Essays Upon Heredity and Kindred Biological Problems
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It seems to be not without value for the appreciation of the questions with which we are dealing to remember that the idea of ‘maternal impressions’ was only comparatively recently believed to be a scientific theory, and that the proofs in support of it were brought forward in form and language as scientific proofs. In Burdach’s book we even meet with detailed ‘proofs’ that violent mental shocks produced by maternal impressions may not only exercise their influence upon one but even upon several children born successively, although with diminishing strength. ‘A young wife received a shock during her first pregnancy upon seeing a child with a hare-lip, and she was constantly haunted with the idea that her child might have the same malformation. She was delivered of a child with a typical hare-lip: her next child had an upper lip with a less-marked cleft; while the third possessed a red mark instead of a cleft.’
Now what can be said about such ‘proofs’? We may probably rightly conjecture that Burdach, who was in other respects a clever physiologist, was in this subject somewhat credulous: but there are also instances about which there is not the slightest doubt. I may remind the reader of a case which has been told by no other than the celebrated embryologist, Carl Ernst von Baer305.
‘A lady was very much upset by a fire, which was visible at a distance, because she believed that it was in her native place. As the latter was seven German miles distant, the impression had lasted a long time before it was possible to receive any certain intelligence, and this long delay affected the mind of the lady so greatly, that for some time afterwards she said that she constantly saw the flames before her eyes. Two or three months afterwards she was delivered of a daughter who had a red patch on the forehead in the form of a flame. This patch did not disappear until the child was seven years old.’ Von Baer added, ‘I mention this case because I am well acquainted with it, for the lady was my own sister, and because she complained of seeing flames before her eyes before the birth of the child, and did not invent it afterwards as the “cause” of the strange appearance.’
Here then we have a case which is absolutely certain. Von Baer’s name is a guarantee for absolute accuracy. Why then has science, in spite of this, rejected the whole idea of the efficacy of ‘maternal impressions’ ever since the appearance of the treatises by Bergmann and Leuckart306?
Science has rejected this idea for many and conclusive reasons, all of which I am not going to repeat here. In the first place, because our maturer knowledge of the physiology of the body shows that such a causal connexion between the peculiar characters of the child and, if I may say so, the corresponding psychical impressions of the mother, is a supposition which cannot be admitted; but also and chiefly because a single coincidence of an idea of the mother with an abnormality in the child does not form the proof of a causal connexion between the two phenomena.
I do not doubt that among the many thousands of present and past students in German Universities, whose faces are covered with scars, there may be one with a son who exhibits a birth-mark on the spot where the father possesses a scar. All sorts of birth-marks occur, and why should they not sometimes have the appearance of a scar? Such a case, if it occurred, would be acceptable to the adherents of the theory of the transmission of acquired characters; it would in their opinion completely upset the views of their opponents.
But how could such a case, if it were really established, be capable of proving the supposed form of hereditary transmission, any more than von Baer’s case could prove the theory of the efficacy of ‘maternal impressions’?
I am of opinion that the extraordinary rarity of such cases strongly enforces the fact that we have to do with an accidental and not a causal coincidence. If scars could be really transmitted, we should expect very frequently to find birth-marks which correspond to scars upon the face of the father,—viz. in almost all cases in which the son had inherited the type of face possessed by the father. If this were so we should have to be seriously concerned about the beauty of the next generation in Germany, as so many of our undergraduates follow the fashion of decorating their faces with as many of these ‘honourable scars’ as possible.
I have spoken of ‘maternal impressions’ because I wished to show that, until quite recently, distinguished and acute scientific men have adhered to an idea, and believed that they possessed the proof of an idea, which has now been completely and for ever abandoned by science. But in addition to this, there is a very close connexion between the theory of the efficacy of maternal impressions and that of the transmission of acquired characters, and sometimes they are even confounded together.
