Since populations of a species frequently become adapted to different local environments, it is not unexpected that some will diverge to the point of being unable to interbreed. If this is the case, the process of speciation has occurred. Although simple answers are tempting, such questions are difficult to answer explicitly. In fact, it is doubtful that simple answers exist since new species may become established via several avenues. The factors important in a particular situation are likely to depend upon the characteristics of the organism, the environment, and the genetic variation available for selection. The term species refers to both a taxonomic category and a biological concept. Taxonomic species are usually based on distinct morphological differences. In most animals, taxonomic species are in general equivalent to biological species where biological species are defined as: Groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.