Willi Hennig

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Emil Hans Willi Hennig (born April 20, 1913 in Dürrhennersdorf , † November 5, 1976 in Ludwigsburg ) was a German biologist . He is considered to be the founder of the phylogenetic system, which is now also known under the name of cladistics . With his work on evolution and systematics, he revolutionized the view of the natural order of living beings. In addition, he was primarily a specialist in two-winged aircraft .

Willi Hennig (1972)


Early years and studies

His mother Marie Emma b. Groß (born June 12, 1885 - † August 3, 1965) worked as a maid and later as a factory worker. His father, Karl Ernst Emil Hennig (* August 28, 1873, † December 28, 1947) was a worker and later a squad leader on the railroad. Willi Hennig had two brothers, Fritz Rudolf Hennig (* March 5, 1915; † November 24, 1990), who later became a pastor , and Karl Herbert (* April 24, 1917, † missing from Stalingrad since January 1943 ).

Dendrophis caudolineolata and Dipsas barnesii

In the spring of 1919 Willi Hennig started school in Dürrhennersdorf, attended elementary school in Taubenheim an der Spree and later in Oppach . According to Rudolf Hennig, the family atmosphere was calm. The father was a balanced person.

In 1927 Willi Hennig moved to the secondary school and boarding school in Klotzsche near Dresden . There it was handed over to the teacher M. Rost, with whom he also lived. Rust was insects friend and made Hennig with the then scientific staff of the Dresden Museum of Zoology , Wilhelm Meise , known. In 1930 Hennig skipped a school year and received his school-leaving certificate on February 26, 1932. As early as 1931, Willi Hennig wrote his homework essay The Position of Systematics in Zoology , which was published posthumously in 1978 and in which he already proved both his interest and his deliberate handling of systematic questions. In addition to school, Hennig volunteered at the museum, where he and Meise carried out a systematic and biogeographical study of the flying snakes of the genus Dendrophis . The result of this collaboration was Willi Hennig's first publication in 1932, which was written together with Meise and was published under the title The snake genus Dendrophis .

Starting with the summer semester of 1932, Willi Hennig studied zoology , botany and geology at the University of Leipzig . During his studies he was also frequently in the Dresden Museum. There he met the curator of the entomological department and researcher on beetles (Coleoptera) Fritz Isidor van Emden (1898-1958). Hennig visited him regularly until Van Emden was expelled by the National Socialists in 1933 because of his Jewish mother. Willi Hennig built a deep friendship with his successor Klaus Günther (1907–1975). On April 15, 1936, Willi Hennig, supervised by his professor Paul Buchner , was able to complete his studies with the dissertation Contribution to the knowledge of the copulatory apparatus of the cyclorrhaphic dipteras . By this time Hennig had already written eight scientific publications. Of these, the revision of the Tyliden (Dipt., Acalypt.) Was the most extensive with 300 pages. In addition, there was further work on two-winged birds and the agamen genus of the kite ( Draco ).

After completing his studies, Hennig got a job as a volunteer at the Museum für Tierkunde Dresden. On January 1, 1937, he received a grant from the German Research Foundation (DFG) and a permanent position at the German Entomological Institute of the Kaiser Wilhelm Society in Berlin-Dahlem . On May 13, 1939, Willi Hennig married his former fellow student Irma Wehnert. By 1945 they had three sons: Wolfgang (* 1941), Bernd (* 1943) and Gerd (* 1945).

Work as a military entomologist

Malaria mosquito

Willi Hennig was called up to the infantry in the winter of 1938 and completed a short training course by the spring of 1939. Since the beginning of World War II , he has been used as an infantryman in Poland , France , Denmark and Russia . In 1942 he was injured by a shrapnel and was subsequently employed as an entomologist ( entomologist ) with the designation of a special leader Z at the Berlin Institute for Tropical Medicine and Hygiene of the Military Medical Academy. Shortly before the end of the war he went to Italy to join the 10th Army, Army Group C, to fight disease and malaria . At the end of the war in May 1945, he was taken prisoner of war as a member of a malaria training team on the Gulf of Trieste in northern Italy and was only released in the autumn. Due to his active participation in the Second World War as a soldier and scientist, Hennig later came under suspicion of being a National Socialist, especially through the Italian biologist and founder of Pan biogeography Leon Croizat . He vehemently rejected these allegations after the war, and there is no evidence that could support this claim. Hennig was not a member of the NSDAP and had not publicly supported or represented the ideologies of National Socialism.

