ru r^ a l a m CD o THE FOUNDATIONS OF ZOOLOGY A COURSE OF LECTURES DELIVERED AT COLUMBIA UNIVERSITY ON THE PRINCIPLES OF SCIENCE AS ILLUSTRATED BY ZOOLOGY Columbia ^Entbcrsttg Biological EDITED BY HENRY FAIRFIELD OSBORN AND EDMUND B. WILSON I. FROM THE GREEKS TO DARWIN By Henry Fairfield Osborn II. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES By Arthur Willey III. FISHES, LIVING AND FOSSIL. An Introductory Study By Bashford Dean IV. THE CELL IN DEVELOPMENT AND INHERITANCE By Edmund B. Wilson V. THE FOUNDATIONS OF ZOOLOGY By W. K. Brooks VI. THE PROTOZOA By Gary N. Calkins VII. REGENERATION By T. H. Morgan VIII. THE DYNAMICS OF LIVING MATTER By Jacques Loeb IX. STRUCTURE AND HABITS OF ANTS. (In preparation) By W. M. Wheeler X. BEHAVIOR OF THE LOWER ORGANISMS. By H. S. Jennings COLUMBIA UNIVERSITY BIOLOGICAL SERIES. V. THE FOUNDATIONS OF ZOOLOGY BY ' */ \ .' <>, WILLIAM KEITH BROOKS, PH.D., LL.D. PROFESSOR OF ZOOLOGY IN THE JOHNS HOPKINS UNIVERSITY SECOND EDITION, THE COLUMBIA UNIVERSITY PRESS 1907 reserved vummi V- 'x-^ J/' I &L£:i COPYRIGHT, 1899, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published January, 1899. Reprinted March, 1907. . J. 8. Cushing & Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. Co H?otet College WHERE I LEARNED TO STUDY, AND, I HOPE, TO PROFIT BY BUT NOT TO BLINDLY FOLLOW, THE WRITINGS OF THAT GREAT THINKER ON THE PRINCIPLES OF SCIENCE GEORGE BERKELEY I HAVE, BY PERMISSION, DEDICATED THIS BOOK CONTENTS LECTURE I PAGE INTRODUCTORY ... 3 LECTURE II HUXLEY, AND THE PROBLEM OF THE NATURALIST 33 LECTURE III NATURE AND NURTURE 49 LECTURE IV LAMARCK 83 LECTURE V MIGRATION IN ITS BEARING ON LAMARCKISM 101 LECTURE VI — PART I ZOOLOGY, AND THE PHILOSOPHY OF EVOLUTION . . . ... 123 LECTURE VI— PART II A NOTE ON THE VIEWS OF G ALTON AND WEISMANN ON INHERITANCE . 143 LECTURE VII GALTON, AND THE STATISTICAL STUDY OF INHERITANCE . . . -153 LECTURE VIII DARWIN, AND THE ORIGIN OF SPECIES . . . . . . .183 LECTURE IX NATURAL SELECTION, AXD THE ANTIQUITY OF LIFE 215 vii viii CONTENTS LECTURE X PAGE NATURAL SELECTION AND NATURAL THEOLOGY 241 LECTURE XI PALEY, AND THE ARGUMENT FROM CONTRIVANCE 269 LECTURE XII THE MECHANISM OF NATURE 287 LECTURE XIII Louis AGASSIZ AND GEORGE BERKELEY 317 LECTURE I INTRODUCTORY "The doctrine of idols bears the same relation to the interpretation of nature as that of sophisms does to common logic. It is the peculiar and perpetual error of the human under- standing to be more moved and excited by affirmations than by negations; whereas it ought duly and regularly to be impartial; nay, in establishing any true axiom the negative instance is the most powerful." — FRAN'CIS BACON. LECTURE I INTRODUCTORY IN this course of lectures I shall give, on many questions, the Scotch verdict of "not proven," and experience warns us that this will be interpreted as an assertion that they are proved or disproved, although no one can, in justice, interpret an admission that a thesis may some time be proved or disproved as belief that either of these things will come about, or as an admission of anything else except a suspension of judgment, for all must hold it the height of folly to found a scientific opinion on lack of evidence. If I sometimes speak of things that are not commonly held to fall within the province of zoology, — if I try now and then for soundings in waters which able pilots tell us are far out of the course of our ship, — I hope they who follow me to the end of our voyage will admit that I have not wandered from our true course ; although it may be well to show now, by way of introduction, how it is that zoologists find themselves face to face with many problems which other men of science have agreed to lay aside as insoluble or irrele- vant. I shall try to show that life is response to the order of nature — in fact, this thesis is the text of most of the lectures; but if it be admitted, it follows that biology is the study of response, and that the study of that order of nature to which response is made is as well within its province as the study of the living organism which responds, for all the knowledge we can get of both these aspects of nature is needed as a preparation for the study of that relation between them which constitutes life. Our interest in all branches of science is vital interest. It is only as living things that we care to 3 4 THE FOUNDATION'S OF ZOOLOGY know. Life is that which, when joined to mind, is knowledge, — knowledge in use ; and we may be sure that all living things with minds like ours are conscious of some part of the order of nature, for the response in which life consists is response to this order. The statement that physical phenomena are natural seems to mean little, but the phenomena of life are so wonderful that many hesitate, even at the present day, to believe that nature can be such a wonderful thing as it must be if the actions of all living things are natural ; and, as I shall try to find out in this course of lectures what we mean by the assertion that living nature is natural, I shall now attempt, by a few illustrations, to give a broad outline of some of the most nota- ble features of the nature of living things. The outer surface or shell of a crab is an excretion that is formed once for all; for while it may stretch a little at the joints, it does not grow, and as the living body must in time become too large for it, new shells, one size larger, are formed from time to time under the old one, which is then thrown off. The frequency of these moultings conforms to the rate of growth. The little crab sheds its shell either before or a few minutes after it is hatched from the egg, and a second moulting takes place within forty-eight hours, but the next interval lasts four or five days, and each successive shell remains useful for a longer time, until a mature crab may pass a year or even longer with- out moulting. The process is natural or mechanical, for nothing the crab can do for itself retards or hastens its growth or the secretion of a new shell ; nor can any part of the process be attributed to its own actions, except so far as these actions are due to its nature, although it will not grow unless it seeks and finds food, nor will the old shell take itself off, unless the crab draws its limbs out by bodily movements which are both complex and violent. Many enemies, man and the hard crab among them, prize the soft crab as a palatable delicacy, and as it is helpless and defenceless while moulting, and until the new. shell has grown hard, the crab hides under the sand or among the grass of the marshes until the dangerous crisis is past. No one can say whether the crab is or is not conscious of its danger, or whether it hides voluntarily or involun- tarily, but