Darwin, and After Darwin Volume Ii Part 19

And, as instances of his more general statements in Chapter XXIII, these may suffice:--

"The direct action of the conditions of life, whether leading to definite or indefinite results, _is a totally distinct consideration from the effects of natural selection_.... The direct and definite action of changed conditions, in contradistinction to the acc.u.mulation of indefinite variations, _seems to me so important_ that I will give a large additional body of miscellaneous facts[171]."

[171] _Ibid._ vol. ii. p. 261.

Then, after giving these facts, and showing how in the case of species in a state of nature it is often impossible to decide how much we are to attribute to natural selection and how much to the definite action of changed conditions, he begins his general summary of the chapter thus:--

"There can be no doubt, from the facts given in the early part of this chapter, that extremely slight changes in the conditions of life sometimes act in a definite manner on our already variable domesticated productions [productions, therefore, with regard to which uniformity and 'stability' of modification are least likely to arise]; and, as the action Of changed conditions in causing general or indefinite variability is acc.u.mulative, so it may be with their definite action. Hence it is possible that _great_ and _definite_ modifications of structure may result from altered conditions acting during a long series of generations. In some few instances a marked effect has been produced quickly on _all_, or _nearly all_, the individuals which have been exposed to some considerable change of climate, food, or other circ.u.mstance[172]."

[172] _Variation_, &c., vol. ii. p. 280.

Once more, in order to show that he retained these views to the end of his life, I may quote a pa.s.sage from the second edition of the _Descent of Man_, which is the latest expression of his opinion upon these points:--

"Each of the endless diversities in plumage, which we see in our domesticated birds, is, of course, the result of some definite cause; and under natural and more uniform conditions, some one tint, _a.s.suming that it was in no way injurious, would almost certainly sooner or later prevail_. The free-intercrossing of the many individuals belonging to the same species would ultimately tend to make any change of colour thus induced _uniform in character_.... Can we believe that the very slight differences in tints and markings between, for instance, the female black-grouse and red-grouse serve as a protection? Are partridges as they are now coloured, better protected than if they had resembled quails?

Do the slight differences between the females of the common pheasant, the j.a.pan and golden pheasants, serve as a protection, or might not their plumage have been interchanged with impunity? From what Mr. Wallace has observed of the habits of certain gallinaceous birds in the East, he thinks that such slight differences are beneficial. For myself, I will only say, I am not convinced[173]."

[173] _Descent of Man_, pp. 473-4.

Yet "convinced" he certainly must have been on merely _a priori_ grounds, had he countenanced Mr. Wallace's reasoning from the general theory of natural selection; and the fact that he here fails to be convinced even by "what Mr. Wallace has observed of the habits of certain gallinaceous birds," appears to indicate that he had considered the question of utility with special reference to Mr. Wallace's opinion.

That opinion was then, as now, the avowed result of a theoretical prepossession; and this prepossession, as the above quotations sufficiently show, was expressly repudiated by Darwin.

Lastly, this is not the only occasion on which Darwin expressly repudiates Mr. Wallace's opinion on the point in question. For it is notorious that these co-authors of the theory of natural selection have expressed divergent opinions concerning the origin by natural selection of the most general of all specific characters--cross-sterility.

Although allowing that cross-sterility between allied species may be of adaptive value in "keeping incipient species from blending," Darwin persistently refused to be influenced by Wallace's belief that it is due to natural selection; i.e. the belief on which alone can be founded the "necessary deduction" with which we have been throughout concerned.

NOTE A TO PAGE 57.

I think it is desirable here to adduce one or two concrete ill.u.s.trations of these abstract principles, in order to show how, as a matter of fact, the structure of Weismann's theory is such as to preclude the possibility of its a.s.sumptions being disproved--and this even supposing that the theory is false.

