Adolf Naef (1883-1949), systematic morphology and phylogenetics

Several authors have highlighted methodological similarities between Naefs systematic morphology and Hennigs phylogenetic systematics. Whereas this may indicate an influence of Naef on Hennig, the relevant issues such as the principle of generality in character analysis and the threefold parallelism of classification, ontogeny and the Fossil Record reach back beyond Naef and Hennig and were widely discussed in the German systematics literature of the late 19th and early 20th Century. The same is true of conceptual issues, such as the discussion of the principle of monophyly, which was first introduced by Haeckel in 1866 (Rieppel 2011b, J Zool Syst Evol Res49:1). In spite of methodological and conceptual agreements, Naefs systematic morphology differed fundamentally from Hennigs phylogenetic systematics. Naef emphasized the role of unbiased observation and the immediate acquaintance of the investigator with the phenomena given in nature as the basis of natural science in general, and of his hierarchy of types in particular. From the hierarchy of types, Naef derived through conceptual-logical analysis the natural system, which above the species level forms a nested hierarchy of intensionally defined classes, denoted by general names. The historical-causal interpretation of the hierarchy of types in turn offers insight into the hypothetical reality of phylogeny. Hennig in contrast denied the possibility of theory-free observation, indeed of assumption-free science in general, and on that basis put metaphysical issues above epistemology. Tying individuality to spatiotemporal location, historicity and causality, Hennig took not only species (as did Naef) but also supraspecific monophyletic taxa as individuals, denoted by proper names. From the species up, the phylogenetic system thus becomes a nested hierarchy of complex wholes of increasing degrees of complexity. Diagnostic characters of species or higher taxa can then no longer define classes (as in Naefs natural system) but are thought to indirectly indicate the phylogenetic relations on which alone the phylogenetic system is to be based.