The Principles of Biology Vol. I/Appendix B(IV)
IV.
WEISMANNISM ONCE MORE
Among those who follow a controversy to its close, not one in a hundred turns back to its beginning to see whether its chief theses have been dealt with. Very often the leading arguments of one disputant, seen by the other to be unanswerable, are quietly ignored, and attention is concentrated on subordinate arguments to which replies, actually or seemingly valid, can be made. The original issue is thus commonly lost sight of.
More than once I have pointed out that, as influencing men's views about Education, Ethics, Sociology, and Politics, the question whether acquired characters are inherited is the most important question before the scientific world. Hence I cannot allow the discussion with Professor Weismann to end in so futile a way as it will do if no summary of results is made. Here, therefore, I propose to recapitulate the whole case in brief. Primarily my purpose is to recall certain leading propositions which, having been passed by unnoticed, remain outstanding. I will turn, in the second place, to such propositions as have been dealt with; hoping to show that the replies given are invalid, and consequently that these propositions also remain outstanding.
But something beyond a summing-up is intended. A few pages at the close will be devoted to setting forth new evidence which has come to light since the controversy commenced—evidence which many will think sufficient in itself to warrant a positive conclusion.
*****
The fact that the tip of the fore finger has thirty times the power of discrimination possessed by the middle of the back, and that various intermediate degrees of discriminative power are possessed by various parts of the skin, was set down as a datum for my first argument. The causes which might be assigned for these remarkable contrasts were carefully examined under all their aspects. I showed in detail that the contrasts could not in any way be accounted for by natural selection. I further showed that no interpretation of them is afforded by the alleged process of panmixia: this has no locus standi in the case. Having proved experimentally, that ability of the fingers to discriminate is increased by practice, and having pointed out that gradations of discriminativeness in different parts correspond with gradations in the activities of the parts as used for tactual exploration, I argued that these contrasts have arisen from the organized and inherited effects of tactual converse with surrounding things, varying in its degrees according to the positions of the parts—in other words, that they are due to the inheritance of acquired characters. As a crowning proof I instanced the case of the tongue-tip, which has twice the discriminativeness of the forefinger-tip: pointing out that consciously, or semi-consciously, or unconsciously, the tongue-tip is perpetually exploring the inner surfaces of the teeth.
Singling out this last case, Professor Weismann made, or rather adopted from Dr. Romanes, what professed to be a reply but was nothing more than the blank form of a reply. It was said that though this extreme discriminativeness of the tongue-tip is of no use to mankind, it may have been of use to certain ancestral primates. No evidence of any such use was given; no imaginable use was assigned. It was simply suggested that there perhaps was a use.
In my rejoinder, after indicating the illusory nature of this proceeding (which is much like offering a cheque on a bank where no assets have been deposited to meet it), I pointed out that had the evidence furnished by the tongue tip never been mentioned, the evidence otherwise furnished amply sufficed. I then drew attention to the fact that this evidence had been passed over, and tacitly inquired why.
No reply.[1]
*****
In his essay on "The All-Sufficiency of Natural Selection," Professor Weismann set out, not by answering one of the arguments I had used, but by importing into the discussion an argument used by another writer, which it was easy to meet. It had been contended that the smallness and deformity of the little toe are consequent upon the effects of boot-pressure, inherited from generation to generation. To this Professor Weismann made the sufficient reply that the fusion of the phalanges and otherwise degraded structure of the little toe, exist among peoples who go barefoot.
In my "Rejoinder" I said that though the inheritance of acquired characters does not explain this degradation in the way alleged, it explains it in a way which Professor Weismann overlooks. The cause is one which has been operating ever since the earliest anthropoid creatures began to decrease their life in trees and increase their life on the earth's surface. The mechanics of walking and running, in so far as they concern the question at issue, were analyzed; and it was shown that effort is economized and efficiency increased in proportion as the stress is thrown more and more on the inner digits of the foot and less and less on the outer digits. So that thus the foot furnishes us simultaneously with an instance of increase from use and of decrease from disuse; a further disproof being yielded of the allegation that co-operative parts vary together, since we have here co-operative parts of which one grows while the other dwindles.
I ended by pointing out that, so far from strengthening his own case, Professor Weismann had, by bringing into the controversy this changed structure of the foot, given occasion for strengthening the opposite case.
No reply.
*****
We come now to Professor Weismann's endeavour to disprove my second thesis—that it is impossible to explain by natural selection alone the co-adaptation of co-operative parts. It is thirty years since this was set forth in The Principles of Biology. In § 166 I instanced the enormous horns of the extinct Irish elk, and contended that in this, and in kindred cases, where for the efficient use of some one enlarged part many other parts have to be simultaneously enlarged, it is out of the question to suppose that they can have all spontaneously varied in the required proportions. In "The Factors of Organic Evolution," by way of enforcing this argument, which had, so far as I know, never been met, I dwelt upon the aberrant structure of the giraffe. And then, in the essay which initiated this controversy, I brought forward yet a third case—that of an animal which, previously accustomed only to walking, acquires the power of leaping.
