August Weismann
August Weismann Germ plasm theory | |
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Awards | Darwin–Wallace Medal (Silver, 1908) |
August Friedrich Leopold Weismann
His main contribution involved
The idea of the Weismann barrier is central to the modern synthesis of the early 20th century, though scholars do not express it today in the same terms. In Weismann's opinion the largely random process of mutation, which must occur in the gametes (or stem cells that make them) is the only source of change for natural selection to work on. Weismann became one of the first biologists to deny Lamarckism entirely.[5] Weismann's ideas preceded the rediscovery of Gregor Mendel's work, and though Weismann was cagey about accepting Mendelism, younger workers soon made the connection.
Weismann is much admired today. Ernst Mayr judged him to be the most important evolutionary thinker between Darwin and the evolutionary synthesis around 1930–1940, and "one of the great biologists of all time".[6]
Life
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 of
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 visited
From 1863, he was
Family
In 1867 he married Mary Dorothea Gruber.
Their son, Julius Weismann (1879–1950), was a composer.
Contributions to evolutionary biology
At the beginning of Weismann's preoccupation with evolutionary theory was 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 compared creationism and evolutionary theory, and concluded 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 accepted evolution as a fact on a par with the fundamental assumptions of astronomy (e.g. Heliocentrism). Weismann's position towards the mechanism of inheritance and its role for evolution changed during his life. Three periods can be distinguished.
German work on cells
Weismann's work on the demarcation between germ-line and soma can scarcely be appreciated without considering the work of (mostly) German biologists during the second half of the 19th century. This was the time that the mechanisms of cell division began to be understood.
Meiosis was discovered and described for the first time in
1868–1881/82
Weismann started 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 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". (This is close to the modern use of the concept that changes in the environment can mediate selective pressures on a population, so leading to evolutionary change.) Weismann also used the classic Lamarckian metaphor of use and disuse of an organ.
1882–1895
Weismann's first rejection of the
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
Experiments on the inheritance of mutilation
The idea that germline cells contain information that passes to each generation unaffected by experience and independent of the somatic (body) cells, came to be referred to as the Weismann barrier, and is frequently quoted as putting a final end to the theory of
Weismann conducted the experiment of removing the tails of 68 white mice, repeatedly over 5 generations, and reporting that no mice were born in consequence without a tail or even with a shorter tail. He stated that "901 young were produced by five generations of artificially mutilated parents, and yet there was not a single example of a rudimentary tail or of any other abnormality in this organ."[12] Weismann was aware of the limitations of this experiment, and made it clear that he embarked on the experiment precisely because, at the time, there were many claims of animals inheriting mutilations (he refers to a claim regarding a cat that had lost its tail having numerous tail-less offspring). There were also claims of Jews born without foreskins. None of these claims, he said, were backed up by reliable evidence that the parent had in fact been mutilated, leaving the perfectly plausible possibility that the modified offspring were the result of a mutated gene. The purpose of his experiment was to lay the claims of inherited mutilation to rest. The results were consistent with Weismann's germ plasm theory.
Awards and Honors
Weismann was elected an International Member of the
Publications by Weismann
- 1868. Über die Berechtigung der Darwin'schen Theorie: Ein akademischer Vortrag gehalten am 8. Juli 1868 in der Aula der Universität zu Freiburg im Breisgau. Engelmann, Leipzig.
- 1872. Über den Einfluß der Isolierung auf die Artbildung. Engelmann, Leipzig.
- 1875. Studien zur Descendenz-Theorie. I. Ueber den Saison-Dimorphismus der Schmetterlinge. Leipzig.
- 1876. Studien zur Descendenztheorie: II. Ueber die letzten Ursachen der Transmutationen. Leipzig.
- 1883. Die Entstehung der Sexualzellen bei den Hydromedusen: Zugleich ein Beitrag zur Kenntniss des Baues und der Lebenserscheinungen dieser Gruppe. Fischer, Jena.
- 1883. Entstehung der Sexualzellen bei den Hydromedusen (in German). Vol. 1. Jena: Fischer.
- 1883. Entstehung der Sexualzellen bei den Hydromedusen (in German). Vol. 2. Jena: Fischer.
- 1885. Die Continuität des Keimplasmas als Grundlage einer Theorie der Vererbung. Fischer, Jena.