as no crab which has not escaped its enemies at the moult- ing season now survives, all the modern edible crabs hide by nature, just as they grow and shed their shells by nature. Some crabs pass INTRODUCTORY 5 most of their lives in places which seem to have been sought, at first, for shelter during the moulting period. A species of Porcellana clings to the lower surface of the broad shell of Limulus, and the Pinnixas live in the burrows which annelids make in the floor of the ocean. I have found a species of Pinnixa living on the shoals at Beaufort, N.C., in the parchment-like tubes with which the annelid Chzetopterus lines its burrow, and as the opening of this tube is too small for a Pinnixa to pass, it must enter while small and pass the rest of its life there. The period of moulting is dangerous, not only because of enemies, but also because of its critical nature, for many crabs die in the act, while others lose their limbs and their gills. The general constitutional disturbance is so great that it is difficult to carry a full-grown crab safely through it in an aquarium. The power to replace lost parts which is so well developed in crabs is an adjustment to meet and compensate for this danger among others. Most of the direct danger comes from the stony hard- ness and inflexibility of the old shell, and the shells of crabs like the Pinnixa, and the female Pinnotheres which lives within the shell of the oyster, are softer than those of more exposed crabs. The hermit-crabs and soldier-crabs live in the spiral shells of gasteropod mollusks, and, as these houses are strong enough to furnish ample protection, all the hinder part of the body of these crabs is covered by a thin flexible shell which may be stripped off without danger, although the claws and other exposed parts are covered by very hard strong shell. When born, the little her- mit-crab is straight and its hind-body carries swimming feet, but when it is about as large as a mosquito, these become converted into knobs for clinging to the inside of the house, and the hind- body becomes twisted into a spiral to fit the inside of the spiral shell. Crabs outgrow the shells of mollusks just as children out- grow their clothes ; and hermit-crabs are always on the watch for new shells, and exhibit what the human observer finds himself disposed to call a lively interest in shells. If half a dozen of them are placed in an aquarium, they soon begin to measure and compare shells, and even to make vacant one that seems eligible, by pulling out its occupant piece by piece and eating him. One 6 THE FOUNDATIONS OF ZOOLOGY that has found or emptied a shell that seems to suit, measures it carefully inside and out, and then, bringing the openings close together, quickly pops out of the old into the new. Then the old shell is compared with the new, and often the body is slipped into each of them repeatedly, and each is allowed to slip nearly off and is then pulled on again, somewhat as a man settles him- self into a new coat. Running is now tried in each shell, a claw keeping a tight clutch on the empty one and dragging it along ; and the movement of drawing the body far into the shell, so that it drops on the sand as if it were empty, is tried in both. It is often many hours before a choice is made, and then the decision often is that the old one is best. It is difficult to witness or to describe this performance with- out attributing to the crab feelings and motives like our own ; yet, while no one can say whether the crab knows what it is about or not, nothing is more certain than that its actions are due to its nature, and not to knowledge of the value of a house, drawn from experience. When I was working as a student in the marine laboratory of Alexander Agassiz, he reared from eggs, in an aquarium, a brood of hermit-crabs which had never seen a shell. I had in my aquarium young gasteropods which I had reared from eggs. Some of them had died, and their empty shells were, at his suggestion, dropped into the water with the crabs, which seized them, almost as soon as they touched the water, and beginning to explore their interior as they were carried to the bottom by the weight of the shells, conducted themselves as if they had many years of experience in the use of molluscan shells as houses. I have seen very young hermit-crabs make houses for themselves out of the cast skins of others, although these afforded no protection ; and I have found a full-grown one in the bowl of a clay pipe so badly broken that it exposed the soft abdomen and was useless ; but the impulse to inhabit shells is almost universally protective and beneficial, although it is as strictly a part of the nature of hermit-crabs as is the twisted abdomen, or the legs and claws, or any other part of the crab's body. The external world presents such variety that few natural ad- justments are so exact and definite that they may not under some INTRODUCTORY 7 circumstances prove disadvantageous or even destructive instead of beneficial, although the perfection of many of the adjustments of Crustacea and insects is marvellous. Some hunting wasps store living spiders in the cells with their eggs to serve as food for their young, but each spider, while alive, is paralyzed and helpless, for when the wasp captures it she stings it through the nerve-centre which directs the movements of the limbs, severely enough to produce paralysis without destroying life ; and Mivart says ("Lessons from Nature," p. 202) that the female wasp does this by nature or without experience. It is often said that the natural activities of living things are innate ; but, so far as this word implies that they take place with- out a stimulus, it is obviously erroneous. The hermit-crab is said to seek a house by nature, and the egg to grow into a specific organism in virtue of its inherent potency ; but this is not strictly true, for while some vital changes may be spontaneous, in one of the many meanings of this word, there is no reason to believe that any change ever takes place, either in living things or any where else, without antecedents which stand in that peculiar rela- tion which we call physical causation. The new-born child is said to seek the breast instinctively, but every nurse knows that it does not seek the breast at all without experience, although it does suck by nature and without instruc- tion the first time the nerves of its lips and tongue are stimulated by contact with the nipple. The instinct of the young hermit-crab cannot be called spontaneous, if, by this word, we mean arbitrary, although it is so promptly called forth by the first sight of a shell. The bodily movements of which the purpose is most obvious are, as a rule, called out in response to changes in the