In the first of his articles in the Contemporary Review (September, 1893), Professor Weismann made no direct reply, but he made an indirect reply. He did not attempt to show how there could have taken place in the stag the "harmonious variation of the different parts that co-operate to produce one physiological result" (p. 311); but he contended that such harmonious variation must have taken place, because the like has taken place in "the neuters of state-forming insects"—"animal forms which do not reproduce themselves, but are always propagated anew by parents which are unlike them" (p. 313), and which therefore cannot have transmitted acquired characters. Singling out those soldier-neuters which exist among certain kinds of ants, he described (p. 318) the many co-ordinated parts required to make their fighting organs efficient. He then argued that the required simultaneous changes can "only have arisen by a selection of the parent-ants dependent on the fact that those parents which produced the best workers had always the best prospect of the persistence of their colony. No other explanation is conceivable; and it is just because no other explanation is conceivable, that it is necessary for us to accept the principle of natural selection" (pp. 318-9).
[This passage initiated a collateral controversy, which, as continually happens, has greatly obscured the primary controversy. It became a question whether these forms of neuter insects have arisen as Professor Weismann assumes, or whether they have arisen from arrested development consequent upon innutrition. To avoid entanglements I must for the present pass over this collateral controversy, intending to resume it presently, when the original issues have been dealt with.]
No one will suspect me of thinking that the inconceivability of the negation is not a valid criterion, since, in "The Universal Postulate," published in the Westminster Review in 1852 and afterwards in The Principles of Psychology, I contended that it is the ultimate test of truth. But then in every case there has to be determined the question—Is the negation inconceivable; and in assuming that it is so in the case named, lies the fallacy of the above-quoted passage. The three separate ways in which I dealt with this position of Professor Weismann are as follows:—
If we admit the assumption that the form of the soldier-ant has been developed since the establishment of the organized ant-community in which it exists, Professor Weismann's assertion that no other process than that which he alleges is conceivable, is true. But I pointed out that this assumption is inadmissible; and that no valid conclusion respecting the genesis of the soldier-ant can be drawn without postulating either the ascertained, or the probable, structure of those pre-social, or semi-social, ants from which the organized social ants have descended. I went on to contend that the pre-social type must have been a conquering type, and that therefore in all probability the soldier-ants represent most nearly the structures of those ancestral ants which existed when the society had perfect males and females and could transmit acquired characters, while the other members of the existing communities are degraded forms of the type.
No reply.
A further argument I used was that where there exist different castes among the neuter-ants, as those seen in the soldiers and workers of the Driver ants of West Africa, "they graduate insensibly into each other" alike in their sizes and in their structures; and that Professor Weismann's hypothesis implies a special set of "determinants" for each intermediate form. Or if he should say that the intermediate forms result from mixtures of the determinants of the two extreme forms, there still remains the further difficulty that natural selection has maintained, for innumerable generations, these intermediate forms which are injurious deviations from the useful extreme forms.
No reply.
One further reason—fatal it seems to me—was urged in bar of his interpretation. No physical cause has been, or can be, assigned, why in the germ-plasm of any particular queen-ant, the "determinants" initiating these various co-operative organs, all simultaneously vary in fitting ways and degrees, and still less why there occur such co-ordinated variations generation after generation, until by their accumulated results these efficient co-operative structures have been evolved. I pointed out that in the absence of any assigned or assignable physical cause, it is necessary to assume a fortuitous concurrence of favourable variations, which means "a fortuitous concourse of atoms;" and that it would be just as rational, and much more consistent, to assume that the structure of the entire organism thus resulted.
No reply.
*****
It is reasonable to suspect that Professor Weismann recognized these difficulties as insuperable, for, in his Romanes Lecture on "The Effect of External Influences upon Development," instead of his previous indirect reply, he makes a direct reply. Reverting to the stag and its enlarging horns, he alleges a process by which, as he thinks, we may understand how, by variation and selection, all the bones and muscles of the neck, of the thorax, and of the fore-legs, are step by step adjusted in their sizes to the increasing sizes of the horns. He ascribes this harmonization to the internal struggle for nutriment, and that survival of the fittest which takes place among the parts of an organism: a process which he calls "intra-individual-selection, or more briefly—intra-selection" (p. 12).