Last year a popular scientific journal quoted the following case as a proof of the transmission of mutilations. I do not, however, wish to imply that the editor must be held responsible for the errors of a correspondent. ‘In November, 1864, a pregnant merino sheep broke its right fore-leg, about two inches above the knee-joint; the limb was put in splints and healed a long time before the following March, when the animal produced young. The lamb possessed a ring of black wool from two to three inches in breadth round the place at which the mother’s leg had been broken, and upon the same leg.’ Now if we even admitted that a ring of black wool could be looked upon as a character which corresponds to the fracture of the mother’s leg, the case could not possibly be interpreted as the transmission of a mutilation, but as an instance of the efficacy of maternal impressions; for the ewe was already pregnant when she fractured her leg. The present state of biological science teaches us that, with the fusion of egg and sperm-cell, potential heredity is determined307. Such fusion determines the future fate of the egg-cell and the individual with all its various tendencies.
Such tales, when quoted as ‘remarkable facts which prove the transmission of mutilations,’ thoroughly deserve the contempt with which they have been received by Kant and His. When the above-mentioned instance was told me, I replied, ‘It is a pity that the black wool was not arranged in the form of the inscription “To the memory of the fractured leg of my dear mother.”’
The tales of the efficacy of ‘maternal impressions’ and of the transmission of mutilations are closely connected, and break down before the present state of biological science. No one can be prevented from believing such things, but they have no right to be looked upon as scientific facts or even as scientific questions. The first was abandoned in the middle of the present century, and the second may be given up now; when once discarded we need not fear that it will ever again be resuscitated.
It is hardly necessary to say that the question as to the transmission of acquired characters is not completely decided by the unconditional rejection of the transmission of mutilations. Although I am of opinion that such transmission does not take place, and that we can explain the phenomena presented by the transformation of species without this supposition, I am far from believing that the question is settled, simply because the transmission of mutilations may be dismissed into the domain of fable. But at all events we have gained this much,—that the only facts which appear to directly prove a transmission of acquired characters have been refuted, and that the only firm foundation on which this hypothesis has been hitherto based has been destroyed. We shall not be obliged, in future, to trouble about every single so-called proof of the transmission of mutilations, and investigation may be concentrated upon the domain in which lies the true decision as to the Lamarckian principle, it may be concerned with the explanation of the observed phenomena of transformation.
If, as I believe, these phenomena can be explained without the Lamarckian principle, we have no right to assume a form of transmission of which we cannot prove the existence. Only if it could be shown that we cannot now or ever dispense with the principle, should we be justified in accepting it. I do not think that I can represent the state of the subject better than by again referring to the metaphor of the ship. We see it moving along with all sails set, we can discern the presence of neither paddles nor screw, and as far as we can judge there is no funnel, nor any other sign of an engine. In such a case we shall not be justified in concluding that an engine is present and has some share in the movement of the vessel, unless the movement is of such a kind that it is impossible to explain it as due to the unaided action of the wind, the current, and the rudder. Only if the phenomena presented by the progress of organic evolution are proved to be inexplicable without the hypothesis of the transmission of acquired characters, shall we be justified in retaining such an hypothesis.
1
Humboldt’s ‘Ausichten der Natur.’
2
This estimate is derived from observation of the time during which these insects are to be seen upon the wing. Direct observations upon the duration of life in this species are unknown to me.
3
[Sir John Lubbock has now kept a queen ant alive for nearly 15 years. See note 2 {note 18 below} on p. 51.—E. B. P.]
4
[After reading these proofs Dr. A. R. Wallace kindly sent me an unpublished note upon the production of death by means of natural selection, written by him some time between 1865 and 1870. The note contains some ideas on the subject, which were jotted down for further elaboration, and were then forgotten until recalled by the argument of this Essay. The note is of great interest in relation to Dr. Weismann’s suggestions, and with Dr. Wallace’s permission I print it in full below.
‘The Action of Natural Selection in Producing Old Age, Decay, and Death.
