Editing Ernst Haeckel (section)

== Embryology and recapitulation theory ==
{{further|Recapitulation theory}}
[[File:Haeckel-embryos-weeks4-6.jpg|thumb|right|Illustrations of dog and human embryos, looking almost identical at 4 weeks then differing at 6 weeks, shown above a 6-week turtle embryo and 8-day hen embryo, presented by Haeckel in 1868 as convincing proof of evolution. The pictures of the earliest embryonic stages are now considered inaccurate.<ref>{{cite journal |last1=Richardson |first1=M. K. |last2=Hanken |first2=J. |last3=Selwood |first3=L. |author-link3=Lynne Selwood |last4=Wright |first4=G. M. |last5=Richards |first5=R. J. |last6=Pieau |first6=C. |last7=Raynaud |first7=A. |year=1998 |title=Letters |journal=Science |volume=280 |issue=5366 |pages=983, 985–6 |doi=10.1126/science.280.5366.983c |pmid=9616084 |s2cid=2497289}}</ref>]]

When Haeckel was a student in the 1850s he showed great interest in [[embryology]], attending the rather unpopular lectures twice and in his notes sketched the visual aids: textbooks had few illustrations, and large format plates were used to show students how to see the tiny forms under a reflecting microscope, with the translucent tissues seen against a black background. Developmental series were used to show stages within a species, but inconsistent views and stages made it even more difficult to compare different species. It was agreed by all European evolutionists that all [[vertebrate]]s looked very similar at an early stage, in what was thought of as a common ideal type, but there was a continuing debate from the 1820s between the Romantic [[recapitulation theory]] that human embryos developed through stages of the forms of all the major groups of adult animals, literally manifesting a sequence of organisms on a [[great chain of being|linear chain of being]], and [[Karl Ernst von Baer]]'s opposing view, stated in [[von Baer's laws (embryology)|von Baer's laws of embryology]], that the early general forms diverged into four major groups of specialised forms without ever resembling the adult of another species, showing affinity to an [[archetype]] but no relation to other types or any [[transmutation of species]]. By the time Haeckel was teaching he was able to use a textbook with woodcut illustrations written by his own teacher [[Albert von Kölliker]], which purported to explain human development while also using other mammalian embryos to claim a coherent sequence. Despite the significance to ideas of transformism, this was not really polite enough for the new popular science writing, and was a matter for medical institutions and for experts who could make their own comparisons.<ref name=hopwood2006 />{{rp|264–267}}<ref>{{harvnb|Darwin|Costa|2011|p=450}}</ref>

=== Darwin, Naturphilosophie and Lamarck ===

Darwin's ''[[On the Origin of Species]]'', which made a powerful impression on Haeckel when he read it in 1864, was very cautious about the possibility of ever reconstructing the history of life, but did include a section reinterpreting von Baer's embryology and revolutionising the field of study, concluding that "Embryology rises greatly in interest, when we thus look at the embryo as a picture, more or less obscured, of the common parent-form of each great class of animals." It mentioned von Baer's 1828 anecdote (misattributing it to [[Louis Agassiz]]) that at an early stage embryos were so similar that it could be impossible to tell whether an unlabelled specimen was of a mammal, a bird, or of a reptile, and Darwin's own research using embryonic stages of [[barnacle]]s to show that they are [[crustacean]]s, while cautioning against the idea that one organism or embryonic stage is "higher" or "lower", or more or less evolved.<ref>{{harvnb|Darwin|1859|pp=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F373&pageseq=457 439–450]}}<br />{{harvnb|Darwin|Costa|2011|pp=439–450}}</ref> Haeckel disregarded such caution, and in a year wrote his massive and ambitious ''Generelle Morphologie'', published in 1866, presenting a revolutionary new synthesis of Darwin's ideas with the German tradition of ''[[Naturphilosophie]]'' going back to [[Johann Wolfgang von Goethe|Goethe]] and with the progressive evolutionism of [[Lamarckism|Lamarck]] in what he called ''Darwinismus''. He used [[morphology (biology)|morphology]] to reconstruct the [[evolutionary history of life]], in the absence of fossil evidence using embryology as evidence of ancestral relationships. He invented new terms, including [[ontogeny]] and [[phylogeny]], to present his evolutionised recapitulation theory that "ontogeny recapitulated phylogeny". The two massive volumes sold poorly, and were heavy going: with his limited understanding of German, Darwin found them impossible to read. Haeckel's publisher turned down a proposal for a "strictly scholarly and objective" second edition.<ref name=hopwood2006 />{{rp|269–270}}

=== Embryological drawings ===
[[File:Tree of life by Haeckel.jpg|upright|thumb|Haeckel's [[tree of life (biology)|tree of life]]]]

