The Development of Phylogenetic Concepts in Hennig's Early Theoretical Publications (1947-1966)

In this paper, we describe the development of Hennig's most important phyloge? netic concepts, which culminated in the publication of the now famous Phylogenetic Systematics in 1966, Hennig proposed strict definitions of monophyly and phylogenetic relationships as early as 1950 in Grundzuge einer Theorie der phylogenetischen Systematise. However, in this edition of the book, the terms "apomorphic" and ''plesiomorphic" were introduced for taxa and not for characters. It was not until 1952 that these terms were consistently applied to characters, hereby for the first time allowing the reconstruction of phylogenetic relationships. But this is not Hennig's sole contribution to systematics, as revealed by a comparison of his Phylogenetic Sys? tematics with publications of the "new systematics" school (e.g., Huxley, 1940, The new system? atics, Oxford Univ. Press, Oxford, England; Mayr et al., 1953, Methods and principles of systematic zoology, McGraw-Hill, New York). Hennig was the person who redirected the interest of sys? tematics to the study of supraspecific taxa after years of focusing on species and infraspecific taxa. (History; phylogenetic systematics; cladistics; monophyly; Hennig; apomorphy; plesio- morphy.) The oldest field of the biological sci? ences, systematics, underwent dramatic changes in the middle of this century. These changes were in part initiated by an entomologist, Willi Hennig, who clarified or, depending on your systematic persua? sion, redefined the goals of phylogenetic systematics in his Phylogenetic Systematics (1966). The history of phylogenetic sys? tematics sensu Hennig has not been exten? sively studied. Surprisingly, most contri? butions that deal with this subject focus on systematists that anticipated Hennig's ideas, were influential in their develop? ment, or dealt with their reception in var? ious countries (Hull, 1988; Craw, 1992