‘Supposing organisms ever existed that had not the power of natural reproduction, then since the absorptive surface would only increase as the square of the dimensions while the bulk to be nourished and renewed would increase as the cube, there must soon arrive a limit of growth. Now if such an organism did not produce its like, accidental destruction would put an end to the species. Any organism therefore that, by accidental or spontaneous fission, could become two organisms, and thus multiply itself indefinitely without increasing in size beyond the limits most favourable for nourishment and existence, could not be thus exterminated: since the individual only could be accidentally destroyed,—the race would survive. But if individuals did not die they would soon multiply inordinately and would interfere with each other’s healthy existence. Food would become scarce, and hence the larger individuals would probably decompose or diminish in size. The deficiency of nourishment would lead to parts of the organism not being renewed; they would become fixed, and liable to more or less slow decomposition as dead parts within a living body. The smaller organisms would have a better chance of finding food, the larger ones less chance. That one which gave off several small portions to form each a new organism would have a better chance of leaving descendants like itself than one which divided equally or gave off a large part of itself. Hence it would happen that those which gave off very small portions would probably soon after cease to maintain their own existence while they would leave a numerous offspring. This state of things would be in any case for the advantage of the race, and would therefore, by natural selection, soon become established as the regular course of things, and thus we have the origin of old age, decay, and death; for it is evident that when one or more individuals have provided a sufficient number of successors they themselves, as consumers of nourishment in a constantly increasing degree, are an injury to those successors. Natural selection therefore weeds them out, and in many cases favours such races as die almost immediately after they have left successors. Many moths and other insects are in this condition, living only to propagate their kind and then immediately dying, some not even taking any food in the perfect and reproductive state.’—E. B. P.]
5
Johannes Müller, ‘Physiologie,’ Bd. I. p. 31, Berlin, 1840.
6
Oken, ‘Naturgeschichte,’ Stuttgart, 1837, Bd. IV. Abth. 1.
7
Brehm, ‘Leben der Vögel,’ p. 278.
8
‘Naturwissenschaftliche Thatsachen und Probleme,’ Populäre Vorträge, Berlin, 1880; vide Appendix.
9
‘Entomolog. Mag.,’ vol. i. p. 527, 1833.
10
Imhof, ‘Beiträge zur Anatomie der Perla maxima,’ Inaug. Diss., Aarau, 1881.
11
Mr. Edwards has meanwhile published these communications in full; cf. ‘On the length of life of Butterflies,’ Canadian Entomologist, 1881, p. 205.
12
When no authority is given, the observations are my own.
13
In the paper quoted above, Edwards, after weighing all the evidence, reduces the length of life from three to four weeks.
14
‘Entomolog. Mag.,’ vol. i. p. 527, 1823.
15
Ibid.
16
Ibid.
17
‘Recherches sur les mœurs des Fourmis indigènes,’ Genève, 1810.
18
These two female ants were still alive on the 25th of September following Sir John Lubbock’s letter, so that they live at least seven years. Cf. ‘Observations on Ants, Bees, and Wasps,’ Part VIII. p. 385; Linn. Soc. Journ. Zool., vol. xv. 1881.
[Sir John Lubbock has kindly given me further information upon the duration of life of these two queen ants. Since the receipt of his letter, the facts have been published in the Journal of the Linnean Society (Zoology), vol. xx. p. 133. I quote in full the passage which refers to these ants:—
‘Longevity.—It may be remembered that my nests have enabled me to keep ants under observation for long periods, and that I have identified workers of Lasius niger and Formica fusca which were at least seven years old, and two queens of Formica fusca which have lived with me ever since December 1874. One of these queens, after ailing for some days, died on the 30th July, 1887. She must then have been more than thirteen years old. I was at first afraid that the other one might be affected by the death of her companion. She lived, however, until the 8th August, 1888, when she must have been nearly fifteen years old, and is therefore by far the oldest insect on record.
