August Weismann

Friedrich Leopold August Weismann (born on January 17th 1834 with Francfort-sur-le-Main, deceased on November 5th 1914 with Freiburg-in-Brisgau) is a biologist and German doctor.

He is the author of the theory on the continuity of the germinatif Plasma, this theory implies that the acquired features by an individual cannot be transmitted hereditarily.

Life

Youth and studies

His/her father, Johann Konrad Weismann (1804-1880), professor of college, had studied the old languages and theology. His/her mother, Elects (1803-1850), is the girl of an important person in charge of the town of Stage. Born on January 17th, 1834 with Francfort-sur-le-Main, August Weismann receives a typical middle-class education of the 19th century: course of music at 4 years, drawing at 14 years, with Frankfurter Städelschen Institut with Jakob Becker (1800-1882). Its piano teacher, impassioned collector of butterflies, learns how to him to capture moths and caterpillars. But, after the baccalaureat, August does not make studies of natural science, for financial reasons, and because of the lack of professional prospects. A family friend, the chemist Friedrich Wöhler (1800-1882) advises studies of medicine to him. Weismann makes its studies with Göttingen until 1856, thanks to part of the heritage of his/her mother. After the final examination, it writes its thesis on the production of hippuric acid in the human body.

Beginning of professional life, first scientific work

At the end of its studies, it accepts at once a station of assistant to the municipal private clinic of Rostock. He writes two articles, one on the hippuric acid in the herbivores, the other on the salinity of the Baltic, for which he obtains two prices, but this work moves away it from its desire for becoming chemist: precision of apothecary him manque.
After a study trip in Vienna, where he visits museums and private clinics, he passes his examination of State of doctor and settles in Frankfurt. During the war between Austria, France and Italy in 1859, it is useful in the army as head doctor. After a stay of studies in Paris, he studies at the university of Giessen near Rudolf Leuckart of 1860 to 1861. From 1861 to 1863, it is, in Frankfurt, with the Schaumburg castle, personal doctor of the Large Duke Stephan, outlaw of Austria.
De 1863 to 1912, it works at the Zoological Institute of the University of Freiburg-in-Brisgau, as directing teacher then.

Weismann, the biologist of the evolution

In its first work Of the justification of the theory of Darwin (1868), Weismann opposes the belief in Creation (Christian) in the theory of the evolution with the following result: many biological facts are interpreted easily by the theory of the evolution, but remain incomprehensible if one interprets them like results of Creation. Starting from this work, Weismann regards - as the modern biologists - the evolution as a fact, than it brings closer to the principles admitted in astronomy, like models it heliocentric solar system. Weismann changes point of view on the role and the functional mechanism of heredity during its life, in three phases.

From 1868 to 1882

Initially, Weismann supports very widespread theses among the biologists of the 19th century. Like Darwin, he explains the observable variability individuals of a species by the heredity of the characters. He believes, like he writes it in 1876, at “the origin of transmutations (=changement of the species) per direct influence of external living conditions”. “If one regards each variation as reaction (sic!) organization with external factors, like a deviation compared to the direction of development inherited, it follows that without a change of the outside world, no evolution of the forms of organization could have taken place.” It uses even the traditional formula of Lamarck of the use and the non-utilization of a body .

In 1879 is born to him a son, the type-setter Julius Weismann.

From 1882 to 1895

In its talk of 1883 on heredity, it draws aside for the first time the hereditary transmission of the acquired features. To argue its thesis, it chooses many examples which it tries to explain with the two theses. For example: How can one explain the specific adaptations of the various castes of workers and soldiers in the ants, whereas they never reproduce? With the theory on the continuity of germinatif plasma, an explanation is possible, here the use and non-utilization cannot on the other hand explain the development of some caractères.
Weismann explains even with the theory on the continuity of germinatif plasma - without managing to convince its contemporaries - examples that Darwin explains by the use and non-utilization , like the degeneration of the wings and the development of the legs in domestic poultry.

Refutation of the heredity of the acquired features

All the biologists heard of the experiment during which August Weismann would have cut the tail to generations of mouse, and always obtained mice with long tail; but very little of them ever took the trouble to read the report of this experiment (as famous and ignored as the receipt of Van Helmont to manufacture mice by spontaneous generation with corn and a dirty shirt). Finer than many current commentators who refer to this experiment (in general without to have studied it), Weismann knows that it is useless and that it does not allow the least conclusion. He even explains it before exposing his results, and repeats it in its conclusion. Among its arguments, he also calls upon the fact that, among people which practice the circumcision since millenia, the children are not born still circoncis.

