in his classical work on heredity, professor j. arthur thomson exhausts the evidence on lamarckism available then (1908) in a manner worthy of the summing-up of an english judge. this is presented to the jury of the biological world and they are still considering it. their verdict and his sentence are not yet delivered, and it may be they will still be long delayed. one might almost use the words of professor bateson, previously quoted, “on our present knowledge the matter is talked out.”
i will make one prophecy in this volume and predict that the fourth edition of this work in 1930 will contain the verdict of the jury and sentence of the distinguished judge to the effect that in the case lamarck v. weismann the plaintiff has won. as in the great war the old contemptibles held their line with the utmost difficulty against the disciplined hosts of the greatest army ever known till then, and yet the latter found their first battle of the marne, so perchance it may be in the present struggle.
i introduce this chapter with an important passage from the above work on the logical position of the argument, in which the two possible methods of establishing the affirmative position of lamarck are given; these are, first, actual experimental proof of transmission, and, second, a collec-tion of facts which cannot be interpreted without the hypothesis of modifica-tion inheritance. the words are:28 “the neo-lamarckians have to show that the phenomena they adduce as illustrations of modifica-tion-inheritance cannot be interpreted as the results of selection operating on germinal variations. in order to do this to the satisfac-tion of the other side, the neo-lamarckians must prove that the characters in question are outside the scope of natural selection, that they are non-utilitarian and not correlated with any useful characters—a manifestly difficult task. the neo-darwinians, on the other hand, have to prove that the phenomena in question cannot be the results of modifica-tion-inheritance. and this is in most cases impossible.”29
i have placed this passage in italics because of its importance from the point of view of the two problems which i am presenting and would remark here that if only all the writers had used professor thomson’s term “modifications” instead of “characters” in the statement of this doctrine much confusion and evasion of plain facts would have been avoided, and yet such workers as the mendelians, if deprived of their clear-cut term “characters” would have been less able to carry on their studies. to this point of terminology i refer below.30
in a world teeming with the life of plants and animals, and in the branch of science which seeks to interpret them, where we enter upon the unknown much sooner than in any other sphere of science, weismann has set out to prove or maintain the most stupendous negative ever framed by the human mind. it would require generations of men to prove this negative, if it were probable, and his case rests mainly on the assumed weakness of his opponents. so what is needed and demanded from the neo-lamarckians is the produc-tion of a few well-attested and verified facts, and, as he admits himself, then it must follow as the night the day that his followers will surrender his characteristic dogma. the more cautious leaders and teachers of the day say that this has not taken place and ask for facts, more facts and still more facts, and this attitude is both judicious and judicial, for example in a teacher so eminent as professor j. arthur thomson. scientific men, in such a position as he occupies with grace and distinc-tion, owe a serious debt of loyalty to ultimate truth and to the inquiring minds of the young students of to-day and to-morrow. those who are in a position of inferior responsibility and honour, and more freedom, just rank and file members of the commons’ house of parliament, may be pardoned if they do not exhibit an excess of deference to authority and if they think for themselves.
two questions.
there are before the scientific jury to-day two very vivid questions.
(1) can modifications in the structure of an individual organism, occurring as a result of its experience, be transmitted?
(2) what is the cause of variation?
if, as weismann taught, the answer to no. 1 is in the negative, there is little use here in trying to answer no. 2, for from the present point of view the two stand or fall together in the study of initiative in evolution. such distributional answers to no. 2 as bateson and de vries may offer do not concern my purpose.
if no. 1 be answered in the affirmative it is sufficient for the purpose of treating initial variations from the lamarckian standpoint, for it is hardly conceivable that nature would neglect so simple and obvious a method of leading upwards and onwards the organisms that inhabit a changing world.
