Some viruses, including HIV, which is responsible for AIDS, evolve even faster than bacteria. Unlike bacteria (as well as plants and animals), which carry their genetic information in the form of DNA, these viruses carry their genetic information in a similar molecule called RNA. When RNA is copied to make a new virus, the process is less accurate and far more mutations occur than when DNA is copied. That means more variety among the offspring and more chances that a few of them will escape the antibodies. In fact, viruses evolve so quickly that the same virus in two individuals often evolves into two different strains. All living organisms adapt to changes in their environment but RNA viruses, like HIV, adapt much faster because they produce more offspring with more variation.