The draft for Hennig's most important work on biological systematics was created during his military service and as a prisoner of war, which he did not publish until 1950. He wrote the rough version in an A4 book with pencil and ballpoint pen; it comprised 170 pages. 25 scientific publications were also produced during the war. Most of the correspondence and literature research was done by his wife.

1950s: Basics of a theory of phylogenetic systematics

Terrestrial vertebrate cladogram

From December 1, 1945 to March 31, 1947, Willi Hennig took over as senior assistant to Friedrich Hempelmann (1878–1954) at the University of Leipzig, substituting for his doctoral supervisor Paul Buchner and giving lectures in general biology, zoology and special insect zoology . On April 1, 1947, he was again employed at the German Entomological Institute in Berlin and gave up his position in Leipzig. From November 1, 1949 he was head of the department for systematic entomology and deputy director of the institute. On August 1, 1950 , he completed his habilitation in zoology at the Brandenburg State University in Potsdam . On 10 October the same year he was appointed professor with teaching, he with lectures on special zoology of invertebrates, systematic zoology and identification exercises fulfilled. In the same year he published the main features of a theory of phylogenetic systematics ; further work on the method of phylogenetic systematics followed in the following years, along with numerous taxonomic work on two-winged birds. His two-volume pocket book on zoology , in which he first used the phylogenetic system in invertebrates, was particularly successful .

He continued to work at the German Entomological Institute in Berlin-Friedrichshagen in the Soviet sector of Berlin. He lived with his family in Berlin-Steglitz in the American sector of West Berlin . On a trip with his son in France on August 13, 1961, he learned of the construction of the Berlin Wall and returned to Berlin to quit his job. A move to East Berlin was out of the question for him, as he himself was anti- communist and had massive problems with the Socialist Unity Party of Germany (SED) of the German Democratic Republic . He had repeatedly given employees of the institute a career start in the Federal Republic. In 1959 he was elected a member of the Leopoldina .

1961 to 1976

Willi Hennig (around 1970)

In West Berlin, Hennig received a provisional position at the Technical University of Berlin as an adjunct professor. He turned down an offer from the US Department of Agriculture to work in the Entomology Research Division in Washington DC , as did the offer from his friend Dilbert Elmo Hardy to come to Honolulu as a Research Fellow at the University of Hawaii . He justified his decision with the education of his sons and the need to have "the cultural witnesses of ancient Greco-Roman Europe within reach". Instead, he took a position at the State Museum for Natural History in Stuttgart , where he became head of the department for genealogical research. In April 1963 he moved to Ludwigsburg - Pflugfelden . The museum's scientific collections had been temporarily stored in Ludwigsburg since the war and remained there until they were housed in the new building of the museum at Löwentor in 1985 .

In Stuttgart he dealt almost exclusively with research on two-winged animals, which he worked on taxonomically. For the Stuttgart contributions to natural history , in which he published a large part of his work, he wrote a total of 29 booklets until his death. His review articles, which he published in the books Flying the Palearctic Region by Erwin Lindner and in the Handbuch der Zoologie , are particularly significant . He also wrote several papers on the cladistic method, above all the article Cladistic analysis or cladistic classification? A reply to Ernst Mayr 1975 as an international response to the criticism of the influential evolutionary biologist Ernst Mayr of his phylogenetic system.

Willi Hennig only visited international institutions abroad twice, although he received numerous invitations to guest lectures. From September 1 to November 30, 1967 he worked at the Entomology Research Institute of the Canada Department of Agriculture in Ottawa, and from August 22 to 30, 1972, he participated in the International Congress of Entomologists in Canberra . On this trip, he and his wife also visited Bangkok , New Guinea and Singapore . He also used his stay in Canada to visit various entomological museum collections in the USA, for example in Cambridge , Chicago , Washington, DC and New York in search of amber inclusions from two-winged birds, which made up a large part of his research work in the late 1960s and early 1970s . At the suggestion of Klaus Günther, who meanwhile held a chair at the Free University of Berlin , Hennig was awarded an honorary doctorate from the university on December 4, 1968 ; for health reasons, however, he was unable to accept the certificate, so it was given to him by Klaus Günther on March 21, 1969 in Stuttgart. On February 27, 1970, at the endeavor of the students, Hennig was appointed honorary professor at the Eberhard Karls University in Tübingen , where he conducted several seminars on individual animal groups.

Willi Hennig died of a heart attack on the night of November 5, 1976 . He had repeatedly canceled lectures in advance with reference to his poor health and suffered a heart attack during the trip to Ottawa. On November 10th he was buried in the Bergfriedhof in Tübingen .

