adds, "This and other efforts to use evolution as a weapon against HIV are an acknowledgement that even with more than two dozen AIDS medications now available, that's still not enough" because HIV is "especially adept at evolving to escape drugs -- an evolutionary process that can take place in weeks and months" (Smith, Boston Globe, 3/13).