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Weisman, August
Weisman, August S Müller-Wille, University of Exeter, Exeter, UK © 2013 Elsevier Inc. All rights reserved.
Glossary Albuminate Protein resulting from action of acid or alkali on albumins, a class of water-soluble monomeric proteins. Germ plasm The total cytoplasm, including the nucleoplasm, of germ cell lineages.
August Friedrich Leopold Weismann – in publications, he would only use his first Christian name – was born on 17 January 1834 in Frankfurt am Main (Figure 1). He was the first of four children of Johann August Weismann (1804–80), who taught classics and literature at a local secondary school. His mother Elise Eleonore (née Lübbren, 1803–50) came from a respectable family as well, and Weismann received a thor ough musical and artistic education from early on. In addition, keeping a herbarium, as well as rearing and collecting butter flies, kept the young boy busy. This interest should gain the upper hand, when in 1852 he enrolled at the University of Göttingen to study medicine. He took courses with the chemist Friedrich Wöhler (1800–82), who had pioneered the synthesis of organic compounds such as urea and oxalic acid, and with the physiologist Rudolf Wagner (1805–64), known mainly for his work on the nucleus of the oocyte and on nerve ganglia. Graduating in 1857 with a thesis on the origin of hippuric acid in the urine of herbivores, Weismann moved to Rostock to work as clinical and later chemical research assistant. He soon discovered, however, that meticulous chemical experiments were not to his liking and moved on to Vienna (1858), Paris (1860), and Gießen (1861) to complete his biological studies. Intermittently, he made an earning as phy sician, first in his hometown, then in the army of the Grand-Duchy of Baden, which supported the Austrian side in the Austro-Piedmontese War, and finally as personal physician of Archduke Stephen Francis Victor of Austria (1817–67). Although his trips brought him into contact with some of the leading contemporary experimental physiologists, such as Carl Ludwig (1816–95) in Vienna and Claude Bernard (1813–78) in Paris, Weismann’s early publications show a decisive incli nation toward more descriptive, anatomical, histological, and embryological work. In 1863, he completed his second thesis, the Habiliation, at the medical faculty of the University of Freiburg im Breisgau. His thesis dealt with insect metamorpho sis and qualified him to lecture in the subjects zoology and comparative anatomy. After a period of teaching these subjects at the University of Freiberg, he was offered a professorship in 1867, when the chair in zoology was moved to the philosophi cal faculty. He retained this position, despite several offers from other universities such as Breslau, Bonn, and Munich, until 1912, 2 years before his death. In 1864, Weismann developed a retinal disease, which made further microscopic studies impossible until 1874, and then again from 1884 to the end of his life. His wife Maria Dorothea, née Gruber, whom he had
Brenner’s Encyclopedia of Genetics, 2nd edition, Volume 7
Pangenesis A theory of inheritance that assumes that the hereditary substance is made up of material deriving from every part of the body. Soma The totality of cells that derive from a zygote through mitotic cell divisions.
married in 1867, became a close research collaborator and thus was crucial in compensating his loss of eyesight. Maria Dorthea died in 1886, and Weismann married again in 1895. Contemporaries considered Weismann as one of the chief protagonists and popularizers of Darwinism, alongside Ernst Haeckel (1834–1919). The majority of Weismann’s publica tions, including his inaugural lecture, were indeed dedicated to subjects of evolutionary theory, and Charles Darwin (1809–82) contributed a preface to an English translation of a collection of Weismann’s evolutionary essays in 1882. In hindsight, however, Weismann stands out as a crucial figure in what Frederick Churchill has called a ‘watershed’ moment in the science of heredity. In the wake of Charles Darwin’s and Francis Galton’s theories of heredity, cell theory moved into the center of considerations of heredity during the 1880s, while phylogeny and ontogeny increasingly came to be viewed as discrete processes. Weismann contributed to these develop ments by putting forward bold postulates and seeking to confirm them through meticulous cytological observations, and occasionally experiments. Experimental organisms included various species of butterflies, but also hydrozoa, daphnids, ostracods, and echinoderms, that were reared in a specially constructed water basin. Weismann developed his theory of heredity in his essay on the continuity of germ plasm (Die Kontinuität des Keimplasmas als Grundlage einer Theorie der Vererbung, 1885) and in his extended work The Germ-Plasm: A Theory of Heredity (1892). Like Carl Wilhelm von Nägeli (1817–91) before him, Weismann distinguished between ‘germ plasm’, ‘hereditary plasm’, or ‘idioplasm’, on the one hand, and the body plasm, or ‘soma’, on the other hand. The former ensured the continu ity of inheritance through the generations; the latter was the origin of the cells of the individual developing organism. But whereas Nägeli, in addition to this functional distinction, asserted that the germ plasm consisted of specific ‘albuminates’, Weismann – like many of his contemporaries such as Hugo de Vries (1848–1935) – subscribed to the assumption that the germ plasm was essentially composed of the same organic molecules – ‘biophores’ as he called them – that were also active in the cytoplasm constituting the soma. However, for Weismann – now in contrast to de Vries, but in accordance with Nägeli – the makeup of the germ plasm was a complicated edifice, a ‘fixed architecture, which has been transmitted his torically’, and that, according to his theory, integrated the ‘biophors’ into ‘determinants’, the determinants into ‘ids’, and
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Weisman, August
Figure 1 August Weismann (1834–1914). Source: Wikimedia Commons.