external world, and they are excited by stimuli which come through the senses ; although many responsive actions are called forth by stimuli which arise within the body and do not reach it through any of the organs of special sense, as the stretching of our limbs while awakening is excited by the vague discomfort of the body; and this is true not only of many bodily movements but of most physiological changes. "To call mind a function of the brain," says Maudsley ("Re- sponsibility in Mental Disease," p. 17), "may lead to much mis- 8 THE FOUNDATION'S OF ZOOLOGY apprehension if it be thereby supposed that the brain is the only organ which is concerned in the function of mind. There is not an organ in the body which is not in intimate relation with the brain by means of its paths of nervous communication, . . . and which does not, therefore, affect more or less plainly and specifi- cally its function as an organ of mind. It is not merely that a palpitating heart may cause anxiety and apprehension, or a dis- ordered liver gloomy feelings, but there are good reasons for be- lieving that each organ has a specific influence on the constitution and function of mind ; an influence not yet set forth scientifically, because it is exerted on that unconscious mental life which is the basis of all that we consciously feel and think. Were the heart of one man," says Maudsley, "to be placed in the body of another, it would probably make no difference in the circulation of the blood, but it might make a real difference in the temper of his mind. So close is the physiological sympathy of parts in the commonwealth of the body, that it is necessary, in the physiologi- cal study of mind, to regard it as a function of the whole organ- ism, as comprehending the whole bodily life." A most notable illustration of the way a complicated adaptive mechanism may be thrown into beneficial response by a physio- logical stimulus, is found in the shad, which, when its bodily structure is excited by the reaction of approaching sexual matu- rity, leaves its home in the ocean and enters upon a journey which, before its path was obstructed by dams, carried it across the broad states of Virginia, Maryland, and Pennsylvania, to its spawning ground in central New York. The excitement of adaptive vital changes in one part of the body by changes in another part is not restricted to the channels afforded by the nervous system. Florists make their plants bloom before their time by confining their roots in small pots. The seeds of an apple are new beings, but the apple itself is part of the substance of the mother-tree, yet the blossoms will not set fruit unless they are fertilized. When a duck's egg is put under a hen, it undergoes a long series of wonderful changes, which all prove, in the end, to be in respon- sive adjustment to the normal life of ducks ; and as the production of a duck by the mere heat of a hen, or that of a lamp in an incu- INTRODUCTORY 9 bator, is incredible, we say the egg is developed by its inherent potency ; but we must use these words with care, for the assertion that the changes which make up this long and marvellous series take place spontaneously is as incredible as the assertion that they are determined by the heat of the hen ; and there is reason to believe that each change in the series transmits to the natural or inherent adaptive mechanism a stimulus which excites in it the performance of the responsive actions which bring about the next change in order. Embryonic development is so delicate and so complicated that we cannot hope to trace, far less to imitate, the action of these stimuli in anything like their natural perfection ; yet we can, now and then, rudely imitate some of them, while, in other cases, we can demonstrate their presence and influence indirectly by preventing them from acting. Some eggs which have begun their development by division into two, four, or eight cells, may be shaken apart with- out destroying their vitality, and when thus separated, a cell which would normally have given rise to half or quarter of an embryo, may give rise to a whole one of one half or one quarter the natural size. Embryologists are rapidly adding, by experimental methods, to our knowledge of the mechanics of development, and it has been known, since the day of Aristotle, that some of the latest stages in the development of the higher animals and of man do not take place in the absence of certain normal physiological stimuli. Male mammals, for example, do not attain bodily perfection until the approach of sexual maturity. In man the beard begins to grow at what is accordingly called the age of pubescence ; the larynx enlarges ; the voice assumes a manly tone ; the shoulders grow broad ; the chest deepens ; and the trunk and limbs begin to differ in relative length from those of women and children. At the same period in the life of a bull his neck and shoulders grow massive and sturdy ; his forehead broadens and becomes cushioned with hair ; and he becomes pugnacious and subject to fits of violent rage. The cock acquires his spurs, his brilliant plumage and other ornaments, and begins to crow. Aristotle pointed out that when young male mammals or birds are prevented from becoming sexually mature, they fail to acquire the distinctive characteristics of their species, and this shows that the completion of this, the final stage 10 THE FOUNDATIONS OF ZOOLOGY in their physical development, is dependent, to a great degree at least, on some constitutional stimulus which is afforded by the changes which take place in the reproductive organs. The existence of rudimentary organs and provisional larval stages is one of the most suggestive facts in the whole range of zoology, and the evidence that these things are a record of past history seems conclusive ; although those who hold that their existence is accounted for by the discovery that they are a "recapitulation" add nothing, after all the centuries, to Aristotle's declaration that they are "for a token." They who are most convinced that the historical significance of these structures is an adequate explanation of their presence, are also most emphatic in their repudiation of teleology, and in the rejection of the belief of Louis Agassiz, that they are part of the language in which the Creator tells us the history of creation ; yet the assertion that their history accounts for their existence is as teleological as anything in Paley. They who believe that inheritance is not the transmission of re- sponsive actions, but the transmission of an adaptive mechanism, and that each change which enters into the history of development is a response to a stimulus, will have no difficulty in understanding that organs which were once adjusted to the