Haeckel, Ernst

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(b. Potsdam, Germany, 16 February 1834; d. Jena, Germany, 9 August 1919)

zoology, embryology, evolution. For the original article on Haeckel see DSB, vol. 6.

Haeckel scholarship has flourished in the decades since the original DSB article was written. Recent assessments have expanded scholars’ understanding of Haeckel’s personality, his animal morphology, his pioneering visual representations of evolutionary concepts, and his ideas on human evolution. Greater attention to popularization among historians of science and greater attention to science among general historians have yielded new assessments of his place in European culture, though consensus remains elusive.

Personality Development . It is impossible to understand Ernst Haeckel’s scientific career without understanding his personality. He was by turns combative and loving, passionate and analytical, and he erected few boundaries between these aspects of his personality. He loved his cousin and first wife, Anna Sethe Haeckel, intensely, and her death on his thirtieth birthday in 1864 deepened his preexisting alienation from traditional Christian beliefs into bitter opposition. His efforts to replace Christian thought and institutions with his own monistic philosophy, which erased the distinctions between spirit and matter, between life and afterlife, and between humans and other animals lent religious and political heat to his evolutionary writings, especially his more popular ones. He became one of the great controversialists of his time; like Thomas Henry Huxley, he embraced battle in public forums, especially over the appropriate roles of science and religion in modern society. Both within and beyond the scientific community, he never missed an opportunity to snipe at those whom he viewed as his enemies, and because he often clung dogmatically to his own ideas, over time he viewed more and more people (including most of his former zoology students) as opponents, or, as he often saw them, betrayers. At the same time, on certain scientific problems he adopted a remarkable analytical flexibility that allowed him to view the same issue (such as organic individuality or evolutionary tree-making) from multiple perspectives and, sometimes, to alter his views in the face of new evidence—an aspect of his thought that has been overshadowed by his dogmatism on philosophical issues.

Morphological Theory . Haeckel is known as one of Europe’s greatest apostles of evolution, but his perspective drew as much from German scientific and philosophical roots as from Charles Darwin. The foundation of Haeckel’s scientific work is his Generelle Morphologie(1866), a difficult, two-volume monograph that sought to establish a new foundation for animal morphology. Although this work was deeply evolutionist and indebted to Darwin in its acceptance of common descent and selection, it also developed ideas that owed little to Darwinian evolution. Central to Haeckel’s morphology was his view of the complex nature of organic individuality, a critical problem for zoologists in the 1850s and early 1860s. Haeckel argued that the scientist should understand organic individuals from three independent perspectives: morphological, physiological, and genealogical. In the vertebrates, with which scientists are most familiar, these three aspects of individuality coincide, but this is not necessary; in many marine invertebrates (such as sponges or siphonophores), a physiological individual is actually formed by a community of morphologically distinct individuals, each of which performs different functions for the common whole, and none of which can survive without the others. Moreover, Haeckel argued, each of these kinds of individuality existed at different levels, with higher levels of individuality (such as the race) subsuming lower ones (such as the nation, the individual human, or the colonial organism), all the way down to the smallest level (the cell). Crucially, in discussing genealogical individuality he posited three levels—the individual as commonly understood, the species, and the phylum, each of which followed the same laws of development. Haeckel’s bio-genetic law, that ontogeny (individual development) recapitulates phylogeny (development of the species), depends crucially on the concept of levels and kinds of individuality. Although it would rapidly transform into a tool for evolutionary research, in its inception the biogenetic law is best understood as an outgrowth of Haeckel’s effort to solve the conundrum of organic individuality, combined with his commitment to the idea of universal development.