At first sight nothing could seem more conclusive on the side of Darwinian or Lamarckian principles than are the facts of hereditary disease, in cases where the disease has unquestionably been acquired by the parents. Take, for example, the case of gout. Here there is no suspicion of any microbe being concerned, nor is there any question about the fact of the disease being one which is frequently acquired by certain habits of life. Now, suppose the case of a man who in middle age acquires the gout by these habits of life--such as insufficient exercise, over-sufficient food, and free indulgence in wine. His son inherits the gouty diathesis, and even though the boy may have the fear of gout before his eyes, and consequently avoid over-eating and alcoholic drinking, &c., the disease may overtake him also. Well, the natural explanation of all this is, that the sins of the fathers descend upon the children; that gout acquired may become in the next generation gout transmitted. But, on the other hand, the school of Weismann will maintain that the reason why the parent contracted the gout was because he had a congenital, or "blastogenetic," tendency towards that disease--a tendency which may, indeed, have been intensified by his habits of life, but which, in so far as thus intensified, was not transmitted to his offspring. All that was so transmitted was the congenital tendency; and all that is proved by such cases as those above supposed, where the offspring of gouty parents become gouty notwithstanding their abstemious habits, is that in such offspring the congenital tendency is even more p.r.o.nounced than it was in their parents, and therefore did not require so much inducement in the way of unguarded living to bring it out. Now, here again, without waiting to consider the relative probabilities of these two opposing explanations, it is enough for the purposes of the ill.u.s.tration to remark that it is obviously impossible to disprove either by means of the other, or by any cla.s.s of facts to which they may severally appeal.

I will give only one further example to show the elusiveness of Weismann's theory, and the consequent impossibility of finding any cases in nature which will satisfy the conditions of proof which the theory imposes. In one of his papers Weismann says that if there be any truth in the Lamarckian doctrine of the transmission of acquired characters, it ought to follow that the human infant should speak by instinct. For, ever since man became human he has presumably been a talking animal: at any rate it is certain that he has been so for an innumerable number of generations. Therefore, by this time the faculty of language ought to have been so deeply impressed upon the psychology of the species, that there ought to be no need to teach the young child its use of language; and the fact that there is such need is taken by Weismann to const.i.tute good evidence in proof of the non-transmissibility of individually acquired characters. Or, to quote his own words, "it has never yet been found that a child could read of itself, although its parents had throughout their whole lives practised this art. Not even are our children able to talk of their own accord; yet not only have their parents, but, more than that, an infinitely long line of ancestors have never ceased to drill their brains and to perfect their organs of speech.... From this alone we may be disposed to doubt whether acquired capabilities in the true sense can ever be transmitted." Well, in answer to this particular case, we have first of all to remark that the construction of even the simplest language is, psychologically considered, a matter of such enormous complexity, that there is no real a.n.a.logy between it and the phenomena of instinct: therefore the fact that Lamarckian principles cannot be applied to the case of language is no evidence that they do not hold good as regards instinct. Secondly, not only the construction, but still more the use of language is quite out of a.n.a.logy with all the phenomena of instinct; for, in order to use, or speak, a language, the mind must already be that of a thinking agent; and therefore to expect that language should be instinctive is tantamount to expecting that the thought of which it is the vehicle should be instinctive--i.e. that human parents should transmit the whole organization of their own intellectual experiences to their unborn children. Thirdly, even neglecting these considerations, we have to remember that language has been itself the product of an immensely long course of evolution; so that even if it were reasonable to expect that a child should speak by instinct without instruction, it would be necessary further to expect that the child should begin by speaking in some score or two of unknown tongues before it arrived at the one which alone its parents could understand. Probably these considerations are enough to show how absurd is the suggestion that Darwinians ought to expect children to speak by instinct. But, now, although it is for these reasons preposterous under any theory of evolution to expect that children should be able to use a fully developed language without instruction, it is by no means so preposterous to expect that, if all languages present any one simple set of features in common, these features might by this time have grown to be instinctive; for these simple features, being common to all languages, must have been constantly and forcibly impressed upon the structure of human psychology throughout an innumerable number of sequent generations. Now, there is only one set of features common to all languages; and this comprises the combinations of vowel and consonantal sounds, which go to const.i.tute what we know as articulate syllables. And, is it not the case that these particular features, thus common to all languages, as a matter of fact actually _are_ instinctive? Long before a young child is able to understand the meanings of any words, it begins to babble articulate syllables; and I do not know that a more striking fact can be adduced at the present stage of the Weismann controversy than is this fact which he has thus himself unconsciously suggested, namely, that the young of the only talking animal should be alone in presenting--and in unmistakably presenting--the instinct of articulation. Well, such being the state of matters as regards this particular case, in the course of a debate which was held at the Newcastle meeting of the British a.s.sociation upon the heredity question, I presented this case as I present it now. And subsequently I was met, as I expected to be met, by its being said that after all the faculty of making articulate sounds might have been of congenital origin. Seeing of how much importance this faculty must always have been to the human species, it may very well have been a faculty which early fell under the sway of natural selection, and so it may have become congenital. Now, be it remembered, I am only adducing this case in ill.u.s.tration of the elusiveness of Weismann's theory. First of all he selects the faculty of articulate speech to argue that it is a faculty which ought to be instinctive if acquired characters ever do become instinctive; and so good does he deem it as a test case between the two theories, that he says _from it alone_ we should be prepared to accept the doctrine that acquired characters can never become congenital. Then, when it is shown that the only element in articulate speech which possibly could have become congenital, actually has become congenital, the answer we receive is a direct contradiction of the previous argument: the faculty originally selected as representative of an acquired character is now taken as representative of a congenital one. By thus playing fast and loose with whatever facts the followers of Darwin may adduce, the followers of Weismann bring their own position simply to this:--All characters which can be shown to be inherited we a.s.sume to be congenital, or as we term it, "blastogenetic," while all characters which can be shown not to be inherited, we a.s.sume to be acquired, or as we term it, "somatogenetic"--and this merely on the ground that they have been shown to be inherited or not inherited as the case may be. Now, there need be no objection to such a.s.sumptions, provided they are recognized as a.s.sumptions; but so long as the very question in debate has reference to their validity as a.s.sumptions, it is closely illogical to adduce them as arguments. And this is the only point with which we are at present concerned.

