CHAPTER XXII.

PANGENESIS AND CONTINUITY OF THE GERM-PLASM: DARWIN’S CONFIDENCE IN PANGENESIS.

[Sidenote: PANGENESIS.]

Darwin’s letters prove that he thought very highly of this hypothesis; and whether the future determine it to be true or erroneous, it must surely rank as among the greatest of his intellectual efforts. In his autobiography he says of it:--

“An unverified hypothesis is of little or no value; but if any one should hereafter be led to make observations by which some such hypothesis could be established, I shall have done good service, as an astonishing number of isolated facts can be thus connected together and rendered intelligible.”

The hypothesis was submitted to Huxley (May 27th, 1865?) in manuscript and alluded to in the letter sent at the same time. An unfavourable reply was evidently received, for we find Darwin writing to Huxley, July 12th (1865?):--

“I do not doubt your judgment is perfectly just, and I will try to persuade myself not to publish. The whole affair is much too speculative; yet I think some such view will have to be adopted, when I call to mind such facts as the inherited effects of use and disuse, &c.”

This last sentence is of great interest, and the same opinion comes out strongly in his published account of the hypothesis, viz. the view that the real facts which imperatively demand some material to pass from the body-cells to the germ-cells in order to account for their hereditary transmission are the effects of use and disuse, or the influence of surroundings--in fact, all those characters which are now called “acquired.” And it is impossible to escape the conclusion that, if acquired characters are transmissible by heredity, an hypothesis which is substantially that of pangenesis will have to be accepted. Darwin did not doubt this transmission, and he framed pangenesis mainly to account for it.

Considerable doubt has of recent years been thrown upon the transmission of acquired characters, and if hereafter this doubt be justified, it will be possible to substitute for pangenesis a hypothesis like the “continuity of the germ-plasm” brought forward by Professor Weismann. A few words indicating the contrast between the two hypotheses may not be out of place.

In Professor Weismann’s hypothesis the germ-plasm contained in the nucleus of the germ-cell possesses, if placed under right conditions, the power of developing into an organism. It is not, however, entirely used up during development, and the part which remains grows and is stored in the germ-cells of the offspring, and ultimately develops into the succeeding generation. Hence parent and offspring resemble each other because they are formed from the same thing. There is no real break between the generations; they are thrown up successively from a continuous line of germ-plasm. In this hypothesis the germ is the essential thing, the body a mere secondary product. It is a theory of Blastogenesis as contrasted with Pangenesis. The hereditary transmission of acquired characters, in which many still believe, is quite irreconcilable with it, and if substantiated would overthrow it altogether.

On the other hand the body-cells are the essential elements of pangenesis, and the germ-cells the mere meeting-places of their representatives and quite devoid of significance on their own account. There is some sort of interruption between successive generations, as the gemmules develop into cells, which again throw off gemmules; the break, however, is bridged by the ancestral gemmules and by the life of the body-cell which intervenes between the gemmule from which it arose and that to which it gives rise.

The remaining chief occasions on which Darwin alludes to pangenesis in his published letters are quoted below; they prove his confidence in the hypothesis and the nature of the hold it had upon his mind.

Later on he again wrote to Huxley on the same subject:--

“I am rather ashamed of the whole affair, but not converted to a no-belief.... It is all rubbish to speculate as I have done; yet, if I ever have strength to publish my next book, I fear I shall not resist ‘Pangenesis,’ but I assure you I will put it humbly enough. The ordinary course of development of beings, such as the Echinodermata, in which new organs are formed at quite remote spots from the analogous previous parts, seems to me extremely difficult to reconcile on any view except the free diffusion in the parent of the germs or gemmules of each separate new organ: and so in cases of alternate generation.”

_To_ LYELL, _August 22nd, 1867_.

“I have been particularly pleased that you have noticed Pangenesis. I do not know whether you ever had the feeling of having thought so much over a subject that you had lost all power of judging it. This is my case with Pangenesis (which is 26 or 27 years old), but I am inclined to think that if it be admitted as a probable hypothesis it will be a somewhat important step in Biology.”

_To_ ASA GRAY, _October 16th, 1867_.

“The chapter on what I call Pangenesis will be called a mad dream, and I shall be pretty well satisfied if you think it a dream worth publishing; but at the bottom of my own mind I think it contains a great truth.”

_To_ HOOKER, _November 17th_ [1867].

“I shall be intensely anxious to hear what you think about Pangenesis; though I can see how fearfully imperfect, even in mere conjectural conclusions, it is; yet it has been an infinite satisfaction to me somehow to connect the various large groups of facts, which I have long considered, by an intelligible thread.”

_To_ FRITZ MÜLLER, _January 30th_ [1868].

“... I should very much like to hear what you think of ‘Pangenesis,’ though I fear it will appear to _every one_ far too speculative.”

_To_ HOOKER, _February 23rd_ [1868].