it is very clear from what is written on the subject of evolution to-day that a point d’appui in the process is earnestly desired by many workers and that weismann’s dogma stops the way. a very significant and important remark is made by professor w. mcdougall
in his small book on physiological psychology, with reference to the inheritance of acquired characters, that it is a “proposi-tion which most biologists at the present time are inclined to deny because they cannot conceive how such transmission can be effected. nevertheless the rejection of this view leaves us with insuperable difficulties when we attempt to account for the evolution of the nervous system, and there are no established facts with which it is incompatible.”31 i am aware that in the scheme of observed nature there is evidence of no iron necessity, that the convenience of psychologists should be provided for, and they, like others of us, have to do the best they can with the tools and the materials which exist, and i agree with professor thomson in his remark on misunderstanding no. 1, “that our first business is to find out the facts of the case, careless whether it makes our interpreta-tion of the history of life more or less difficult,”32 but i am persuaded that he will not treat lightly such a statement, from such a source, on such a subject as that i have quoted from professor mcdougall. as to his second statement on the same page “that in the supply of terminal variations, whose transmissibility is unquestioned, there is ample raw material for evolution” it is important as an opinion, and no more, and there is in the present connec-tion, an elusiveness about it which prevents one allowing it to pass. it should be noted that stress is laid upon the term “variations” and from the context this means congenital full-blown “characters” such as those that weismann says are provided in the germ guided by selection. at any rate, initial modifications are not signified by professor thomson’s remark. so for evolution of forms of life it is possible the assertion may be true, but apart from distribu-tion of variations, under the process called amphimixis, some starting point is required for the initial and wholly useless stages of many variations. these may or may not become “characters” or adaptive.
what the problems are not.
the ground may be cleared here by saying what our problems are not. there is no question as to whether lamarckism or darwinism represents the predominant partner in the story of life; there is no question of the “relative importance of natural selection and the lamarckian factors in organic evolution,” though such a question may arise when once lamarckism has received its passport from the authorities; but the time is not yet. nor is it a question as to the reason why adaptive modifications are so constantly
present in the germ. it is not a question of nature or nurture, but perhaps may be found to be a study of nature and nurture. it is not a question of mendelian analysis, nor as to the distribu-tion of either mutations on the one hand, nor of minute fluctuating variations on the other. the problems are therefore limited in scope and ambition, and are none the worse for that, as being better open to correc-tion or support.
the problems considered.
it seems but natural to most persons who contemplate with any care the ever-changing and progressive drama of life in plants and animals that unquestionably the dramatis person? by their individual response to the environments and exercise of their functions must contribute a share, however small, to their offspring. when first this view presents itself to their minds they resent as “unnatural” any other possibility. but, alas! they find that such a conclusion is not permitted in those regions where alone the white light of science shines. here the writ of a priori does not run. the spirit of inquiry makes its challenge to every presupposi-tion and every assertion in its province—even those of current science. i have shown that this particular assump-tion of the natural man was firmly challenged by weismann, who was not the first, but the greatest, biologist to teach that modifications are not transmitted. accordingly, agreeable and convenient as it would be to assume the lamarckian hypothesis as a working one, it needs in the present day to be supported by evidence before this can be allowed. facts, then, against weismann’s dogma are demanded and of such a kind as will satisfy so powerful an advocate of his own views. in passing it may be remarked again that there is nothing so misleading as facts, except statistics, and for both sides to bear in mind the warning of a french writer that in such inquiries as this we should be careful lest we find the facts for which we are looking.
to meet the conditions laid down in professor thomson’s canon i propose to describe certain phenomena which are adduced as instances of modifications in certain mammals whose structure and mode of life are intimately known, and whose ancestry is little in dispute.33 the most convincing of these lines of evidence are those which are shown to be outside the range of any form of selection, as well as the distributional factors of mendel and
de vries. it is well to enumerate here the six different factors in organic evolution which might claim a share in the produc-tion of such humble phenomena as form the subject-matter of this volume—they are:
1. personal selection of darwin.
2. sexual selection.
3. histonal or cellular selection of roux.
4. germinal selection.
5. inheritance according to mendelian principles.
