of the other. Mimicry can result in an evolutionary arms race if mimicry negatively affects the model, and the model can evolve a different appearance from the mimic.p161 Mimicry should not be confused with other forms of convergent evolution that occurs when species come to resemble each other by adapting to similar lifestyles that have nothing to do with a common signal receiver. Mimics may have different models for different life cycle stages, or they may be polymorphic, with different individuals imitating different models, such as in Heliconius butterflies. Models themselves may have more than one mimic, though frequency dependent selection favours mimicry where models outnumber mimics. Models tend to be relatively closely related organisms, but mimicry of vastly different species is also known. Most known mimics are insects, though many other examples including vertebrates are also known. Plants and fungi may also be mimics, though less research has been carried out in this area. Etymology Use of the word mimicry dates to 1637. It derives from the Greek term mimetikos, "imitative", in turn from mimetos, the verbal adjective of mimeisthai, "to imitate". Originally used to describe people, "mimetic" was used in zoology from 1851, "mimicry" from 1861. Classification Many types of mimicry have been described. An overview of each follows, highlighting the similarities and differences between the various forms. Classification is often based on function with respect to the mimic (e.g., avoiding harm). Some cases may belong to more than one class, e.g., automimicry and aggressive mimicry are not mutually exclusive, as one describes the species relationship between model and mimic, while the other describes the function for the mimic (obtaining food). The terminology used is not without debate and attempts to clarify have led to new terms being included. The term "masquerade" is sometimes used when the model is inanimate but it is differentiated from "crypsis" in its strict sense by the potential response of the signal receiver. In crypsis the receiver is assumed to not respond while a masquerader confuses the recognition system of the receiver that would otherwise seek the signaller. In the other forms of mimicry, the signal is not filtered out by the sensory system of the receiver. These are not mutually exclusive and in the evolution of wasp-like appearance, it has been argued that insects evolve to masquerade wasps since predatory wasps do not attack each other but this mimetic resemblance also deters