external world may, after this adjustment has lost its meaning, be still retained, because they furnish physiological stimuli, which excite developmental changes in the organic mechanism. If a physiological stimulus from the male reproductive organs excites the growth of weapons of defence, would the preservation of rudiments of these organs, by natural selection, for this useful purpose, be anything more than might be expected ; even if some change in the method of reproduction should make their primary function useless? Is there any evidence that any change which is due to nature, from the segmentation of the egg to old age, ever takes place without a stimulus, or are the actions which are due to nature beneficial, except so far as the environment is, on the average, like the ancestral environment ? Since the gentle stimulation of the lips and tongue has been associated, in the past history of human infants, with the presence of milk which may be extracted INTRODUCTORY II by sucking, the adjustment is beneficial ; although the infant does not, as a matter of fact, obtain any milk at first, and although a finger or a rubber nipple on an empty bottle, or any other object of suitable size and texture, in the mouth of a hungry infant, excites the nerves and muscles so as to call forth the act of suck- ing, and, so far, to satisfy the calls of nature. Preyer says "when I put into the mouth of the screaming child, whose head alone was as yet born, the ivory pencil or a finger, the child began to suck, opened its eyes, and seemed, to judge from its countenance, to be most agreeably affected. In the case of another child, which cried out immediately after its head emerged from the womb, I put my finger, three minutes later, into the child's mouth, and pressed it on the tongue. At once all crying ceased, a brisk sucking began, and the expression of the countenance, which had been hitherto discontented, became suddenly altered. The child, not yet fully born, seemed to expe- rience something agreeable, and therewith — during the sucking of the finger — the eyes were widely opened." Although changes which are directly due to nature do not take place without a stimulus, they do take place mechanically, or independently of experience, under the natural stimulus, or under any other which is applied in the same way. The blow- fly, which is stimulated by the odor of putrid flesh to lay its eggs where the larvae will find abundant food, sometimes lays them on the stinking arum, misled by its odor. In this case the deceptive stimulus resembles the normal one in certain sensible qualities, but it is most important, for reasons which will be given later, to note that the natural responses of living things may be called forth by any stimulus which is similar in its mode of application to the normal or natural stimulus, whether it is or is not similar in any sensible properties except those which act as the stimulus. The finger, which feels like a nipple, stimulates the infant and calls out the sucking response, but electrical stimulation of the lips and tongue, if applied with sufficient skill, might give the same result, although this does not resemble the nipple in any sensible qualities except the ones which effect the stimulation. In the order of nature each stimulus is a sign with a signifi- cance, and our own reason, which consciously apprehends the 12 THE FOUNDATIONS OF ZOOLOGY significance of natural signs, generally approves the responsive actions of living things, although we find that these living things are often misled by signs which we know to be illusions, which, while similar in some respects to those to which the organic mechanism is adjusted, signify something quite different from the normal or customary course of events. As the nature of living things often leads to injurious or de- structive actions, instinct is said to be blind or mechanical ; for while no one can say whether the actions of the hermit-crab or those of the blow-fly, or those of the human infant, are voluntary or not, they are no more than the nature of these living things would lead one to expect, and this is as true when they are beneficial as it is when they mislead. If the adjustments between living things and the external world were always beneficial, I do not see how the question whether or not their actions are voluntary could present itself ; but the complexity of external nature is inexhaustible, and few natural adjustments are beneficial under all circumstances, for even a response to gravitation may mislead. A growing plant needs the moisture and the soluble food which it may find under ground, in course of nature, by follow- ing the stimulus of gravity, and it also needs the sunlight and the air which, in the normal or natural order of things, are to he reached by upward growth. As the seed germinates, the radicle, stimulated by gravity, grows downwards, while the plumule, which does not differ essentially from the radicle in specific gravity, is impelled by its nature to grow upwards under the same stimulus; but each part grows by means of internal energy, and, while gravity is the stimulus which throws it into action, it is not the means by which the vital changes are brought about. The response is beneficial, and the stimulus seems as trust- worthy as anything in nature ; yet the seeds often fall into places where it misleads. If a germinating seed be placed on the edge of a horizontal wheel which turns slowly at a rate which makes the centrifugal force somewhat greater than the weight of the seed, the plumule grows towards and the radicle away from the centre, although no seeds which act thus can grow up to produce seeds in their turn. If plants think, a matter on which INTRO D UCTOR Y 1 3 I do not here express an opinion, they must know the order of nature to which they respond, and in that case the seed on the wheel would seem to be not only misled but deceived, exactly as a brood of chicks seems to us to be deceived by an imitation of the call of the mother hen; but the essential point is that, whether they know it or not, the changes in living things which are directly due to nature are beneficial only so far as the condi- tions of their life are, on the average, essentially like those in which the lives of their ancestors were passed. Now the order, of nature presents infinite diversity : the differ- ent ways in which events may be combined are innumerable ; and no natural response can be judicious or beneficial under all cir- cumstances. We accordingly find, in all the living things we know best, and are most intimately concerned with, a wonderful provision of their nature, by means of which those of their actions which are most apt to mislead are improved and perfected and