Significance of the work of Willi Hennig

At the center of Willi Hennig's work are his work on phylogenetics, which has made him internationally known. In addition to this basic work, Hennig was also extremely productive as an entomologist in the field of dipterology and other taxonomic research areas.

Taxonomic works

Schnaken (Tipulidae)

The main focus of Willi Hennig's taxonomic research was on insects, in particular the Diptera. Willi Hennig worked on this group of animals meticulously and became the first to describe a large number of new species. Unlike in classical entomology, he did not limit himself to the morphological description of the animals, but basically put his results in a phylogenetic and biogeographical context. As a very good draftsman and observer, he provided all descriptions with detailed illustrations. Until 1945, Hennig described 13 classic two-winged families in twelve parts and a total of 431 pages, illustrated with 26 plates, for Erwin Lindner 's collection of flies in the Palearctic region .

Building on his treatment of the two-winged species and various other animal groups such as reptiles , Hennig developed a number of important fundamental questions that would later lead to the development of the phylogenetic system. He devoted himself to the question of why the independent consideration of characteristics in larvae and adults (adult animals) of different insect groups often led to different classification in the system. As a solution, he developed the concept, especially in his work Die Larvaformen der Dipteren , according to which only those characteristics may be taxonomically used that have emerged in evolution ( apomorphies ), while unchanged characteristics ( plesiomorphies ) are not used. In doing so, he showed that morphologically similar organisms are not necessarily more closely related than morphologically different organisms.

Amber research

Amber with inclusion

Willi Hennig saw the study of amber fossils as a way of checking his ideas and concepts . Hennig examined the characteristics of two-winged birds preserved in amber and published the results in his first paper on the subject in 1938. In 1964 he received access to the amber collection of the Georg-August University in Göttingen . In the following years Hennig wrote 17 papers on two-winged birds in Baltic amber and three papers on inclusions in amber from Lebanon . In his work Tribal History of Insects , Hennig tried to chronologically classify the development of characteristics and species splitting processes on the basis of amber inclusions.

Hennig always emphasized, however, that no fossils are required for the development of hypotheses about kinship and evolution, since these should be based solely on the presence of characteristics of recently living organisms. According to Schmitt (2002), a dialogue between Hennig and the Berlin paleontology professor Walter Gross at the Museum für Naturkunde in Berlin has come down to us. After Gross had repeatedly asserted that fossils were essential for phylogenetic evidence, Hennig said: "I am not interested in your fossils."

Phylogenetic systematics

As already shown in his biography, Willi Hennig's main work is the development of a strictly phylogenetic system and the methodology applicable to it. He replaced a taxonomy, which was largely based on similarities and related forms, with a system based on genealogical, i.e. evolutionary, relatedness. Hennig built on earlier work, for example by Walter Zimmermann , which already required a system based on the evolutionary relationship. Hennig's main contribution here was, above all, the development of the methodology and the theoretical background with which this requirement could be realized.

In his early works, Hennig called for the phylogenetic relationships of the organisms to be adhered to in the systematics, but he himself did not yet provide any means of defining them. In 1936 he found that the relationship cannot be determined solely through homologies and convergences . In 1943 he demanded an assessment of morphological similarities to determine the relationship. What this evaluation should look like, however, was formulated by Hennig in his 1950 work, Basic Principles of a Theory of Phylogenetic Systematics . Here he differentiated for the first time between independently preserved heritage ( plesiomorphies ) and progressive features ( apomorphies ). While the plesiomorphies are already present in the ancestral forms of the organisms to be considered, the latter are only formed as evolutionary new features and represent the sole basis of the system

“The species that can be distinguished in today's world of organisms are summarized according to their origin through the decay of older parent species in such a way that the higher categories include several lower species groups, which are assumed to have arisen through the disintegration of one parent species, apart from them no other living species can be derived. "

- from problems of biological systematics , 1947

With this requirement, Willi Hennig formulates the monophyletic group as a summary of all organisms derived from a common parent species, which Ernst Haeckel already implicitly described in his work General Morphology of Organisms .

Hennig dealt with the term homology, originally introduced by Richard Owen as a morphological similarity and coined by Adolf Remane as a kinship feature with specific characteristics (homology criteria), and criticized above all the lack of a concrete definition of the term. For a better understanding he introduces the terms “synapomorphy” for a common apomorphic characteristic of two sister groups and “autapomorphic” as a newly acquired characteristic of a monophyletic group. Only synapomorphism can be used as an argument for a relationship. In comparison to convergence, i.e. the similar characteristics of two organisms acquired independently of one another, Hennig also wrote:

"A little consideration, however, easily shows that the phylogenetic system would lose all ground if it initially understood all synapomorphies as convergences and wanted to demand proof of the opposite in any case."

