Editing Ernst Haeckel (section)

== Research ==
[[File:Haeckel Actiniae.jpg|upright|thumb|Sea anemones from Ernst Haeckel's ''[[Kunstformen der Natur]]'' (Art forms of Nature) of 1904]]

Haeckel was a [[zoologist]], an accomplished artist and illustrator, and later a professor of [[comparative anatomy]]. Although Haeckel's ideas are important to the history of [[evolutionary theory]], and although he was a competent [[invertebrate]] [[anatomist]] most famous for his work on [[radiolaria]], many speculative concepts that he championed are now considered incorrect. For example, Haeckel described and named hypothetical ancestral [[microorganism]]s that have never been found.<ref>{{cite book|first=Ronald A.|last=Jenner|title=Ancestors in Evolutionary Biology Linear Thinking about Branching Trees|location=Cambridge|publisher=Cambridge University Press|year=2022|page=110|isbn=978-1-31622-666-7|url=https://books.google.com/books?id=aHZ6EAAAQBAJ}}</ref>

He was one of the first to consider [[psychology]] as a branch of [[physiology]]. He also proposed the kingdom ''[[Protista]]''<ref name=HaeckelDE /> in 1866. His chief interests lay in [[evolution]] and life development processes in general, including development of nonrandom form, which culminated in the beautifully illustrated ''[[Kunstformen der Natur]]'' (''Art forms of nature''). Haeckel did not support [[natural selection]], rather believing in [[Lamarckism]].<ref>Ruse, M. 1979. ''The Darwinian Revolution''. Chicago: University of Chicago Press.</ref>

[[File:Haeckel vs von Baer.svg|thumb|upright=1.7|Embryology theories of Ernst Haeckel and [[Karl Ernst von Baer]] compared]]

Haeckel advanced a version of the earlier [[recapitulation theory]] previously set out by [[Étienne Serres]] in the 1820s and supported by followers of [[Étienne Geoffroy Saint-Hilaire]] including [[Robert Edmond Grant]].<ref>{{harvnb|Desmond|1989|pp=53–53, 86–88, 337–340}}</ref> It proposed a link between [[ontogeny]] (development of form) and [[phylogeny]] (evolutionary descent), summed up by Haeckel in the phrase "[[ontogeny recapitulates phylogeny]]". His concept of recapitulation has been refuted in the form he gave it (now called "strong recapitulation"), in favour of the ideas [[Karl Ernst von Baer#Baer's laws (embryology)|first advanced by Karl Ernst von Baer]]. The strong recapitulation hypothesis views ontogeny as repeating forms of adult ancestors, while weak recapitulation means that what is repeated (and built upon) is the ancestral embryonic development process.<ref>Richardson and Keuck, (Biol. Review (2002), 77, pp. 495–528) show that it is a simplification to suppose that Haeckel held the recapitulation theory in its strong form. They quote Haeckel as saying "If [recapitulation] was always complete, it would be a very easy task to construct whole phylogeny on the basis of ontogeny.  … There is certainly, even now, a number of lower vertebrate animals (e.g. some Anthozoa and Vermes) where we are authorised to interpret each embryological form directly as the historical representation or portrait-like silhouette of an extinct ancestral form. But in a great majority of animals, including man, this is not possible because the infinitely varied conditions of existence have led the embryonic forms themselves to be changed and to partly lose their original condition (Haeckel, 1903: pp. 435–436)"</ref> Haeckel supported the theory with [[embryo drawings]] that have since been shown to be oversimplified and in part inaccurate, and the theory is now considered an oversimplification of quite complicated relationships, however comparison of embryos<ref name="Watts et al., 2019">{{cite journal |author1=Watts E |author2=Levit GS |author3=Hossfeld U |title=Ernst Haeckel's contribution to Evo-Devo and scientific debate: a re-evaluation of Haeckel's controversial illustrations in US textbooks in response to creationist accusations. | journal=Theory Biosci | year= 2019 | volume= 138 | issue= 1 | pages= 9–29 | pmid=30868433 | doi=10.1007/s12064-019-00277-3 | s2cid=76663562 | doi-access=free }}</ref> remains a powerful way to demonstrate that all animals are related. Haeckel introduced the concept of [[heterochrony]], the change in timing of [[embryonic development]] over the course of evolution.<ref name=Horder>{{cite book |author=Horder, Tim |chapter=Heterochrony |title=Encyclopedia of Life Sciences |publisher=John Wiley & Sons |date=April 2006 }}</ref><ref name="Hall 2003">{{cite journal |last1=Hall |first1=B. K. |title=Evo-Devo: evolutionary developmental mechanisms |journal=International Journal of Developmental Biology |date=2003 |volume=47 |issue=7–8 |pages=491–495 |pmid=14756324}}</ref>

[[File:Ernst Haeckel and von Miclucho-Maclay 1866.jpg|thumb|upright|Haeckel (left) with [[Nicholai Miklukho-Maklai]], his assistant, in the [[Canary Islands|Canaries]], 1866]]
[[File:Pithecanthropus Alalus.1894.jpg|left|thumb|Portrait of two <nowiki>''P. alalus''</nowiki>, speculative species]]
Haeckel was a flamboyant figure, who sometimes took great, non-scientific leaps from available evidence. For example, at the time when Darwin published ''[[On the Origin of Species by Means of Natural Selection]]'' (1859), Haeckel postulated that evidence of human evolution would be found in the [[Dutch East Indies]] (now [[Indonesia]]).  At that time, no remains of human ancestors had yet been identified.  He described these theoretical remains in great detail and even named the as-yet unfound species, ''Pithecanthropus alalus'', and instructed his students such as [[Richard Hertwig|Richard]] and [[Oskar Hertwig]] to go and find it.{{Citation needed|date=August 2019}}

One student did find some remains: a Dutchman named [[Eugène Dubois]] searched the [[East Indies]] from 1887 to 1895, discovering the remains of [[Java Man]] in 1891, consisting of a skullcap, thighbone, and a few teeth. These remains are among the oldest hominid remains ever found. Dubois classified Java Man with Haeckel's ''Pithecanthropus'' label, though they were later reclassified as ''[[Homo erectus]]''. Some scientists of the day suggested<ref>{{cite book|url=https://books.google.com/books?id=N26AAAAAMAAJ|title=The Red Ape: Orang-utans and Human Origins|first=Jeffrey H.|last=Schwartz|publisher=Houghton Mifflin|year=1987|isbn=9780395380178}}</ref> Dubois' Java Man as a potential intermediate form between modern humans and the common ancestor we share with the other [[great apes]]. The current consensus of anthropologists is that the direct ancestors of modern humans were African populations of ''[[Homo erectus]]'' (possibly ''[[Homo ergaster]]''), rather than the Asian populations exemplified by Java Man and [[Peking Man]]. (Ironically, a new human species, ''[[Homo floresiensis]]'', a dwarf human type, has recently been discovered in the island of Flores).<ref>{{Cite journal|last1=Martin|first1=Robert D.|last2=MacLarnon|first2=Ann M.|last3=Phillips|first3=James L.|last4=Dobyns|first4=William B.|date=2006|title=Flores hominid: New species or microcephalic dwarf?|journal=The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology|language=en|volume=288A|issue=11|pages=1123–1145|doi=10.1002/ar.a.20389|pmid=17031806|issn=1552-4892|doi-access=free}}</ref>