A German zoologist who originated phylogenetics. He was awarded his Ph.D. by the University of Leipzig in 1947 and conducted research on Drosophila larvae. His book, Grundzüge einer Theorie der phylogenetischen Systematik (1950), made no immediate impact, but when an English translation appeared in 1966, as Phylogenetic Systematics (with a second edition in 1979), it suddenly achieved authoritative status (comparable, perhaps, to The Origin of Species!). Hennig argued that, as taxonomy aims to depict relationships and the only objective meaning of ‘related’ means sharing a common ancestor, taxonomy must be based on phylogeny. This struck an immediate chord. Hennig coined such terms as apomorphic, plesiomorphic, and sister groups, and offered a redefinition of monophyly (see monophyletic), which he insisted must be paramount in taxonomy.