We should expect that our domesticated plants and animals should vary most, inasmuch as these have been subjected to changed conditions which would disturb the memory, and, breaking the chain of recollection, through failure of some one or other of the associated ideas, would thus directly and most markedly affect the reproductive system. Every reader of Mr. Darwin will know that this is what actually happens, and also that when once a plant or animal begins to vary, it will probably vary a good deal further; which, again, is what we should expect—the disturbance of the memory introducing a fresh factor of disturbance, which has to be dealt with by the offspring as it best may. Mr. Darwin writes: “All our domesticated productions, with the rarest exceptions, vary far more than natural species” (“Plants and Animals,” &c., vol. ii. p. 241, ed. 1875).
On my third supposition, i.e., when the difference between parents has not been great enough to baffle reproduction on the part of the first cross, but when the histories of the father and mother have been, nevertheless, widely different—as in the case of Europeans and Indians—we should expect to have a race of offspring who should seem to be quite clear only about those points, on which their progenitors on both sides were in accord before the manifold divergencies in their experiences commenced; that is to say, the offspring should show a tendency to revert to an early savage condition.
That this indeed occurs may be seen from Mr. Darwin’s “Plants and Animals under Domestication” (vol. ii. p. 21, ed. 1875), where we find that travellers in all parts of the world have frequently remarked “on the degraded state and savage condition of crossed races of man.” A few lines lower down Mr. Darwin tells us that he was himself “struck with the fact that, in South America, men of complicated descent between Negroes, Indians, and Spaniards seldom had, whatever the cause might be, a good expression.” “Livingstone” (continues Mr. Darwin) “remarks, ‘It is unaccountable why half-castes are so much more cruel than the Portuguese, but such is undoubtedly the case.’ An inhabitant remarked to Livingstone, ‘God made white men, and God made black men, but the devil made half-castes.’” A little further on Mr. Darwin says that we may “perhaps infer that the degraded state of so many half-castes is in part due to reversion to a primitive and savage condition, induced by the act of crossing, even if mainly due to the unfavourable moral conditions under which they are generally reared.” Why the crossing should produce this particular tendency would seem to be intelligible enough, if the fashion and instincts of offspring are, in any case, nothing but the memories of its past existences; but it would hardly seem to be so upon any of the theories now generally accepted; as, indeed, is very readily admitted by Mr. Darwin himself, who even, as regards purely-bred animals and plants, remarks that “we are quite unable to assign any proximate cause” for their tendency to at times reassume long lost characters.
If the reader will follow for himself the remaining phenomena of reversion, he will, I believe, find them all explicable on the theory that they are due to memory of past experiences fused, and modified—at times specifically and definitely—by changed conditions. There is, however, one apparently very important phenomenon which I do not at this moment see how to connect with memory, namely, the tendency on the part of offspring to revert to an earlier impregnation. Mr. Darwin’s “Provisional Theory of Pangenesis” seemed to afford a satisfactory explanation of this; but the connection with memory was not immediately apparent. I think it likely, however, that this difficulty will vanish on further consideration, so I will not do more than call attention to it here.
The instincts of certain neuter insects hardly bear upon reversion, but will be dealt with at some length in Chapter XII.
V. We should expect to find, as was insisted on in the preceding section in reference to the sterility of hybrids, that it required many, or at any rate several, generations of changed habits before a sufficiently deep impression could be made upon the living being (who must be regarded always as one person in his whole line of ascent or descent) for it to be unconsciously remembered by him, when making himself anew in any succeeding generation, and thus to make him modify his method of procedure during his next embryological development. Nevertheless, we should expect to find that sometimes a very deep single impression made upon a living organism, should be remembered by it, even when it is next in an embryonic condition.
That this is so, we find from Mr. Darwin, who writes (“Plants and Animals under Domestication,” vol. ii. p. 57, ed. 1875)—“There is ample evidence that the effect of mutilations and of accidents, especially, or perhaps exclusively, when followed by disease” (which would certainly intensify the impression made), “are occasionally inherited. There can be no doubt that the evil effects of the long continued exposure of the parent to injurious conditions are sometimes transmitted to the offspring.” As regards impressions of a less striking character, it is so universally admitted that they are not observed to be repeated in what is called the offspring, until they have been confirmed in what is called the parent, for several generations, but that after several generations, more or fewer as the case may be, they often are transmitted—that it seems unnecessary to say more upon the matter. Perhaps, however, the following passage from Mr. Darwin may be admitted as conclusive:—
“That they” (acquired actions) “are inherited, we see with horses in certain transmitted paces, such as cantering and ambling, which are not natural to them—in the pointing of young pointers, and the setting of young setters—in the peculiar manner of flight of certain breeds of the pigeon, &c. We have analogous cases with mankind in the inheritance of tricks or unusual gestures.” . . . (“Expression of the Emotions,” p. 29).
In another place Mr. Darwin writes:—
“How again can we explain the inherited effects of the use or disuse of particular organs? The domesticated duck flies less and walks more than the wild duck, and its limb bones have become diminished and increased in a corresponding manner in comparison with those of the wild duck. A horse is trained to certain paces, and the colt inherits similar consensual movements. The domesticated rabbit becomes tame from close confinement; the dog intelligent from associating with man; the retriever is taught to fetch and carry; and these mental endowments and bodily powers are all inherited” (“Plants and Animals,” &c., vol. ii. p. 367, ed. 1875).