Re: Do you think that viruses and bacteria will someday evolve?

Bacteria, viruses, and all other life forms are always evolving. Evolution is a part of life. Each type of life form has its own particular evolution rate, which is influenced by many factors, such as mutation rate (some organisms have better error-checking of replication of the DNA than others, some have DNA damage-repair genes, etc.) the population size, changes in the environment, mode of reproduction (sexual reproduction allows more recombination than asexual reproduction, which is essentially cloning).

Some bacterial, viral and eukaryotic pathogens (a pathogen is a species that causes harm to its host - the protist that causes malaria is an example of a eukaryotic pathogen) will become non-pathogenic over time either because the pathogen evolves to become harmless or because the host evolves a better defense. Some non-pathogenic organisms will become pathogenic over time.

To be more correct, what we observe in evolution is most often not an entire species evolving in the same direction so that all individuals become pathogenic or non-pathogenic at the same time (unless the change was a change in the host). Instead we observe increasing diversity over time, such that some strains of the organism gain or loose pathogenicity while others gain or loose other traits. The E. coli strains 0157:H8 and 0157:H7 are two examples of E. coli that have apparently gained pathogenic potential - most strains of E. coli are harmless or even beneficial to their host.

It is not possible for an organism to survive if it kills every host it infects so rapidly that the current host does not have a chance to pass the pathogen on to another host, or if the pathogen kills off the entire species that it depends on. This is only true if the pathogen depends on the host exclusively. There are bacteria that normally live in the soil that can kill humans or other mammals but their normal life is in the soil and they do not depend on mammals for survival. Bacteria and viruses that are obligated to live within a small host range tend to evolve to not kill off that host, because those that do kill too soon go extinct with the host.

Frank Ryan wrote a book called "Virus X" in which he talks about the idea that viruses may be beneficial to one species of mammal if they are less harmful to that species than they are to competing species. For example a mouse virus that make mice sick but kills rats could be benificial to the mouse if it prevents rats from multiplying and eating the grain that the mice need for food. Over time, mice that carry this virus will do better than mice that don't, if the rats are more of a competition for survival than the sickness caused by the mouse virus.