the ids into ‘idants’. One can roughly equate the last of these entities with what we now call chromosomes. Weismann thought that the biophors formed a depository in the nucleus, and that parts of this depository could, in the course of ontogenesis, selectively diffuse into the cytoplasm, where they would be used as material for the construction of differentiated cells. In Weismann’s theory, the germ plasm was deployed in a regular fashion in the course of development from the egg to the adult organism. At the same time, the complete historical architecture of the germ plasm remained spatially and physiologically separated in the germ line from the differentiating body and was therefore unaffected by its modifications. The most important consequence of this theory, from today’s point of view, was the rejection of any kind of causal feedback from differentiated body cells into germ cells, and hence the elimination of any possibility for an inheritance of acquired characteristics. Darwin had still entertained both possibilities in his ‘preliminary hypothesis of pangenesis’, and many contemporaries of Weismann, including Haeckel, still regarded the inheritance of acquired characteristics as unpro blematic. Weismann tried to demonstrate its ineffectiveness in a series of mutilation experiments with rats. The voluminous literature on Weismann’s theory often overlooks the fact, however, that Weismann by no means
implied that the germ line was totally isolated from its envir onment. His experiments with butterflies, for example, took for granted such a direct – and directed – influence by the environ ment. Accordingly, Weismann assumed that heritable differences in the wing color of the butterfly Polyommatus phlaeas, whose home range extended from the north to the south of Europe, could be ascribed to the differences in climatic conditions and supply of nutrition, particularly to different regional temperatures. In his butterfly cultures, he thus worked with temperature stimuli and investigated whether he could experimentally induce the effects that in nature had been pro voked by environmental gradients or seasonal succession and had become fixed by selection. In addition, Weismann believed that the hereditary material was changed in its composition by recombination through sexual reproduction (what he called ‘amphimixis’) and processes of ‘germinal selection’, that is, differential reproduction of the organic components of the germ plasm. The idea that the hereditary material remains unaffected by the bodies that pass it on – subsequently referred to as ‘Weismann’s barrier’ – became one of the cornerstones of clas sical genetics and was also adopted in Francis Crick’s formulation of the ‘central dogma’ of molecular biology according to which no sequence information can be passed
Weisman, August on from proteins to DNA. In thus assessing Weismann’s contributions to the twentieth-century genetics, one should not overlook two important aspects of his theory of heredity that reveal its nineteenth-century origin. First, Weismann did not believe that the hereditary material consisted of a separate, chemical substance. It rather consisted of the same elementary units as the soma, namely, of biophores, which unlike genes possessed vital capacities. Second, Weismann believed that the hereditary material exhibited a complex, historically grown architecture, which prefigured its deployment in development, and was the result of phylogeny. Both of these assumptions would be rejected by early geneticists in the twentieth century, such as Carl Correns and Wilhelm Johannsen. The latter in particular liked to polemicize against the ‘morphological spirit’ that Weismann’s work still exemplified.
327
See also: Cell Determination; Cell Lineage; Chromosome; Crick, Francis Harry Compton; Germ Cell; Lamarck, Jean Baptiste.
Further Reading Churchill FB (1968) August Weismann and a break from tradition. Journal of the History of Biology 1: 91–112. Churchill FB (1987) From heredity theory to ‘Vererbung’: The transmission problem, 1850–1915. Isis 78: 337–364. Weismann A (1889–1892) Essays Upon Heredity and Kindred Biological Problems. Oxford: Clarendon Press. http://www.biodiversitylibrary.org/item/43243 (accessed April 2012). Weismann A (1893) The Germ-Plasm: A Theory of Heredity. New York: Scribner’s Sons. http://www.biodiversitylibrary.org/item/66760 (accessed April 2012). Winther RG (2001) August Weismann on germ-plasm variation. Journal of the History of Biology 34: 517–555.