That I do not explain as he does the co-adaptation of co-operative parts, Professor Weismann ascribes to my having overlooked this "principle of intra-selection"—an unlucky supposition, as we see. But I do not think that when recognizing it a generation ago, I should have seen its relevancy to the question at issue, had that issue then been raised, and I certainly do not see it now. Full reproduction of Professor Weismann's explanation is impracticable, for it occupies several pages, but here are the essential sentences from it:—
The connecting sentences, along with those which precede and succeed, would not, if quoted, give to the reader clearer conceptions than these by themselves give. But when disentangled from Professor Weismann's involved statements, the essential issues are, I think, clear enough. In the case of the stag, that daily working together of the numerous nerves, muscles, and bones concerned, by which they are adjusted to the carrying and using of somewhat heavier horns, produces on them effects which, as I hold, are inheritable, but which, as Professor Weismann holds, are not inheritable. If they are not inheritable, what must happen? A fawn of the next generation is born with no such adjustment of nerves, muscles and bones as had been produced by greater exercise in the parent, and with no tendency to such adjustment. Consequently if, in successive generations, the horns go on enlarging, all these nerves, muscles, and bones, remaining of the original sizes, become utterly inadequate. The result is loss of life: the process of adaptation fails. "No," says Professor Weismann, "we must conclude that the germ-plasm has varied in the needful manner." How so? The process of "intra-individual selection," as he calls it, can have had no effect, since the cells of the soma cannot influence the reproductive cells. In what way, then, has the germ-plasm gained the characters required for producing simultaneously all these modified co-operative parts. Well, Professor Weismann tells us merely that we must suppose that the germ-plasm acquires a certain sensitiveness such as gives it a proclivity to development in the requisite ways. How is such proclivity obtainable? Only by having a multitude of its "determinants" simultaneously changed in fit modes. Emphasizing the fact that even a small failure in any one of the co-operative parts may be fatal, as the sprain of an over-taxed muscle shows us, I alleged that the chances are infinity to one against the needful variations taking place at the same time. Divested of its elaboration, its abstract words and technical phrases, the outcome of Professor Weismann's explanation is that he accepts this, and asserts that the infinitely improbable thing takes place!
Either his argument is a disguised admission of the inheritableness of acquired characters (the effects of "intra-selection") or else it is, as before, the assumption of a fortuitous concourse of favourable variations in the determinants—"a fortuitous concourse of atoms."
*****
Leaving here this main issue, I return now to that collateral issue named on a preceding page as being postponed—whether the neuters among social insects result from specially modified germ-plasms or whether they result from the treatment received during their larval stages.
For the substantiation of his doctrine Professor Weismann is obliged to adopt the first of these alternatives; and in his Romanes Lecture he found it needful to deal with the evidence I brought in support of the second alternative. He says that "poor feeding is not the causa efficiens of sterility among bees, but is merely the stimulus which not only results in the formation of rudimentary ovaries, but at the same time calls forth all the other distinctive characters of the workers" (pp. 29-30); and he says this although he has in preceding lines admitted that it is "true of all animals that they reproduce only feebly or not at all when badly and insufficiently nourished:" a known cause being thus displaced by a supposed cause. But Professor Weismann proceeds to justify his interpretation by experimentally-obtained evidence.
He "reared large numbers of the eggs of a female blow-fly"; the larvæ of some he fed abundantly, but the larvæ of others sparingly; and eventually he obtained, from the one set flies of full size, and from the other small flies. Nevertheless the small flies were fertile, as well as the others. Here, then, was proof that innutrition had not produced infertility; and he contends that therefore among the neuter social insects, infertility has not resulted from innutrition. The argument seems strong, and to many will appear conclusive; but there are two differences which entirely vitiate the comparison Professor Weismann institutes.
One of them has been pointed out by Mr. Cunningham. In the case of the blow-fly the food supplied to the larvæ though different in quantity was the same in quality; in the case of the social insects the food supplied, whether or not different in quantity, differs in quality. Among bees, wasps, ants, &c., the larvæ of the reproductive forms are fed upon a more nitrogenous food than are the larvæ of the workers; whereas the two sets of larvæ of the blow-fly, as fed by Professor Weismann, were alike supplied with highly nitrogenous food. Hence there did not exist the same cause for non-development of the reproductive organs. Here, then, is one vitiation of the supposed parallel. There is a second.
