Are the Effects of Use and Disuse Inherited?

35

In the six largest breeds the shortening of the sternum is nearly twice as great as in the three smaller breeds which remain nearest the rock-pigeon in size. We can hardly suppose that use-inheritance especially affects the eight breeds that have varied most in size. If we exclude these, there is only a total shortening of 7 per cent. to be accounted for.

36

Variation of Animals and Plants under Domestication, i. 183, 186.

37

Variation of Animals and Plants under Domestication, i. 130, 135; ii. 288.

38

Encyclopædia Britannica, article "Zoology."

39

Variation of Animals and Plants under Domestication, ii. 367.

40

Variation of Animals and Plants under Domestication, ii. 367. Why then does the cheetah inherit ancestral habits so inadequately that it is useless for the chase unless it has first learned to hunt for itself before being captured? (ii. 133).

41

Descent of Man, p. 33.

42

Origin of Species, pp. 210, 211.

43

E. S. Delamer on Pigeons and Rabbits, pp. 132, 103. For other points referred to, see pages 133, 102, 100, 95, 131.

44

Origin of Species, pp. 188, 110; Descent of Man, pp. 32-35; Variation of Animals and Plants under Domestication, ii. 289, 293. Use or disuse during lifetime of course co-operates, and in some cases, as in that of the canoe Indians, may be the principal or even perhaps the sole cause of the change.

45

For the importance of panmixia as invalidating Darwin's strongest evidence for use-inheritance – namely, that drawn from the effects of disuse in highly-fed domestic animals where there is supposed to be no economy of growth – see Professor Romanes on Panmixia, Nature, April 3, 1890.

46

Descent of Man, p. 33.

47

Descent of Man, p. 33.

48

Variation of Animals and Plants under Domestication, i., 453.

49

Descent of Man, p. 33.

50

Descent of Man, p. 33.

51

Wallace shows that the changes in our domestic animals, if spread over the thousands of years since the animals were first tamed, must be extremely insignificant in each generation, and he concludes that such infinitesimal effects of use and disuse would be swallowed up by the far greater effects of variation and selection (Darwinism, p. 436). Professor Romanes has replied to him in the Contemporary Review (August 1889), showing that this is no disproof of the existence of the minor factor, inasmuch as slight changes in each generation need not necessarily be matters of life and death to the individual, although their cumulative development by use-inheritance might eventually become of much service. But selection would favour spontaneous variations of a similarly serviceable character. The slightest tendency to eliminate the extreme variations in either direction would proportionally modify the average in a breed. Use-inheritance appears to be so relatively weak a factor that probably neither proof nor disproof of its existence can ever be given, owing to the practical impossibility of disentangling its effects (if any) from the effects of admittedly far more powerful factors which often act in unsuspected ways. Thus wild ducklings, which can easily be reared by themselves, invariably "die off" if reared with tame ones (Variation, &c., i. 292, ii. 219). They cannot get their fair share in the competition for food, and are completely eliminated. Professor Romanes fully acknowledges that there is the "gravest possible doubt" as to the transmission of the effects of disuse (Letter on Panmixia, Nature, March 13, 1890).

52

Variation of Animals and Plants under Domestication, ii. 287-289.

53

Descent of Man, pp. 612, 131.

54

A very able anatomist of my acquaintance denies the inheritance of mutilations and injuries, although he strongly believes in the inheritance of the effects of use and disuse.

55

Variation of Animals and Plants under Domestication, i. 467-469. Lost toes were only seen by Dr. Dupuy in three young out of two hundred. Obersteiner found that most of the offspring of his epileptic guinea-pigs were injuriously affected, being weakly, small, paralysed in one or more limbs, and so forth. Only two were epileptic, and both were weakly and died early (Weismann's Essays, p. 311). A morbid condition of the spinal cord might affect the hind limbs especially (as in paraplegia) and might occasionally cause loss of toes in the embryo by preventing development or by ulceration. Brown-Séquard does not say that the defective feet were on the same side as in the parents (Lancet, Jan., 1875, pp. 7, 8).

56

Variation of Animals and Plants under Domestication, ii. 57.

57

Ibid., ii. 392. Perhaps it might be better to suppose that the best gemmules were sacrificed in repairing the injured nerve, and hence only inferior substitutes were left to take their place, and could only imperfectly reproduce the injured part of the nervous system in offspring.

58

Hence perhaps Mr. Spencer's error in representing the epileptic liability as permanent and as coming on after healing (Factors of Organic Evolution, p. 27).

59

It is not claimed that the imperfect foot was on the same side of the body as in the parent, and where parents had lost all the toes of a foot, or the whole foot, the few offspring affected usually had lost only two toes out of the three, or only a part of one or two or three toes. Sometimes the offspring had toes missing on both hind feet, although the parent was only affected in one. One diseased ear and eye in the parent was "generally" or "always" succeeded by two equally affected ears and eyes in the offspring (cf. Pop. Science Monthly, New York, xi. 334). The important law of inheritance at corresponding periods was also set aside. Gangrene or inflammation commenced in both ears and both eyes soon after birth (pointing possibly to infection of some kind); the epileptic period commenced "perhaps two months or more after birth," while the loss of toes had occurred before birth. In no case, as Weismann points out, is the original mutilation of the nervous system ever transmitted. Even where an extirpated ganglion was never regenerated in the parent, the offspring always regained the part in an apparently perfect condition. On the whole the conflicting results ought to be as puzzling to those who may attribute them to a universal tendency to inherit the exact condition of parents as they are to those who, like myself, are sceptical as to the existence of such a law or tendency.