Glossary Albuminate Protein resulting from action of acid or alkali on albumins, a class of water-soluble monomeric proteins. Germ plasm The total cytoplasm, including the nucleoplasm, of germ cell lineages.
August Friedrich Leopold Weismann – in publications, he would only use his first Christian name – was born on 17 January 1834 in Frankfurt am Main (Figure 1). He was the first of four children of Johann August Weismann (1804–80), who taught classics and literature at a local secondary school. His mother Elise Eleonore (née Lübbren, 1803–50) came from a respectable family as well, and Weismann received a thor ough musical and artistic education from early on. In addition, keeping a herbarium, as well as rearing and collecting butter flies, kept the young boy busy. This interest should gain the upper hand, when in 1852 he enrolled at the University of Göttingen to study medicine. He took courses with the chemist Friedrich Wöhler (1800–82), who had pioneered the synthesis of organic compounds such as urea and oxalic acid, and with the physiologist Rudolf Wagner (1805–64), known mainly for his work on the nucleus of the oocyte and on nerve ganglia. Graduating in 1857 with a thesis on the origin of hippuric acid in the urine of herbivores, Weismann moved to Rostock to work as clinical and later chemical research assistant. He soon discovered, however, that meticulous chemical experiments were not to his liking and moved on to Vienna (1858), Paris (1860), and Gießen (1861) to complete his biological studies. Intermittently, he made an earning as phy sician, first in his hometown, then in the army of the Grand-Duchy of Baden, which supported the Austrian side in the Austro-Piedmontese War, and finally as personal physician of Archduke Stephen Francis Victor of Austria (1817–67). Although his trips brought him into contact with some of the leading contemporary experimental physiologists, such as Carl Ludwig (1816–95) in Vienna and Claude Bernard (1813–78) in Paris, Weismann’s early publications show a decisive incli nation toward more descriptive, anatomical, histological, and embryological work. In 1863, he completed his second thesis, the Habiliation, at the medical faculty of the University of Freiburg im Breisgau. His thesis dealt with insect metamorpho sis and qualified him to lecture in the subjects zoology and comparative anatomy. After a period of teaching these subjects at the University of Freiberg, he was offered a professorship in 1867, when the chair in zoology was moved to the philosophi cal faculty. He retained this position, despite several offers from other universities such as Breslau, Bonn, and Munich, until 1912, 2 years before his death. In 1864, Weismann developed a retinal disease, which made further microscopic studies impossible until 1874, and then again from 1884 to the end of his life. His wife Maria Dorothea, née Gruber, whom he had
Brenner’s Encyclopedia of Genetics, 2nd edition, Volume 7
Pangenesis A theory of inheritance that assumes that the hereditary substance is made up of material deriving from every part of the body. Soma The totality of cells that derive from a zygote through mitotic cell divisions.
married in 1867, became a close research collaborator and thus was crucial in compensating his loss of eyesight. Maria Dorthea died in 1886, and Weismann married again in 1895. Contemporaries considered Weismann as one of the chief protagonists and popularizers of Darwinism, alongside Ernst Haeckel (1834–1919). The majority of Weismann’s publica tions, including his inaugural lecture, were indeed dedicated to subjects of evolutionary theory, and Charles Darwin (1809–82) contributed a preface to an English translation of a collection of Weismann’s evolutionary essays in 1882. In hindsight, however, Weismann stands out as a crucial figure in what Frederick Churchill has called a ‘watershed’ moment in the science of heredity. In the wake of Charles Darwin’s and Francis Galton’s theories of heredity, cell theory moved into the center of considerations of heredity during the 1880s, while phylogeny and ontogeny increasingly came to be viewed as discrete processes. Weismann contributed to these develop ments by putting forward bold postulates and seeking to confirm them through meticulous cytological observations, and occasionally experiments. Experimental organisms included various species of butterflies, but also hydrozoa, daphnids, ostracods, and echinoderms, that were reared in a specially constructed water basin. Weismann developed his theory of heredity in his essay on the continuity of germ plasm (Die Kontinuität des Keimplasmas als Grundlage einer Theorie der Vererbung, 1885) and in his extended work The Germ-Plasm: A Theory of Heredity (1892). Like Carl Wilhelm von Nägeli (1817–91) before him, Weismann distinguished between ‘germ plasm’, ‘hereditary plasm’, or ‘idioplasm’, on the one hand, and the body plasm, or ‘soma’, on the other hand. The former ensured the continu ity of inheritance through the generations; the latter was the origin of the cells of the individual developing organism. But whereas Nägeli, in addition to this functional distinction, asserted that the germ plasm consisted of specific ‘albuminates’, Weismann – like many of his contemporaries such as Hugo de Vries (1848–1935) – subscribed to the assumption that the germ plasm was essentially composed of the same organic molecules – ‘biophores’ as he called them – that were also active in the cytoplasm constituting the soma. However, for Weismann – now in contrast to de Vries, but in accordance with Nägeli – the makeup of the germ plasm was a complicated edifice, a ‘fixed architecture, which has been transmitted his torically’, and that, according to his theory, integrated the ‘biophors’ into ‘determinants’, the determinants into ‘ids’, and
doi:10.1016/B978-0-12-374984-0.01691-0
325
326
Weisman, August
Figure 1 August Weismann (1834–1914). Source: Wikimedia Commons.
