[Various (1967)] the production of a projectile point, changes in proportion, of weight, of choice of material, may came about in a number of ways, from individual fancy or discovery to movement to a new locale or exposure to new ideas. Phases of chronological significance are to be expected, therefore, and the tradition continues until changes have obliterated its "specific theme." Thus the tradition-phase concept comprehends both the "lumpers" and the "splitters" among typologists. Obviously the lumpers recognize and emphasize the tradition, the splitters the phases. For an analogy which will explain phases it is helpful to turn to biology. There is a definition by W. W. Howells (1966:46) of what is presently understood by the word "species" which, with appropriate deletions for the fact that artifacts are inanimate, can help us realize what is meant by tradition and phases. Howells writes: "By today's definition a species typically consists of a series of local or regional populations that may exhibit minor differences of form or color but that otherwise share a common genetic structure and pool of genes and are thus able to breed across population lines." For "populations " substitute "collections," for "color," substitute "material," delete "genetic" before "structure" and the qualification about genes and interbreeding that follow; and the analogy between an artifact tradition and its phases and a biological species and its subspecies becomes clear.