The Generelle Morphologie also incorporated Haeckel’s first efforts to found a new science of “promorphology,” which would analyze the geometry of organic forms to establish the fundamental possibilities that constrained their development. This impulse was strongly influenced by his studies of the radiolaria, a group of radially symmetrical but otherwise highly varied marine organisms. It also reveals other debts, both to his early mineralogical studies and to the Romantic tradition, especially as represented by Lorenz Oken and Carl Gustav Carus. Although Haeckel did not succeed in establishing promorphology as a basic biological science, it remained critical to his thinking throughout his life. His interest in nature’s symmetries would undergird much of his invertebrate systematics, especially of the radiolaria, and late in his life he would again stress the importance of the pro-morphological “foundational forms” (Grundformen) in his Systematische Phylogenie(3 vols., 1894–1896; Systematic phylogeny). Although he failed to gain a substantial following for promorphology among biologists, he did better among artists. His symmetrical images and his naturalistic theory of aesthetics, which resulted in his Kunstformen der Natur(1899; Art Forms in Nature, 1974), would have a strong influence on the Jugendstil movement in the decorative arts.

Representing Embryos and Ancestors . Haeckel is better known for two visual forms—the comparative embryological grid and the phylogenetic tree—than any particular piece of writing. In developing both, he brought into general usage two of the most important visual representations of evolutionary thought.

Perhaps his most enduring legacy has been a series of illustrations of vertebrate embryos depicting their similarity at the earliest stages of development and their increasing differentiation. The first version appeared in the initial edition of Natürliche Schöpfungsgeschichte(1868; The

History of Creation, 1875); Haeckel developed it in subsequent editions and in his Anthropogenie (1874; Evolution of Man, 1883), where it reached its most elaborated expression. This visual codification of comparative embryology has persisted across more than a century of biology textbooks as striking evidence of commonality of form and descent, long after the “biogenetic law” with which it was associated fell out of favor as a theoretical guide to research. In 1997 embryologist Michael K. Richardson, with others, published a series of photographs of embryos of the same species that Haeckel had used at the same developmental stages as those in the latter’s illustrations. These revealed that Haeckel must have edited his original forms substantially in order to draw out the similarities— to the point of distorting their truthfulness. Richardson’s work revived charges of fraud that had dogged Haeckel from the images’ first appearance in the early 1870s.

Recent historical work has situated these illustrations within the conventions of popular and professional illustration. Whereas idealized or schematized images have generally been accepted as having heuristic value in popular and educational forums before and after Haeckel, this approach has been less acceptable for evidentiary claims in professional research work. Haeckel’s illustrations attracted criticism not just because they were tendentious but also because his writing (and figures) lay at the boundaries of these two genres, where the rules of evidence were hazy. The controversy over the truthfulness of his pictures has distracted attention from their major achievement (arguably, the one that has made them endure): Haeckel redrew different embryos to the same scale and in the same position, which facilitated direct comparison of embryo types in a way that had never existed before. Thus, even as it typologized embryos more extensively than had been done previously, lending weight to charges of falsification of the visual record, Haeckel’s gridlike illustration offered a new step toward rendering comparative embryology practical.

Equally liminally placed between research and popularization were his visually striking phylogenetic trees. Unlike Darwin’s famous “branching tree” diagram in On the Origin of Species (1859), which looked little like a tree, Haeckel’s trees resembled productions of nature. His most famous tree, originally published in the Anthropogenie, encapsulated his progressive hierarchy through the thick oaklike trunk running from the ancestral Monera at the base to humans at the top. But like much of Haeckel’s thought, this represented just one of his perspectives. In fact, he experimented with numerous forms of trees, ranging from typographically dominated ones connecting taxonomic group names with straight lines to a variety of shrub- and kelp-like images in different efforts to convey simultaneously degrees of taxonomic similarity, levels of complexity, and historical emergence. One phylogenetic tree in the Generelle Morphologie places the genus “Homo” on a tiny branch in the upper-right-hand corner—a startling contrast to the more familiar oak tree image. Other trees, working at broader or lower taxonomic levels, do not include humans at all.