developed by normal use, so that we are no longer able to tell what they will do from knowledge of their nature alone, since their actions are in part dependent on their training and expe- rience, and on their individual contact with the world. The question whether capacity for improvement through con- tact with the world is natural or not is much easier to ask than to answer. Are the benefits that attend training and education and experience part of the nature of living things, or do they add to nature something it did not before contain ? Is knowledge of the world around us part of our nature, or does it add something new on to our nature ? If it is natural, do we simply find or dis- cover our nature, or do we make it or any part of it ourselves ? Any answer we try to give is attended with difficulties. If living things make any part of their nature, the word must mean much more than is recognized in common usage ; and yet the assertion that knowledge and experience and training add nothing to 'the nature of living beings is beset by difficulties which at first sight seem equally grave. In some cases we can show that improvement by training is no more than might have been expected, for we can imitate it by means of stimuli which have nothing in common with the natural stimuli except the manner of their application. Normal 14 THE FOUNDATIONS OF ZOOLOGY use strengthens muscles and increases their aptitude for doing their work, but as muscles may also be strengthened by massage, their improvement by use is no more than their nature might have led us to look for; nor do we find any more difficulty in attributing this beneficial response to nature than we find in the same explanation of the house-hunting actions of crabs. All who have to do with animals admit that training can do no more for them than to make the best of their natural capa- city, for they differ greatly in power to profit by experience; and the nature of each species sets impassable bounds to the power of individual animals to improve by practice. No one hesitates to attribute to deficient structure the inability of idiots to learn, and all admit that men of genius are born and not made, yet many hesitate to confess that their own more commonplace capacity for profiting by practice and growing wiser with experi- ence is strictly limited by their nature, although this may be quite obvious to others. All know too well also that a dose of alcohol may make a man remember what never happened outside his own disordered brain, and perform responsive actions which, while criminal, might be prudent and commendable if the remembered experience were not a delusion ; although the effects of contact with the world are usually far too complicated and diversified to be artifi- cially imitated. As we are quite unable to tell with any minute accuracy what an animal with capacity for training will do under a stimulus, we must rely upon indirect evidence to show what the real significance of experience is. If a chick is stung by the first honey-bee it catches, its future actions may be adjusted to the natural law that bees are danger- ous; but if, before it is stung, it has captured and eaten stingless drones, it may act in accordance with the wider law that while bees are good for food some are dangerous. A careful observer, Mr. Oilman Drew, tells me that the chicks that are most destruc- tive to bees pick out the drones, and he believes that these are the chicks which, before they were stung, learned to catch and eat bees, and that they have afterwards learned to let the sting- ing workers alone. „• If slight differences in the mere order of events which are otherwise so much alike may lead to such differences in the con- INTRODUCTORY 1 5 duct of individual animals of the same species, it is clear that even if we believe that sufficient knowledge of their nature would enable us to predict their conduct, this knowledge is unattainable, for we cannot possibly know all the complicated personal history of any one animal. We must also remember that even if we prove that individual animals acquire, by contact with the ex- ternal world, nothing but what their nature provides for, this does not show that they are compelled to make of themselves all that their nature permits, for the effects of experience are often injurious or destructive. There is, unfortunately, no incompati- bility between the system of things and unprofitable experience, for it is, to say the least, no harder to corrupt or injure nature by injudicious or pernicious training than it is to make the best of it. Romanes tells us ("Mental Evolution in Animals," p. 215) of a hen that had reared three successive broods of ducklings in suc- cessive years, and then hatched out a brood of nine chickens : " The first day she was let out she disappeared, and after a long search my sister," his informant writes, "found her beside a little stream, which her successive broods of ducklings had been in the habit of frequenting. She had got four of her chickens into the water, which, fortunately, was very shallow at the time. The other five were all standing on its margin, and she was endeavoring by all sorts of coaxing hen-language, and by pushing each chicken in turn with her bill, to get them into the water also." In the normal course of the history of chicks, the response to the order of nature which experience is said to have called out in this hen, would be rapidly fatal to her posterity; and it would be easy to give other illustrations to show that the changes which are called forth in living things by the influence of the world around them, are beneficial only so far as this external world is, on the average, substantially the same as that to which the actions of their ancestors were adjusted. The snake that swallows hens' eggs, like its ancestors, profits like them ; but the snake that swallows a china nest-egg dies from indigestion. I shall try to show that this fact, and others like it, mean that while the changes would not take place without practice or training, their character is due to nature, and not to experience. It is almost impossible to contemplate the actions of animals 1 6 THE FOUNDATIONS OF ZOOLOGY that profit by experience, without attributing them to conscious intelligence, and it is even harder to speak or write of them, with- out using words which imply that they are altogether such as human actions would be under like conditions, for our words are adapted to human needs; but, hard as it is, we must, so far as possible, distinguish what we actually observe from what we infer from our knowledge of ourselves. He who considers the relation between mind and matter should try to determine clearly what he knows and does not know about the distribution