Part 8 (1/2)
III. We should expect to find a predominance of s.e.xual over as.e.xual generation, in the arrangements of nature for continuing her various species, inasmuch as two heads are better than one, and a locus poenitentiae is thus given to the embryo--an opportunity of correcting the experience of one parent by that of the other. And this is what the more intelligent embryos may be supposed to do; for there would seem little reason to doubt that there are clever embryos and stupid embryos, with better or worse memories, as the case may be, of how they dealt with their protoplasm before, and better or worse able to see how they can do better now; and that embryos differ as widely in intellectual and moral capacity, and in a general sense of the fitness of things, and of what will look well into the bargain, as those larger embryos--to wit, children--do. Indeed it would seem probable that all our mental powers must go through a quasi-embryological condition, much as the power of keeping, and wisely spending, money must do so, and that all the qualities of human thought and character are to be found in the embryo.
Those who have observed at what an early age differences of intellect and temper show themselves in the young, for example, of cats and dogs, will find it difficult to doubt that from the very moment of impregnation, and onward, there has been a corresponding difference in the embryo--and that of six unborn puppies, one, we will say, has been throughout the whole process of development more sensible and better looking--a nicer embryo, in fact--than the others.
IV. We should expect to find that all species, whether of plants or animals, are occasionally benefited by a cross; but we should also expect that a cross should have a tendency to introduce a disturbing element, if it be too wide, inasmuch as the offspring would be pulled hither and thither by two conflicting memories or advices, much as though a number of people speaking at once were without previous warning to advise an unhappy performer to vary his ordinary performance--one set of people telling him he has always. .h.i.therto done thus, and the other saying no less loudly that he did it thus;-- and he were suddenly to become convinced that they each spoke the truth. In such a case he will either completely break down, if the advice be too conflicting, or if it be less conflicting, he may yet be so exhausted by the one supreme effort of fusing these experiences that he will never be able to perform again; or if the conflict of experience be not great enough to produce such a permanent effect as this, it will yet, if it be at all serious, probably damage his performances on their next several occasions, through his inability to fuse the experiences into a harmonious whole, or, in other words, to understand the ideas which are prescribed to him; for to fuse is only to understand.
And this is absolutely what we find in fact. Mr. Darwin writes concerning hybrids and first crosses:- ”The male element may reach the female element, but be incapable of causing an embryo to be developed, as seems to have been the case with some of Thuret's experiments on Fuci. No explanation can be given of these facts any more than why certain trees cannot be grafted on others.”
I submit that what I have written above supplies a very fair prima facie explanation.
Mr. Darwin continues:-
”Lastly, an embryo may be developed, and then perish at an early period. This latter alternative has not been sufficiently attended to; but I believe, from observations communicated to me by Mr.
Hewitt, who has had great experience in hybridising pheasants and fowls, that the early death of the embryo is a very frequent cause of sterility in first crosses. Mr. Salter has recently given the results of an examination of about five hundred eggs produced from various crosses between three species of Gallus and their hybrids; the majority of these eggs had been fertilised; and in the majority of the fertilised eggs, the embryos had either been partially developed, and had then perished, or had become nearly mature, but the young chickens had been unable to break through the sh.e.l.l. Of the chickens which were born more than four-fifths died within the first few days, or at latest weeks, 'without any obvious cause, apparently from mere inability to live,' so that from the five hundred eggs only twelve chickens were reared” (”Origin of Species,”
249, ed. 1876).
No wonder the poor creatures died, distracted as they were by the internal tumult of conflicting memories. But they must have suffered greatly; and the Society for the Prevention of Cruelty to Animals may perhaps think it worth while to keep an eye even on the embryos of hybrids and first crosses. Five hundred creatures puzzled to death is not a pleasant subject for contemplation. Ten or a dozen should, I think, be sufficient for the future.
As regards plants, we read:-
”Hybridised embryos probably often perish in like manner . . . of which fact Max Wichura has given some striking cases with hybrid willows . . . It may be here worth noticing, that in some cases of parthenogenesis, the embryos within the eggs of silk moths, which have not been fertilised, pa.s.s through their early stages of development, and then perish like the embryos produced by a cross between distinct species” (Ibid).
This last fact would at first sight seem to make against me, but we must consider that the presence of a double memory, provided it be not too conflicting, would be a part of the experience of the silk moth's egg, which might be then as fatally puzzled by the monotony of a single memory as it would be by two memories which were not sufficiently like each other. So that failure here must be referred to the utter absence of that little internal stimulant of slightly conflicting memory which the creature has always. .h.i.therto experienced, and without which it fails to recognise itself. In either case, then, whether with hybrids or in cases of parthenogenesis, the early death of the embryo is due to inability to recollect, owing to a fault in the chain of a.s.sociated ideas. All the facts here given are an excellent ill.u.s.tration of the principle, elsewhere insisted upon by Mr. Darwin, that ANY great and sudden change of surroundings has a tendency to induce sterility; on which head he writes (”Plants and Animals under Domestication,” vol. ii. p.
