Karl Ernst von Weismann

“ The cloud of impenetrable mystery hangs over the development and still more over the origin of life. If we strain our eyes to pierce it, with the foregone conclusion that some solution is and must be attainable, we shall only mistake for discoveries the figments of our own imagination. Prof. Weismann adds another reason for his belief in natural selection, which is certainly characteristic of the time in which we live. "It is inconceivable," he says, "that there should be another principle capable of explaining the adaptation of organisms without assuming the help of a principle of design." ”

“ To us moderns the question at issue has a diminished significance. For over all such debates a change has been brought by Weismann's challenge for evidence that use and disuse have any transmitted effects at all. Hitherto the transmission of many acquired characteristics had seemed to most naturalists so obvious as not to call for demonstration. ”

“ It was not merely an idle sneer of the witty Frenchman, that science has not yet explained how an ancestor can transmit what he has not got himself. He cannot always transmit all that he himself actually possesses of nature's gifts. Vitality becomes lowered, and the type degenerates. Weismann has emphasized this idea in his doctrine of "panmixia," or the withdrawal of selection, which always results in degeneration. Selection, artificial or natural, may serve to counteract this universal tendency of organic life, but only approximately. ”

“ For my own part, at all events, I cannot see why this microscopical atom of “ovogenetic idio-plasm” should not simply be left to be absorbed among the millions of cells that afterwards go to form the foetus.
Again, as regards the second polar body, Weismann’s theory of it is framed to explain, (a) how the excess of germ-plasm is got rid of in each ontogeny, and (b) why [43] the offspring of the same parents do not all precisely resemble one another. These, be it observed, are the only two functions which Weismann’s theory of polar bodies subserves in relation to his theory of germ-plasm. ”

“ He accepts the position that purely physiological conditions set a limit to the number of years that can be attained by each kind of multicellular organism, but holds that these conditions leave room for a considerable amount of variation. Duration of life, in fact, according to Weismann, is a character that can be influenced by the environment and that by a process of natural selection can be adapted to the conditions of existence of different species.
If a species is to maintain its existence or to increase, it is obvious that its members must be able to replace the losses caused by death. ”

“ How far this criticism had the effect of causing Professor Weismann to abandon his theory of variation being exclusively due to amphimixis, as Professor Hartog appears to think (Nature, May 11, 1893, p. 28) , is immaterial. But it must be observed that as far back as February, 1890, Professor Weismann in his answer to Professor Vines’ criticism wrote the passage already quoted on page 152.
[62] It is almost needless to say that no fault is to be found with Weismann for having thus reversed his opinion touching one of his fundamental postulates. Consistency is no merit in a man of science ”

“ In a world teeming with the life of plants and animals, and in the branch of science which seeks to interpret them, where we enter upon the unknown much sooner than in any other sphere of science, Weismann has set out to prove or maintain the most stupendous negative ever framed by the human mind. ”

“ Weismann thinks will, in thousands of generations, effect the observed reduction of the eyes: the process being that at each successive stage in the decrease, there must take place variations in the size of the eye, some larger, some smaller, than the size previously reached, and that in virtue of the economy, those having the smaller will continually survive and propagate, instead of those having the larger. ”

“ Weismann’s theory on the other hand, while adopting the first assumption, rejects the second; and assumes in its stead that living material exists in “two kinds,” only one of which has been continuous, while the other is discontinuous—being, in fact, formed anew at each ontogeny. Therefore, to my mind, it seems more needful to argue the point wherein his theory differs from these other theories of heredity, than it is to argue the point wherein it agrees with them. We look to him for a proof of the discontinuity of somato-plasm much more than we do for a proof of the continuity of germ-plasm. ”

“ Therefore, supposing (with Darwin and others) that living material is all of one kind, and continuous, the fact on which Weismann relies admits of being explained without resorting to his more complex supposition of living material in two kinds, the one perpetually continuous, and the other interrupted at each ontogeny.
For these reasons it appears to me that, so far as the argument from “inconceivability” is concerned, it makes at least as much against the theory of germ-plasm as it does against the theory of pangenesis ”

“ It has been affirmed that 'Nature is economical' and will not expend energy in building an unnecessary organ. Weismann has suggested that the only reason why we have eyes at all is because Natural Selection is constantly weeding out poor eyes. Withdraw the necessity for good eyes, and poor eyes and good eyes will have an equal chance of surviving. ”

“ It is to be noticed that Weismann’s conception of the processes of ontogeny is strictly evolutionary, and in so far is a reversion to the general opinion of biologists of the 17th and 18th centuries. These supposed that the germ-cell contained an image-in-little of the adult, and that the process of development was a mere unfolding or evolution of this, under the influence of favouring and nutrient forces. ”

“ It is common ground that they believe the organism to be wound up, so to say, for a definite period, but have no very definite theory as to how this period is determined. A. Weismann, on the other hand, in a well-known essay on the duration of life, has developed a theory to explain the various fashions in which the gift of life is measured out to different kinds of creatures. ”

“ Now the above-mentioned Darwinian principles of transmutation are certainly not simple forces of nature like those underlying the development of the individual, i.e. chemico-physical forces, and it cannot be said à priori whether in one of these principles—perhaps in variability or in correlation—there may not lie concealed a metaphysical principle in addition to the physical forces. In fact it has lately been asserted by Edward von Hartmann286 that the theory of selection is not a mechanical explanation, since it combines forces which are only partly mechanical and in part directive. ”

