Karl Ernst von Baer

German embryologist

• Born: February 29, 1792
• Birthplace: Piep, near Jerwen, Estonia
• Died: November 28, 1876
• Place of death: Dorpat, Estonia

Baer gained his greatest fame early in his career through his discovery of the mammalian egg and his contributions to the understanding of embryological development. In his later years, Baer would turn his attention to anthropological investigations, including the state of primitiveness of various races, and to geological studies, especially in Russia.

Early Life

During the mid-sixteenth century, an ancestor of Karl Ernst von Baer (behr) emigrated from Prussia to Livonia, and one of that ancestor’s descendants bought an estate in Estonia during the mid-seventeenth century. He was made a member of the Prussian nobility, and by the time of Karl’s father, Magnus Johann von Baer, the estate at Piep was of modest size. Karl’s father was trained in law and served as a public official. Karl’s parents were first cousins, and they had seven daughters and three sons. Because of the large size of the family, Karl was sent to live with his father’s childless brother and wife on a nearby estate. It was there that Karl began to cultivate his love of botany and natural history.

Baer entered medical school at the University of Dorpat in 1810 but apparently never planned on a medical career. Instead, upon graduation, he continued his studies in Berlin, Vienna, and finally Würzburg. There he studied under the anatomist Ignaz von Döllinger, a disciple of the German Romantic Friedrich Schelling, and was inspired to devote himself to the study of comparative embryology. In 1819, Baer finally received an appointment as an anatomy professor at Königsberg, where he stayed until 1834. That allowed him to marry Auguste von Medem, a resident of Königsberg, on January 1, 1820. They had five sons, of whom one died in childhood and a second of typhus at the age of twenty-one, and one daughter.

During Baer’s tenure at Königsberg, he established himself as a brilliant embryologist and made his initial discoveries of the mammalian egg. His initial contributions are found in the first two volumes of Karl Friedrich Burdach’s Die Physiologie als Erfahrungswissenschaft (1826-1828; physiology as empirical science). A small brochure entitled De ovi mammalium et hominis genesis epistola (1827; The Discovery of the Mammalian Egg , 1956) appeared at about the same time. In 1834, he left Königsberg for the Academy of Sciences in St. Petersburg, and in 1837 the still-unfinished second volume of his animal embryology was published, with the two volumes now entitled Über Entwickelungsgeschichte der Thiere (1828-1837; on the developmental history of animals). A portion of the missing material for this volume was published posthumously in 1888.

Life’s Work

While at the University of Würzburg, Baer was encouraged by Döllinger and Christian Heinrich Pander to continue the largely unknown work of Caspar Friedrich Wolff concerning the detailed development of the hen’s egg. Baer expanded that research to include a wide range of organisms, and the results of his studies virtually assured the epigeneticists of victory in their battle with the preformationists. He was the first to discover and describe the mammalian egg (first found in Burdach’s house dog), and he concluded that “every animal which springs from the coition of male and female is developed from an ovum, and none from a simple formative liquid.” This important theoretical statement, although based on German Naturphilosophie and rejected by later embryologists in the vitalistic terms understood by Baer, allowed for reproductive and embryological studies to continue on a doctrinally unified basis and hence permitted the development of comparative embryology as a discipline.

In addition to describing mammalian and other vertebrate ova, Baer described the developing embryo. One of his major conceptual innovations was that he could see the individual organism as a historical entity that underwent a developmental process. He thus examined organisms at various stages of development, and he was one of the first to describe the process in terms of the formation of germ layers and the gradual production of organs and body parts. Conducting research for the second volume of his monumental work, he examined and compared the developmental processes of different organisms.

In the process, Baer discovered the notochord (the flexible supportive rod ventral to the nerve chord, which is characteristic of all chordates) in the chicken embryo; explained the significance of the gill slits and gill arches, which Martin Rathke had earlier discovered in the embryo; and then explained the cause of the amnion formation. Finally, he described the development of the urogenital system, the formation of the lungs, the development of the digestive canal, and the formation of the nervous system. These findings are detailed and commented on in his pioneering Über Entwickelungsgeschichte der Thiere.

Baer is best known for his remarks in the fifth scholium of this work, in which he argued against a single scala naturae (chain of being); presented a parody of Jean-Baptiste de Monet, chevalier de Lamarck; rejected evolution in any form as well as the idea that embryos of higher animals pass through the adult forms of the lower animals; and proposed his own laws of individual development. His comparative embryology had led him to the same conclusions that Georges Cuvier’s comparative anatomy had produced, that is, that instead of a single chain of being, there were essentially four animal types. He further argued that comparative embryology actually provided better data than did comparative anatomy for classifying animals. Baer’s method for classifying organisms was based on the fact that all animal embryos begin as a single fertilized egg. According to Baer, they diverged immediately into one of four types of development. Vertebrate embryos can be distinguished from the annulate embryos (essentially worms), which in turn are different from the embryos of the mollusks, and all of which differ from the radiata (echinoderms).

In addition, Baer argued that the more general traits of the group of animals to which an embryo belongs appear earlier in individual development than the specialized characteristics; that the more general form always precedes a more specialized form; that every embryo of a given form, rather than passing through the stages of other forms, instead diverges more and more from them; and that, as a result, the embryo of a higher form never resembles the adult of lower animals but only the embryonic form of those animals. He concluded that development takes place from homogeneous and general to heterogeneous and special and that ontological development reflects divergence from other forms rather than parallelism or recapitulation. With this latter conclusion, he thus argued against Johann Meckel’s law of parallel development and against Ernst Haeckel’s biogenetic law of ontogeny recapitulating phylogeny.