NOTE B TO PAGE 89.

In answer to this ill.u.s.tration as previously adduced by me, Mr. Poulton has objected that the benefit arising from the peculiar mode of stinging in question is a benefit conferred, not on the insect which stings, but upon its progeny. The point of the ill.u.s.tration however has no reference to the maternal instinct (which here, as elsewhere, I doubt not is due to natural selection); it has reference only to the particular instinct of selective stinging, which here ministers to the purposes of the other and more general instinct of rearing progeny. Given then the maternal instinct of stinging prey for the use of progeny, the question is--What first determined the ancestors of the Sphex to sting their prey only in nine particular points? Darwin's answer to this question is as follows:--

"I have been thinking about Pompilius and its allies. Please take the trouble to read on perforation of the corolla by Bees, p. 425 of my 'Cross-fertilization,' to end of chapter. Bees show so much intelligence in their acts, that it seems not improbable to me that the progenitors of Pompilius originally stung caterpillars and spiders, &c., in any part of their bodies, and then observed by their intelligence that if they stung them in one particular place, as between certain segments on the lower side, their prey was at once paralyzed. It does, not seem to me at all incredible that this action should then become instinctive, i.e. memory transmitted from one generation to another. It does not seem necessary to suppose that when Pompilius stung its prey in the ganglion it intended or knew that their prey would keep long alive. The development of the larvae may have been subsequently modified in relation to their half-dead, instead of wholly dead prey; supposing that the prey was at first quite killed, which would have required much stinging.

Turn this over in your mind," &c.

Weismann, on the other hand, can only suppose that this intensely specialized instinct had its origin in fortuitous variations in the psychology of the species. But, neglecting the consideration that, in order to become fixed as an instinct by natural selection, the particular variation required must have occurred in many different individuals, not only in the first, but also in the sequent generations, the chances against its occurring only once, or in but one single individual case, are many thousands if not millions to one.