While the development of an embryo follows in a rude way the phyletic metamorphoses passed through by its ancestry, the order of development of organs is often gradually modified by the needs of particular species: the structures being developed in such order as conduces to self-sustentation and the welfare of offspring. Among other results there arise differences in the relative dates of maturity of the reproductive system and of the other systems. It is clear, à priori, that it must be fatal to a species if offspring are habitually produced before the conditions requisite for their survival are fulfilled. And hence, if the life is a complex one, and the care taken of offspring is great, reproduction must be much longer delayed than where the life is simple and the care of offspring absent or easy. The contrast between men and oxen sufficiently illustrates this truth. Now the subordination of the order of development of parts to the needs of the species, is conspicuously shown in the contrast between these two kinds of insects which Professor Weismann compares as though their requirements were similar. What happens with the blow fly? If it is able to suck up some nutriment, to fly tolerably, and to scent out dead flesh, various of its minor organs may be more or less imperfect without appreciable detriment to the species: the eggs can be laid in a fit place, and that is all that is wanted. Hence it profits the species to have the reproductive system developed comparatively early—in advance, even, of various less essential parts. Quite otherwise is it with social insects, which take such remarkable care of their young; or rather to make the case parallel—quite otherwise is it with those types from which the social insects have descended, bringing into the social state their inherited instincts and constitutions. Consider the doings of the mason-wasp, or mason-bee, or those of the carpenter-bee. What, in these cases, must the female do that she may rear members of the next generation? There is a fit place for building or burrowing to be chosen; there is the collecting together of grains of sand and cementing them into a strong and water-proof cell, or there is the burrowing into wood and there building several cells; there is the collecting of food to place along with the eggs deposited in these cells, solitary or associated, including that intelligent choice of small caterpillars which, discovered and carried home, are carefully packed away and hypnotized by a sting, so that they may live until the growing larva has need of them. For all these proceedings there have to be provided the fit external organs—cutting instruments, &c., and the fit internal organs—complicated nerve-centres in which are located these various remarkable instincts, and ganglia by which these delicate operations have to be guided. And these special structures have, some if not all of them, to be made perfect and brought into efficient action before egg-laying takes place. Ask what would happen if the reproductive system were active in advance of these ancillary appliances. The eggs would have to be laid without protection or food, and the species would forthwith disappear. And if that full development of the reproductive organs which is marked by their activity, is not needful until these ancillary organs have come into play, the implication, in conformity with the general law above indicated, is that the perfect development of the reproductive organs will take place later than that of these ancillary organs, and that if innutrition checks the general development, the reproductive organs will be those which chiefly suffer. Hence, in the social types which have descended from these solitary types, this order of evolution of parts will be inherited, and will entail the results I have inferred.
If only deductively reached, this conclusion would, I think, be fully justified. But now observe that it is more than deductively reached. It is established by observation. Professor Riley, Ph.D., late Government Entomologist of the United States, in his annual address as President of the Biological Society of Washington,[3] on January 29, 1894, said:—
Though what has been shown of the Termites has not been shown of the other social insects, which belong to a different order, yet, considering the analogies between their social states and between their constitutional requirements, it is a fair inference that what holds in the one case holds partially, if not fully, in the other. Should it be said that the larval forms do not pass into the pupa state in the one case as they do in the other, the answer is that this does not affect the principle. The larva carries into the pupa state a fixed quantity of tissue-forming material for the production of the imago. If the material is sufficient, then a complete imago is formed. If it is not sufficient, then, while the earlier formed organs are not affected by the deficiency, the deficiency is felt when the latest formed organs come to be developed, and they are consequently imperfect.
Even if left without reply, Professor Weismann's interpretation commits him to some insuperable difficulties, which I must now point out. Unquestionably he has "the courage of his opinions;" and it is shown throughout this collateral discussion as elsewhere. He is compelled by accumulated evidence to admit "that there is only one kind of egg from which queens and workers as well as males arise."[4] But if the production of one or other form from the same germ does not result from speciality of feeding, what does it result from? Here is his reply:—
"The courage of his opinions," which Professor Weismann shows in this assumption, is, however, quite insufficient. For since he himself has just admitted that there is only one kind of egg for queens, workers, and males, he must at any rate assume three sets of "determinants." (I find that on a subsequent page he does so.) But this is not enough, for there are, in many cases, two if not more kinds of workers, which implies that four sets of determinants must co-exist in the same egg. Even now we have not got to the extent of the assumption required. In the address above referred to on "Social Insects from Psychical and Evolutional Points of View," Professor Riley gives us (p. 33) the—
Forms in a Termes Colony under Normal Conditions.
1. Youngest larvæ.   
| |||
| 2. Larvæ [of those] unfit for reproduction.  
|
3. Larvæ [that will be] fit for reproduction.
| ||
| 4. Larvæ of workers. | 6. Workers. |
5. Larvæ of soldiers. | 7. Soldiers. |
8. Nymphs of 1st form. | 10. Winged forms. | 11. True royal pairs. |
9. Nymphs of 2nd form. |
Hence as, in this family tree, the royal pair includes male and female, it results that there are five different adult forms (Grassi says there are two others) arising from like eggs or larvæ; and Professor Weismann's hypothesis becomes proportionately complicated. Let us observe what the complications are.
It often happens in controversy—metaphysical controversy more than any other—that propositions are accepted without their terms having been mentally represented. In public proceedings documents are often "taken as read," sometimes with mischievous results; and in discussions propositions are often taken as thought when they have not been thought and cannot be thought. It sufficiently taxes imagination to assume, as Professor Weismann does, that two sets of "ids" or of "determinants" in the same egg are, throughout all the cell-divisions which end in the formation of the morula, kept separate, so that they may subsequently energize independently; or that if they are not thus kept separate, they have the power of segregating in the required ways. But what are we to say when three, four, and even five sets of "ids" or bundles of "determinants" are present? How is dichotomous division to keep these sets distinct; or if they are not kept distinct, what shall we say to the chaos which must arise after many fissions, when each set in conflict with the others strives to produce its particular structure? And how are the conquering determinants to find they ways out of the mêlée to the places where they are to fulfil their organizing functions? Even were they all intelligent beings and each had a map by which to guide his movements, the problem would be sufficiently puzzling. Can we assume it to be solved by unconscious units?
