Goethe origin of species
A general overview of Goethe's metamorphology theory, aka "evolution" as Darwin would later, citing Goethe, popularize, showing Goethe’s views of monkey-human common origins (Ѻ) and his notion of the urpflanze (Ѻ) or “primordial plant”, a general model of the origin of plants, animals, and humans, each of which by 1809 were believed to originated from a combination of morphological forces and chemical reaction mechanism.
In geniuses on, Goethe on evolution refers to the origin of species (animals and plants) views of Johann Goethe, i.e. the proto-evolution or precursory evolution theory views of humans, animals, and plants, or “metamorphology” as he referred to it. Goethe, in 1784, discovered the human intermaxillary bone, thought to be unique to animals only, thus yielding anatomical proof of common origin; in his 1790 Metamorphosis of Plants (see: metamorphosis), he outlined a theory of form change in plants; he outlined his newly discovered principle further in his 1795 “Sketch of a General Introduction to Comparative Anatomy”; from 1796 to 1809, with the publication of his Elective Affinities, he explained his principle of “moving order” (bewegliche ordnung) at the chemical level for humans and chemicals, in terms of affinity chemistry and the force of elective affinity (forerunner to the modern free energy view of evolution).

Overview
In circa 1770, Dutch physician Petrus Camper (1722-1789) proposed the Biblically-friendly theory, which quickly became dogma, that the anatomical difference between man and animal was the missing intermaxillary bone in man, this being the distinguishing feature between man and monkey. [13]

In 1775 to 1786, Goethe was, in an effort to disprove Camper, began studying elephant bones, the formation of mosses, and was discussing a book with Charlotte von Stein which asserted that humans were originally plants and animals; about which Owen Barfield, in his “Goethe and Evolution” (1949), summarizes as follows: [12]

“Was Goethe then an introvert? Mainly interested in ferreting about among those half-formed emotions and impulses and huge creative forces which move in a mysterious way within us, we are told, as the forces of nature drive us and shape us from without? Not for a moment. He was the most exact and conscientious observer of plants and animals and the physical structure of man – especially his bones. Nothing delighted him more than the loan of an elephant-skull. He seems to have been about as good at borrowing other people’s bones as Coleridge was at borrowing other people’s books; and at least one rather aggrieved letter, which is still extant, suggests that he was not always much better at returning them. Incidentally I think Charlotte von Stein has been a little unfairly treated by some of Goethe’s biographers. The intellectual and active life of that lady between the years 1775 and 1786 must have been something of a marathon. When she was not mugging up Spinoza in Latin as well as German – or inspecting musty skulls, she was always liable to get an urgent request from Goethe for ‘mosses of all sorts, if possible with the roots – and wet’.

In the same letter Charlotte speaks of a "new book" which makes it probable that men were originally plants and animals. And this brings me to the hardest part of my task. For I have to try to describe the origin of something new in the world of thought. Or rather – which makes it still harder – something then new, but now very familiar to us all. I do not mean a theory. The absence of that is easy enough to look back on. No, I mean an image or construct, a meaning, a Vorstellung, a Bild, as the Germans say – whatever word or phrase you choose, as long as you grasp that it is not a theory I am talking about, but rather the raw stuff about which theories are formed.”
Goethe intermaxillary bone
Sketches of Goethe's 1784 discovery of the intermaxillary bone in animals (left) and humans (right), see: human intermaxillary bone, thus giving "evidence" of a common origin of form, thus disproving the then-prevalent separate creation theory; the oft-cited starting point for modern evolution theory.

In 1784, Goethe disproved the then-prevailing theory that humans and other animals were not related in origin because humans had no intermaxillary bone, whereas animals did, by discovering, via fossil investigation the human intermaxillary bone, which he pronounced in a missive to Johann Herder from Jena, March 27, at night (quote to right):

“I have found neither gold nor silver, but something that unspeakably delights me—the human Os intermaxillary! I was comparing human and animal skulls with Loder, hit up the right track, and behold—Eureka! Only, I beg of you, not a word—for this must be a great secret for the present. You ought to be very much delighted too, for it is like the keystone to anthropology—and it’s there, no mistake! But how?”