- 1886. "Ueber den Rückschritt in der Natur". Deutsche Rundschau. 48: 437.
- 1887. Zur Frage nach der Vererbung erworbener Eigenschaften. In: Biol. Zbl. 6:33–48
- 1887. Über die Zahl der Richtungskörper und über ihre Bedeutung für die Vererbung. Fischer, Jena.
- 1889 Translations: Essays upon Heredity Oxford Clarendon Press – Full online text[15]
- 1892. Das Keimplasma: eine Theorie der Vererbung. Fischer, Jena.
- 1893 Translation: Germ-Plasm, a theory of Heredity Charles Scribner's Sons – Full online text
- 1892. Aufsätze über Vererbung und angewandet biologische Fragen. Fischer, Jena.
- 1893. Die Allmacht der Naturzüchtung: eine Erwiderung an Herbert Spencer. Jena. Translated and published in the Contemporary Review, 1893. The all-sufficiency of natural selection. A reply to Herbert Spencer. Contemporary Review 64: 309-338
- 1902. Vorträge über Deszendenztheorie: Gehalten an der Universität zu Freiburg im Breisgau. Fischer, Jena. 2 volums
References
- ^ a b Romanes, George John. An examination of Weismannism. The Open court publishing company in Chicago 1893 [1]
- ^ Germ-Plasm, a theory of heredity (1893)- Full online text. Esp.org. Retrieved on 2012-02-25.
- ^ Huxley, Julian 1942. Evolution, the modern synthesis. p. 17
- S2CID 23808208.
- ^ Essays upon heredity (1889) Oxford Clarendon Press – Full online text. Esp.org. Retrieved on 2012-02-25.
- ^ Mayr, Ernst 1982. The growth of biological thought. Harvard. p. 698
- ^ a b public domain: Chisholm, Hugh, ed. (1911). "Weismann, August". Encyclopædia Britannica. Vol. 28 (11th ed.). Cambridge University Press. p. 499. One or more of the preceding sentences incorporates text from a publication now in the
- ^ Gaup, Ernst 1917. August Weismann: sein Leben und sein Werk. Fischer, Jena.
- ^ 100 Greatest Discoveries – Carnegie Institution Archived 2007-09-27 at the Wayback Machine at carnegieinstitution.org
- ^ The Science Channel :: 100 Greatest Discoveries: Biology Archived 2006-10-24 at the Wayback Machine at science.discovery.com
- ^ Although, of course, Ernst Haeckel had; but he was not a cytologist.
- ISBN 978-0-12-805477-2. Originally published in Weismann's 1889 Essays Upon Heredity.
- ^ "APS Member History". search.amphilsoc.org. Retrieved 2024-01-22.
- ^ "August Weismann". www.nasonline.org. Retrieved 2024-01-22.
- ^ "Review of Essays upon Heredity and kindred Biological Problems by August Weismann". The Quarterly Review. 170: 370–393. April 1890.
Sources
- Churchill, Frederick B. (1 March 1968). "August Weismann and a break from tradition". Journal of the History of Biology. 1 (1): 91–112. S2CID 84694824.
- Churchill, Frederick B. (1 December 1970). "Hertwig, Weismann, and the Meaning of Reduction Division circa 1890". Isis. 61 (4): 429–457. S2CID 46321527.
- Löther, Rolf 1990. Wegbereiter der Genetik: Gregor Johann Mendel und August Weismann. ISBN 3-8171-1130-4
- Risler H. 1968. August Weismann 1834–1914. In: Berichte der Naturforschenden Gesellschaft Freiburg im Breisgau. 77–93
- Risler H. 1985. August Weismanns Leben und Wirken nach Dokumenten aus seinem Nachlass. In: Freiburger Universitätsblätter Heft 87/88, Freiburg. 23–42
- Romanes, George John 1893. An Examination of Weismannism. London, Longmans.
External links
- Media related to August Weismann at Wikimedia Commons
- Works by or about August Weismann at Wikisource
- Works by August Weismann at Project Gutenberg
- Works by or about August Weismann at Internet Archive
- Biography, bibliography and access to digital sources in the Virtual Laboratory of the Max Planck Institute for the History of Science
- Newspaper clippings about August Weismann in the 20th Century Press Archives of the ZBW