Thus even had Professor Weismann shown that the special structures of the different individuals in an insect-community are not due to differences in the nurtures they receive, which he has failed to do, he would still be met by this difficulty in the way of his own view, in addition to the three other insuperable difficulties grouped together in a preceding section.
*****
The collateral issue, which has occupied the largest space in the controversy, has, as commonly happens, begotten a second generation of collateral issues. Some of these are embodied in the form of questions put to me, which I must here answer, lest it should be supposed that they are unanswerable and my view therefore untenable.
In the notes he appends to his Romanes Lecture, Professor Weismann writes:—
It is curious to see put forward in so triumphant a manner, by a professed naturalist, a question so easily disposed of. I answer it by putting another. How does it happen that among those moths of which the female has but rudimentary wings, she continues to endow the males of her species with wings? How does it happen, for example, that among the Geometridæ, the peculiar structures and habits of which show that they have all descended from a common ancestor, some species have winged females and some wingless females; and that though they have lost the wings the ancestral females had, these wingless females convey to the males the normal developments of wings? Or, still better, how is it that in the Psychidæ there are apterous worm-like females, which lay eggs that bring forth winged males of the ordinary imago form? If for males we read workers, the case is parallel to the cases of those social insects, the queens of which bequeath characteristics they have themselves lost. The ordinary facts of embryonic evolution yield us analogies. What is the most common trait in the development of the sexes? When the sexual organs of either become pronounced, the incipient ancillary organs belonging to the opposite sex cease to develop and remain rudiments, while the organs special to the sex, essential and nonessential, become fully developed. What, then, must happen with the queen-ant, which, through countless generations, has ceased to use certain structures and has lost them from disuse? If one of the eggs which she lays, capable, as Professor Weismann admits, of becoming queen, male, or worker of one or other kind, does not at a certain stage begin actively to develop its reproductive system, then those organs of the ancestral or pre-social type which the queen has lost begin to develop, and a worker results.
Another difficulty in the way of my view, supposed to be fatal, is that presented by the Honey-ants—aberrant members of certain ant-colonies which develop so enormously the pouch into which the food is drawn, that the abdomen becomes little else than a great bladder out of which the head, thorax, and legs protrude. This, it is thought, cannot be accounted for otherwise than as a consequence of specially endowed eggs, which it has become profitable to the community for the queen to produce. But the explanation fits in quite easily with the view I have set forth. No one will deny that the taking in of food is the deepest of vital requirements, and the correlative instinct a dominant one; nor will any one deny that the instinct of feeding young is less deeply seated—comes later in order of time. So, too, every one will admit that the worker-bee or worker-ant before regurgitating food into the mouth of a larva must first of all take it in. Hence, alike in order of time and necessity, it is to be assumed that development of the nervous structures which guide self-nutrition, precedes development of the nervous structures which guide the feeding of larvæ. What, then, will in some cases happen, supposing there is an arrested development consequent on innutrition? It will in some cases happen that while the nervous centres prompting and regulating deglutition are fully formed, the formation of those prompting and regulating the regurgitation of the food into the mouths of larvæ are arrested. What will be the consequence? The life of the worker is mainly passed in taking in food and putting it out again. If the putting out is stopped its life will be mainly passed in taking in food. The receptacle will go on enlarging and it will eventually assume the monstrous form that we see.[6]
Here, however, to exclude misinterpretations, let me explain. I by no means deny that variation and selection have produced, in these insect-communities, certain effects such as Mr. Darwin suggested. Doubtless ant-queens vary; doubtless there are variations in their eggs; doubtless differences of structure in the resulting progeny sometimes prove advantageous to the stirp, and originate slight modifications of the species. But such changes, legitimately to be assumed, are changes in single parts—in single organs or portions of organs. Admission of this does not involve admission that there can take place numerous correlated variations in different and often remote parts, which must take place simultaneously or else be useless. Assumption of this is what Professor Weismann's argument requires, and assumption of this we have seen to be absurd.
Before leaving the general problem presented by the social insects, let me remark that the various complexities of action not explained by inheritance from pre-social or semi-social types, are probably due to accumulated and transmitted knowledge. I recently read an account of the education of a butterfly, carried to the extent that it became quite friendly with its protector and would come to be fed. If a non-social and relatively unintelligent insect is capable of thus far consciously adjusting its actions, then it seems a reasonable supposition that in a community of social insects there has arisen a mass of experience and usage into which each new individual is initiated; just as happens among ourselves. We have only to consider the chaos which would result were we suddenly bereft of language, and if the young were left to grow up without precept and example, to see that very probably the polity of an insect community is made possible by the addition of intelligence to instinct, and the transmission of information through sign-language.
*****
There remains now the question of panmixia, which stands exactly where it did when I published the "Rejoinder to Professor Weismann."