After expressing a fear that Pangenesis is still-born because of the difficulty with which it is understood, he says:--

“You will think me very self-sufficient, when I declare that I feel _sure_ if Pangenesis is now still-born it will, thank God, at some future time reappear, begotten by some other father, and christened by some other name. Have you ever met with any tangible and clear view of what takes place in generation, whether by seeds or buds, or how a long-lost character can possibly reappear; or how the male element can possibly affect the mother plant, or the mother animal, so that her future progeny are affected? Now all these points and many others are connected together, whether truly or falsely is another question, by Pangenesis. You see I die hard, and stick up for my poor child.”

_To_ WALLACE, _February 27th_ [1868].

“You cannot well imagine how much I have been pleased by what you say about ‘Pangenesis’.... What you say exactly and fully expresses my feeling, viz. that it is a relief to have some feasible explanation of the various facts, which can be given up as soon as any better hypothesis is found. It has certainly been an immense relief to my mind; for I have been stumbling over the subject for years, dimly seeing that some relation existed between the various classes of facts.... You have indeed pleased me, for I had given up the great god Pan as a still-born deity.”

_To_ HOOKER, _February 28th_ [1868].

“I see clearly that any satisfaction which Pan may give will depend on the constitution of each man’s mind.... I heard yesterday from Wallace, who says (excuse horrid vanity), ‘I can hardly tell you how much I admire the chapter on “Pangenesis.” It is a _positive comfort_ to me to have any feasible explanation of a difficulty that has always been haunting me, and I shall never be able to give it up till a better one supplies its place, and that I think hardly possible, &c.’ Now his foregoing [italicised] words express my sentiments exactly and fully: though perhaps I feel the relief extra strongly from having during many years vainly attempted to form some hypothesis. When you or Huxley say that a single cell of a plant, or stump of an amputated limb, has the ‘potentiality’ of reproducing the whole--or ‘diffuses an influence,’ these words give me no positive idea;--but, when it is said that the cells of a plant, or stump, include atoms derived from every other cell of the whole organism and capable of development, I gain a distinct idea. But this idea would not be worth a rush, if it applied to one case alone; but it seems to me to apply to all the forms of reproduction--inheritance--metamorphosis--to the abnormal transposition of organs--to the direct action of the male element on the mother plant, &c. Therefore I fully believe that each cell does _actually_ throw off an atom or gemmule of its contents;--but whether or not, this hypothesis serves as a useful connecting link for various grand classes of physiological facts, which at present stand absolutely isolated.”

_To_ V. CARUS, _March 21st_ [1868].

“... Sir C. Lyell says to every one, ‘You may not believe in “Pangenesis,” but if you once understand it, you will never get it out of your mind.’ And with this criticism I am perfectly content. All cases of inheritance and reversion and development now appear to me under a new light.”

_To_ FRITZ MÜLLER, _June, 1868_.

“I have yet hopes that you will think well of Pangenesis. I feel sure that our minds are somewhat alike, and I find it a great relief to have some definite, though hypothetical view, when I reflect on the wonderful transformations of animals,--the re-growth of parts,--and especially the direct action of pollen on the mother-form, &c. It often appears to me almost certain that the characters of the parents are ‘photographed’ on the child, only by means of material atoms derived from each cell in both parents, and developed in the child.”

_To_ ASA GRAY, _May 8th_ [1868].

“Your article in the _Nation_ [March 19th] seems to me very good, and you give an excellent idea of Pangenesis--an infant cherished by few as yet, except his tender parent, but which will live a long life. There is parental presumption for you!”

_To_ E. RAY LANKESTER, _March 15th_ [1870].

“I was pleased to see you refer[L] to my much despised child, ‘Pangenesis,’ who I think will some day, under some better nurse, turn out a fine stripling.”

_To_ WALLACE, _August 28th, 1872_.

“Notwithstanding all his [Dr. Bastian’s] sneers I do not strike my colours as yet about Pangenesis.”

In the second edition of “Animals and Plants,” Beale’s criticism of the hypothesis is alluded to with characteristic candour and humour:--“Dr. Lionel Beale (_Nature_, May 11th, 1871, p. 26) sneers at the whole doctrine with much acerbity and some justice.” Galton’s paper before the Royal Society (March 30th, 1871), upon the results of inter-transfusion of blood as destructive of pangenesis, was answered by Darwin in _Nature_ (April 27th, 1871). He did “not allow that pangenesis has as yet received its death-blow, though from presenting so many vulnerable points its life is always in jeopardy.”

Galton had argued that the gemmules present in the blood of one individual would be expected to pass into the other individual and to produce hereditary effects on its offspring. This, however, did not occur. Romanes repeated these experiments under more rigid conditions, but with the same negative results; equally negative were the effects of his transplantation of skin from one animal to another, although the skin grew quite successfully in its new position.