Abstract
The development of resistance of viruses to anti-viral agents often is presented as a modern example of evolution by mutations and, by extension, as clear evidence for Darwinism. A literature review shows that many examples of the acquisition of resistance are not due to mutations, but in nearly all cases they are a result of complex, built-in genetic and molecular biological defense systems. The extant literature indicates that those examples that are due to mutations are in nearly all cases due to loss mutations and do not result in a gain of genetic information.