After showing that the interpretation I put upon his view was justified by certain passages quoted; and after pointing out that one of his adherents had set forth the view which I combated—if not as his view yet as supplementary to it; I went on to criticize the view as set forth afresh by Professor Weismann himself. I showed that as thus set forth the actuality of the supposed cause of decrease in disused organs, implies that minus variations habitually exceed plus variations—in degree or in number, or in both. Unless it can be proved that such an excess ordinarily occurs, the hypothesis of panmixia has no place; and I asked, where is the proof that it occurs.
No reply.
Not content with this abstract form of the question I put it also in a concrete form, and granted for the nonce Professor Weismann's assumption: taking the case of the rudimentary hind limbs of the whale. I said that though, during those early stages of decrease in which the disused limbs were external, natural selection probably had a share in decreasing them, since they were then impediments to locomotion, yet when they became internal, and especially when they had dwindled to nothing but remnants of the femurs, it is impossible to suppose that natural selection played any part: no whale could have survived and initiated a more prosperous stirp in virtue of the economy achieved by such a decrease. The operation of natural selection being out of the question, I inquired whether such a decrease, say of one-half when the femurs weighed a few ounces, occurring in one individual, could be supposed in the ordinary course of reproduction to affect the whole of the whale species inhabiting the Arctic Seas and the North Atlantic Ocean; and so on with successive diminutions until the rudiments had reached their present minuteness. I asked whether such an interpretation could be rationally entertained.
No reply.
Now in the absence of replies to these two questions it seems to me that the verdict must go against Professor Weismann by default. If he has to surrender the hypothesis of panmixia, what results? All that evidence collected by Mr. Darwin and others, regarded by them as proof of the inheritance of acquired characters, which was cavalierly set aside on the strength of this alleged process of panmixia, is reinstated. And this reinstated evidence, joined with much evidence since furnished, suffices to establish the repudiated interpretation.
In the printed report of his Romanes Lecture, after fifty pages of complicated speculations which we are expected to accept as proofs, Professor Weismann ends by saying, in reference to the case of the neuter insects:—
Most readers of the foregoing pages will think that since Professor Weismann has left one after another of my chief theses without reply, this is rather a strong assertion; and they will still further raise their eyebrows on remembering that, as I have shown, where he has given answers his answers are invalid.
*****
And now we come to the additions which I indicated at the outset as having to be made—certain evidences which have come to light since this controversy commenced.
When, by a remembered observation made in boyhood, joined with the familiar fact that worker-larvæ can be changed into the larvæ of queens by feeding, I was led to suggest that probably all the variations of form in the social insects are consequent on differences of nurture, I was unaware that observations and experiments were being made which have justified this suggestion. Professor Grassi has recently published accounts of the food-habits of two European species of Termites, shewing that the various forms are due to feeding. He is known to be a most careful observer, and some of the most curious of his facts are confirmed by the collection of white ants exhibited by Dr. David Sharp, F.R.S., at the soirée of the Royal Society in May last. He has favoured me with the following account of Grassi's results, which I publish with his assent:—
"The soldier is not however a mere instance of simple arrested development. It is true that there is in it arrested development of the sexual organs, but this is accompanied by change of form of other parts—changes so extreme that one would hardly suppose the soldier to have any connection with either the young or the adult of the winged forms.
"Now according to Grassi the whole of the individuals when born are undifferentiated forms (except as to sex), and each one is capable of going on the natural course of development and thus becoming a winged insect, or can be deviated from this course and made into a soldier; this is accomplished by the White Ants by special courses of feeding.
"The evidence given by Grassi is not conclusive as to the young being all born alike; and it may be that there are some individuals born that could not be deviated from the natural course and made into soldiers. But there is one case which seems to show positively that the deviation Grassi believes to occur is real, and not due to the selection by the ants of an individual that though appearing to our eyes undifferentiated is not really so. This is that an individual can be made into a soldier after it has visibly undergone one half or more of the development into a winged form. The Termites can in fact operate on an individual that has already acquired the rudiments of wings and whose head is totally destitute of any appearance of the shape of the armature peculiar to the soldier, and can turn it into a soldier; the rudiments of the wings being in such a case nearly entirely re-absorbed."Grassi has been for many years engaged in investigating these phenomena, and there is no reason for rejecting his statement. We can scarcely avoid accepting it, and if so, Professor Weismann's hypothesis is conclusively disposed of. Were there different sets of "determinants" for the soldier-form and for the winged sexual form, those "determinants" which had gone a long way towards producing the winged sexual form, would inevitably go on to complete that form, and could not have their proclivity changed by feeding.
[Yet more evidence to the like effect has since become known. At the meeting of the Entomological Society, on March 14, 1894 (reported in Nature, March 29):—
Another similarly conclusive verification I published in Nature for December 6, 1894, under the title "The Origin of Classes among the 'Parasol' Ants." The letter ran as follows:—
"'The history of my nests is as follows: Nos. 1 and 2 were both taken (August 9) on the same day, while destroying nests in the Gardens, and were portions of separate nests but of the same species. No. 3 was procured on September 5, and is evidently a different although an allied species to Nos. 1 and 2.
