August Weismann
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Friedrich Leopold August Weismann (b. January 17, 1834 in Frankfurt am Main; d. November 5, 1914 in Freiburg im Breisgau) was a German biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin.
Weismann advocated the germ plasm theory, stating that a multicellular organism consists of germ cells that pass on hereditary information, and somatic cells that perform body functions. The germ cells are not affected by anything the body learns or any ability it acquires during its life, and cannot pass this information on to the next generation, this is called the Weismann barrier. This eventually led to the rediscovery of Gregor Mendel's work, though Weismann never accepted Mendelism. Weismann also conducted one of the seminal experiments disproving Lamarckism. By cutting the tails off mice for twenty-one generations and seeing that the twenty-second generation still had tails, Weismann demonstrated that the injury was not passed on to the offspring and thus that acquired characteristics are not heritable (see Neo-Darwinism).[1]
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[edit] Life
[edit] Youth and studies
Weismann was born a son of high school teacher Johann (Jean) Konrad Weismann (1804-1880), a graduate of ancient languages and theology, and his wife Elise (1803-1850), née Lübbren, the daughter of the county councillor and mayor von Stade, on January 17, 1834 in Frankfurt am Main. He had a typical 19th century bourgeois education, receiving music lessons from the age of four, and drafting and painting lessons from Jakob Becker (1810-1872) at the Frankfurter Städelsche Institut from the age of 14. His piano teacher was a devoted butterfly collector and introduced him to the collecting of imagos and caterpillars. But studying Natural Sciences was out of the question due to the cost involved and limited job prospects. A friend of the family, Friedrich Wöhler (1800-1882), recommended studying medicine. A foundation from the inheritance of Weismann's mother allowed him to take up studies in Göttingen. Following his graduation in 1856, he wrote his dissertation on the synthesis of hippuric acid in the human body.
[edit] Professional life
Immediately after university, Weismann took on a post as assistant at the Städtische Klinik (city clinic) in Rostock. Weismann successfully submitted two manuscripts, one about hippuric acid in herbivores, and one about the salt content of the Baltic Sea, and won two prizes. The paper about the salt content dissuaded him from becoming a chemist, since he felt himself lacking in apothecarial accuracy.
After a study visit to see Vienna's museums and clinics, he graduated as a medical doctor and settled in Frankfurt. During the war between Austria, France and Italy in 1859, he became Chief Medical Officer in the military. During a leave from duty, he walked Northern Italy and Tyrol. After a sabbatical in Paris, he worked with Rudolf Leuckart (1822-1898) at the University of Gießen, nonetheless to return to Frankfurt as personal physician to the banished Grand Duke Stephan of Austria, at Schaumburg Castle (from 1861 to 1863).
From 1863, he was lecturer, from 1865 professor and from 1873 to 1912 Ordinarius for zoology and director of the zoological institute at Albert Ludwig University of Freiburg in Breisgau.
[edit] Contributions to evolutionary biology
At the beginning of Weismann's preoccupation with evolutionary theory is his grappling with Christian creationism as a possible alternative. In his work Über die Berechtigung der Darwin'schen Theorie (On the justification of the Darwinian theory) he compares creationism and evolutionary theory, concluding that many biological facts can be seamlessly accommodated within evolutionary theory, but remain puzzling if considered the result of acts of creation.
After this work, Weismann accepts evolution as a fact on a par with the fundamental assumptions of astronomy (e.g. Heliocentrism). Weismann's position towards mechanism of inheritance and its role for evolution changed during his life. Three periods can be distinguished.
[edit] 1868-1881/82
Weismann starts out believing, like many other 19th century scientists, among them Charles Darwin, that the observed variability of individuals of one species is due to the inheritance of sports (Darwin's term). He believed, as written in 1876, that transmutation of species is directly due to the influence of environment. He also wrote, "if every variation is regarded as a reaction (sic) of the organism to external conditions, as a deviation of the inherited line of development, it follows that no evolution can occur without a change of the environment". (Note that this is close to the Modern use of the concept that changes in the environment can mediate selective pressures on a population, in all but very few cases leading to evolutionary change.) Weismann also used the classic Lamarckian metaphor of use and disuse of an organ.
[edit] 1882-1895
Weismann's first of the inheritance of acquired traits was in a lecture in 1883, titled "On inheritance" ("Über die Vererbung"). Again, as in his treatise on creation vs. evolution, he attempts to explain individual examples with either theory. For instance, the existence of non-reproductive castes of ants, such as workers and soldiers, cannot be explained by inheritance of acquired characters. Germ plasm theory, on the other hand, does so effortlessly.
Even though Weismann could explain Darwin's original examples for "use and disuse", such as the tendency to have degenerate wings and stronger feet in domesticated waterfowl, he did not convert his contemporaries.
[edit] 1896-1910
Weismann worked on the embryology of sea urchin eggs, and in the course of this observed different kinds of cell division, namely equatorial division and reductional division, terms he coined (Äquatorialteilung and Reduktionsteilung respectively).
His germ plasm theory states that multicellular organisms consist of germ cells containing heritable information, and somatic cells that carry out ordinary bodily functions.
The germ cells are influenced neither by environmental influences nor by learning or morphological changes that happen during the lifetime of an organism, and so this information is lost after each generation. This discovery eventually led to the rediscovery of Gregor Mendels work.
[edit] Some written work
- Über die Berechtigung der Darwin'schen Theorie. Leipzig 1868
- Über den Einfluß der Isolierung auf die Artbildung. Jena 1872
- Studien zur Descendenztheorie: II. Ueber die letzten Ursachen der Transmutationen. Leipzig 1876
- Die Continuität des Keimplasmas als Grundlage einer Theorie der Vererbung. Jena 1885
- Zur Frage nach der Vererbung erworbener Eigenschaften. In: Biol. Zbl. 6 (1886):33-48
- Über die Zahl der Richtungskörper und über ihre Bedeutung für die Vererbung. Jena 1887
- Das Keimplasma - eine Theorie der Vererbung. Jena 1882
- Aufsätze über Vererbung und angewandet biologische Fragen. Jena 1892
- Die Allmacht der Naturzüchtung: eine Erwiderung an Herbert Spencer. Jena 1893
- Vorträge über Deszendenztheorie. 2 Bde. 1902
[edit] Literature
- Rolf Löther: Wegbereiter der Genetik: Gregor Johann Mendel und August Weismann. Verlag Harri Deutsch, Frankfurt am Main 1990, ISBN 3-8171-1130-4
- H. Risler: August Weismann 1834-1914. In: Berichte der Naturforschenden Gesellschaft Freiburg im Breisgau, 1968, S. 77-93
- H. Risler: August Weismanns Leben und Wirken nach Dokumenten aus seinem Nachlass. In: Freiburger Universitätsblätter, Heft 87/88, Freiburg 1985, S. 23-42
[edit] References
- ^ The German biologist August Weismann (1834-1914) published the results of an experiment in which he consistently cut the tails of mice one generation after another, for 22 generations. He observed that the offspring of those mice were not at all born with shortened tails. Based on that, he totally denied Lamarck's "inheritance of acquired characteristics" and advocated, instead, evolution based only on natural selection alone. His position came to be known as "Neo-Darwinism." The Path to the Contemporary Theory of Evolution
