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Karl Ernst Von Baer

Von Baer: bibliographical excerpts

"Karl Ernst von Baer (1792-1876) was a paragon of nineteenth-century science (Raikov, 1968). After studying with Burdach in dorpat and with Dollinger in Wurzburg, he received a professorship at Konigsberg in 1819. There he published the first part of his Entwickelungsgeschichte der Thiere in 1828 and reported his discovery of the mammalian ovum in 1827. In 1834 he gave up embryology and moved to St. Petersburg. This sudden decision recalls Rossini's abandonment of opera at the height of his fame and may have had a similar cause: nervous breakdown and the threat of ill health. In Russia, von Baer led expeditions to Novaya Zemlya and the Caspian Sea, founded Russian anthropology, made notable advances in ecology, established the law relating erosion of river banks to the earth's rotation, and, at the end of his long life, wrote some essays attacking the new Darwinian theory. ... His intransigent opposition to recapitulation arose more from a general philosophy than from his observations on the embryology of the chick. Von Baer devotes his fifth scholium to an attack on recapitulation..." (Gould, S.J. (1977) Ontegeny and Phylogeny. Cambridge: Belknap Press. p. 52-3)

"Yet von Baer had achieved more of the victory than modesty allowed him to state, for he had posited a general law of all biological development and, through it, thought he had glimpsed the essence of all development (Entwicklung): the homogenous, coursely structured, general, and potential develops into the heterochronous, finely built, special and determined. This law of differentiation is much more than a postulate brought forth in the fifth scholium to counter recapitulation; it is the law of biological development, the single tendency of all change. This law of differentiation is the unifying theme of von Baer's entire work." (Gould, S.J. (1977) Ontegeny and Phylogeny. Cambridge: Belknap Press. p. 61)

"Baer, who was one of those most active in inducing Pander to make his investigations, and who retained the liveliest interest in them after his departure from Wurzburg, began his own much more comprehensive researches in 1819, and nine years later published, as the fruit of these researches, a work on "The History of the Evolution of Animals," which even now is generally and rightly considered the most important and valuable contribution to embryological literature. This book, a true model of careful, experimental investigation, combined with ingenious philosophical speculation, appeared in two parts; the first in the year 1828, the second in 1837. It is the firm foundation on which the whole history of the evolution of the individual rests to this day, and so far surpasses its predessors, including Pander's outline, that, next to the labours of Wolff, it must be regarded as the most important basis of modern Ontogeny. As Baer, who died at Dorpat in November, 1876, was one of the greatest naturalists of our century, and has exerted a most important influence on other branches of Biology also, it may be of interest to give some account of the life of this extraordinary man. Karl Ernst Baer was born in 1792, in Esthonia, on the little estate of Piep, which his father owned. He studied at Dorpat from 1810 to 1814, and then went to Wurzburg, where Dollinger not only initiated his in Comparative Anatomy and Ontogeny, but also exercised over him, by his own interest in philosophical studies, a highly stimulating influence." (Haeckel, E (1897) The Evolution of Man: A Popular Exposition of the Principle Points of Human Ontogeny and Phylogeny, vols. 1 and 2: Appleton, New York p. 53-54)

"Karl Ernst von Baer (1792-1876) directly examined the physiological and anatomical development of embryos and fetuses in many different species of mammals, birds, fishes, and invertebrates, and examined them more intensively than possibly any other scientist before of since his time. He published his observations--and his reflections on his observations--in two volumes of his big book, Ueber Entwickelungsgeschichte der Thiere, the first volume being published in 1828 and the second in 1837. Von Baer's systematic observations, and the laws of individual development that he correctly generalized from them, had an overwhelming significance in that they gave the necessary impetus to the beginning science of embryology and put an end to the preformance--epigenesis debate. Von Baer's work also had a convoluted influence on Charles Darwin's formulation of his theory of evolution and Ernst Haeckel's biogenetic law that said (incorrectly) that ontogeny recapitulates phylogeny. ....Von Baer's observations signaled the end of the epigenesis--preformation debate because he observed over and over again that all of the various parts and functions of the embryo and fetus arise successively (i.e. epigenetically) during the course of embryonic and fetal development in all of the various species he observed. Von Baer is very specific on this point, stating that "All is transformation, nother is development de novo" (translated by Oppenheimer, 1967, from von Baer, 1828, p. 156). For example, von Baer said that when nerves are formed there was not an empty space in the tissue beforehand but that nerves differentiated out of what was formerly homogenous tissue. He began his observations at the earliest stages of development when the organism is composed of the initial germ layers, from which arise all of the various distinctive components of the adult animal." (Gottlieb, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 6)

