What Is a Species?

A common but somewhat difficult question to answer is, “What is a species?” The easy answer is “all of the same kind.” This answer might be expanded to mention that the members of a species have mutual fertility and that a species is reproductively isolated from other species. These latter two claims do not entirely fit, however. Thus, the struggle to define the term species goes on. The claim that a species is all of the same kind, however, still holds.