Evolutionary Classification
Evolutionary classification combines aspects of both phenetic and cladistic systematic. Evolutionary taxonomists attempt to show in their classification both the evolutionary relationships and the degrees of similarity among organisms. It is impossible, however, to represent both similarities and genealogies accurately in a single classification system because rates of evolution among groups of organisms and among different traits within groups of organisms are often highly variable. Therefore, evolutionary taxonomists must compromise between their 'two goals. This need not be confusing as long as the nature of the compromise is clearly indicated so that users of the system know how the taxonomic categories were constructed. With a simple and hypothetical example we can illustrate how different approaches lead to different classification of organisms even when they use the same data. Six characters have been measured, and each one can have either the ancestral state (0) or a derived one (1). In this example, evolutionary reversal of character states are: not found but in real life some reversals may occur. Given these character states, we can compare the four species phenetically and cladistically. The phenetic similarity calculation is based on the number of shared characteristics that are in the derived