Emil Hans Willi Hennig (20 April 1913 – 5 November 1976) was a German biologist and zoologist who is considered the founder of phylogenetic systematics, otherwise known as cladistics. In 1945 as a prisoner of war, Hennig began work on his theory of cladistics, which he published in German in 1950, with a substantially revised English translation published in 1966. With his works on evolution and systematics he revolutionised the view of the natural order of beings. As a taxonomist, he specialised in dipterans (true flies). Hennig coined the key terms synapomorphy, symplesiomorphy, and paraphyly. He also asserted, in his "auxiliary principle", that "the presence of apomorphous (apomorphy) characters in different species 'is always reason for suspecting kinship [i.e., that species belong to a monophyletic group], and that their origin by convergence should not be presumed a priori' (Hennig, 1953). This was based on the conviction that 'phylogenetic systematics would lose all ground on which it stands' if the presence of apomorphous characters in different species were considered first of all as convergences (or parallelisms), with proof to the contrary required in each case." This has been viewed as an application of the parsimony principle to the interpretation of characters, an important component of phylogenetic inference. He is also remembered for Hennig's progression rule in cladistics, which argues controversially that the most primitive species are found in the earliest, central part of a group's area.
Biography
Early years and studies Hennig was born in Dürrhennersdorf, Upper Lusatia. His mother Marie Emma, née Groß, worked as a maid and, later, factory worker. His father Karl Ernst Emil Hennig was a rail worker. Willi had two brothers, Fritz Rudolf Hennig, who became a minister, and Karl Herbert, who went missing at the Battle of Stalingrad in 1943. In the spring of 1919, Willi Hennig started school in Dürrhennersdorf, and subsequently was at school in Taubenheim an der Spree and Oppach. Rudolf Hennig described the family as calm; his father possessed an even temperament. As of 1927, Willi Hennig continued his education at the Realgymnasium and boarding school in Klotzsche near Dresden. Here he met his first mentor M. Rost, a science teacher, whom he lived with in a house known as the "Abteilung". Rost had an interest in insects and introduced Hennig to Wilhelm Meise, who worked as a scientist at the Dresdener Museum für Tierkunde (State Museum of Zoology, Dresden). In 1930, Hennig skipped a year, and graduated on 26 February 1932. As early as 1931, Willi Hennig composed an essay entitled Die Stellung der Systematik in der Zoologie ("The state of systematics in zoology") as part of his school work, published posthumously in 1978. It showed his interest as well as his deliberate treatment of systematic problems. Besides school, Hennig worked as a volunteer at the museum and, in collaboration with Meise, saw to the systematic and biogeographical investigation of the "flying" snakes of the genus Dendrophis that became his first published work. From the summer semester of 1932 onwards, Hennig read zoology, botany and geology at the University of Leipzig. He would continue to visit the Museum in Dresden. There, he met the curator of the entomological collection, the Dipteran expert Fritz Isidor van Emden. Hennig saw him regularly until van Emden was expelled from National Socialist Germany for having a Jewish mother and wife. Hennig developed a deep friendship with Emden's successor, Klaus Günther. Hennig concluded his studies with a dissertation entitled, Beiträge zur Kenntnis des Kopulationsapparates der cyclorrhaphen Dipteren. By this time, Hennig had published eight scientific papers. Besides his 300-page revision of the Tylidae (now classed as Micropezidae), there were further papers on Diptera and the agamid genus Draco of gliding lizards. After his studies, Hennig was Volontär at the State Museum for Zoology in Dresden. On 1 January 1937, he obtained a scholarship from the Deutsche Forschungsgemeinschaft (DFG) to work at the German Entomological Institute of the Kaiser-Wilhelm-Gesellschaft in Berlin-Dahlem. On 13 May 1939, Hennig married his former fellow student Irma Wehnert. By 1945, they had three sons, Wolfgang (born 1941), Bernd (born 1943) and Gerd (born 1945).
As a military entomologist Willi Hennig was drafted in 1938 to train for the infantry and concluded this course in 1939. As of the start of World War II, he was deployed in the infantry in Poland, France, Denmark and Russia. He was injured by grenade shrapnel in 1942 and was subsequently used as entomologist at the Institute for Tropical Medicine and Hygiene in Berlin, carrying the rank of a Sonderführer (Z). Just before the war ended, he was sent to Italy to the 10th Army, Heeresgruppe C, to fight malaria and other epidemic diseases. At the end of the war in May 1945, he was captured by the British while he was with the Malaria training corps at the Gulf of Trieste, and was only released in the autumn. Through his active participation in war as soldier and scientist Hennig was later subjected to accusations that he had been a member of the National Socialist party, especially by the Italian biologist and founder of panbiogeography, Leon Croizat. No evidence has been officially presented to support the claim. There is no report of Hennig supporting the National Socialist party views publicly on any occasion. Hennig did believe that Nazi Germany would win World War II. During his time as prisoner of war, Hennig began to draft his most important contribution to systematics, not published until 1950. The rough draft was composed with pencil and ballpoint pen into an A4 exercise book, spanning 170 pages. During the war, he also published a further 25 scientific papers. Most of the correspondence and literature research was conducted by his wife, Irma.
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