The specific observation that led Goethe to this fertile conception of evolution, is found in Goethe’s monograph on the intermaxillary bone, written as early as 1786. Prior to this publication, it was known that in most vertebrates (mammalia, birds, amphibia, and fishes) that the upper jaw consists of two bones, the upper jaw-bone and the intermaxillary bone. The former always contains in the mammalia the molar and canine teeth, the latter the incisors. Humans, being distinguished from all other animals by the absence of the projecting snout, have, on the contrary, on each side only one bone, the upper jaw-bone, containing all the teeth. This being so, according to Helmholtz, Goethe discovered in human the skull faint traces of the sutures, which in animals unite the upper and middle jaw-bones, and thus concluded from it that man had originally possessed an upper jaw-bone.

In circa 1794, Goethe came to learn German physician Johann Blumenbach's formative drive theory, which came to be a framework for part of the mechanism of the operation of his developing metamorphology theory.

By 1795, following more studies in osteology, Goethe had become convinced of the universality of his “newly discovered principle”, and was able to define the idea in his “Sketch of a General Introduction to Comparative Anatomy”, wherein he laid down with the utmost confidence and precision, that “all differences in the structure of animals must be looked upon as variations of a single primitive type, induced by the coalescence, the alteration, the increase, the diminution, or event the complete removal of singe parts of the structure.”

In 1790, Goethe, in his treatise on the metamorphosis of plants, according to Helmholtz, worked out the principles behind the transformation of stem-leaves into sepals and petals, and of sepals and petals into stamens, nectaries, and overaies, just as the “anterior extremity of vertebrate animals takes different forms, becoming in man and apes an arm, in other animals a paw with claws, or a forefoot with a hoof, or a fin, or a win, but always retains the same divisions, the same positions, and the same connection with the trunk, all resembling each other to a certain extent in origin and composition, and even under certain conditions passing from one form into the other.” [2]

Goethe (1784)
A depiction of Goethe circa 1780 ruminating on a theory of common descent of humans, animals, and plants from chemicals; and his searching for an discovering the human intermaxillary bone (1784), upon which he built his metamorphology theory, aka "evolution" as Darwin would popularize things.
In 1831, Goethe, in his Story of My Botanical Studies, wrote: [9]

“The ever-changing display of plant forms, which I have followed for so many years, awakens increasingly within me the notion: The plant forms which surround us were not all created at some given point in time and then locked into the given form, they have been given… a felicitous mobility and plasticity allows them to grow and adapt themselves to many different conditions in many different places.”

Goethe’s last writings were said to have been devoted to defending Saint-Hilaire. [7]

Helmholtz | On
In 1853, German physician-physicist Hermann Helmholtz, in his essay “On Goethe’s Scientific Researches”, summarized that Goethe’s studies of comparative botany and comparative anatomy led him to “a happy glimpse of an all-pervading law” of the conception that the differences in the anatomy different animals or morphology of different plants are to be “looked upon as variations from a common phase or type, induced by differences of habit, locality, or food.”

In 1892, Helmholtz reiterated on Goethe’s metamorphosis theory, that Goethean morphology had so shaped nineteenth-century biology that it paved the way for Darwin’s theory. [2]

Darwin | On
In 1861, Charles Darwin, in the third edition of his On the Origin of Species, cites Goethe as the oldest forerunner to his theory of the origin of species, as follows:

“It is rather a singular instance of the manner in which similar views arise at about the same time that Goethe in Germany, Erasmus Darwin in England, and Geoffroy Saint-Hilaire in France, came to the same conclusion on the origin of species, in the years 1794-95.”

Robert J. Richards, in his “Did Goethe and Schelling Endorse Species Evolution? (2011), asserts that Darwin learned of Goethe’s so-named “transmutation” of species theory from Geoffroy Hilaire. [11]

Goethe's 1786-1795 theories on metamorphosis and variation of plant and animal species, as being descendant common ancestors, through a process of transformation, had a significant influence on English naturalist Charles Darwin and the reception of his 1859 Origin of Species.

“We see that our researches on the fixity or the variation of the species, lead us directly to the ideas issued by two men justly famous, Geoffroy Saint-Hilaire and Goethe.”

This passage was also cited by Darwin. In total, in his in his 'Historical Sketch', on those who advocated variations on a theory of origin of species, prior to 1859, Darwin gives thirty-four authors who believe in the modification of species, or at least disbelieve in separate acts of creation, of which twenty-seven have written on special branches of natural history or geology, in which the two foremost of these, according to Darwin, are Goethe and Geoffroy.

