Introduction

Ernst Haeckel (1834–1919) was the first zoology professor at Jena University and one of the most influential biologists of his time. His ideas were widely received throughout Europe and North America and beyond. His influence transcended the natural sciences, and his monist philosophy had far-reaching political consequences. One way of investigating the actual influence of a scientist on both science and society is to investigate the correspondence between the scientist and his or her peers. At a time when communication was based on letters and other written material, such as the Haeckel era, surveys of a scientist’s correspondence are valuable tools for evaluating her network activity and standing in the scientific community. While the Haeckel reception has been documented to a certain extent in several countries in continental Europe, the Haeckel reception in Scandinavia has received little attention, although Haeckel is known to have corresponded with Swedish scientists and cultural figures. Haeckel also visited Sweden twice, in 1897 and again in 1907. Some of his books were also translated into Swedish. In 1907, Haeckel, at the bicentennial of the birth of Carolus Linnaeus, received the Linnaeus medal and became a doctor honoris causa at Uppsala University.

We have investigated Haeckel’s correspondence with Swedes, using the archives in the Ernst Haeckel House in Jena, and at the Center for History of Science at the Royal Swedish Academy of Sciences (RSAS) in Stockholm. Ninety-six letters from Swedish-speaking correspondents (all written in German) to Haeckel were found in Jena, most of them from scientists (Hossfeld and Breidbach 2005). Often, the letters from Haeckel to members of the RSAS could be found in the archives of the Center for History of Science. We have earlier presented a first report in Swedish and German (Olsson and Hossfeld 2005, 2006), focused on the correspondence between Haeckel and fellow scientists, and this is an extended English version. It gives an indication of the breadth of topics that were covered. It also highlights the relationships between the Swedish scientists, including their conflicting political views.

The international Haeckel reception

The ideas presented by Charles Darwin in his 1859 book “On the Origin of Species…” were received with great enthusiasm in Germany by researchers like Ernst Haeckel, August Weismann, and Oscar Hertwig. Haeckel published his main scientific contribution already in 1866, the two-volume Generelle Morphologie der Organismen (Haeckel 1866a, b). The ideas presented therein were popularised by Haeckel in 1868, when Natürliche Schöpfungsgeschichte (Natural History of Creation) was published and (unlike Generelle Morphologie) translated into several languages. In Haeckel’s work, his science is inseparable from his world view, and in particular, his materialist, Lamarckian, eugenic, and monist views had influence on not only scientists but also on politicians scattered widely along the political spectrum. Despite Haeckel’s important role, no “Haeckel Industry” comparable to the “Darwin Industry” has developed. In the Ernst Haeckel House in Jena—Haeckel’s villa which houses the Haeckel Archive and the history of science department—around 46,000 letters, postcards, etc., have now been catalogued in a new project and provides in future easy access for researchers interested in Haeckel’s correspondence.Footnote 1

If we summarise briefly the international Haeckel reception, a few main topics can be discerned, such as:

  1. 1.

    Philosophical questions (such as Haeckel’s monism) and their relation to research in morphology in Haeckel’s time. Two exhibits exemplify this; one in 1999 in Linz, Austria “Lebenswunder. Vom Ursprung des Lebens zur Gentechnik” (Aescht et al. 1998), and one “Monismus um 1900. Wissenschaftskultur und Weltanschauung” in the Ernst Haeckel House in Jena (Ziche 2000; Weber 2000; Nöthlich et al. 2006; Weber et al. 2008).

  2. 2.

    The artistic and aesthetic side of Haeckel’s work. Kunstformen der Natur (1899) was reissued in 1998 in German and in English, a catalogue from an exhibit on Haeckel and Italy (HAECKEL E L`ITALIA. La vita come scienza e come storia) was mainly devoted to this topic, and Breidbach (1998, 2001, 2006, 2012), Kockerbeck (1997) and others have written on it.

  3. 3.

    The relationship between Haeckel’s work and National Socialism has been treated by several authors (e.g. Deichmann 1996; Richards 2007, 2013; Hossfeld 2016).

