Hennig, Emil Hans Willi

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(b. Dürrhennersdorf, near Zittau, Germany, 20 April 1913; d. Ludwigsburg, near Stuttgart, Federal Republic of Germany, 5 November 1976)

entomology, theory of taxonomy.

The eldest of three sons of Emil Hennig. a railway official, and of Emma Gross Hennig, Willi Hennig attended the elementary school of his native village and learned English, French, and Latin from a local doctor. His secondary education was obtained at the Höhere Schule in Dresden. In 1932 he entered the University of Leipzig to study natural history (zoology, botany, geology); in 1936 he submitted a doctoral dissertation devoted to the genitalia of Diptera. After some months of personal research at the Staatliches Museum für Tierkunde in Dresden, Hennig joined the staff of the Deutsches Entomologisches Institut (DEI) in Berlin in January 1937. He married Irma Wehnert in 1939; they had three sons. Except during the war, he worked at the DEI until August 1961 as scholar, assistant director, and vice-director, publishing a great many of his dipterological writings in its periodicals (Arbeiten über morphologische und taxonomische Entomologie aus Berlin-Dahlem, Arbeiten über physiologische und angewandte Entomologie aus Berlin-Dahlem, und Beiträge zur Entomologie).

During the first half of World War II, Hennig was an infantryman in Poland, France, Denmark, and Russia; he was wounded in Russia in 1942. In the following years he served in mosquito control groups in Germany, in Greece, and in Italy, where he was taken prisoner of war. After the war he began the redaction of his Grundziige einer Theorie der phylogenetischen Systematik (published in 1950), the first draft of which was written while he was a prisoner of war.

In August 1961, although working at the DEI in East Berlin, Hennig resided in West Berlin. The erection of the Berlin Wall forced him to resign from the DEI at the very time he was to succeed the retiring director. He remained for two years in West Berlin as a professor at the Technische Universitat. During this difficult period he completed the German manuscript of what became Phylogenetic Systematics (1966).

In spite of employment offers from foreign institutions. Hennig did not wish to leave Germany. In April 1963 he accepted appointment as director of the Abteilung für Phylogenetische Forschung at the Ludwigsburg branch of the Staatliches Museum für Naturkunde in Stuttgart. He spent the rest of his life there, publishing numerous dipterological contributions in Stuttgarter Beiträge Zur Naturkunde. Although he found in West Germany all the opportunities for the continuation of his work and for international research travels to Canada, the United States, and Australia, Hennig never forget Berlin and the Middle European way of science of his youth.

Hennig received an honorary doctorate from the Free University of Berlin. He was honorary professor at the University of Tübingen, member of the Deutsche Akademie Leopoldina der Naturforscher in Halle. foreign member of the Royal Swedish Academy of Sciences, and honorary member of the Society of Systematic Zoology. He received the Fabricius Medal of the Deutsche Entomologische Gesellschaft and the Gold Medal of the American Museum of Natural History (New York) and of the Linnean Society of London.

Although Hennig’s first scientific publication (1932) was devoted to the taxonomy of the snake genus Dendrophis and was followed by other herpetological contributions, he was nevertheless an entomologist: his first publication on insects, which dealt with the copulatory organs of Diptera Tylidae, appeared in 1934. His doctoral dissertation on the copulatory apparatus of the higher Diptera was published in 1936 in Zeitschrift für Morphologie und Ökologie der Tiere. The majority of his 150 later publications concern the genitalia, wings, larvae, taxonomy, biogeography, paleontology, and phylogeny of Diptera. Besides original descriptive papers and revisions published in the periodicals of the DEI and of the Stuttgart Museum, this corpus includes monographs on major topics (Larvenformen der Dipteren), regions (New Zealand), or families (in Lindner’s Die Fliegen… he treated fourteen families, including the difficult and enormous Muscidae and Anthomyiidae). In 1973 he revised the Diptera section in Kükenthal’s Handbuch der Zoologie.

It is impossible to analyze this immense body of achievements here. There are, however, two important points: (1) the profusion of species in a large and homogeneous order of insects with complete metamorphosis, such as the Diptera, was an ideal background for the birth and the testing of an extensional methodology of taxonomy; (2) the discussion among dipterists of Hennig’s first ideas (1936) on the taxonomic congruence gave impetus to his research on larvae and on a consequent methodology of classification.

In spite of the impressive volume of his dipterological works, Hennig deserves more attention than would usually be paid to a classical taxonomist. This attention is required by five major books and some preliminary sketches, all devoted to the theory of method in phylogenetic taxonomy.