the ids into ‘idants’. One can roughly equate the last of these entities with what we now call chromosomes. Weismann thought that the biophors formed a depository in the nucleus, and that parts of this depository could, in the course of ontogenesis, selectively diffuse into the cytoplasm, where they would be used as material for the construction of differentiated cells. In Weismann’s theory, the germ plasm was deployed in a regular fashion in the course of development from the egg to the adult organism. At the same time, the complete historical architecture of the germ plasm remained spatially and physiologically separated in the germ line from the differentiating body and was therefore unaffected by its modifications. The most important consequence of this theory, from today’s point of view, was the rejection of any kind of causal feedback from differentiated body cells into germ cells, and hence the elimination of any possibility for an inheritance of acquired characteristics. Darwin had still entertained both possibilities in his ‘preliminary hypothesis of pangenesis’, and many contemporaries of Weismann, including Haeckel, still regarded the inheritance of acquired characteristics as unpro blematic. Weismann tried to demonstrate its ineffectiveness in a series of mutilation experiments with rats. The voluminous literature on Weismann’s theory often overlooks the fact, however, that Weismann by no means
implied that the germ line was totally isolated from its envir onment. His experiments with butterflies, for example, took for granted such a direct – and directed – influence by the environ ment. Accordingly, Weismann assumed that heritable differences in the wing color of the butterfly Polyommatus phlaeas, whose home range extended from the north to the south of Europe, could be ascribed to the differences in climatic conditions and supply of nutrition, particularly to different regional temperatures. In his butterfly cultures, he thus worked with temperature stimuli and investigated whether he could experimentally induce the effects that in nature had been pro voked by environmental gradients or seasonal succession and had become fixed by selection. In addition, Weismann believed that the hereditary material was changed in its composition by recombination through sexual reproduction (what he called ‘amphimixis’) and processes of ‘germinal selection’, that is, differential reproduction of the organic components of the germ plasm. The idea that the hereditary material remains unaffected by the bodies that pass it on – subsequently referred to as ‘Weismann’s barrier’ – became one of the cornerstones of clas sical genetics and was also adopted in Francis Crick’s formulation of the ‘central dogma’ of molecular biology according to which no sequence information can be passed
Weisman, August on from proteins to DNA. In thus assessing Weismann’s contributions to the twentieth-century genetics, one should not overlook two important aspects of his theory of heredity that reveal its nineteenth-century origin. First, Weismann did not believe that the hereditary material consisted of a separate, chemical substance. It rather consisted of the same elementary units as the soma, namely, of biophores, which unlike genes possessed vital capacities. Second, Weismann believed that the hereditary material exhibited a complex, historically grown architecture, which prefigured its deployment in development, and was the result of phylogeny. Both of these assumptions would be rejected by early geneticists in the twentieth century, such as Carl Correns and Wilhelm Johannsen. The latter in particular liked to polemicize against the ‘morphological spirit’ that Weismann’s work still exemplified.
327
See also: Cell Determination; Cell Lineage; Chromosome; Crick, Francis Harry Compton; Germ Cell; Lamarck, Jean Baptiste.
Further Reading Churchill FB (1968) August Weismann and a break from tradition. Journal of the History of Biology 1: 91–112. Churchill FB (1987) From heredity theory to ‘Vererbung’: The transmission problem, 1850–1915. Isis 78: 337–364. Weismann A (1889–1892) Essays Upon Heredity and Kindred Biological Problems. Oxford: Clarendon Press. http://www.biodiversitylibrary.org/item/43243 (accessed April 2012). Weismann A (1893) The Germ-Plasm: A Theory of Heredity. New York: Scribner’s Sons. http://www.biodiversitylibrary.org/item/66760 (accessed April 2012). Winther RG (2001) August Weismann on germ-plasm variation. Journal of the History of Biology 34: 517–555.