Haeckel's aim was a reformed morphology with evolution as the organising principle of a cosmic synthesis unifying science, religion, and art. He was giving successful "popular lectures" on his ideas to students and townspeople in [[Jena]], in an approach pioneered by his teacher [[Rudolf Virchow]]. To meet his publisher's need for a popular work he used a student's transcript of his lectures as the basis of his ''Natürliche Schöpfungsgeschichte'' of 1868, presenting a comprehensive presentation of evolution. In the Spring of that year he drew figures for the book, synthesising his views of specimens in Jena and published pictures to represent types. After publication he told a colleague that the images "are completely exact, partly copied from nature, partly assembled from all illustrations of these early stages that have hitherto become known". There were various styles of [[embryological drawings]] at that time, ranging from more schematic representations to "naturalistic" illustrations of specific specimens. Haeckel believed privately that his figures were both exact and synthetic, and in public asserted that they were schematic like most figures used in teaching. The images were reworked to match in size and orientation, and though displaying Haeckel's own views of essential features, they support von Baer's concept that vertebrate embryos begin similarly and then diverge. Relating different images on a grid conveyed a powerful evolutionary message. As a book for the general public, it followed the common practice of not citing sources.<ref name=hopwood2006 />{{rp|270–274}}

[[File:Embryo - copies.jpg|thumb|left|In 1868 Haeckel illustrated von Baer's observation that early embryos of different species could not be told apart by using the same woodcut three times as dog, chick and turtle embryos: he changed this in the next edition.]]
The book sold very well, and while some anatomical experts hostile to Haeckel's evolutionary views expressed some private concerns that certain figures had been drawn rather freely, the figures showed what they already knew about similarities in embryos. The first published concerns came from [[Ludwig Rütimeyer]], a professor of zoology and comparative anatomy at the [[University of Basel]] who had placed fossil mammals in an evolutionary lineage early in the 1860s and had been sent a complimentary copy. At the end of 1868 his review in the ''Archiv für Anthropologie'' wondered about the claim that the work was "popular and scholarly", doubting whether the second was true, and expressed horror about such public discussion of man's place in nature with illustrations such as the evolutionary trees being shown to non-experts. Though he made no suggestion that embryo illustrations should be directly based on specimens, to him the subject demanded the utmost "scrupulosity and conscientiousness" and an artist must "not arbitrarily model or generalise his originals for speculative purposes" which he considered proved by comparison with works by other authors. In particular, "one and the same, moreover incorrectly interpreted woodcut, is presented to the reader three times in a row and with three different captions as [the] embryo of the dog, the chick, [and] the turtle". He accused Haeckel of "playing fast and loose with the public and with science", and failing to live up to the obligation to the truth of every serious researcher. Haeckel responded with angry accusations of bowing to religious prejudice, but in the second (1870) edition changed the duplicated embryo images to a single image captioned "embryo of a mammal or bird". Duplication using galvanoplastic stereotypes ([[Stereotype (printing)|clichés]]) was a common technique in textbooks, but not on the same page to represent different eggs or embryos. In 1891 Haeckel made the excuse that this "extremely rash foolishness" had occurred in undue haste but was "bona fide", and since repetition of incidental details was obvious on close inspection, it is unlikely to have been intentional deception.<ref name=hopwood2006 />{{rp|275–276;282–286}}

The revised 1870 second edition of 1,500 copies attracted more attention, being quickly followed by further revised editions with larger print runs as the book became a prominent part of the optimistic, nationalist, anticlerical "culture of progress" in [[Otto von Bismarck]]'s new [[German Empire]]. The similarity of early vertebrate embryos became common knowledge, and the illustrations were praised by experts such as [[Michael Foster (physiologist)|Michael Foster]] of the [[University of Cambridge]]. In the introduction to his 1871 ''[[The Descent of Man, and Selection in Relation to Sex]]'', Darwin gave particular praise to Haeckel, writing that if ''Natürliche Schöpfungsgeschichte'' "had appeared before my essay had been written, I should probably never have completed it". The first chapter included an illustration: "As some of my readers may never have seen a drawing of an embryo, I have given one of man and another of a dog, at about the same early stage of development, carefully copied from two works of undoubted accuracy" with a footnote citing the sources and noting that "Häckel has also given analogous drawings in his ''Schöpfungsgeschichte.''" The fifth edition of Haeckel's book appeared in 1874, with its frontispiece a heroic portrait of Haeckel himself, replacing the previous controversial image of the heads of apes and humans.<ref name=hopwood2006 />{{rp|285–288}}<ref>{{harvnb|Darwin|1871|pp=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F937.1&pageseq=17 4], [http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F937.1&pageseq=27 14–17]}}</ref>