“ It has not unfrequently been observed, at any rate in mammals, that when a female has borne progeny to a male of one variety, and subsequently bears progeny to a male of another variety, the younger progeny presents a more or less unmistakable resemblance to the father of the older one. Now, this is a fact to which Weismann has nowhere alluded ”

“ These facts not only tell against an unknown vitalistic principle of evolution, but in general against the idea of the determination of the great paths of evolution by purely internal causes. If there were a principle of evolution the dissimilarity in the duration of life could not be so excessive; if there were a 'senile stage' of species and a natural death of species comparable to the natural death of individuals, it would not have been possible for most of the Nautilidæ to have been restricted to the Silurian epoch, and yet for one species to have continued to live till now ”

“ Weismann's theory in its entirety is a finely conceived molecular hypothesis, but it is devoid of empirical basis. The notion of the absolute and permanent independence of the germ-plasm, as distinguished from the soma-plasm, is purely speculative; as is also the theory of germinal selection. The determinants, ids, and idants, are purely hypothetical elements. The experiments that have been devised to demonstrate their existence really prove nothing. ”

“ Such an ontogeny, predetermined in every detail, would no more produce an organism fit for life, than—as Roux has aptly put it—would a commander be victorious, who, instead of giving general instructions to his chief officers as to the placing and movements of their troops, should in advance issue detailed orders for the conduct of every one down to the lieutenants, or even to each private soldier. The influences which encounter organisms during their development are never exactly similar, and to adapt themselves to these the organisms must have a certain amount freedom. ”

“ Weismannism, vīs′man-izm, n. the doctrine in biology of August Weismann (born 1834) —that acquired characters are not transmitted, function and environment affecting the individual only, not the species, the sole source of evolutionary change being the intermingling of germ-plasma which occurs in fertilisation, and the condition of progress being found in the action of natural selection on the germinal variations which thus arise. ”

“ Death is thus not necessary or universal but is derived and is, in a sense, a product of slow development; and we can conceive a stage of evolution in which natural death did not occur at all but was always due to external accidents. Indeed, Weismann goes so far as to say that the difference between the germ and the soma is so great that the latter, with all its fortunes, has little or no influence upon the former; and by his doctrine that acquired traits and qualities are not inheritable he seems to draw a hard and fast line separating the mortal from the immortal parts or organisms. ”

“ Similarly, it seems to me, whatever cogency there may be in Weismann’s objection to Darwin’s theory on the score that it must assume “an unknown controlling force in order to marshal the molecules,” is equally great as regards his own. True, Weismann has a lot to say about the control which nucleo-plasm can exercise on cell-formation, and germ-plasm on marshalling successive stages of ontogeny ”

“ A considerable number of German breeders support the contention of Weismann that telegony is as yet unproved, and it may be pointed out that in Germany, on the whole, breeders have had a more scientific education than in England, and that in that country science is regarded with less aversion or contempt than is usually the case among so-called practical men in England. ”

“ The fact is that Weismann is particularly strong in his belief in heredity—so strong as to give almost no weight to any possible process of intervention in its original workings. He simply holds that the transmission of "acquired character" is not proven, and he doubts the fact of these "acquired" transmissions. In his illustrations he deals chiefly (when in the higher animals) with mutilations, and in the human race shows that the most proficient linguist does not produce children who can read without being taught! ”

“ No doubt the worst of these experiments were not really experiments at all, but cruelties committed by cruel men who were attracted to the laboratory by the fact that it was a secret refuge left by law and public superstition for the amateur of passionate torture. But there is no reason to suspect Weismann of Sadism. Cutting off the tails of several generations of mice is not voluptuous enough to tempt a scientific Nero. It was a mere piece of one-eyedness; and it was Darwin who put out Weismann's humane and sensible eye. He blinded many another eye and paralyzed many another will also. ”

“ It is enough to remark, in conclusion, that the game is not worth the candle. It was originally well worth Weismann’s while to sustain his fundamental postulate of the absolute stability of germ-plasm, because he was able to rear upon it his whole theory of evolution. ”

“ Here, then, we have actual proof of “hereditary individual variations” among a-sexually propagating organisms, sufficient in amount to have given origin, not merely to “individual differences,” but to innumerable species, and even genera. Consequently Weismann allows that the criticism abolishes this line of evidence in favour of the absolute stability of germ-plasm [26] . Consquently, also, we must now add, in whatever measure the alleged fact would have corroborated the theory had it been proved to be a fact, in that measure is the theory discredited by proof that [91] it is not a fact. ”

“ A “tendency to variation” implies that a large number of individuals produce varieties resembling the model to be imitated, and664 this—at least according to Von Hartmann—must take place in each of the successive generations, so that by this means, combined with heredity, the useful variation becomes increased. But how comes it that this “tendency to variation” coincides with the existence of the model both in time and place? Can this be due to accident if the two have not a common cause? The upholders of a directive power will certainly not admit this ”

“ I do not mean to pose as a supporter of all Weismann's views, but he seems to me to have a clearer conception of the problem of inheritance of acquired characters and of the nature of the proof necessary to solve it than almost any other man. At the same time there is hardly an author who is more misquoted and misrepresented—he is one of Darwin's chief rivals in this respect. ”