With the publication of the second volume of Über Entwickelungsgeschichte der Thiere in 1837, Baer had transformed embryology into a modern laboratory science. Moreover, he had produced a theoretical framework that would greatly influence evolutionary thought even though he would strongly maintain a lifelong antievolutionary position. Charles Darwin, for example, used embryological evidence to support his theory and noted that he agreed with Baer’s view of divergence rather than the competing doctrine of recapitulation. Darwin also used Baer’s standard for judging an organism to be “higher” than another as being related to the degree of differentiation of parts and specialization of function.

By the time the second volume of his great embryological work was published, Baer had left Königsberg for reasons that are not well understood and had settled in St. Petersburg, working at the Academy of Sciences. In 1846, he took a position with the academy in comparative anatomy and physiology, a decision that was related to his long-term interest in anthropology. Under the academy’s auspices, he made a number of expeditions to such places as Novaya Zemlya, Lapland, the North Cape, and other regions of Russia as well as England and continental Europe. He collected specimens and made a number of geological discoveries. Although none of his work in these areas was as significant as his embryological achievements, he was instrumental in the founding of the Society of Geography and Ethnology of St. Petersburg and became a cofounder of the German Anthropological Society.

Baer retired from the academy in St. Petersburg in 1862 because of increasing problems with his vision and hearing. In 1867, he went to Dorpat, where he continued his studies and writing until November, 1876, when he died at the age of eighty-four.

Significance

Karl Ernst von Baer’s contributions to the fledgling science of embryology in the nineteenth century were immeasurable. Methodologically and conceptually he provided the basis for further research. However, apart from his empirical findings, little remains in modern biology of Baer’s embryology. His adherence to German Idealism and Naturphilosophie, including the use of vitalistic explanations in embryological development, and his fervent antievolutionary position caused many scientists in the latter part of the century to ignore him. Nevertheless, his contributions were viewed as monumental during his time. He published more than three hundred papers on topics ranging from embryology and entomology to anthropology, Russian fisheries, and the routes of Odysseus’s voyage. He was honored and respected by scientists throughout the world, and admired and loved for his loyalty and wit by his Estonian neighbors.

Bibliography

Baer, Karl Ernst von. Autobiography of Karl Ernst von Baer. Edited by Jane Oppenheimer. Translated by H. Schneider. Canton, Mass.: Science History, 1986. This relatively long autobiography was first published by the Estonian Knights in 1864 on the golden jubilee of Baer’s doctorate. Oppenheimer provides a very helpful preface.

‗‗‗‗‗‗‗. Correspondence: Karl Ernst von Baer (1792-1876), Anton Dohrn (1840-1909). Edited by Christiane Groeben, translated by Christiane Groeben and Jane M. Oppenheimer. Philadelphia: American Philosophical Society, 1993. A translation of the German correspondence between Baer and Dohrn, a zoologist who was influenced by Baer and Darwin. Includes an introduction by Oppenheimer, a Baer scholar.

Coleman, William. Biology in the Nineteenth Century: Problems of Form, Function, and Transformation. New York: Cambridge University Press, 1977. Chapter 3 provides an excellent context for Baer’s embryological work as it details the advances in cytology, explains the arguments between preformationists and epigeneticists, and describes the contributions Baer made to the understanding of ontogeny.

Gilbert, Scott F. A Conceptual History of Modern Embryology. Baltimore: Johns Hopkins University Press, 1994. Collection of essays exploring the concepts underlying modern embryology and evolutionary biology. Includes an essay about theories by Baer and other embryologists regarding induction, or the processes that determine the fate of embryonic cells and the development of tissues and organs.

Gould, Stephen Jay. “Abscheulich! (Atrocious!)” Natural History 109, no. 2 (March, 2000): 42. Describes the lives of Baer and two other scientists—Louis Agassiz and Ernst Haeckel—who became involved in the debate over Darwin’s theory of evolution. Explains the trio’s contributions to the debate.

Lovejoy, Arthur O. “Recent Criticism of the Darwinian Theory of Recapitulation: Its Grounds and Its Initiator.” In Forerunners of Darwin, 1745-1859, edited by Bentley Glass et al. Baltimore: Johns Hopkins University Press, 1968. Lovejoy explains why so many misread Baer. Describes Baer’s four embryological laws; examines Darwin’s misreading of Baer and Baer’s fallacies in his criticism of Darwin’s theory.

Oppenheimer, Jane M. “An Embryological Enigma in the Origin of Species.” In Forerunners of Darwin, 1745-1859, edited by Bentley Glass et al. Baltimore: Johns Hopkins University Press, 1968. Oppenheimer explores the professional relationship between Darwin and Baer. She examines the various ideas that each developed independently of the other and the diverse ways in which each incorporated these ideas into a total system. Provides an understanding of why Darwin used many of Baer’s findings while rejecting his conclusion, and why Baer was unable to support Darwin’s evolutionary position.

Ospovat, Dov. “The Influence of Karl Ernst von Baer’s Embryology, 1828-1859.” Journal of the History of Biology 9 (Spring, 1976): 1-28. Discusses the degree of influence that Baer’s embryological explanations had during his life, especially in terms of their ability to dislodge the earlier theory of recapitulation. Clarifies the content of Baer’s theories and shows the similarities and differences to other theories then available. Ospovat also explains why he disagrees with some of the Baerean scholarship, including the articles by Oppenheimer and Lovejoy cited above.

Winsor, Mary P. Starfish, Jellyfish, and the Order of Life: Issues in Nineteenth Century Science. New Haven, Conn.: Yale University Press, 1976. Although this book is not specifically about Baer, it is concerned with the issues and debates that surrounded his work and the work of other embryologists, comparative anatomists, taxonomists, and proponents of evolution. For that reason, it provides the scientific and philosophical context for understanding Baer.