Essays Upon Heredity and Kindred Biological Problems

‘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.

62

The views of most biologists who have worked at this subject agree in all essentials with that expressed above. Bütschli says (Bronn’s ‘Klassen und Ordnungen des Thierreichs,’ Protozoa, p. 148): ‘The process of encystment does not appear to have originally borne any direct relation to reproduction: it appears on the contrary to have taken place originally,—as it frequently does at the present day,—either for the protection of the organism against injurious external influences, such as desiccation or the fatal effects of impure water, etc.; and also to enable the organism, after taking up an unusually abundant supply of food, to assimilate it in safety.’ Balbiani (‘Journ. de Micrographie,’ Tom. V. 1881, p. 293) says in reference to the Infusoria, ‘Un petit nombre d’espèces, au lieu de se multiplier à l’état de vie active, se reproduisent dans une sorte d’état de repos, dit état d’enkystement. Ces sortes de kystes peuvent être désignés sous le nom de kystes de reproduction, par opposition avec d’autres kystes, dans lesquels les Infusoires se renferment pour se soustraire à des conditions devenues défavorables du milieu qu’ils habitent, le manque d’air, le dessèchement, etc.—ceux-ci sont des kystes de conservation....’

63

This is of importance in so far as single individuals might be thus compelled to encyst even when the existing external conditions of life do not require it. The substance which Actinosphaerium, for example, employs in the secretion of its thick siliceous cyst must have been gradually accumulated by means of a process peculiar to the species. We can scarcely be in error if we assume that the silica accumulated in the organism cannot increase to an unlimited extent without injury to the other vital processes and that the secretion of the cyst must take place as soon as the accumulation has exceeded a certain limit. Thus we can understand that encystment may occur without any external necessity. Similarly, certain Entomostraca (e. g. Moina) produce winter-eggs in a particular generation, and these are formed even when the animals are kept in a room protected from cold and desiccation.

64

Upon this point Professor Gruber intends to publish an elaborate memoir.

65

This view has not even been proved for Actinosphaerium, upon which Götte chiefly relies. The observations which we now possess merely indicate that the animal contracts to the smallest volume possible. Compare F. E. Schulze, ‘Rhizopodenstudien,’ I, Arch. f. mikr. Anat. Bd. 10, p. 328; and Karl Brandt, ‘Ueber Actinosphaerium Eichhornii,’ Inaug. Diss.; Halle, 1877.