of mind. Is not the view of the matter to which all should agree, about as follows ? I know my mental state and the things- 1 see and feel by the best of all evidence. While I have not this sort of evidence for anything else, doubt that my fellow-men are rational would be regarded as insane ; for he who acts as if his fellow-men have no feelings, is justly abhorred by all, unless, indeed, he is held in honor as a military hero. "A close study of the dog," says Agassiz, "might satisfy every one of the similarity of his impulses with those of man, and those impulses are regulated in a manner which discloses psychical faculties in every respect of the same kind as those of man ; moreover, he expresses by his voice his emotions and his feelings, with a precision which may be as intelligible to man as the articulate speech of his fellow-men. His memory is so retentive that it frequently baffles that of man. And though all these faculties do not make a philosopher of him, they certainly place him, in that respect, upon a level with a consider- able proportion of poor humanity." " When animals fight with one another, when they associate for a common purpose, when they warn one another in danger, when they come to the rescue of one another, when they display pain or joy, they manifest impulses of the same kind as those which are considered among the moral attributes of man. The range of their passions is even as extensive as that of the human mind, and I am at a loss to distinguish a difference in kind between them, however much they may differ in degree and in the manner in which they are expressed." " I confess," says Agassiz, " I could not say in what the mental faculties of a child differ from those of a young chim- panzee." INTRO D UCTOR Y 1 7 While the evidence does not have that highest degree of value which I find in my own feelings, good common sense seems to demand that the burden of proof fall on those who hold that apes and dogs and elephants are not rational. "Who," asks Agassiz, "is the investigator, who having once recognized such a similarity between certain faculties of man and those of the higher animals, can feel prepared, in the present stage of our knowledge, to trace the limit where this community of nature ceases ? " As for myself, I try to treat all living things, plants as well as animals, as if they may have some small part of a sensitive life like my own, although I know nothing about the presence or absence of sense in most living things ; and am no more prepared to make a negative than a positive statement. While it is non- sense to regard trees and rocks and lakes as endowed with mind, it is nonsense because we know nothing about it, and not because it is untrue ; for it is no less nonsense to assert that stones are unconscious than to assert that they are conscious. Morgan says ("Habit and Intelligence," p. 41), "To some chicks I threw cinnabar larvae, distasteful caterpillars conspicuous by alternating rings of black and golden yellow. They were seized at once, but dropped uninjured; the chicks wiped their bills — a sign of distaste — and . seldom touched the caterpillars a second time. The cinnabar larvae were then removed, and thrown in again towards the close of the day. Some of the chicks tried them once, but they were soon left. The next day the young birds were given brown loopers and green cabbage-moth cater- pillars. These were approached with some suspicion, but pres- ently one chick ran off with a looper, and was followed by others, one of which stole and ate it. In a few minutes all the cater- pillars were cleared off. Later in the day they were given some more of these edible caterpillars, which they ate freely ; and then some cinnabar larvae. One chick ran, but checked himself, and, without touching the caterpillar, wiped his bill — a memory of the nasty taste being apparently suggested at the sight of the yellow and black caterpillar; another seized one and dropped it at once. A third subsequently approached a cinnabar as it crawled along, gave the danger note, and ran off. Then I threw in more edible c 1 8 THE FOUNDATIONS OF ZOOLOGY caterpillars, which again were eaten freely. The chicks had thus learnt to distinguish by sight between the nice and nasty cater- pillars." " The cinnabar caterpillars are, as I have said, conspicuously marked with alternating yellow and black rings. It would seem that the end of this conspicuousness is to render association in the individual experience of young birds more rapid and more certain ; there does not appear to be any congenital and instinc- tive avoidance of such caterpillars with warning colors. The net result of these observations is that, in the absence of parental guidance, the young birds have to learn for themselves what is good to eat, and what is distasteful, and have no instinctive aversions." In his discussion of these most instructive observations, the author says, p. 150: "A chick sees for the first time in its life a cinnabar larva, instinctively pecks at it under the influence of the visual stimulus ; seizes it, and under the influence of the taste- stimulus instinctively shrinks. So far we have instinct and automatism. Presently we throw to it another similar caterpillar. Instinct and automatism alone would lead to a repetition of the previous series of events ; seeing, seizing, tasting, and shrinking. The oftener the experiment was performed, the more smoothly would the organic mechanism work, the more definitely would the same sequence be repeated — seeing, seizing, tasting, shrinking. Is this what we actually observe ? Not at all. On the second occasion the chick, under the influence of the previous experience, acts differently. Though he sees, he does not seize, but shrinks without seizing. We believe that there is a revival in memory of the nasty taste. And in this we seem justified, since we may observe that sometimes the chick on such occasions wipes the bill on the ground as he does on experiencing an unpleasant taste, though he has not touched the larvae. The chick, then, does not continue to act merely from instinct and like an automa- ton. His behavior is modified in the light of previous experi- ence." So far as our senses tell us, actions of this sort are, in all respects, like many we observe in our fellow-men, and attribute to consciousness and memory and reason; and as a mistaken belief INTRODUCTORY 19 that the brutes are conscious can do no harm, while belief that they are unconscious might, if mistaken, bring untold misery upon dumb brutes from brutal men, it seems well that we should con- tinue to describe their actions in subjective language ; although nothing is more obvious than that, while we know their actions, we only infer the existence of