It is not strictly correct to say that the Hennigian revolution in taxonomy is equivalent to the Darwinian one in biology. Darwin concentrates on the processes of evolution. Whereas Hennig, discarding the various models of processes grounded on utility, success, and adaptation, focuses on a taxonomy of results, that is, objects and attributes. Considering without any restriction that living taxa are genealogically linked, he restored the taxonomic prevalence of lineages over characters. This constitutes his improvement on Darwin, Indeed. Hennig refuted the false assumption of an equivalence between the relationships of descent and those of similarity, and refused the phenetic compromise that Darwin accepted as inescapable.

Hennig’s requisite for genealogical objectivity of taxa implied an extensional judgement (that is, among numerous taxa) of the phylogenetic recency of the characters; such an appreciation is the inverse of an intensional measure (that is, involving numerous characters) of the phenetic distance between the taxa. This is hardly compatible with the pheneticism of “numerical” taxonomy. However, the conflict is not, as often stated, between qualitative and quantitative appraisals; it is between extensional and intensional ways of thinking.

An extensional appraisal of the relative recency of characters must decide whether they represent apomorphies—that is. evolutive states—proper to some smaller recent taxa or plesiomorphies—that is. evolutive states—shared by many members of large older taxa. This decision makes it possible to construct monophyletic taxa (taxa that contain a given ancestor plus all its codescendants). Taxa that share the same apomorphy are considered Schwestergruppe (sister groups). Starting from the smallest of them, the monophyletic arrangement is constructed by continuous chaining of synapomorphies of rising “rank.” that is, by nesting of sister taxa of growing magnitude. This method breaks with the extensional method of Ernst Haeckel, which, starting from symplesiomorphies, cannot guarantee the completeness of taxa.

The key terms of Hennig’s operational logic number only four: apomorphy, plesiomorphy, sister group, and monophyly. This logic has been called “cladism” by its opponents, a designation rejected by Hennig but easily adopted by his followers.

Thereversals in taxonomy from an intensional logic to an extensional one, and from symplesiomorphic constructs to synapomorphic ones were not immediately perceived as a true revolution. Initially, Hennig’s methodology was almost totally overlooked; from 1966 to 1975 it stirred considerable opposition from both the process taxonomists (G.G. Simpson, Ernst Mayr, A.J. Cain), who claimed they were the “evolutionary” taxonomists par excellence, and the intensional-pattern taxonomists (P. H. A. Sneath, Robert R. Sokal), who called themselves the true “numerical” taxonomists.

Although he received much recognition from his peers, Hennig was disappointed at the slow reception of his Grundzüge of 1950; he regretted the poor English version of his Phylogenetic Systematics of 1966, which was printed without his consent; and he suffered from the attacks of his former compatriot Ernst Mayr, to which he replied in 1974. All these disappointments, controversies, and dissatisfactions have been studied in their historical and epistemological details by Dupuis (1979, 1984).

Since 1975, Hennig’s methodology has received increasing attention in many countries and fields of biology (zoology, paleontology, botany, molecular biology). This is well illustrated by the fact that the on-line citational bank SCISEARCH, although very incomplete, indicates a growing number of citations for Hennig’s major books (1950, 1966): for the years 1974–1976, 79 references; for 1977–1979, 155; for 1980–1982, 158; for 1983–1985, 212. The Willi Hennig Society, established in 1981, publishes the journal Cladistics.

The price of the growing success of Hennig’s ideas is not small. Saether (1986) denounces “postHennigian deviations” that prove to be neither extensional (the various “cladistifications” of intensional procedures) nor even genealogical (the) “transformed cladism,” born in part from the vicariance biogeography). In such conditions, the edition by Wolfgang Hennig of some of his father’s works—particularly the 1961 text of Phylogenetische Systematik (1982)—is a well-timed service for biologists.


1. Original Works. A reasonably complete bibiography of Hennig’s publications is in Beiträge zur Entomologie, 28 (1978), 169–177. His books or monographs include Die Larvenformen der Dipteren, 3 vols. (Berlin, 1948–1952, repr. 1968); Grundzüge einer Theorie der phylogenetischen Systematik (Berlin, 1950; repr. Königstein, 1981); Muscidae, 2 vols. (Stuttgart, 1955–1964), pt, 63b of Erwin Lindner’s Die Fliegen des paläarktischen Region; The Diptera Fauna of New Zealand, Petr Wygodsinsky, trans. (Honolulu, 1966); Phylogenetic Systematics, D. Dwight Davis and Rainer Zangerl, trans. (Urbana, III., 1966; repr. 1979), a revision of Grundzüge … and a rather poor translation of a German manuscript of 1961, also available in an excellent Spanish translation of the manuscript, Elementos de una sistemática filogenética (Buenos Aires, 1968), and in German edited by Hennig’s son Wolfgang, Phylogenetische Systematik (Berlin. 1982); Anthomyiidae (Stuttgart, 1966–1976). pt. 63a of Erwin Lindners’ Die Fliegen der paläarktischen Region; Die Stammesgeschichte der Insekten (Frankfurt. 1969), translated by Adrian C. Pont as Insect Phylogeny (Chichester, England, and New York, 1981);’ Diptera (Zweiflügler),” in Kükenthal’s Handbuch der Zoologie, IV. 2, pt. 2. no. 31 (Lieferung 20) (1973); and Augfaben und Probleme stammesgeschichtlicher Forschung (Berlin and Hamburg, 1984).

