Human evolution theory utilizing concepts of neoteny & female sexual selection
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August Weismann

August Weismann: bibliographical excerpts

"What then is the nature of transmitted changes if it was recognized that the results of learning, as well as other acquired habits, were not inherited? Weismann answered this question: "In the first place it may be argued that external influences may not only act on the mature individual, or during its development, but that they may also act at a still earlier period upon the germ-cell from which it arises. It may be imagined that such influences of different kinds might produce corresponding minute alterations in the molecular structure of the germ-plasm, and as the latter is, according to our supposition, transmitted from one generation to another, it follows that such changes would be hereditary." [notes states quote from Weismann's, The Signifiance of Sexual Reproduction in the Theory of Natural Selection p. 277] We should pay special attention to this excerpt, since it contains the idea Weismann repeated many times, that the germ-plasm can change under the influence of external conditions. It is important to remember this idea of Weismann, especially since it was forgotten by all who, in the polemic with Weismann, referred only to his insistence on the durability of germ-plasm in the face of influences from outside (on the part of the soma and surrounding environment). According to Weismann, heritable changes, which depended on external influences, were combined during amphimixis, that is, with the mixture of the germ-plasm of father and mother in sexual reproduction." (Blacher, L. I. (1982) The Problem of the Inheritance of Acquired Characters. Amerind Publishing: New Delhi p. 91)

"As his discussion shows, his refutation of the "inheritance of acquired characters" applied to the first two categories only. As this work abundantly shows, environmentally acquired characters can become heritable through the process of gentic assimulation, without requiring the reversal of genetic transcription and translation. Weismann found, with regard to the climatic influence, that when the pupae of the German form of a lycaenid butterfly Polymmatus phlaeas was exposed to much higher temperatures, none of the emerged adults resembled the darkest form of sothern veriety eleus. Further, a reverse experiment was made by subjecting caterpillars of the Naples form to very low temperature in rearing. The result was that none was as light colored as the ordinary German form. From these results Weismann concluded that German and Naples forms are constitutionally (genetically) distinct. Weismann (1892, p.401) said, 'A somatogenic character is not inherited in this case, but the modifying influence--temperature--affects the primary constituents of the wings in each individual, i.e. a part of the soma--as well as germplasm contained in the germ of animals.' Weismann (1892, p. 405) even went so far so to say, "In many animals and plants influences of temperature and environment may very possibly produce hereditary variations." Thus contrary to the prevailing belief, Weismann was a neo-Lamarckist, as Darwin was (1972, p. v.). In 1904 Weismann again referred to P. phlaeas in the same context, although he also referred to cases in which environmental inpacts such as nutrition and climatic factors have not affected the germ plasm (e.g., alpine plants, plant galls). In fact, Weismann's theory as a whole was not inconsistent with the Baldwin effect (discussed in Chap. 5). However, what happened later was that his general statement of refutation of the inheritance of acquired characters alone was taken seriously, and it provided a strong theoretical basis for the development of neo-Darwinism." (Matsuda, Ryuichi (1987) Animal Evolution in Changing Environments, with Special Reference to Abnormal Metamorphosis. N.Y.: Wiley Press pp.40-41)

"In 1883, Weismann, in an essay on heredity, announced the opinion that characters acquired by the body could be transmitted to the reproductive cells, and could not therefore be inherited. This doctrine rests on the relation of the germ-cells to those of the rest of the body, which is expressed in the following language of his predecessor Jaeger: 'Through a great series of generations the germinal protoplasm retains its specific properties, dividing in every reproduction into an ontogenetic portion and a phylogenetic portion, which is reserved to form the reproductive material of the mature offspring. This reservation of the phylogenetic material I described as the continuity of the germ-protoplasm.... Encapsulated in the ontogentic material the phylogenetic protoplasm is sheltered from external influences, and retains its specific and embryonic characters.' ... Weismann has, however, subsequently modified his views to a considerable extent. He has always admitted the doctrine of Lamarck to be applicable to the evolution of the types of unicellular organisms. His experiments on the effect of temperature on the production of changes of color in butterflies, showed that such changes were not only effected, but were sometimes inherited. This he endeavors to explain as follows. [from The Germ Plasm, Comtemporary Science Series, 1893, p. 406] 'Many climatic variations may be due wholly or in part, to the simultaneous variation of corresponding determinants in some parts of the soma and in the germ-plasm of the reproductive cells.'" (Cope, CD (1896) Organic Evolution. Open Court Publishing: London pp. 10-12)