mental accompaniments. For all any one knows to the contrary young chicks may learn what is good to eat and what is unpleasant, and may readily associate the appearance with the taste, and those who hold that they are un- conscious may justly be called upon by Morgan to prove their opinion ; but I cannot agree with him that his studies show that they are conscious, for in sober and scientific truth all they show is that the chicks rapidly acquire power to respond to certain optical stimuli by actions which are adjusted to those flavors which in course of nature are associated with certain optical properties. They who live in the hope that the actions which the chick performs only after what we call experience, will sometime be proved as mechanical as the response of the growing seedling to gravitation, may appeal to the rapid progress which physiol- ogists are making in the localization of the functions of the brain, as evidence that their hope is well founded. They may say that there is good reason to believe that, if the localized and specialized brain-cells which are stimulated through the eyes and the optic nerves by the yellow and black rings of the cinnabar caterpillar, could be stimulated by electricity or in any other way with sufficient delicacy and skill, all the other changes which make up the response would follow mechanically ; that the nervous discharge from these cells would be accompanied, as it has been before, by the stimulation of those localized cells which were origi- nally stimulated by the pernicious flavor, and that the nervous discharge from them would inhibit the seizing movements, and that whether the chick is conscious or not, the establishment of the response by experience is no more than might have been expected from our knowledge of the functions of the nervous system. If we answer that this is as yet unproved, inasmuch as no one is able now, or is at all likely to soon be able, to even demon- 20 THE FOUNDATIONS OF ZOOLOGY strate, far less to imitate, in the brain of the chick, any struct- ural equivalent to its experience, we may be told that no one expects complete inductive proof of any scientific generalization ; that he who refuses to admit that all water consists of H2O until chemists have decomposed every drop of water in the ocean is lacking in good sense; and that it is equally unreasonable to de- mand the artificial imitation of all the responses of living things before we admit that all response is mechanical. To this we must answer that no great harm can be done if the chemist interprets the admission that we have not the slight- est reason to doubt that every drop of water is decomposable into hydrogen and oxygen as an assertion that all water is so decom- posable, since, for all the ordinary purposes of chemistry, the negative admission and the positive assertion may be treated as if they were synonymous. The case is very different when the subject under consideration is not chemistry, but the nature of knowledge, for we are about to enter a field where we may easily lose our way unless we distinguish inference from perception, to the best of our ability. The utmost the physiologist is warranted in asserting is that, for all one knows to the contrary, every response may be mechanical; and I think all thoughtful students must so far agree with him as to admit that belief that any of the responsive actions of living beings are not mechanical is highly unwise and precarious, in view of the condition and prospects of modern physiology ; although we must, in my opinion, also admit that not one single vital response has as yet been completely ana- lyzed, or resolved, from beginning to end, into phenomena of matter and motion ; for I am myself unable to discover, in the present status of biology, any demonstration of error in the assertion that life is different from matter and motion. However this may be, we know, by evidence which no one can question, that many actions are attended by memory, and by con- scious experience, and by volition and reason and a sense of moral responsibility. Many beneficial responses are known to be judicious and reasonable, and many voluntary acts are known to be right or wrong. As these convictions seem, at first sight, to be contradictory to the opinion that, for all we know to the contrary, all response may INTRODUCTORY 21 be mechanical, we must ask whether this contradiction is real or only apparent. As this question has, in one form or another, vexed the mind of man for untold ages, no one would be so bold as to attempt a final answer in few words; but I hope all who follow me to the end may find reason to ask themselves whether the con- tradiction may not, after all, be a matter of words rather than a real difficulty, for I shall try to review, at one time and another, some of the evidence which has convinced many thoughtful men that this apparently insoluble puzzle has arisen from an erroneous and un- scientific conception of the meaning of the mechanism of nature. This evidence seems so clear and conclusive that I cannot see how any one who has mastered it can find any contradiction between anything we find in our nature and the ultimate reduction of all nature, including all the phenomena of life and of mind, to mechani- cal principles; for most students of the principles of science agree that natural knowledge is no more than the discovery of the order of nature; although a moment's thought is enough to show that the fact that events do take place in order is no reason why they should, or even why they should take place at all. Order is no explanation, but a thing to be explained. The proof that there is no necessary antagonism between me- chanical explanations of human life and belief in volition and duty and moral responsibility seems to me to be very simple and easy to understand. If the subject takes us into deep waters, this is because we are compelled to examine the reason why the impres- sion that these things are antagonistic has so widely prevailed; for the view of the matter to which I hope to call your attention is, in itself, by no means difficult or obscure. Science is still in its infancy, and we know so little that I have no sympathy with those who discount the possibilities of future dis- covery and assert that life is merely a question of matter and motion, although I know no reason why this should not, some day, be proved, nor am I able to see why any should find this admis- sion alarming. However this may be, I am convinced that they stand on treacherous ground, who base positive opinions on negative evi- dence, and believe that anything in our nature is inconsistent with mechanics. 