6. inheritance of mutations.
there is a somewhat severe and ill-defined condition attached to the formula in question for it demands that such modifications as will satisfy the neo-darwinians shall not be correlated with any useful character.34 if such a conditio sine qua non were taken too literally it would at once foreclose the case as to the possibility of transmission of modifications at all, the questions of issue ought in that case never to have been raised—and, cadit qu?stio. this cannot be the intention of the biologist who propounds the formula. it could not reasonably be carried so far as to insist that a modifica-tion arising from a certain habit, active or passive, in an animal, and which on that account, and on paper, may loosely be said to be ‘correlated’ with it, is to be ruled out. that would be tantamount to saying for example, that, because an animal must lie down in a certain attitude when it rests, or walk or run in a certain manner, in other words that it is useful to exist, certain modifications claimed to be due to these fundamental parts of existence must be excluded from the inquiry. the neo-darwinian is not a critic easy to be entreated, but that he would not claim. let me take one example of what i mean. a short-haired dog will spend a considerable part of its daily life, and presumably a long line of ancestors did so too, lying with its forelegs planted in front of its chest and its head either raised in the air when awake or resting on the upper surface of the forelegs (of course the familiar attitude of a dog with its body and head curled up and fore-legs doubled is not referred to here). if the hairy coat be examined over its neck and jaw, which lie in this attitude, on and against the forelegs, a remarkable reversal of the direction of the hairs is found and the outline of this forms an accurate mould of the surface applied to the forelegs. this is transmitted of course from previous generations of domestic dogs. a precisely analogous reversal of the hairs is found on the under or extensor surfaces of the forelegs, matching with wonderful
exactness the area of pressure of these on the ground, and anyone can see it who has a canine friend of the fox-terrier type. long-haired dogs display it less neatly outlined. an instance such as this cannot be excluded from the evidence forthcoming because it is correlated with the useful “character” of lying in a certain attitude. such a phenomenon, many similar to which will be seen later, had at any rate an origin de novo at some time in the ancestral stock, and in some way. to discover these is part of my business. the boldest neo-darwinian will not claim that this arrangement of a dog’s hair arose by selectional processes within the germ either in the initial or completed stages.
correlation.
the term “correla-tion” is somewhat scornfully said by weismann to be “unquestionably a fine word,” and it has indeed in biological writings a very varied set of meanings. i will not vex the reader with a reference to our old friend mesopotamia, but mention what dr. vernon in variation in animals and plants says of the term, referring to the relation between stature and head-index in man: “such a statement must vary according to the notion of the observer as to what does and what does not constitute correla-tion.”35 the most approved and precise meaning of the loose term in question is that associated with the work of the biometricians, and a few examples from dr. vernon’s book will show how far this concep-tion of correla-tion is removed from the literal applica-tion of professor thomson’s formula. dr. vernon treats of such phenomena as the correla-tion of the long heads of greyhounds with length of legs, contrasting them with the shortened heads and legs of bull-dogs. he describes also the correla-tion in man between the stature and length of forearm from elbow to tip of middle finger, correlated measurements of crabs, of external structures of prawns, the tufts of polish fowls correlated with perforations in the skull, also certain constitutional peculiarities with colour of skin. these few cases are enough to give an idea of the more precise and fairer accepta-tion of the term, but while these form a useful subject for minute study it may be remarked that they agree also with lamarckian factors as to their origin and development. they are much more in line with darwin’s use of the word and are strangely reminiscent of the well-known example of the irish elk with its great head and horns which was brought forward in favour of lamarckism by herbert spencer. they
breathe an atmosphere of physiology rather than anatomy, or function than form.
enough has been said here by way of defining the terms of the issue. the negative we have to sustain is that the following facts and observations declare that certain small modifications cannot be governed by selection and are not correlated with useful characters. it will be shown later that professor thomson’s stringent condition is not in all of them compiled with, but that, in spite of this, the probability of their being valid examples of lamarckism in practice is immense.