Evolution is the process of biological change over time. Such changes, especially at the genetic level are accomplished by a complex set of evolutionary mechanisms that act to increase or decrease genetic variation. Because of their rapid development and reproduction (i.e., high generation rate), evidence of the fundamental molecular mechanisms of evolution are especially apparent in studies of bacteria and viral microorganisms. Immunological adaptation has a profound effect on fitness and survivability.

Evolutionary theory is the cornerstone of modern biology, and unites all the fields of biology under one theoretical umbrella to explain the changes in any given gene pool of a population over time. Evolutionary theory is theory in the scientific usage of the word. It is more than a hypothesis; there is an abundance of observational and experimental data to support the theory and its subtle variations. These variations...