A theory derived by Ronald A. Fisher (1890-1962) from two earlier theories, namely, Batesian mimicry as announced by Henry W. Bates (1825-1892) in 1861 and Müllerian mimicry published by Fritz Müller (1821-1897) in 1879. The evolution of mimicry such that a unprotected organism (e.g., a caterpillar) acquires the colour or form of a unpalatable species (e.g., a snake) for the predators was taken by Fisher as a example of natural selection at work that reduces the probability of an attack by looking or sounding like a dangerous, poisonous or noxious species. The theory is not without problems as there are difficulties in making clear-cut distinctions between mimicry and, for example, camouflage or crypsis (the ability for an organism to blend in with its surroundings). The theory led to the inclusion of altruism in evolutionary theory. In fact, similarities between mimics and models concerns not only appearance, but also behavior (as well as scent, sounds and location).
See Imitation, Macroevolution (or horizontal evolution) and microevolution (or vertical evolution), (Modern synthesis, Theory of natural selection