Typology and empiricism in taxonomy

Abstract

The term typology has been used in taxonomy to imply procedures and philosophies of somewhat diverse meanings. Not all typological work meets every criterion suggested for such work by various authors. Some of these criteria are untenable when viewed in the context of modern biological theory, while others seem eminently reasonable in the light of present day knowledge. Mere reference to a work as typological will not convey to the reader or listener a clear idea why a reviewer has decided that it merits the term. Similarly, it would be improper to attach automatic derogatory implications to the adjective “typological”, since it is only those aspects of typological procedure which cannot be defended or maintained today that would merit such a connotation. The classificatory philosophy of many proponents of typology is based on a platonic idealism. To consider a taxonomic type as an abstract idea seems of doubtful utility at best and is certainly beyond the realm of scientific inquiry. The method by which types are obtained must be indicated without ambiguity. In classical typological work this is generally not done, and reconstructions relying on the metamorphosis of parts are often rather vague and controversial. Similarly, abstractions relying either on weighted or unweighted averages of the characters in the taxa to be studied are of questionable value. It would appear that character variation of individuals within taxa or of taxa within higher taxa must in some way be accounted for, if types are to be defined which will represent the natural order in the system. The choice of characters must also be clearly defined and defensible. A priori weighting or preference of some characters over others, based on either presumed phylogenetic importance or logical or functional primacy, is an unjustifiable procedure. Equal weighting and use of all characters leads directly into an empirical approach, which attempts to classify organisms on the basis of all available evidence, without preconceived notions about their arrangement. Such a procedure also arrives at a classification from which types may be abstracted, but does so by clearly defined and previously determined criteria, and does not rely on hypotheses based on certain preliminary conclusions in order to reinforce its argument. The empirical approach, the most notable example of which in recent years has been the development of numerical taxonomy, has definite typological aspects which, however, appear to this writer to be of value and preferable to the phylogenetic method. Smirnov's statistical method of constructing types is contrasted with results obtained by numerical taxonomy. The latter appear preferable from several points of view.