‘Moreover, what is very extraordinary, she continued to lay fertile eggs. This remarkable fact is most interesting from a physiological point of view. Fertilization took place in 1874 at the latest. There has been no male in the nest since then, and, moreover, it is, I believe, well established that queen ants and queen bees are fertilized once for all. Hence the spermatozoa of 1874 must have retained their life and energy for thirteen years, a fact, I believe, unparalleled in physiology.’
‘I had another queen of Formica fusca which lived to be thirteen years old, and I have now a queen of Lasius niger which is more than nine years old, and still lays fertile eggs, which produce female ants.’
Both the above-mentioned queens may have been considerably older, for it is impossible to estimate their age at the time of capture. It is only certain (as Sir John Lubbock informs me in his letter) that they must have been at least nine months old (when captured), as the eggs of F. fusca are laid in March or early in April.’ The queens became gradually ‘somewhat lethargic and stiff in their movements (before their death), but there was no loss of any limb nor any abrasion.’ This last observation seems to indicate that queen ants may live for a much longer period in the wild state, for it is stated above that the chitin is often greatly worn, and some of the limbs lost (see pp. 48, 51, and 52).—E. B. P.]
19
A. von Berlepsch, ‘Die Biene und ihre Zucht,’ etc., 3rd ed.; Mannheim, 1872.
20
E. Bevan, ‘Ueber die Honigbiene und die Länge ihres Lebens;’ abstract in Oken’s ‘Isis,’ 1844, p. 506.
21
Dalyell, ‘Rare and Remarkable Animals of Scotland,’ vol. ii. p. 203; London, 1848.
22
[Mr. J. S. Haldane has kindly obtained details of the death of the sea anemone referred to by the author. It died, by a natural death, on August 4, 1887, after having appeared to become gradually weaker for some months previous to this date. It had lived ever since 1828 in the same small glass jar in which it was placed by Sir John Dalyell. It must have been at least 66 years old when it died.—E.B.P.]
23
Bronn, ‘Klassen und Ordnungen des Thierreichs,’ Bd. III. p. 466; Leipzig.
24
Bronn, l. c.
25
Cf. the article ‘Mort’ in the ‘Encyclop. Scienc. Méd.’ vol. M. p. 520.
26
Roux, in his work ‘Der Kampf der Theile im Organismus,’ Jena 1881, has attempted to explain the manner in which division of labour has arisen among the cells of the higher organisms, and to render intelligible the mechanical processes by which the purposeful adaptations of the organism have arisen.
27
von Berlepsch, ‘Die Biene und ihre Zucht,’ etc.
28
Oken, ‘Isis,’ 1844, p. 506.
29
von Berlepsch, l. c., p. 165.
30
Cf. August Gruber, ‘Der Theilungsvorgang bei Euglypha alveolata,’ and ‘Die Theilung der monothalamen Rhizopoden,’ Z. f. W. Z., Bd. XXXV. and XXXVI., p. 104, 1881.
31
Cf. Victor Hensen, ‘Physiologie d. Zeugung,’ p. 152.
32
Cf. J. Carrière, ‘Ueber Regeneration bei Landpulmonaten,’ Tagebl. der 52. Versammlg. deutsch. Naturf. pp. 225-226.
33
Pflüger, ‘Ueber den Einfluss der Schwerkraft auf die Theilung der Zellen und auf die Entwicklung des Embryo,’ Arch. f. Physiol. Bd. XXXII. p. 68, 1883.
34
Victor Hensen in his ‘Physiologie der Zeugung,’ Leipzig, 1881, p. 216.
35
That is for the preservation of its life.
36
Compare Weismann, ‘Die Entstehung der Sexualzellen bei den Hydromedusen,’ Jena, 1883.
37
It is doubtful whether Magosphaera should be looked upon as a mature form; but nothing hinders us from believing that species have lived, and are still living, in which the ciliated sphere has held together until the encystment, that is the reproduction, of the constituent single cells.