[[File:Haeckel Anthropogenie 1874.jpg|thumb|right|1874 illustration from ''Anthropogenie'' showing "very early", "somewhat later" and "still later" stages of embryos of fish (F), salamander (A), turtle (T), chick (H), pig (S), cow (R), rabbit (K), and human (M)]]

=== Controversy ===
Later in 1874, Haeckel's simplified embryology textbook ''Anthropogenie'' made the subject into a battleground over Darwinism aligned with Bismarck's ''[[Kulturkampf]]'' ("culture struggle") against the Catholic Church. Haeckel took particular care over the illustrations, changing to the leading zoological publisher Wilhelm Engelmann of Leipzig and obtaining from them use of illustrations from their other textbooks as well as preparing his own drawings including a dramatic double page illustration showing "early", "somewhat later" and "still later" stages of 8 different vertebrates. Though Haeckel's views had attracted continuing controversy, there had been little dispute about the embryos and he had many expert supporters, but [[Wilhelm His Sr.|Wilhelm His]] revived the earlier criticisms and introduced new attacks on the 1874 illustrations.<ref>Wilhelm His. ''Unsere Körperform und das physiologische Problem ihrer Entstehung''. F. C. W. Vogel, Leipzig 1875.</ref> 

Expert anatomists were critical of Haeckel's work. Catholic priests also opposed Haeckel's views. Specifically, Haeckel's critics accused him of manipulating the embryo drawings to make the early stages of different species look more similar. They claimed that the drawings of four-week dog and human embryos had been copied without attribution from other sources, and changed by expanding dog's head and reducing the human head, moving the eye, and exaggerating the size of the human tail.  Haeckel himself considered the drawings stylized and illustrative, but his detractors considered them forgery and fraud.<ref name=hopwood2006 />{{rp|270-271,288–296,299}}

While it has been widely claimed that Haeckel was charged with fraud by five professors and convicted by a university court at Jena, there does not appear to be an independently verifiable source for this claim.<ref>{{citation|last=Richards|first=Robert J.|author-link=Robert J. Richards|title=Ernst Haeckel and the Struggles over Evolution and Religion|url=https://books.google.com/books?id=byJk8Ea0WSQC&pg=PA89|access-date=22 February 2016|volume=10|year=2005|publisher=Universitätsverlag Göttingen|isbn=978-3-938616-39-0|pages=89–115|journal=Annals of the History and Philosophy of Biology}}</ref> Recent analyses (Richardson 1998, Richardson and Keuck 2002) have found that some of the criticisms of Haeckel's embryo drawings were legitimate,{{citation needed|date=March 2025}} but others were unfounded.<ref>Michael K. Richardson. 1998. "Haeckel's embryos continued". ''Science'' 281:1289, quoted in NaturalScience.com webpage [http://naturalscience.com/ns/letters/ns_let17.html Re: ''Ontogeny and phylogeny''] {{webarchive|url=https://web.archive.org/web/20061114003612/http://naturalscience.com/ns/letters/ns_let17.html |date=14 November 2006 }}: A Letter from Richard Bassetti; Editor's note.</ref><ref>"While some criticisms of the drawings are legitimate, others are more tendentious", Richardson and Keuck "Haeckel's ABC of evolution and development", ''Biol. Rev.'' (2002), '''77''', pp. 495–528. Quoted from p. 495.</ref> There were multiple versions of the embryo drawings, and Haeckel rejected the claims of fraud. It was later said that "there is evidence of sleight of hand" on both sides of the feud between Haeckel and [[Wilhelm His Sr.|Wilhelm His]].<ref>Richardson & Keuck 2001. See for example, their Fig. 7, showing His's drawing of the forelimb of a deer embryo developing a clef, compared with a similar drawing (Sakurai, 1906) showing the forelimb initially developing as a digital plate with rays. Richardson and Keuck say "Unfortunately His's embryos are mostly at later stages than the nearly identical early stage embryos illustrated by Haeckel [top row of Haeckel's drawing]. Thus they do not inform the debate and may themselves be disingenuous." p. 518.</ref> [[Robert J. Richards]], in a paper published in 2008, defends the case for Haeckel, shedding doubt against the fraud accusations based on the material used for comparison with what Haeckel could access at the time.<ref>{{Cite journal|title=Haeckel's embryos: fraud not proven |first=Robert J. | last=Richards |journal=Biology & Philosophy |year=2009 |volume=24 |pages=147–154 |doi=10.1007/s10539-008-9140-z |citeseerx=10.1.1.591.9350 |s2cid=13416916 |url=http://home.uchicago.edu/~rjr6/articles/Haeckel--fraud%20not%20proven.pdf}}</ref>