“I frankly also acknowledge that I undertook these experiments only with back-plate, because I could hope to obtain another thing from it only negative results. But like these results, even negative, did not seem to me not completely deprived of value for the solution of the hanging question, and as the many defenders of the heredity of the acquired features did not prepare themselves to corroborate their opinion by the experiment, I asserted themselves this small work. : What proves these experiments? Do they once and for all refute the opinion of the possibility of transmission of the mutilations? Certainly not of the first blow. One could not raise decisive objection, from the theoretical point of view, if somebody wanted to support that the heredity of the mutilations needs thousand generations to become visible, because we cannot evaluate a priori the force of the influences able to modify germinatif plasma, and we can learn only by the experiment during how much generations they must act before appearing outside. ”

In addition, its good intelligence of the texts makes him differentiate the mutilations and the acquired features more naturally. One can indeed object that the mutilations do not correspond at all to the functional modifications acquired by the animal in the biology of Lamarck (in the case of Darwin, it is impossible to specify), since those, contrary to these, are acquired actively by the animal (for Lamarck, the neck of the giraffe lengthens because it extends it itself by grazing the high sheets, and not because an experimenter draws to him on the head).

“I do not need to say only the rejection of the heredity of the mutilations does not solve the question of the heredity of the acquired features. Although for myself I am confirmed always more in this idea that this transmission does not take place, and that we must seek to explain, without resorting to this assumption, the phenomena whom the transformation of the species introduces to us, I am however very distant to look at this problem like definitively solved by the fact of the possibility of rejecting into the field of the fable the heredity of the mutilations. ”

Most of the argumentation of Weismann is not intended to prove that the acquired features are not héritables, but that the observations and the experiments which are advanced as evidence of the heredity of the acquired features are not admissible, or are interpretable in another manner. If Weismann is not placed on an experimental level, it is because it knows very well that it is completely useless here: the possibility of proving in experiments the heredity (or the not-heredity) of the acquired features exists only on paper, and there is some naivety to imagine that the amputation of the tail of the mice or the cats has something to see with the evolution of the species. Moreover Weismann writes explicitly that it is on the basis of a theoretical point of view that it was brought to deny the heredity of the acquired features. The data should not be reversed: it is on the basis of the theory of germinatif plasma that Weismann denies the heredity of the acquired features; it is not on the basis of an observation of the not-heredity of the acquired features that it works out this theory of germinatif plasma.

If it is obviously not possible to prove that the heredity of the acquired features does not exist (one can prove an inexistence only for simple processes), there is theoretically a possibility of proving its existence - it would be enough to find of it an example irrefutable -, but this possibility remains very " théorique" would be this only by the definition of the acquired features to take into account.

Noble Denis in music of the life, beyond the genome (ED. threshold, 2006) evokes some work in this direction. Rejecting the idea that the genes constitute a program governing the organization, he sees the genome rather as a database in which the cellular metabolism can for the synthesis of the proteins (idea also put forward by Henri Atlan). To causality ascending , which goes from gene to the organization, only which is allowed today in biology, it considers that there exists also a downward causality , which goes from the organization to genes, left feedback as it is current to see some in the complex systems. The latter, according to methods which remain to be discovered, could more easily produce modifications of the genome and a way more adaptive than the chance of the changes only allowed up to now.

More still than heredity of such or such particular acquired feature, it is the continuity of a physical process through the generations which was rejected by the Darwinism, and it is it whom Weismann replaced by the continuity of the germinatif plasma (which will become the genome at the XXe century). A continuity of substance is much easier to conceive than the continuity of a physical process. It is undoubtedly the main reason of its adoption (even if it is not acknowledged).

From 1896 to 1910

Weismann works on the embryonic development of eggs of sea urchin, in which it observes various forms of the cellular division, the formation of the plate equatorial and the Méiose, and introduced these concepts in biology of the cellular Division.
Il defends the theory of the germinatif Plasma, according to which the pluricellular organizations consist of germinal cells, containing hereditary information, and of somatic cells, carrying out the vital functions. The germinal cells neither are influenced by what the body learns, nor by any capacities that it acquires with the length of its life, and cannot thus transmit these capacities to the following generation. That involves the redécouverte work of Gregor Mendel

It receives the Médaille Darwin and the medal of money Darwin-Wallace in 1908.

See too

External bonds

a biography of August Weismann on infoscience
bibliographical Biography and reference to the numerical sources in project VLP of the Institute max Planck of history of sciences

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