  4. 4.

    Haeckel’s influence on Social Darwinism has also provoked a certain interest (e.g. Becker 1990; Sandmann 1990; Hawkins 1997).

  5. 5.

    The biogenetic law (“Biogenetisches Grundgesetz”) which Haeckel (re)formulated in 1872 (Fritz Müller and others had the idea before him). Ever since Haeckel published his biogenetic law, there have been accusations that the pictures of embryos which he used to illustrate his thesis were forgeries (Hopwood 2015; Hossfeld et al. 2016; Olsson et al. 2017).

  6. 6.

    Institutional, museological, and biological themes in connection with the writing of a new history of the Friedrich Schiller University in Jena (Hossfeld and Olsson 2003).

Haeckel and Sweden

We are most of all interested in investigating what influence Haeckel’s scientific (e.g. the biogenetic law) and philosophical (e.g. monism) might have had in the Swedish context, and to compare this with the international Haeckel reception, in, for example Austria and Italy.

As far as we know, no major investigation has been undertaken of the Haeckel reception in Sweden, although Haeckel corresponded with several Swedish scientists and leading cultural figures. He also travelled to Sweden in 1897 and 1907, and several of his books were translated into Swedish. Haeckel corresponded with Swedes over five decades (1869–1919). In the Haeckel Archive, there are letters, postcards, and telegrams from 39 Swedish sources. Among these we find well-known scientists like Svante Arrhenius, Wilhelm Leche, Sven Lovén, and Oscar Montelius, and A. G. Nathorst and Gustav Retzius, as well as the explorer Sven Hedin and the physician and social reformer Anton Nyström. In Jena, letters from Haeckel are rarely found. In the archives of the Center for History of Science at the Royal Swedish Academy of Sciences in Stockholm, we have sometimes found these missing letters when the correspondent was a member of the Academy and had his personal archive. In other cases, this is much more difficult.

Haeckel’s correspondence with Swedish scientists

We have chosen Leche, Lovén, Gustaf Retzius, Hedin, and Norström as examples to indicate the breadth of topics that Haeckel discussed with his Swedish colleagues. We present each of these correspondents briefly, before describing the contents of the correspondence.

Wilhelm Leche (1850–1927, as shown in Fig. 1), had studied with Haeckel’s former colleague and close friend Carl Gegenbaur (in 1877, when Gegenbaur had moved from Jena to Heidelberg). Leche became the first professor of zoology at (what is now) the University of Stockholm. A short biography was written by Stensiö (1926). His research clearly followed in the footsteps of Gegenbaur and mostly concerned vertebrate comparative anatomy, in particular, tooth morphology. He was also chairman of the Swedish Society for Eugenics (Svenska sällskapet för rashygien), which was founded in 1909, and politically radical (left-wing social democrat). Leche was a member of the board of the Stockholm Workers Institute (started by Anton Nyström, see below). Maybe the most interesting letter (out of four) from Leche to Haeckel dates from 1911. Leche tries to explain the 1908 Nobel prize incident (detailed in the accompanying article), when the Literature prize went to another professor in Jena, Rudolf Eucken. Haeckel thought that he did not get it because of his materialist world view. Leche wrote that he knows about this only by hearsay, but that considering the composition of the Swedish Academy, with “a bishop, an emissary, a librarian etc. and only two or three, which can be characterized as poets, although this academy is especially designated to the art of poetry”, he is nor surprised. He goes on to complain that none of the really important Swedish authors—Strindberg, Heidenstam, and Fröding—is a member of the academy. “This is exactly what one should expect when conservatives like Retzius make up all the boards”. He points out that Retzius is allowed to take part in deciding “no less than 3 Nobel prizes”. Haeckel visited Leche’s zoology department in Stockholm in 1897 when travelling to Sweden, Finland and Russia. They also exchanged books and papers. Leche is perhaps the clearest example of how the research programme started by Gegenbaur and Haeckel in Jena was brought into Swedish academia.

