Paleontologists are developing progressively more interest in the biologic aspects of fossils. Some, who are particularly conscious of the deficiencies that mark much of the paleontology of the past, seem to accept uncritically certain ideas that are current among neontologists and especially geneticists. This applies, for example, to the concept of the so-called biologic species which is defined as an integrated, reproductively isolated, breeding group. Such a concept is useful, and the existence of such groups deserves recognition but they are too theoretical to have much practical value. Species have been viewed in many different ways, and the principal species concepts are compared. Fundamentally, the species is a taxonomic unit as demonstrated by more than 200 years of usage by biologists. Therefore, the redefinition of species as breeding groups is ill-advised. The taxonomic species is indispensable, and changing the meaning of a well known word only necessitates the substitution of a new term for exactly the same thing. A species definition is suggested that takes into account modern biologic thought, fits the requirements of paleontologists, and should be acceptable to many neontologists.