Hennig’s papers include “Die Schlangengattung Dendrophis,” in Zoologischer Anzeiger, 99 (1932), 273–297, with W. Meise; “Zur Kenntnis der Kopulationsorgane der Tyliden (Micropeziden, Dipt. Acalypt.),” ibid., 107 (1934), 67–76; “Beiträge zur Kenntnis der Kopulationsapparates der cyclorrhaphen Dipteren.” in Zeitschrift für Morphologie und Oekologie der Tiere, 31 (1936), 328– 370; “Beziehungen zwischen geographischer Verbreitung and systematischer Gliederung bei einiger Dipterenfamilien …” in Zoologischer Anzeiger, 116 (1936), 161–175; “Ein Beitrag zum Problem der ‘Beziehungen zwischen Larvenund Imaginalsystematik, ’” in Arbeiten über morphologische und taxonomische Entomologie aus Berlin-Dahlem, 10 (1943), 138–144: “Probleme der biologischen Systematik,” in Forschung and Fortschritte, 21– 23 (1947), 276–279; “Zur Klärung einiger Begriffe der phylogenetischen Systematik,” ibid., 25 (1949), 136–138; “Kritische Bemerkungen zum phylogenetischen System der Insekten,” in Beiträge zur Entomologie, 3 (spec, iss., Festschrift Sachtleben) (1953), 1–85; “Phylogenetic Systematics,” in Annual Review of Entomology, 10 (1965), 97–116; “Kritische Bemerkungen zur Frage ‘Cladistic Analysis or Cladistic Classification, ’” in Zeitschrift für zoologische Systematik und Evolutionsforschung, 12 (1974), 279–294, translated by C. D. Griffiths and edited by G. Nelson as’ Cladistic Analysis or Cladistic Classification? A Reply to Ernst Mayr, ’ in Systematic Zoology, 24 (1975). 244–256—Mayr’s article is “Cladistic Analysis or Cladistic Classification?” in Zeitschrift für zoologische Systematik und Evolutionsforschung, 12 (1974), 94–128.

II. Secondary Literature. Peter Ax, “Willi Hennig, 20.4.1913 bis 5.11.1976,” in Verhandlungen der Deutschen zoologischen Gesellschaft, 70 (1977), 346–347, and Das phylogenetische System (Berlin, 1941), translated by R.P.S. Jefferies as The Phylogenetic System (Chichester, England, and New York, 1987); George Byers, “In Memoriam. Willi Hennig (1913–1976),” in Journal of the Kansas Entomological Society, 50 (1977), 272–274; Claude Dupuis, “The Hennigo-Cladism: A Taxonomic Method Born of Entomology,” in Abstracts of the Sixteenth International Congress of Entomology (Kyoto, 1980), 15, “Permanence et actualité de la systématique: La systématique…de…Hennig,” in Cahiers des naturalistes, 34 (1979), 1–69 (about 400 references), “La volonté dêetre entomologiste…” in Bulletin de la Société entomologique de France, 88 (1983), 18–38, “Haeckel or Hennig? The Gordian Knot of Characters, Development. and Procedures in Phylogeny,” in Human Development, 27 (1984). 262–267, “Willi Hennig’s Impact on Taxonomic Thought,” in Annual Review of Ecology and Systematics, 15 (1984). 1–24, and’ Darwin et les taxinomies d’aujourd’hui, ’ in L’ordre et la diversité du vivant (Paris, 1986): S. Kiriakoff. “Nécrologie: Willi Hennig (1913–1976),” in Bulletin et annales de la Société royale belge d’entomologie, 113 (1977), 240–243; Ole Saether, ’ The Myth of Objectivity— Post-Hennigian Deviations, ’ in Cladistics, 2 (1986), 1– 13; D. Schlee, “In Memoriam. Willi Hennig 1903–1976.” in Entomologica germanica, 4 (1978), 377–391; R. T. Schuh and P. Wygodzinsky, ’ Willi Hennig, ’ in Systematic Zoology, 26 (1977), 104–104; and E.O. Wiley, Phylogenetics (New York, 1981).

Claude Dupuis

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