Haeckel | On
In 1864, Ernst Haeckel, in a letter to Charles Darwin, cited Goethe, Kant, and Hilaire as forerunners to Darwin's theory of evolution: [10]

“The history of the theory of descent is also extremely interesting and I witness with great joy, how even a long time ago, the greatest German philosophers and thinkers have a priori proclaimed this theory to be the only possible way of understanding the origin of species. But you, through the epoch-making discovery of ‘Natural Selection’ and ‘Struggle for life’, have for the first time provided the concrete proof for that abstract statement. The most beautiful expression of this was given by our greatest poet, Goethe, in his Essays on Morphology, and, most especially, in the review of Geoffroy's ‘Principes de Philosophie zoologique'’, written shortly before his death. I find that in the excellent biography of Goethe by your compatriot Lewes, this great merit of Goethe's is perfectly appreciated (in the tenth Chapter of book V entitled ‘The poet as a man of science’). Our greatest philosopher, Kant, has also expressed himself in equally decided terms as being for the ‘Theory of Epigenesis’, as he calls it. Indeed, all possible organic manifestations of nature, both in animal and vegetable life are thus so simply and harmoniously explained, that I do not understand how so many and such learned naturalists can still be opposed to your view.”

Haeckel further corresponded with Darwin on Goethe's theories in 1868 (Jun 22 and Nov 9) and in 1871 (Ѻ); not to mention that the two met in person at some point.

In 1899, Haeckel summarized Goethe’s evolution theory as follows: [3]

“It is easy to understand that these prevalent ideas of the absolute unchangeability and supernatural creation of organic species could not satisfy the more penetrating thinkers. We find several eminent minds already, in the second half of the last century, busy with the attempt to find a natural explanation of the ‘problem of creation.’ Pre-eminent among them was the great German poet and philosopher, Wolfgang Goethe, who, by his long and assiduous study of morphology, obtained, more than a hundred years ago, a clear insight into the intimate connection of all organic forms, and a firm conviction of a common natural origin. In his famed Metamorphosis of Plants (1790) he derived all the different species of plants from one primitive type, and all their different organs from one primitive organ—the leaf. In his vertebral theory of the skull he endeavored to prove that the skulls of the vertebrates —including man—were all alike made up of certain groups of bones, arranged in a definite structure, and that these bones are nothing else than transformed vertebrae. It was his penetrating study of comparative osteology that led Goethe to a firm conviction of the unity of the animal organization; he had recognized that the human skeleton is framed on the same fundamental type as that of all other vertebrates— ‘built on a primitive plan that only deviates more or less to one side or other in its very constant features, and still develops and refashions itself daily.’ This remodelling, or transformation, is brought about, according to Goethe, by the constant interaction of two powerful constructive forces—a centripetal force within the organism, the ‘tendency to specification’, and a centrifugal force without, the tendency to variation, or the ‘idea of metamorphosis’; the former corresponds to what we now call heredity, the latter to the modern idea of adaptation.”

Haeckel, to note, goes on to summarized that Goethe's work on the origin of species of plants and animals, did "not amount to more than certain general conclusions".

Sherrington
In 1949, Charles Sherrington, curiously, in his ignorance, supposedly, in a second edition of one of his books, disparaged Goethe via the following assertion: [10]

“There is no reason to believe that Goethe had a remote inkling of the concept of evolution, though admirers, strained the words of some poem or apothegm, have called him Darwin’s precursor.”

In 1952, Otto Haas, in his “Goethe and Evolution”, devotes eight pages to correct Sherrington. [10]

Goethe poem
Sketch of Goethe’s research and poem entitled Ginkgo Biloba which gives a hint of what he was digging for in his work on comparative botany. [6]
Other
It should be noted that Ernst Haeckel and Lester Ward considered Geoffroy Saint-Hilaire's contributions to evolutionary theory to be relatively insignificant and instead ranked Jean Lamarck along side Erasmus Darwin and Goethe. While both Haeckel and Ward agree that Erasmus Darwin was the least important of the three they disagree on whom was most important. Haeckel ranks his fellow countryman Goethe at the top while Ward considers Lamarck's body of work to be superior. [8]

