A Practical Criticism of Hennig-Brundin “Phylogentic Systematics” and Antarctic Biogeography

Darlington, P. J., Jr. (Museum of Comparative Zoology, Harvard Univ., Cambridge, Mass.) 1970. A practical criticism of Hennig-Brundin "Phylogenetic Systematics" and Antarctic biogeography. Syst. Zool., 19:1-18.-Hennig's (1966) Phylogenetic Systematics is primarily concerned with cladism. The central thesis is that all taxa must be monophyletic in a special, rigid sense, and that their rank must be determined solely by time of origin. Secondary concepts are that species split in a very simple way; that one of two daughter species derived from a common ancestor will deviate more than the other; that species divide only dichotomously and that phylogenies must be dichotomous; that rates of evolution and divergence are constant and the same in different groups, unless known to be different; that relative primitiveness established at time of species-splitting remains characteristic of groups throughout their history; and that primitive groups remain at or near their places of origin. These concepts are all oversimplified, in part illogical, not consistent with real situations that are common in nature, and of no practical use in systematics or biogeography. Brundin (1966) accepts and further oversimplifies Hennig's concepts and applies them uncritically in classification of southern chironomid midges and antarctic biogeography. His supposed history of antarctic land connections, beginning in the Jurassic, is based on application of Hennig's erroneous secondary concepts, on an imaginary parallelism between chironomids and birds, and on an arbitrary decision that chironomids cannot cross water gaps although they occur in aereal plankton. His conclusions are probably wrong as to dating, as to directions of dispersal, and as to existence of continuous land connections. Existing chironomids may really have dispersed during or not long before the Tertiary, along the edges of Antarctica, and across water gaps between the southern tips of the continents and Antarctica. Introduction. The publication in 1966 of an English edition of Willi Hennig's Phylogenetic Systematics has finally made this difficult but important work available to non-Germans, and Lars Brundin (1966) has summarized Hennig's ideas and applied them to the classification of southern chironomid midges and to antarctic zoogeography. (Shorter papers by these two authors, e.g. Brundin, 1968, seem to me to add nothing of importance to the works cited.) It must be understood from the beginning that Hennig's title is misleading. His book is concerned with a very special kind of phylogenetic systematics now often called cladism. Many other systematists, including myself, try to make their classifications phylogenetic without being bound by the special concepts and practices of the cladists. The central thesis of cladism is that taxonomic categories must be monophyletic in a special, rigid sense, and that their rank must be determined by time of origin rather than by degree of difference or extent of diversification. However, cladism as advocated by Hennig and Brundin includes other assumptions and procedures which affect the course and results of their work and which deserve more attention than they have usually received. Hennig's book has been reviewed three times in American journals as well as in Nature (see reference list at the end of the present paper; one of the reviewers, Byers, covers Brundin's work too). However, the reviews have necessarily been limited to generalities and have not considered the author's ideas and methods in detail. Work I am now doing on carabid beetles of New Guinea has reached a point where I need to know more about the practical applications of cladism, especially in zoogeography. I have therefore written the present paper. It is not a general consideration of cladism (for which see Mayr, 1969:70ff, 211ff, 230) and it does not repeat the general comments