Biologist, born in Frankfurt, WC Germany. He studied at Göttingen, and became professor of zoology at Freiburg (1867). He is best known for his theory of germ plasm (1886), a hereditary substance of which only one half was passed on to the next generation cells. This is now recognized as a forerunner of the DNA theory.
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. 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.
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 von Stade, on January 17, 1834 in Frankfurt am Main. A foundation from the inheritance of Weismann's mother allowed him to take up studies in Göttingen.
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.
After a study visit to see Vienna's museums and clinics, he graduated as a medical doctor and settled in Frankfurt.
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.
His son, the composer Julius Weismann, was born in 1879.
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. Weismann's position towards mechanism of inheritance and its role for evolution changed during his life.
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). (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.
1882-1895
Weismann's first rejection of the inheritance of acquired traits was in a lecture in 1883, titled "On inheritance" ("Über die Vererbung").
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.
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.
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