Fig. 1
figure 1

Wilhelm Leche. RSAS archives

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Sven (Ludvig) Lovén (1809–1895, Fig. 2) was a pioneering marine biologist (founder of the Kristineberg marine station) and explorer of the arctic, and professor of invertebrate zoology at the Natural History Museum (Naturhistoriska Riksmuséet) in Stockholm. Theel (1903) has written a short biography of Lovén. When Haeckel wrote to Lovén, it was to a well-known older colleague and the correspondence is about scientific matters only. Lovén wrote back (three letters) to thank Haeckel for sending him his beautiful monographs. They also exchanged specimens and photographs of each other. Lovén also wrote to inform Haeckel that he had successfully lobbied (with his colleagues the zoologist Liljeborg and the palaeontologist Lindström) to get Haeckel elected as foreign member of the Royal Swedish Academy of Sciences (in 1882).

Fig. 2
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Sven Lovén. RSAS archives

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(Magnus) Gustav Retzius (1842–1919, Fig. 3) was professor of Anatomy at the Karolinska Institute (the medical school in Stockholm), and a well-known neuroanatomist, antropologist, and ethnologist. Fürst (1921) has written a short biography of his colleague and friend Retzius. Retzius was wealthy, especially after having married Anna Hierta, and published most of his scientific work in 19 large folio volumes called “Biologische Untersuchungen” (Biological investigations) at Gustav Fischer Verlag in Jena, largely at his own expense. Among Retzius’ papers, one also finds descriptions of the dissected brains of scientists, for example the astronomer Hugo Gyldén and the mathematician Sophie (Sonja) Kowalewsky. Politically, Retzius became more and more conservative and used his influence against left-wing colleagues, such as Wilhelm Leche.

Fig. 3
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Gustaf Retziue sitting in front of his magesterial “Biologische Untersuchenungen”. RSAS archives

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Haeckel was impressed by Retzius’s anatomically detailed work (e.g. on nervous and connective tissue with Axel Key), and of course by the beautiful drawings, which he mentions repeatedly. Retzius wrote 14 letters to Haeckel and received 6 in return. Retzius praises Haeckel’s beautiful illustrations, and it is clear that two researchers for whom images and imagery are important can appreciate each others work. Retzius was enthusiastic about Haeckel’s scientific ideas, but did not enter into discussion of them. In 1901, Haeckel started the “scientific society Ethophysis”, into which he invited those he viewed as being the top scientists of his time. Of the first 24 scientists invited to become members, Retzius was the only one from Scandinavia. Retzius accepted the invitation. Haeckel and Retzius sent their scientific printed work to each other and exchanged compliments, apparently equally convinced about the great value of their work.

Sven Hedin (1865–1952) was a famous explorer and geographer, and notorious for being “German friendly” and an admirer of Adolf Hitler. Eric Wennerholm has written a somewhat hagiographic biography of Hedin. We found one letter from Hedin to Ernst Haeckel in the Haeckel Archive. It is dated Stockholm, 17 February 1916. In this letter, Sven Hedin thanked Haeckel for the book “Ewigkeit. Weltkriegsgedanken über Leben und Tot, Religion und Entwicklungslehre” (“Eternity. World War thoughts on life and death, religion and evolutionary theory”), which he had just received. Hedin was impressed by the “many deep and magnificent thoughts and with the proof that the great scientist yet, despite advanced age, works and thinks just as freshly and brilliantly as always in times gone by. It is an honour and a joy for me to have this reminder of the great age”. The First World War was ongoing, and Hedin had a clear standpoint. He wrote “Germany must win—this is a question of vital importance also for us Northern Germans (‘Nordgermanen’). Hopefully great and glorious news will soon arrive”.

Anton Nyström—Antichrist!

From Anton Nyström (1842–1931) see Frängsmyr (1964 for a biography), left-wing radical, physician, and educator, a letter sent on 9 April 1909 (Fig. 4), is kept in the Haeckel Archive. Haeckel marked the letter “Antichrist!” As a trained systematist, Haeckel often put letters into categories and labelled them accordingly, upon a quick first reading. But “Antichrist” was a rare label. In the letter, Nyström presents himself as an “old admirer and pupil” of Haeckel. Nyström’s book “Christianity and free thought”, published in Swedish, was to be published in German translation in Berlin. Nyström needed a preface by “a prominent German scientist and thinker”. He could not think of anyone better suited than Haeckel, with his “rare combination of exact scientific research and philosophy”.