143, ed. 1875):-
”It would appear that any change in the habits of life, whatever their habits may be, if great enough, tends to affect in an inexplicable manner the powers of reproduction.”
And again on the next page:-
”Finally, we must conclude, limited though the conclusion is, that changed conditions of life have an especial power of acting injuriously on the reproductive system. The whole case is quite peculiar, for these organs, though not diseased, are thus rendered incapable of performing their proper functions, or perform them imperfectly.”
One is inclined to doubt whether the blame may not rest with the inability on the part of the creature reproduced to recognise the new surroundings, and hence with its failing to know itself. And this seems to be in some measure supported--but not in such a manner as I can hold to be quite satisfactory--by the continuation of the pa.s.sage in the ”Origin of Species,” from which I have just been quoting--for Mr. Darwin goes on to say:-
”Hybrids, however, are differently circ.u.mstanced before and after birth. When born, and living in a country where their parents live, they are generally placed under suitable conditions of life. But a hybrid partakes of only half of the nature and condition of its mother; it may therefore before birth, as long as it is nourished within its mother's womb, or within the egg or seed produced by its mother, be exposed to conditions in some degree unsuitable, and consequently be liable to perish at an early period . . . ” After which, however, the conclusion arrived at is, that, ”after all, the cause more probably lies in some imperfection in the original act of impregnation, causing the embryo to be imperfectly developed rather than in the conditions to which it is subsequently exposed.” A conclusion which I am not prepared to accept.
Returning to my second alternative, that is to say, to the case of hybrids which are born well developed and healthy, but nevertheless perfectly sterile, it is less obvious why, having succeeded in understanding the conflicting memories of their parents, they should fail to produce offspring; but I do not think the reader will feel surprised that this should be the case. The following anecdote, true or false, may not be out of place here:-
”Plutarch tells us of a magpie, belonging to a barber at Rome, which could imitate to a nicety almost every word it heard. Some trumpets happened one day to be sounded before the shop, and for a day or two afterwards the magpie was quite mute, and seemed pensive and melancholy. All who knew it were greatly surprised at its silence; and it was supposed that the sound of the trumpets had so stunned it as to deprive it at once of both voice and hearing. It soon appeared, however, that this was far from being the case; for, says Plutarch, the bird had been all the time occupied in profound meditation, studying how to imitate the sound of the trumpets; and when at last master of it, the magpie, to the astonishment of all its friends, suddenly broke its long silence by a perfect imitation of the flourish of trumpets it had heard, observing with the greatest exactness all the repet.i.tions, stops, and changes. THE ACQUISITION OF THIS LESSON HAD, HOWEVER, EXHAUSTED THE WHOLE OF THE MAGPIE'S STOCK OF INTELLECT, FOR IT MADE IT FORGET EVERYTHING IT HAD LEARNED BEFORE” (”Percy Anecdotes,” Instinct, p. 166).
Or, perhaps, more seriously, the memory of every impregnate ovum from which every ancestor of a mule, for example, has sprung, has reverted to a very long period of time during which its forefathers have been creatures like that which it is itself now going to become: thus, the impregnate ovum from which the mule's father was developed remembered nothing but horse memories; but it felt its faith in these supported by the recollection of a VAST NUMBER of previous generations, in which it was, to all intents and purposes, what it now is. In like manner, the impregnate ovum from which the mule's mother was developed would be backed by the a.s.surance that it had done what it is going to do now a hundred thousand times already.
All would thus be plain sailing. A horse and a donkey would result.
These two are brought together; an impregnate ovum is produced which finds an unusual conflict of memory between the two lines of its ancestors, nevertheless, being accustomed to SOME conflict, it manages to get over the difficulty, AS ON EITHER SIDE IT FINDS ITSELF BACKED BY A VERY LONG SERIES OF SUFFICIENTLY STEADY MEMORY. A mule results--a creature so distinctly different from either horse or donkey, that reproduction is baffled, owing to the creature's having nothing but its own knowledge of itself to fall back upon, behind which there comes an immediate dislocation, or fault of memory, which is sufficient to bar ident.i.ty, and hence reproduction, by rendering too severe an appeal to reason necessary--for no creature can reproduce itself on the shallow foundation which reason can alone give. Ordinarily, therefore, the hybrid, or the spermatozoon or ovum, which it may throw off (as the case may be), finds one single experience too small to give it the necessary faith, on the strength of which even to try to reproduce itself. In other cases the hybrid itself has failed to be developed; in others the hybrid, or first cross, is almost fertile; in others it is fertile, but produces depraved issue. The result will vary with the capacities of the creatures crossed, and the amount of conflict between their several experiences.
The above view would remove all difficulties out of the way of evolution, in so far as the sterility of hybrids is concerned. For it would thus appear that this sterility has nothing to do with any supposed immutable or fixed limits of species, but results simply from the same principle which prevents old friends, no matter how intimate in youth, from returning to their old intimacy after a lapse of years, during which they have been subjected to widely different influences, inasmuch as they will each have contracted new habits, and have got into new ways, which they do not like now to alter.
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 a.s.sociated 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.