- from Critical Comments on the Phylogenetic System of Insects , 1953

Until the 1960s, Willi Hennig's theories were almost exclusively noticed in German-speaking countries and almost only by entomologists, although the botanist Warren Herbert Wagner (1920–2000) based an investigation into the Diellia fern genus for the first time in 1952 - later after named him - introduced Wagner parsimony . It was mainly through the Swedish dipterologist Lars Zakarias Brundin (1907–1993) that Hennig's point of view was able to spread among entomologists in English-speaking countries. It was not until around 1960 that Hennig was asked by Dwight Davis (1908–1965) to publish his theories in English; he himself offered to translate it. This was done in cooperation with Rainer Zangerl, who continued this alone after Davis' death. The result was Phylogenetic Systematics in 1966 (published as the German version Phylogenetic Systematics posthumously in 1982 by Wolfgang Hennig ). Together with the summary published under the same title in the Annual Review of Entomology in 1965 , this work ensured the international breakthrough of the phylogenetic method according to Willi Hennig. Terms such as apomorphic and plesiomorphic have become part of the standard terminology of modern evolutionary theory. Hennig's terminology is used consistently by many authors, including the well-known biologist Stephen Jay Gould , without explicitly mentioning the originator.

Criticism and Effect

Like many other innovations in science, Hennig's theories were not accepted uncritically in the scientific world. It is less the statement that the taxonomy and the evaluation of the relationships always have to follow the evolution that led to the criticism. This was generally accepted in research circles and only met with rejection from traditional biologists due to the very difficult recognition of homologies and the reading direction.

Above all, the abandonment of classical taxonomic units, which definitely cannot be shown to be monophyletic, has not been and is not generally recognized to this day, but critically questioned. One of the main opponents of this practice was the evolutionary biologist Ernst Mayr . Mayr explicitly emphasized that he found the determination of the phylogenetic relationship with Hennig's method of phylogenetic systematics (which he called "cladistics") to be correct and extremely important and supported the reconstruction of cladogenesis with the underlying species divisions.

However, in addition to the pure sequence of species splitting events, other important aspects must also be taken into account, above all the question of the "ecological role" and the "evolutionary success" of a taxon. The resulting classification of organisms should continue to take place in the form of categorical ranks and should be separated from the phylogenetic analysis. Mayr advocated a separation of phylogenetic analysis and the creation of a system. The result of the phylogenetic analysis can be displayed in the form of a graphical branching scheme (cladogram), but it is redundant to transfer the determined phylogenetic relationships one-to-one into a system. He advocated the retention of paraphyletic taxa (which only contain descendants of one parent species, but not all) in certain cases.

Mayr cited the reptiles as an example . Although the last ancestral species of all reptiles is also ancestral species of birds and mammals , the latter taxa are not regarded as subgroups of the traditional group of reptiles. According to Mayr, reptiles should be preserved as a unit and should continue to be differentiated from birds, as the latter represented something evolutionarily new and successful.

Hennig protested against this singling out of individual taxa from larger groups because no objective criteria can be given for it. Hennig did not consider it feasible to implement two different classification principles in one system. The degree of phylogenetic (i.e. genealogical) kinship, on the other hand, can be measured unambiguously and objectively, namely with the number of exclusively common ancestors: two taxa in question are more closely related than one of them with a third if they have at least one ancestor in common which they do not share with the third taxon.

The implementation of the phylogenetic system according to Hennig dragged on in the scientific community for several decades: even today, the method has not yet been able to fully establish itself due to the above-mentioned points of criticism and because of the adherence to the well-known classical system. In addition, the discussion and the application of cladistics have so far taken place almost exclusively in research and hardly penetrated outside. This is the reason for the lack of cladistic systematics in current textbooks and general descriptions in lexicons and other reference works.

In the scientific system, however, there is no serious alternative to Hennig's methods today. It is assumed that these will become generally accepted in a further developed form in the future. Above all, the international continuation of Hennig's approaches, for example by Wiley (1981), Watrous & Wheeler (1981) and a number of other authors, lead to an ever increasing acceptance of cladistics. In addition, there are investigations in molecular biology and other data-intensive research, the analysis of which is based on evaluation software. These computer programs apply modified methods formulated by Hennig and evaluate the result on the basis of the principle of economy based on the slightest change in characteristics that can be assumed. One of the first of these cladist programs was developed in 1986 and named " Hennig86 " after Willi Hennig .