Humanity, Race, and Language . Although Haeckel’s original scientific investigations were confined to invertebrates, his influence lay in his broader evolutionary claims, especially about humans. Controversially at the time (though in concert with Darwin), he naturalized humans fully, arguing that they were different only in degree from other animals, not in kind. Unlike Darwin, his species criteria did not emphasize interbreeding; using morphological and linguistic criteria, he derived twelve “species” of humans that derived from a single hypothetical prelinguistic Urmensch. In close interaction with the Jena linguist August Schleicher (whose evolutionary trees of language relationships were inspired by his Haeckel-recommended reading of Darwin’s On the Origin of Species), Haeckel developed the idea of a phylogenetic tree of human racial types in which language differences (along with the physical features of hair texture) played the most critical role as distinguishing criteria. This tree combined history and progress into a single vertical scale. It both embraced and reinforced the hierarchical racialism of his time, placing the “smooth-haired” Australian aboriginals at the bottom of his scale, followed by the “woolly-haired” Hottentots and Papuans. “Indo-Germans,” of course, rested at the top, with “Semites” (later “Hamosemites”) just behind them (suggesting that Haeckel, though sharing the ethnocentrism of his class, was not the virulent anti-Semite that some have supposed). Numerous details of this tree changed over time as new evidence appeared, reminding us that it was not purely a figment of preexisting racial assumptions. Yet Haeckel’s characterization of races as different “species” lent his authority to post-Darwinian racism.

Haeckel’s Influence . Haeckel’s magnetic and effusive presence and his passionate dedication to the causes of evolution, morphology, and monism have led recent historians to seek to assess his influence, with differing results. He attracted thousands of students to his lectures at the tiny University of Jena, yet few became zoologists, and nearly all of those who did would later part company with him over major features of his system. In contrast to his close friend and colleague, Carl Gegenbaur, who developed a loyal school, Haeckel was more successful in supporting those in other fields who shared his general evolutionary views than in sustaining a scientific research program. Although he gained an early reputation as a serious invertebrate zoologist and systematist, his massive synthetic theoretical works, the Generelle Morphologie and the Systematische Phylogenie, attracted far fewer adherents than he had hoped. By contrast, his more popular books went through many editions, which he continually revised, and were translated into other languages. The Natürliche Schöpfungsgeschichte, based on his Jena lecture course, went through eleven German editions between 1868 and its final version in 1911, with translations into English, French, Swedish, and Russian; the Anthropogenie had six editions (1874–1910), plus translations into English, French, Bulgarian, and Turkish; and Die Welträthsel(1899; Riddles of the universe, most unfortunately mis-titled Riddle of the Universe in its English-language editions, which began in 1900) had at least nine editions (though some were unchanged); as a whole text or as selections, it has been translated into English, Spanish, Chinese, Japanese, Russian, Hungarian, Uighur, Hebrew, and Hindi.

Haeckel’s “popular” science did not exactly fall into the better-established popular genres of anecdotal natural history, dialogues for well-bred ladies, or the emerging popular science writings for mass-circulation periodicals (though later in life he would publish some accounts of his travel to exotic places, engaging in one of the most popular nonfiction genres). His most successful books contained often dense scientific and philosophical argumentation and were seeded with neologisms that the serious reader had to track closely to follow the argument—for every new term that gained entry into the common vocabulary, such as ontogeny, phylogeny, and ecology, Haeckel produced a handful that failed to become accepted. Thus, as successful as Haeckel’s popular works were, these remained at the technical end of the popular spectrum; indeed, his ideas themselves were subject to further simplification and clarification by mass-audience writers such as Wilhelm Boelsche and Carus Sterne (the pen name of Ernst Krause).

Haeckel’s standing as a scientist lent particular weight to his pronouncements in some circles, and some historians have identified him as a leading proponent of eugenics, racism, and anti-Semitism and as the source for both the ideology of Fascism and German National Socialism. There is little doubt that he believed in a hierarchy of human types and found eugenics a logical step for a rational society following evolutionary principles, but he shared these views with many—perhaps most— scientifically educated Europeans of his time, just as he shared his German nationalism with many contemporaries. Scholars divide over the significance of his pronouncements on these issues, and therefore over his role as a shaper of German and European cultural and political attitudes. His primary commitments were always to evolution, morphology, and monism, areas in which his influence is uncontested.