38
Or is an exception perhaps afforded by the nutritive cells of the egg, which occur in many animals?
39
Or more precisely, they must give up as many molecules as would correspond to the number of the kind of cell in question found in the mature organism.
40
See Darwin, ‘The Variation of Animals and Plants under Domestication,’ 1875, vol. ii. chapter xxvii. pp. 349-399.
41
To this class of phenomena of course belong those acts of will which call forth the functional activity of certain groups of cells. It is quite clear that such impulses do not originate in the constitution of the tissue in question, but are due to the operation of external causes. The activity does not arise directly from any natural disposition of the germ, but is the result of accidental external impressions. A domesticated duck uses its legs in a different manner from, and more frequently than a wild duck, but such functional changes are the consequence of changed external conditions, and are not due to the constitution of the germ.
42
Upon this subject Pflüger states—‘I have made myself accurately acquainted with all facts which are supposed to prove the inheritance of acquired characters,—that is of characters which are not due to the peculiar organization of the ovum and spermatozoon from which the individual is formed, but which follow from the incidence of accidental external influences upon the organism at any time in its life. Not one of these facts can be accepted as a proof of the transmission of acquired characters.’ l. c. p. 68.
43
‘Physiologie der Zeugung.’
44
See ‘Ueber die Uebung,’ Berlin, 1881.
45
This principle was, I believe, first pointed out by Seidlitz. Compare Seidlitz, ‘Die Darwin’sche Theorie,’ Leipzig, 1875, p. 198.
46
W. Roux, ‘Der Kampf der Theile im Organismus,’ Leipzig, 1881.
47
Compare Born in ‘Zoolog. Anzeiger,’ 1883, No. 150, p. 537.
48
O. C. Marsh, ‘Odontornithes, a Monograph on the extinct toothed Birds of North America,’ Washington, 1880.
49
C. Darwin, ‘Variation of Animals and Plants under Domestication.’ Vol. I.
50
Compare ‘Der thierische Wille,’ Leipzig, 1880.
51
Steller’s interesting account of the Sea-cow (Rhytina Stelleri) proves that this suggestion is valid. This large mammal was living in great numbers in Behring Strait at the end of the last century, but has since been entirely exterminated by man. Steller, who was compelled by shipwreck to remain in the locality for a whole year, tells us that the animals were at first without any fear of man, so that they could be approached in boats and could thus be killed. After a few months however the survivors became wary, and did not allow Steller’s men to approach them, so that they were difficult to catch.—A. W., 1888.
52
Compare Schneider, ‘Der thierische Wille.’
53
[The author refers to the Academy of Arts at Munich. S. S.]
54
Compare Darwin’s ‘Descent of Man.’
55
‘Studien zur Descendenztheorie, I. Ueber den Saison-Dimorphismus der Schmetterlinge.’ Leipzig, 1875. English edition translated and edited by Professor Meldola, ‘Studies in the Theory of Descent,’ Part I.
56
The colours which have been called forth by sexual selection must also be included here.
57
Wilhelm Roux, ‘Der Kampf der Theile im Organismus.’ Leipzig, 1881.
58
Consult ‘Studien zur Descendenztheorie, IV. Über die mechanische Auffassung der Natur,’ p. 303, etc. Translated and edited by Professor Meldola; see ‘Studies in the Theory of Descent,’ p. 677, &c.
59
‘Ueber den Ursprung des Todes,’ Hamburg and Leipzig, 1883.
60
As in the case of the bodies of monks on the Great St. Bernard, or the dried-up bodies in the well-known Capuchine Monastery at Palermo.
61
Professor Gruber informs me that among the Infusoria of the harbour of Genoa, he has observed a species which encysts upon one of the free-swimming Copepoda. He has often found as many as ten cysts upon one of these Copepods, and has observed the escape of their contents whenever the water under the cover-glass began to putrefy. Here advantage is probably gained in the rapid transport of the cyst by the Crustacean.