"'Finding neither of my nests had a queen, I procured one from another nest about to be destroyed, and placed it with No. 1 nest. It was received by the workers, and at once attended by a numerous retinue in royal style. On August 30 I removed the queen from No. 1 and placed it with No. 2, when it was again received in a most loyal manner....
"'Ants taken from Nos. 1 and 2 and placed with No. 3 were immediately destroyed by the latter, and even the soldiers of No. 3, as well as workers or nurses, were destroyed when placed with Nos. 1 and 2.
"'In nest No. 2, from which I removed the queen on August 30, there are now in the pupa stage several queens and several males. The forms of ant in nests Nos. 1 and 2 are as follows: (a) queen, (b) male (both winged, but the queen loses its wings after marital flight), (c) large workers, (d) small workers, and (e) nurses. In nest No. 3 I have not yet seen the queen or male, but it possesses—(a) soldier, (b) larger workers, (c) smaller workers, and (d) nurses; but these are different in form to those of nests No. 1 and No. 2. Probably we might add a third form of worker, as there are several sizes in the nest....
"'It is curious that in No. 1 nest, from which the queen was removed on August 30, new queens and males are now being developed, while in No. 2 nest, where the queen is at present, nothing but workers have been brought out, and if a queen larva or pupa is placed there it is at once destroyed, while worker larvæ or pupæ are amicably received. In No. 3 all the eggs, larvæ, and pupæ collected with the nest have been hatched, and no eggs have since made their appearance to date. There is no queen with this nest.... On November 14 I attempted to prove by experiment how small a number of "parasol" ants it required to form a new colony. I placed two dozen of ants (one dozen workers and one dozen nurses) in two separate nests, No. 4 and No. 5. With No. 4 I placed a few larvæ with a few rose petals for them to manipulate. With No. 5 I gave a small piece of nest covered with mycelium. On the 16th these nests were destroyed by small foraging ants, known as the "sugar" or "meat" ant, and I had to remove them and replace with a new colony. My notes on these are not sufficiently lengthy to be of much importance. But I noted four eggs laid on the 16th, or two days after being placed in their new quarters; no queen being present. The experiment is being continued. I may mention that in No. 4 nest, in which no fungus was present, the larvæ of all sizes appeared to change into the pupæ stage at once for want of food [a fact corresponding with the fact I have named as observed by myself sixty years ago in the case of wasp larvæ]. The circumstance tends to show that the development of the insect is influenced entirely by the feeding it gets in the larva stage.
"'In nest No. 2 before the introduction of a queen there were no eggs or larvæ. The first worker was hatched on October 27, or fifty-seven days afterwards, and a continual succession has since been maintained, but as yet (November 19) no males or queens have made their appearance.'
"In a letter accompanying the report, Mr. Hart says:—
"'Since these were published, my notes go to prove that ants can practically manufacture at will, male, female, soldier, worker, or nurse. Some of the workers are capable of laying eggs, and from these can be produced all the various forms as well as from a queen's egg.
"'There does not, however, appear to be any difference in the character of the food; as I cannot find that the larger larvæ are fed with anything different to that given to the smaller.'
"These results were obtained before the recent discussion of the question commenced, and joined with the other evidence entirely dispose of those arguments which Prof. Weismann bases on facts furnished by the social insects."]The other piece of additional evidence I have referred to, is furnished by two papers contributed to The Journal of Anatomy and Physiology for October 1893 and April 1894, by R. Havelock Charles, M. D., &c. &c., Professor of Anatomy in the Medical College, Lahore. These papers set forth the differences between the leg-bones of Europeans and those of the Punjaub people—differences caused by their respective habits of sitting in chairs and squatting on the ground. He enumerates more than twenty such differences, chiefly in the structures of the knee-joint and ankle-joint. From the résumé of his second paper I quote the following passages, which sufficiently show the data and the inferences:—
"8. The sitting postures of Orientals are the same now as ever. They have retained the habits of their ancestors. The Europeans have not done so.
"9. Want of use would induce changes in form and size, and so, gradually, small differences would be integrated till there would be total disappearance of the markings on the European skeleton, as no advantage would accrue to him from the possession of facets on his bones fitting them for postures not practised by him.
"10. The facets seen on the bones of the Panjabi infant or fœtus have been transmitted to it by the accumulation of peculiarities gained by habit in the evolution of its racial type—in which an acquisition having become a permanent possession, 'profitable to the individual under its conditions of life,' is transmitted as a useful inheritance.
"11. These markings are due to the influence of certain positions, which are brought about by the use of groups of muscles, and they are the definite results produced by actions of these muscles.