Fig. 4
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Letter from Anton Nyström to Ernst Haeckel. Haeckel has written “Antichrist” on the letter. Ernst Haeckel House Archives

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Then Nyström goes on to describe his struggles with “theology and the dogmatic teachings of the church”, and how he fights for the “propagation of the scientific world view” through the Workers Institute (“Arbetarinstitutet”), a “popular science academy” which he had founded together with other left-leaning intellectuals (like Wilhelm Leche), who wanted to further the education of workers. Nyström then describes the cultural struggle (“Kulturkampf”) between the church and other conservatives and radicals like himself. He complains that at a meeting he “once had against me one bishop and seven priests”, but prevailed anyway. “The effect of the priests on the audience equalled zero”. Nyström also informed Haeckel that a member of parliament had motioned for the separation of church and state, something which finally happened, but only in the year 2000—nowhere near as fast as Nyström would have liked. Obviously, Nyström saw Haeckel as an important ally in his “Kulturkampf”.

Haeckel and his admirers

In addition to letters from colleagues, active in science or medicine, we found a different type of letters in the Haeckel archive. These letters are often very emotional and were written by young writes, often students, who had been inspired by Haeckel’s books with an artistic (e.g. “Art Forms in Nature”) or philosophical (e.g. “Natural History of Creation”, “Riddles of the World”) content. These are letters from the “Haeckel fan club” that are full of admiration for Ernst Haeckel. Haeckel’s monism was of course viewed with scepticism among Christians and/or conservatives, which made it all the more interesting for many young men and women. Examples of this kind of correspondence from Sweden include letters and postcards from Therese (and Elsa) Gyldén and from Gärda Lidforss and her cousin Karin Videgren. In her book about her brother the botanist Bengt Lidforss (Lidforss af Geijerstam 1945), Gärda Lidforss writes that she read Haeckel’s “Natural History of Creation” in the summer of 1890, together with her cousin (p. 56). They wrote a letter to Haeckel and even received a letter from Haeckel and one of his books “Indische Reisebriefe”. In addition, Haeckel sent them some shorter pamphlets and his portrait photograph. The girls were very surprised and happy about this.

In the Haeckel archive, we found three letters in German from Gärda Lidforss and Karin Videgren. The letter from 30 June 1890 is signed by both of them and they thank Haeckel for the portrait photograph and the letter “by which you made us very happy and proud”. They also send pictures of themselves dressed in traditional clothing and express the wish to visit Jena when they are older “and maybe have money for this“. They also mention that they study natural science at Lund University in southern Sweden inspired by the world view that Haeckel describes in “Natural History of Creation”.

Haeckel also inspired at least one future Swedish zoology professor, Torsten Pehrson. He was a professor at Stockholm University from 1948 until 1956. In his history of the zoology department at Stockholm University (available only as a manuscript in Swedish), he recalls his first meeting with the zoology professor, Wilhelm Leche. Leche asked him about his interest in zoology, and how Pehrson had become interested in becoming a zoologist. Pehrson said that his interest went back to when in high school “with glowing eyes” he had read Haeckel’s “Natural History of Creation”. This pleased Leche much more than the more common background among zoology students as insect collectors.

Conclusion

This first overview of Haeckel’s correspondence with Swedes shows that Haeckel’s political and philosophical as well as scientific ideas were received with, often, great admiration. We never find severe criticism of Haeckel’s ideas in the letters. Haeckel corresponded with many leading scientists and cultural figures in Sweden, and it is probably the case that not only the philosophical ideas like monism, but also Darwinism, largely entered Sweden via Haeckel’s popular books. The extent of Haeckel’s influence, however, can only be gauged by further studies of the Haeckel reception.