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August Weismann
August Weismann

Friedrich Leopold August Weismann (Birth. January 17, 1834 in Frankfurt am Main; Death. Events 38 BC - Octavian marries Livia Drusilla. 1287 - King Alfonso III of Aragon invades Minorca Year 1834 ( MDCCCXXXIV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Common November 5, 1914 in Freiburg im Breisgau, ) was a German biologist[2]. Events 1499 - Publication of the Catholicon in Treguier ( Brittany) Year 1914 ( MCMXIV) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Common year Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. A biologist is a Scientist devoted to and producing results in Biology through the study of Organisms Typically biologists study organisms and their relationship Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin. Ernst Walter Mayr ( July 5, 1904, Kempten, Germany &ndash February 3, 2005, Bedford Massachusetts U Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life


Weismann advocated the germ plasm theory, according to which (in a multicellular organism) inheritance only takes place by means of the germ cells—the gametes such as egg cells and sperm cells. Germ plasm or polar plasm is a zone found in the cytoplasm of the Egg cells of some Model organisms (such as Caenorhabditis elegans Germ cells are progenitors of the Gametes. These singled out cells move through the gut to the developing Gonads and undergo mitotic proliferation followed A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete Other cells of the body—somatic cells—do not function as agents of heredity. Somatic cells are any cells forming the body of an organism as opposed to Germline cells The effect is one-way: germ cells produce somatic cells, and more germ cells; the germ cells are not affected by anything the somatic cells learn or any ability the body acquires during its life. Genetic information cannot pass from soma to germ plasm and on to the next generation. This is referred to as the Weismann barrier. The Weismann barrier is the principle that hereditary information moves only from genes to body cells and never in reverse

This idea, if true, would rule out the inheritance of acquired characteristics as proposed by Jean-Baptiste Lamarck, which Charles Darwin considered highly probable as the cause of change on which natural selection acts. Jean-Baptiste Pierre Antoine de Monet Chevalier de Lamarck ( August 1, 1744 &ndash December 18, 1829) was a French Soldier Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life However, it was only an idea, and as such required experimental proof. In fact, since it is a negative idea, final proof would consist in proving that all conceivable means by which so-called soma to germline transmission might occur do not in fact operate. Weismann, who of course knew nothing of the complexity of modern genetic theory, was in no position to provide such proof.

The Weismann barrier is often confused with the Central dogma of molecular biology which is incorrectly said to be a restatement of Weismann's idea by Francis Crick. The central dogma of molecular biology was first enunciated by Francis Crick in 1958 and re-stated in a Nature paper published in 1970 Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004 Ph In fact the central dogma states only that protein is not known to be capable of copying to either RNA or DNA [1]. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl The two ideas are mistakenly linked because the central dogma has often been re-stated in broader terms, including a statement that RNA cannot copy to DNA (which is now known to be untrue). The inheritance of acquired characteristics, if it occurs, requires modification of DNA in the gametes, or germ cells, and one way in which this might occur is by copying from RNA. However, it would be wrong in any case to suppose that this is the only way, and the two ideas are quite separate, just as the concepts of natural selection and Lamarckism are not in conflict, since natural selection constitutes only half of Darwin's theory of evolution, the other half being genetic change, the mechanism of which was largely a mystery to Darwin, who knew nothing of random mutation or its causes. Lamarckism (or Lamarckian evolution) is the once widely accepted idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring (also

Despite these observations, the idea of the Weissman Barrier is central to what is now the generally accepted theory of evolution, founded on the Modern evolutionary synthesis. eVolution is the third Album by eLDee, it was due to be released in 2008 According to this theory, variations occur from time to time in the individuals of a population, as a result of genetic mutations which occur to some extent naturally, by copying errors, but can also be caused by chemicals known as mutagens or by ionising radiation, especially X-rays or cosmic rays. In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism In Biology, a mutagen ( Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation X-radiation (composed of X-rays) is a form of Electromagnetic radiation. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on Some variations are reproductively more successful than others so that through this indirect process, aided by the further processes of crossing over, and assortative mating the genetic structure of a breeding group gradually changes. Assortative mating (also called assortative pairing) takes place when sexually reproducing Organisms tend to Mate with individuals that are like In Weismann's opinion this 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. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete Weismann was one of the first biologists to deny soft inheritance entirely. Soft inheritance is the term coined by Ernst Mayr to include such ideas as Lamarckism.