"12. The effects of the use of the muscles mentioned in No. 11 are transmitted to the offspring, for the markings are present in the fœtus-in-utero, in the child at birth, and in the infant.
"13. The markings are instances of the transmission of acquired characters, which heritage in the individual, function subsequently develops."No other conclusion appears to me possible. Panmixia, even were it not invalidated by its unwarranted assumption as above shown, would be out of court: the case is not a case of either increase or decrease of size but of numerous changes of form. Simultaneous variation of co-operative parts cannot be alleged, since these co-operative parts have not changed in one way but in various ways and degrees. And even were it permissible to suppose that the required different variations had taken place simultaneously, natural selection cannot be supposed to have operated. The assumption would imply that in the struggle for existence, individuals of the European races who were less capable than others of crouching and squatting, gained by those minute changes of structure which incapacitated them, such advantages that their stirps prevailed over other stirps—an absurd supposition.
And now I must once more point out that a grave responsibility rests on biologists in respect of the general question; since wrong answers lead, among other effects, to wrong beliefs about social affairs and to disastrous social actions. In me this conviction has unceasingly strengthened. Though The Origin of Species proved to me that the transmission of acquired characters cannot be the sole factor in organic evolution, as I had assumed in Social Statics and in The Principles of Biology, published in pre-Darwinian days, yet I have never wavered in the belief that it is a factor and an all-important factor. And I have felt more and more that since all the higher sciences are dependent on the science of life, and must have their conclusions vitiated if a fundamental datum given to them by the teachers of this science is erroneous, it behoves these teachers not to let an erroneous datum pass current: they are called on to settle this vexed question one way or other. The times give proof. The work of Mr. Benjamin Kidd on Social Evolution, which has been so much lauded, takes Weismannism as one of its data; and if Weismannism be untrue, the conclusions Mr. Kidd draws must be in large measure erroneous and may prove mischievous.
Postscript.—Since the foregoing pages have been put in type there has appeared in Natural Science for September, an abstract of certain parts of a pamphlet by Professor Oscar Hertwig, setting forth facts directly bearing on Professor Weismann's doctrine respecting the distinction between reproductive cells and somatic cells. In The Principles of Biology, § 77, I contended that reproductive cells differ from other cells composing the organism, only in being unspecialized. And in support of the hypothesis that tissue-cells in general have a reproductive potentiality, I instanced the cases of the Begonia phyllomaniaca and Malaxis paludosa. In the thirty years which have since elapsed, many facts of like significance have been brought to light, and various of these are given by Professor Hertwig. Here are some of them:—
These evidences, furnished by independent observers, unite in showing, firstly, that all the multiplying cells of the developing embryo are alike; and, secondly, that the soma-cells of the adult severally retain, in a latent form, all the powers of the original embryo-cell. If these facts do not disprove absolutely Professor Weismann's hypothesis, we may wonderingly ask what facts would disprove it?
Since Hertwig holds that all the cells forming an organism of any species primarily consist of the same components, I at first thought that his hypothesis was identical with my own hypothesis of "physiological units," or, as I would now call them, constitutional units. It seems otherwise, however; for he thinks that each cell contains "only those material particles which are bearers of cell-properties," and that organs "are the functions of cell-complexes." To this it may be replied that the ability to form the appropriate cell-complexes, itself depends upon the constitutional units contained in the cells.
- ↑ In "The All-Sufficiency of Natural Selection" (Contemporary Review, Sept., 1893, p. 311), Professor Weismann writes:—"I have ever contended that the acceptance of a principle of explanation is justified, if it can be shown that without it certain facts are inexplicable." Unless, then, Prof. Weismann can show that the distribution of discriminativeness is otherwise explicable, he is bound to accept the explanation I have given, and admit the inheritance of acquired characters.
- ↑ Prof. Weismann is unaware that the view here ascribed to Roux, writing in 1881, is of far earlier date. In the Westminster Review for January, 1860, in an essay on "The Social Organism," I wrote:—"One more parallelism to be here noted, is that the different parts of a social organism, like the different parts of an individual organism, compete for nutriment; and severally obtain more or less of it according as they are discharging more or less duty." (See also Essays, i, 290.) And then, in 1876, in The Principles of Sociology, vol. i, § 247, I amplified the statement thus:—"All other organs, therefore, jointly and individually, compete for blood with each organ ... local tissue-formation (which under normal conditions measures the waste of tissue in discharging function) is itself a cause of increased supply of materials ... the resulting competition, not between units simply, but between organs, causes in a society, as in a living body, high nutrition and growth of parts called into greatest activity by the requirements of the rest." Though I did not use the imposing phrase "intra-individual-selection," the process described is the same.
- ↑ Proceedings of the Biological Society of Washington, vol. ix.
- ↑ Romanes Lecture, p. 29.
- ↑ Ibid., p. 35.
- ↑ This interpretation harmonizes with a fact which I learn from Prof. Riley, that there are gradations in this development, and that in some species the ordinary neuters swell their abdomens so greatly with food that they can hardly get home.