"Important as these and many other discoveries of Baer's were in the Ontogeny of Vertebrates, yet the great importance of his researches rested especially on the fact that he was the first to apply the comparative method to the study of the evolution. It was, of course, the Ontogeny of Vertebrates, and principally of Birds and Fishes, that Baer first and especially investigates. Yet he by no means limited himself to these; for he included various Invertebrates in his investigations. The most general result of these comparative embryological researches was the Baer assumed four totally diferent courses of evolution for the four principal groups of the animal kingdom. These four chief groups, or types, which at that time had just begun to be distinguished, in consequence of George Cuvier's researches in Comparative Anatomy, are (1) Vertebrates (Vertebrata); (2) Articulated animals (Arthropoda); (3) Soft-bodied animals (Mollusca); and (4) the lower animals, which at that time were all erroneously grouped under the term Radiata. Cuvier, in the year 1816, demonstrated for the first time that these four groups of the animal kingdom show very essential and typical distinctions in their whole inner structure, and in the arrangement and position of the organic systems; that, on the other hand, the internal structure of all animals of one type, for example, of all Vertebrates, is essentially similar, notwithstanding the great variety of outward forms. Baer, however, independently and almost simultaneously, furnished proof that the four groups develop from the egg by entirely different processes, and further, that the order of the series of embryonic forms in the course of evolution is from the very beginning identical in all animals of the same type, but, on the other hand, different in those of different types. Up to that time, in making a classification of the animal kingdom, an endeavor had always been made to arrange all animals, from the lowest to the highest, from the infusoria to man, in a single connected series of forms; and the false idea had always been maintained, that there was a single unbroken gradation of development from the lowest animal to the highest. Cuvier and Baer proved that this conception is totally erroneous,--and that, on the contrary, there are four wholly distinct types of animals, which must be distinquished not only as to their anatomical structure, but also as to their embryonic evolution." (Haeckel, E (1897) The Evolution of Man: A Popular Exposition of the Principle Points of Human Ontogeny and Phylogeny, vols. 1 and 2: Appleton, New York p. 56-57)

[quoting von Baer] " 'The grade of development ...of an animal body consists of the greater or lesser extent of heterogeneity in the parts that compose it ... The more homogenous ... the entire mass of the body, the lower the state of development. We have reached a higher state if nerve and muscle, blood, and cell-material ... are sharply differentiated. The more different they are, the more developed the animal. (p.207)' From this view of development, recapitulation cannot possibly occur. the embryonic vertebrate, at every stage, is an undeveloped and imperfect vertebrate; if can represent no adult animal whatever. Embryology is differentiation, not a climb up the ladder of perfection. 'The vertebrate embryo is, at the beginning, already a vertebrate; at no time is it identicle with an invertebrate animal. An adult animal possessing the vertebrate type and exhibiting as little histological and morphological differentiation as the embryos of vertebrates is not known. Thus, is their development, the embryos of vertebrates pass through no (known) adult stage of another animal.' On this basis, von Baer enunciates his famous laws of development, the epitome of his contribution (and probably the most important words in the history of embryology); '1. The general features of a large group of animals appear earlier in the embryo than the special features. 2. Less general characters are developed from the most general, and so forth, until finally the most specialized appear. 3. Each embryo of a given species, instead of passing through the stages of other animals, departs more and more from them. 4. Fundamentally therefore, the embryo of a higher animal is never like (the adult of) a lower animal, but only like its embryo. (p.224)." (Gould, S.J. (1977) Ontegeny and Phylogeny. Cambridge: Belknap Press. p. 55-6)

"Since evolutionary classification depends upon the identification of homologies linking diverse animals to common ancestors, von Baer's laws state a basic principle in phyletic reconstruction: "Community in embryonic structure reveals community of descent" (1859, p. 449). (Gould, S.J. (1977) Ontegeny and Phylogeny. Cambridge: Belknap Press. p. 71)

"Von Baer had appended a statement to his fourth law: "It is only because the least developed animal forms are but little removed from the embryonic condition that they retain a certain similarity with the embyros of higher animal forms" (1828, p. 224). To von Baer, this was a mere corollary added only to dispel a recapitulatory interpretation of his beliefs: the embryo repeats no adult stage, but a "low" adult may resemble its own embryo simply because it fails to differentiate much further." (Gould, S.J. (1977) Ontegeny and Phylogeny. Cambridge: Belknap Press. p. 72)



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