  • with W. Meise: The snake genus Dendrophis. In: Zoologischer Anzeiger. 99.1932, pp. 273-297.
  • Revision of the genus "Draco" (Agamidae). In: Temminckia. 1.1936, pp. 153-220.
  • Relationships between geographical distribution and systematic classification in some Dipteran families: a contribution to the problem of the classification of higher-order systematic categories. In: Zoologischer Anzeiger. 116.1936, pp. 161-175.
  • Problems of biological systematics. In: Researches and Advances. 21 / 23.1947, pp. 276-279.
  • The larval forms of the Diptera. 3 volumes. Akademie-Verlag, Berlin 1948–1952.
  • Basics of a theory of phylogenetic systematics. German Central Publishing House, Berlin 1950.
  • Critical remarks on the phylogenetic system of insects. Contributions to entomology. Volume 3 (special issue). 1953, pp. 1-85.
  • Phylogenetic Systematics. Univ. Illinois Press, Urbana 1966.
  • The tribal history of the insects. Waldemar Kramer, Frankfurt am Main 1969.
  • "Cladistic analysis or cladistic classification?" A reply to Ernst Mayr. In: Systematic Zoology 24.1975, pp. 244-256.
  • Tribal history of the chord dates. Parey, Berlin 1983.
  • Tasks and problems of genealogical research. Parey, Berlin 1984.
  • Paperback of Special Zoology. Part 1 and 2: Invertebrates I and II. Part 3: Vertebrates I. Part 4: Vertebrates II. Fischer, Jena; German, Frankfurt, Thun, Zurich. Newer editions edited or edited by Wolfgang Hennig (son) and Gerhard Mickoleit.


  • Günther Peters: About Willi Hennig as a researcher personality . In: Meeting reports of the Society of Friends of Natural Science in Berlin. Berlin 34.1995, pp. 3-10.
  • Wolf-Ernst Reif Problematic issues of cladistics 2: Hennigian species concept Neues Jahrbuch Geol. Paläont., Abh., Volume 231, 2004, pp. 37-65, from the same series Part 9: Hennig's phylogenetic systematics , Volume 235, 2005 , Pp. 289-342, part 22: Hennig's understanding of phylogenetic trees , Volume 242, 2006, pp. 371-383
  • Dieter Schlee: In Memoriam Willi Hennig 1913–1976. A biographical sketch. In: Entomologica Germanica. Fischer, Stuttgart 4.1978, ISSN  0340-2266 , pp. 377-391.
  • Michael Schmitt : Willi Hennig. in: Ilse Jahn , Michael Schmitt (Ed.): Darwin & Co. II - The history of biology in portraits. Beck, Munich 2001. ISBN 3-406-44642-6 , pp. 316–343, 541–546.
  • Michael Schmitt: Willi Hennig as an academic teacher. in: J. Schulz (Ed.): Focus on the history of biology. For the 80th birthday of the biology historian Ilse Jahn. Akadras, Berlin 2002, ISBN 3-00-009209-9 , pp. 53-64.
  • Michael Schmitt: Willi Hennig and the Rise of Cladistics. In: A. Legakis, S. Sfenthourakis, R. Polymeni, M. Thessalou-Legaki (eds.): The New Panorama of Animal Evolution. Proceedings of the 18th International Congress of Zoology. Pensoft Publ., Sofia, Moscow 2003, ISBN 954-642-164-2 , pp. 369-379.
  • Michael Schmitt: From Taxonomy to Phylogenetics - Life and Work of Willi Hennig , XVI + 208 S., Brill, Leiden - Boston, 2013, ISBN 978-90-04-21928-1 .
  • Jürgen Vogel, Willi R. Xylander: Willi Hennig - A natural scientist from Upper Lusatia with world renown. Research into his family history as well as childhood and youth. Reports of the natural research society Oberlausitz. 7 / 8.1999, ISSN  0941-0627 , pp. 131-141.
  • Quentin Wheeler et al .: Heed the father of cladistics. In: Nature . Volume 496, No. 7445, 2013, pp. 295-296, doi: 10.1038 / 496295a

Web links


  1. a b [Schmitt 2013, p. 24]
  2. Ernst Mayr: Cladistic analysis or cladistic classification? . In: Journal of Zoological Systematics and Evolutionary Research . 12, No. 1, pp. 94-128. doi : 10.1111 / j.1439-0469.1974.tb00160.x .
  3. ^ Willi Hennig: Cladistic Analysis or Cladistic Classification ?: A Reply to Ernst Mayr . In: Systematic Zoology . 24, No. 2, 1975, pp. 244-256. doi : 10.2307 / 2412765 .
This version was added to the list of excellent articles on February 19, 2005 .