"Weismann recognized an important and unequal cellular dichotomy: Germ-line (or sex) cells create both the sex cells and the somatic (or body) cells of offspring individuals. The implication is enormous: What happens to the cells of an individual's body, its somatic cells, during its lifetime cannot affect its sex cells, which are present from an early stage in development. In a single blow, Weismann removed the possibility of the inheritance of acquired characteristics. That notion had been the linchpin of Lamarck's evolutionary mechanics, and was adopted even by Darwin in the sixth edition of the Origin as he tried to placate his critics." (Eldredge, Niles (1999) The Pattern of Evolution. W. H. Freeman: New York p. 121)

"Weismann, on the other hand, reversed the attention which had been directed to the body as a source of variation, and concentrated his attention upon the germ itself as the source of emergent change. He postulated a germ plasm which was basicly immortal and inviolable. By this he meant that the reproductive cells are isolated early and are passed along unchanged from individual to individual in the history of the race. By "unchanged" is meant unaffected by exterior environmental influences. All changes which emerge in the plylogeny of a given organism must therefore emerge from the alteration or elimination of particular hereditary determiners within the germ plasm itself, not from "messenger" determiners carried into the germ from sources in the adult body. ... In summary then, we may say that while it has long since been disproved that the determiners engage in a struggle for existence within the germ cell, the main features of Weismann's system have been retained as the actual basis of modern genetics. Germ cells come from other germ cells and are not derived from body cells. Germinal continuity is complete, but not somatic continuity. This is the reverse of Darwin's position, and Weismann's victory over the conception of pangenesis marked the declining influence of Lamarckian theories of inheritance. As Weismann himself commented, "The transmission of acquired characters is an impossibility, for if the germ plasm is not formed anew in each individual but is derived from that which preceded it, its structure and above all its molecular constitution connot depend upon the indidual in which it happens to occur..."" (Eiseley, L (1958) Darwin’s Centry. Anchor Books: New York pp. 218- 219)

"Thus, the Mendelian genetic distribution gives twenty-five dominant, fifty dominant-recessive, twenty-five recessive, or 1DD, 2DR, 1RR, with the phenotype expression being three dominant to one recessive. This is an example of the simplest possible hereditary mechanism, where you have one factor (gene) for one trait, and one trait of a pair of traits being dominant and the other recessive. In such a simple genetic or factorial system, the inheritance is discontinuous (all or none); tall or short, wrinkled or smooth, yellow or green, etc. In fact, however, most traits of most organisms are multifactorially or polygenically determined and phenotypic variation is most often continous. Nonetheless, the results of Mendel showed that certain factors of inheritance behave in a lawful manner especially if one focuses on particular traits in well-chosen varieties. The biometricians incorporated the discontinous Mendelian factors into their genetic system by asserting that the traits they were measuring were multifactorial and so gave continous distributions with otherwise discontinous or independently assorted genes. This sort of conception allowed the genes to be looked on as self-contained packets of inheritance that give rise to certain traits and can be passed on from generation to generation. The one gene-one trait idea conformed well with Weismann's preformationistic concept to different portions of the germ containing the rudiment for specific later-developing traits inthe organism. The self-contained nature of the packets of inheritance fits well with the notion that the germ is impervious to influences from the somatic cells, which influence was a necessary component fo the unacceptable Lamarckian transmission of inherited characters. It is imporant for us to realize that concepts concerning genes and the mechanism of heredity at this time were inferences based on observatons of phenotypic development." (Gilbert, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 80)



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