In 2003, Carl Becker, in his A Modern Theory of Evolution (2003), surmised that Goethe, in his bone discovery, had “discovered the evolution of the human being from the ape”, a concept that prior to him had only existed as a metaphor in occult tradition: the ape representing man untransformed by alchemy. [1]

Quotes
The following are related quotes:

“How deeply Goethe had penetrated into their character by these philosophic studies of the ‘construction and reconstruction of organic natures,’ and how far, therefore, he must be considered the most important precursor of Darwin and Lamarck.”
Ernst Haeckel (1882), “The Systems of Darwin, Goethe, and Lamarck” [5]

“About the end of the eighteenth century fruitful suggestions and even clear presentations of this or that part of a large evolutionary doctrine came thick and fast, and from the most divergent quarters. Especially remarkable were those from Erasmus Darwin in England, Maupertuis in France, Oken in Switzerland, and Herder, and, most brilliantly of all, from Goethe in Germany.”
— Andrew White (1896), A History of Warfare of Science with Theology in Christendom [9]

“I often think of the different ways Goethe and Darwin got at evolution. Goethe had the poetic conception of it all right; Darwin worked it out step by step. Who's ahead? And which has any business scoffing at the other?”
— Susan Glaspell (c.1915) (Ѻ)

References
1. Becker, Carl J. (2003). A Modern Theory of Evolution (pg. 97). iUniverse.
2. Helmholtz, Hermann. (1995). Science and Culture: Popular and Philosophical Essays (ch. 1: On Goethe’s Scientific Researches (1853), pgs. 1-17; ch. : On the Interaction of the Natural Forces (1854), pgs. 18-45; ch. 5: On the Conservation of Force, pgs. 96-; ch. 14: Hermann von Helmholtz: an Autobiographical Sketch (1891), pgs. 381-92; ch: Goethe’s Presentiments of Coming Scientific Ideas (1892), pgs. 393-412) (editor: David Cahan). University of Chicago Press.
3. Haeckel, Ernst. (1899). The Riddle of the Universe: at the Close of the Nineteenth Century (translator: Joseph McCabe) (pgs. 74-75). Harper & Brother, 1900.
4. (a) Darwin, Charles. (1861). Origin of Species (A Historical Sketch, pgs. viii-xix; quote, pg. xv), 3rd edition. Publisher.
(b) Darwin, Charles. (1872). Origin of Species (Goethe, pgs. 13, 22, 207; A Historical Sketch, pgs. 11-), 6th ed. New York: American Home Library Co.
5. (a) Haeckel, Ernst. (1882). "The Systems of Darwin, Goethe, and Lamarck", Lecture given at Eisenach.
(b) Haeckel, Ernst. (1899). The Riddle of the Universe: at the Close of the Nineteenth Century (translator: Joseph McCabe) (pgs. 75-76). Harper & Brother, 1900.
6. Nicoaou, K.C. and Montagnon, Tamsyn. (2008). Molecules that Changed the World (pg. 160). Wiley-VCH.
7. Frenay, Robert. (2006). Pulse: the Coming Age of Systems and Machines Inspiried by Living Things (pg. 12). MacMillan.
8. Ward, Lester F. (1879). Haeckel's Genesis of Man, or, History of the Development of the Human Race: Being a review of his "Anthropogenie", and Embracing a Summary Exposition of His Views and of Those of the Advanced German School of Science (pgs. 8-13). E. Stern & Co.
9. Goethe and the Idea of Evolution (section) – Wikipedia.
10. Haas, Otto. (1952). “Goethe and Evolution” (abs), Osiris, 10:35-42.
11. (a) Haeckel, Ernst. (1864). “Letter to Charles Darwin” (Ѻ), Aug 10.
(b) Richards, Robert J. (2011). “Did Goethe and Schelling Endorse Species Evolution?” (pdf), Romanticism and Evolution, The University of Western Ontario, 14, May.
12. Barfield, Owen. (1949). “Goethe and Evolution” (Ѻ), The Listener, 42:945-46.
13. (a) Hellmich S. (1982). “The Intermaxillary Bone and Goethe’s Mephistopheles” (abs), Laryngol Rhinol Otol (Stuttg). 61(10):552-6.
(b) Petrus Camper – Wikipedia.

Further reading
● Steiner, Rudolf. (1921). “Goethe and the Evolution of Consciousness” (Ѻ), Lecture at Dornach, Aug 19.

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