Nørregade 10, 1165 København, Denmark
Fabricius studied at the University of Copenhagen in 1762.
Fabricius studied at the gymnasium at Altona and entered the University of Copenhagen in 1762. Later the same year he traveled together with his friend and relative Johan Zoëga to Uppsala, where he studied under Carl Linnaeus for two years.
Fabricius was appointed a professor in Copenhagen in 1770, and in 1775 or 1776, the University of Kiel appointed Fabricius professor of natural history and economics, promising that they would build a natural history museum and a botanical garden. Although he tried to resign three times, on one occasion only being prevented by an appeal from his students to the Danish King and Duke of Schleswig, Christian VII, Fabricius held the position at Kiel for the rest of his life.
During his time in Kiel, Fabricius repeatedly traveled to London in the summer to study the collections of British collectors, such as Joseph Banks and Dru Drury. Towards the end of his career, Fabricius spent much of his time living in Paris, where he frequently met with naturalists such as Georges Cuvier and Pierre André Latreille; he was also interested into the events of the French Revolution. On hearing of the British attack on Copenhagen in 1807, Fabricius returned to Kiel, damaging his already fragile health. He died on March 3, 1808, at the age of 63.
Two basic principles guided Fabricius' approach to entomological systematics; he distinguished, on the one hand, between the artificial and the natural characters; and, on the other hand, he stressed the importance of the various structures of the mouth. The terminology he applied to categories of higher systems differed somewhat from modern terminology: he used the words “classis” for “order” and “ordo” for what is called “family”; furthermore, he founded his system on the genus and the species, which in his opinion constituted the main bases. It seemed especially important to Fabricius that genera were the natural combinations of related species.
He believed that “classes” and “ordines” were artificial concepts. He seems to have understood that even genera can be classified into the natural system - the nearest equivalent to our present “families” - but he probably understood that the time was not yet ripe, that scientific knowledge and general outlook were too narrow for such classification. He thought (not without hesitation) of one large system based on the structure of the mouth organs as being the natural system.
It was Fabricius’ greatest ambition to build a system based on the naturally defined genera, without doubt a definite and new contribution to insect systematics. He considered this more important than a dry description of the various species.
Less known than Fabricius' contributions in the field of insect systematics are his evolutionistic ideas and speculations. He considered systematics to be a means to understanding important scientific functions and phenomena in general. Many of his ideas concerning evolution sound amazingly modern. For instance, he considered it possible that a species could be formed through mixing existing species (i.e., some form of hybridization) and through morphological adaptation and modification. In his opinion, such phenomena caused an unbelievable wealth of forms and species of living organisms. Fabricius could not believe in haphazard creation and definitely thought that man originated from the great apes. He also discussed the influence of environment on the development of the species, as well as some selective phenomena (females prefer the strongest males, etc.).
Henriksen called him the "Father of Lamarckism."
Fabricius was a member of the German Academy of Sciences Leopoldina.
Fabricius did not lead the life of a sedentary scientist. He did much traveling, both on the Continent and in Great Britain. He also went to Norway, Austria, Switzerland, and Russia. On these trips, he came in close contact with the best-known scientists of his time and visited the greatest museums.
Fabricius was an extrovert who was liked and appreciated everywhere, and his personality helped to create a fruitful mutual exchange of information and ideas.
Fabricius was married and had three children. His daughter died in an accident in Paris, but he was survived by two sons, who both studied medicine.