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. Gregor Johann Mendel ( July 20, 1822 &ndash January 6, 1884) was

Weismann is much admired today. Ernst Mayr judged him to be the most important evolutionary thinker between Darwin and the evolutionary synthesis around 1930-40 (Mayr 1982). Ernst Walter Mayr ( July 5, 1904, Kempten, Germany &ndash February 3, 2005, Bedford Massachusetts U

Contents

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[3]. Events 38 BC - Octavian marries Livia Drusilla. 1287 - King Alfonso III of Aragon invades Minorca Year 1834 ( MDCCCXXXIV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Common 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. Friedrich Wöhler (31 July 1800 - 23 September 1882 was a German Chemist, best-known for his synthesis of Urea, but also the first to isolate several 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[4]. Hippuric acid ( Gr hippos, horse ouron, urine is an Organic acid found in the Urine of Horses and other herbivores

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. Tyrol is a region in Western Central Europe, which included the present day Austrian state of Tyrol (consisting of North Tyrol and East 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). Karl Georg Friedrich Rudolf Leuckart ( October 7, 1822 - February 6, 1898) was a German Zoologist who was born in Halmstedt The University of Gießen (German Universität Gießen) is officially called Justus Liebig-Universität Gießen after its most famous member

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. "Creationism" can also refer to Creation myths in general or to a concept about the origin of the soul. 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). In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. Weismann's position towards mechanism of inheritance and its role for evolution changed during his life. Three periods can be distinguished.

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). Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life 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.

1882-1895

Weismann's first rejection of the inheritance of acquired traits was in a lecture in 1883, titled "On inheritance" ("Über die Vererbung"). inheritance of acquired characters (or characteristics) is the hereditary mechanism by which changes in physiology acquired over the life of an organism (such as muscle enlarged 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. Germ plasm or polar plasm is a zone found in the cytoplasm of the Egg cells of some Model organisms (such as Caenorhabditis elegans

Even though Weismann used this theory to 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. Germ cells are progenitors of the Gametes. These singled out cells move through the gut to the developing Gonads and undergo mitotic proliferation followed Somatic cells are any cells forming the body of an organism as opposed to Germline cells

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. Gregor Johann Mendel ( July 20, 1822 &ndash January 6, 1884) was

Weismann barrier: Cutting off mice tails

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 Lamarck and the inheritance of acquired characteristics. Jean-Baptiste Pierre Antoine de Monet Chevalier de Lamarck ( August 1, 1744 &ndash December 18, 1829) was a French Soldier While Weisman based the idea on his limited knowledge of cells and his (largely wrong) theory of Germ Plasm, he is also widely quoted as having 'proved' the non-existence of Lamarckian inheritance by the experiment of chopping of the tails of fifteen hundred mice, repeatedly over 20 generations, and reporting that no mouse was ever born in consequence without a tail. In fact he states 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 any other abnormality of the organ'[5]. Despite the fact that this experiment has been repeatedly declared invalid, both then and today, many modern textbooks continue to declare that Weismann 'proved' that inheritance of acquired characteristics does not occur. It is also often reported that his experiments were not needed since generations of Jews and others had practised circumcision, without any observed effect on offspring. Male circumcision is the removal of some or all of the Foreskin (prepuce from the Penis. In fact Weismann was aware of the limitations of his 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 specifically 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. He carried out his experiment in order to lay such claims, regarding mutilation specifically, to rest. What Lamarck and others actually claimed was the inheritance of characteristics acquired through necessity, or effort, or will, or environment, which is quite different.

In fact, Weismann, who knew almost nothing of the complexities of modern genetics, was in no position to declare such a barrier, especially since proving that something cannot happen requires investigation of every conceivable mechanism by which it might just happen. The philosopher Henri Bergson explained this well as long ago as 1911 in response to Weismann's assertion when he said, in his book Creative Evolution: After having been affirmed as a dogma, the transmissibility of acquired characteristics has been no less dogmatically denied, for reasons drawn a priori from the supposed nature of germinal cells. It is well known how Weissmann was led, by his hypothesis of the continuity of the germ-plasm, to regard the germinal cells - ova and spermatozoa - as almost independent of the somatic cells. Starting from this, it has been claimed, and is still claimed by many, that the hereditary transmission of an acquired character is inconceivable. But if, perchance, experiment should show that acquired characteristics are transmissible, it would prove thereby that the germ-plasm is not so independent of the somatic envelope as has been contended, and the transmissibility of acquired characters would become ipso facto conceivable; which amounts to saying that conceivability and inconceivability have nothing to do with the case, and that experience alone must settle the matter. [2] Bergson goes on to describe the difficulties that arise in such experiment, of separating the effect of habit from a natural aptitude that may have existed to induce the habit.

The dogmatic nature of Weismann's assertion was seriously challenged in the 1980's and 1990's by the Australian immunologist, Ted Steele [6]who presents considerable evidence for what is now known as soma to germline transfer in his book Lamarck's Signature. Prof Edward J (Ted Steele is a controversial Australian molecular immunologist formerly with the University of Wollongong, now listed as a visiting fellow at the Australian There has been a recent revival in what is known as Neo-Lamarckism

Some written work


See also

Literature

References

  1. ^ Crick, F. (1970): Central Dogma of Molecular Biology. Nature 227, 561-563. PMID 4913914
  2. ^ Bergson, Henri, and Arthur Mitchell. 1944. Creative evolution. New York: Modern library. Page 78 [1]
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