The goal of cladistic systematics is to discern sister-group relations (cladistic relations) by the methods of cladistic analysis and to represent them explicitly and unambiguously in cladograms and cladistic classifications. Cladists have selected cladistic relations to represent for two reasons: cladistic relations can be discerned with reasonable certainty by the methods of cladistic analysis and they can be represented with relative ease in cladograms and classifications. Cladists argue that features of phylogeny other than cladistic relations cannot be discerned with sufficient (...) certainty to warrant attempting to represent them in either cladograms or classifications and could not be represented if they could. I argue that a better alternative is to work toward improving methods of cladistic analysis (or else to supplement them with other methods) so that such features of phylogeny can be discerned and to devise methods of representation capable of representing them in both cladograms and classifications. However, cladograms and classifications cannot represent everything about phylogeny. It is better to represent one or two aspects of phylogeny explicitly and unambiguously than nothing at all. (shrink)

The foundations of systematics lie in ontology, not in subjective epistemology. Systems and their elements should be distinguished from classes; only the latter are constructed from similarities. The term classification should be restricted to ordering into classes; ordering according to systematic relations may be called systematization.The theory of organization levels portrays the real world as a hierarchy of open systems, from energy quanta to ecosystems; followingHartmann these systems as extended in time are considered the primary units of reality. Organization levels (...) should be distinguished from levels of differentiation within each organization level.Certain biological systems, such as species, continue to be misinterpreted as classes, particularly by logicians unfamiliar with modern biological theory. Replacement of Aristotelian definitions of species by “polytypic” definitions achieves nothing, because species are individual systems which can be defined from an ontological viewpoint only as wholes. The dispute whether classes are real per se or only in individuals is of no scientific importance; irrespective of which view is taken, any ordering of physical objects into classes constitutes an hypothesis about the structure of the real world.The distinction between essential and contingent characters is relevant only to classification. There are no universal rules for evaluating characters for purposes of systematization. Character statements do not form separate linear sequences. The search for “unit characters” in an absolute sense is futile. All real characters are reducible to relations and are in principle measurable, although there are limitations on the extent to which this can be presently achieved.The concept of the sexual species is fundamental to theories of biosystematics. Sexual species may be defined as lineages consisting at any given time of series of populations between which genetic exchange can occur and delimited in time by two successive processes of speciation. Linnaean nomenclature needs modification; in its traditional form it is appropriate only to non-truncated hierarchies, whereas real phylogenies form truncated hierarchies. In consequence of the distinction between systematization and classification it is concluded that, while taxa may be classified into age classes or evolutionary grades, their limits as taxa can be no different in either case. Classification into evolutionary grades remains an imprecise endeavour, since no general measure of evolutionary differentiation has been devised.The spatial and temporal extent of ecosystems, the postulated basic units of ecosystematics, remains unclarified. Nevertheless there are grounds for expecting progress in this field as the energetic relations between organisms become better understood. Biotic communities are not “abstract” classes, but systematic units. Physiognomic classification should not be confused with systematization of plant communities; both approaches contribute to an understanding of vegetational structure. (shrink)

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. (shrink)

Karl Popper has been one of the few philosophers of sciences who has influenced scientists. I evaluate Popper's influence on our understanding of evolutionary theory from his earliest publications to the present. Popper concluded that three sorts of statements in evolutionary biology are not genuine laws of nature. I take him to be right on this score. Popper's later distinction between evolutionary theory as a metaphysical research program and as a scientific theory led more than one scientist to misunderstand his (...) position on evolutionary theory as a scientific theory. In his later work Popper also introduced what he took to be improvements of evolutionary theory. Thus far these improvements have had almost no influence on evolutionary biology. I conclude by examining the influence of Popper on the reception of cladistic analysis. (shrink)

The author proposes a system of identification, positional, and phyletic numbers for taxa that makes possible a significant relationship between numerical classification and phylogeny.