The reunification of Germany has eased access to Haeckel’s voluminous notes and correspondence, held at the Ernst-Haeckel-Haus of the University of Jena. No comprehensive bibliography of Haeckel’s published writings, including translations and posthumous reprints, exists. The most complete bibliography of his original German writings remains that of Thilo Krumbach (1919), reprinted in Heberer (1968).

Breidbach, Olaf. Visions of Nature: The Art and Science of Ernst Haeckel. Munich, Germany; and London: Prestel, 2006.

Di Gregorio, Mario A. From Here to Eternity: Ernst Haeckel and Scientific Faith. Göttingen, Germany: Vandenhoeck and Ruprecht, 2005.

Gasman, Daniel. Haeckel’s Monism and the Birth of Fascist Ideology. New York: P. Lang, 1998.

Heberer, Gerhard, ed., Der gerechtfertigte Haeckel. Einblicke in seine Schriften aus Anlaæ des Erscheinens seines Hauptwerkes “Generelle Morphologie der Organismen” vor 100 Jahren. Stuttgart, Germany: Gustav Fischer Verlag, 1968. Includes selections from Haeckel’s main writings as well as biographical and autobiographical sketches and the most complete bibliography of Haeckel’s work, reprinted from Thilo Krumbach 1919 (below).

Hopwood, Nick. “Pictures of Evolution and Charges of Fraud: Ernst Haeckel’s Embryological Illustrations.” Isis 97 (2006): 260–301.

Kockerbeck, Christoph. Ernst Haeckels “Kunstformen der Natur” und ihr Einfluss auf die deutsche bildende Kunst der Jahrhundertwende. Frankfurt am Main, Germany: P. Lang, 1986.

Krausse, Erika. Ernst Haeckel. 2nd ed. Leipzig, Germany: Teubner, 1987. A brief but thorough biography.

Krumbach, Thilo. “Die Schriften Ernst Haeckels.” Die Naturwissenschaften 7 (1919): 961–966. The most complete available listing of his works, including popular and newspaper articles.

Lebrun, David. Proteus: A Nineteenth-Century Vision. A film by David Lebrun. Brooklyn, NY: First Run-Icarus Films, 2004. An outstanding film on Haeckel’s efforts to unify science and art, with particular attention to the radiolaria.

May, Walther. Ernst Haeckel: Versuch einer Chronik seines Lebens und Wirkens. Leipzig, Germany: Barth, 1909. Contains a fairly complete bibliography of Haeckel’s writings and an invaluable listing of biographical articles and books on Haeckel and “Haeckelismus” up to 1909.

Nyhart, Lynn K. Biology Takes Form: Animal Morphology and the German Universities, 1800–1900. Chicago: University of Chicago Press, 1995. Places Haeckel’s program of evolutionary morphology in the intellectual, institutional, and disciplinary context of the German universities.

Richards, Robert J. The Tragic Sense of Life: Ernst Haeckel and the Struggle over Evolutionary Thought. Chicago: University of Chicago Press, forthcoming.

Richardson, Michael K., and Gerhard Keuck. “Haeckel’s ABC of Evolution and Development.” Biological Reviews 77 (2002): 495–528. Reviews recent scientific and historical assessments of Haeckel’s embryological arguments and illustrations and their utility for phylogenetic reasoning. Contains an extensive bibliography.

Rinard, Ruth. “The Problem of the Organic Individual: Ernst Haeckel and the Development of the Biogenetic Law.” Journal of the History of Biology 14 (1981): 249–276.

Weikart, Richard. From Darwin to Hitler: Evolutionary Ethics, Eugenics, and Racism in Germany. New York: Palgrave Macmillan, 2004.

Lynn K. Nyhart