22 THE FOUNDATIONS OF ZOOLOGY / " Conscience, the last acquired faculty," says Maudsley, " is the first to suffer when disease invades the mental organization. One of the first symptoms of insanity — one which declares itself before there is any intellectual derangement, before the person's friends suspect even that -he is becoming insane — is a deadening or com- plete perversion of the moral sense. In extreme cases it is observed that the modest man becomes presumptuous and exacting, the chaste man lewd and obscene, the honest man a thief, and the truthful man an unblushing liar. Short of this, however, there is an observable impairment of the finer moral feelings — a something different, which the nearest friends do not fail to feel, although they cannot always describe it. Now these signs of moral perversion are really the first symptoms of a mental derangement which may, in its further course, go through all the degrees of intellectual disorder, and end in destruction of mind, with visible destruction of the nerve- cells which minister to mind. Is the end, then, dependent upon organization, and is the beginning not ? " " Note, again, the effect which a severe attack of insanity some- times produces upon the moral nature of the individual. The per- son entirely recovers his reason ; his intellectual faculties are as acute as ever, but his moral character is changed ; he is no longer the moral man that he was; the shock has destroyed the finest part of his organization. Henceforth his life may be as different from his former life as, in an opposite direction, was the life of Saul of Tarsus from the life of Paul the Apostle to the Gentiles. An attack of epilepsy has produced the same effects, effacing the moral sense as it effaces the memory sometimes, and one of the most striking phe- nomena observed in asylums is the extreme change in the moral character in the epileptic which precedes and heralds the approach of his fits. A fever or an injury to the head has, in like manner, transformed the moral character." Passing this subject by for the present, it is clear that, consciously or unconsciously, arbitrarily or naturally, freely or of necessity, every living thing responds to some part of the order of nature, and that the study of this order is part of biology; for there are many reasons, besides those we have considered, why the biologist should have peculiar interest in the principles of science. His studies bring him into intimate contact with certain conceptions which play such a INTRODUCTORY 23 subordinate part in the other sciences that it falls to him to assert their importance, since they are so little regarded outside his circle that students in other lines often fail to catch what he has in mind. Among these are the principle of genetic continuity and the prin- ciple of fitness, with all that they imply. For all I know to the contrary, the principle of fitness may be universal, and the order of nature may be the order of fitness ; and again, for all I know to the contrary, all significant resemblances between the phenomena of nature may be due to genetic continuity ; but, at the present day, these principles hold no prominent place in the minds of those who deal with the not-living, and their introduction among the principles of science is due to the biologists. Now only a moment's thought is needed to discover how great are the difficulties that attend the application of these principles. What do we mean by the genetic continuity of life ? How are we to interpret the facts of embryology ? How many perplexing intricacies face us if we undertake, with William Harvey, "to seek the truth regarding the following difficult questions : Which and what principle is it whence motion and generation proceed ? Whether is that which in the egg is cause, artificer, and principle of generation, and of all the vital and vegetative operations, — conservation, nutrition, growth, — innate or superadded ? and whether does it inhere primarily, of itself, and as a kind of nature, or intervene by accident, as a physician in curing disease ? Whether is that which transfers an egg into a pullet inherent or acquired ? " "In truth," says Harvey, "there is no proposition more mag- nificent to investigate or more useful to ascertain than this : How are all things formed by an univocal agent ? How does the like ever generate its like ? Why may not the thoughts, opinions, and manners now prevalent, many years hence return again, after an intermediate period of neglect ? " 1 As we find embryologists, two hundred and fifty years aft'er these words were written, still vexing themselves over the question, — Whether is that which transfers an egg into a pullet inherent or acquired? — it is clear that we cannot hope for much progress in the investigation of this magnificent proposition unless we can deter- mine what we mean by that metaphysical notion, inherent potency. 1 Harvey, " De Generatione," pp. 274-582. 24 THE FOUNDATION'S OF ZOOLOGY " By way of escape from the metaphysical Will-o'-the-Wisps generated in the marshes of literature and theology, the serious student is sometimes bidden," says Huxley, "to betake himself to the solid ground of physical science. But the fish of immortal memory, who threw himself out of the frying-pan into the fire, was not more ill advised than the man who seeks sanctuary from philosophical persecution within the walls of the observatory or the laboratory ; for metaphysical speculation follows as closely upon physical theory as black care upon the horseman." l If, as modest biologists, we were to assert that the biological aspects of the physical sciences are the only basis for rational interest in these sciences, our good friends in physical and chemical laboratories would, no doubt, charge us with arrogance, although I think they must admit that the principles of science, as dis- tinguished from the concrete sciences, are part of biology. We cannot investigate response to the order of nature without asking what the order of nature is. What are the properties of things and of thought that convince us of its existence ? What is this conviction worth ? What are the methods by which knowledge of this order is acquired and perfected and extended ? How far are these methods and instruments trustworthy? Are any limits to their application known, and, if so, how known? To all these questions the zoologist has a peculiar right to ask answers, in addition to the right which he shares with other stu- dents of science. "The Mind, her acts and faculties," says Berkeley, "furnish a new and distinct class of objects, from the contemplation whereof arise other notions, principles, and verities. It may therefore be pardoned if this rude essay doth, by insensible transitions, draw the reader into remote inquiries and speculations, that were not, perhaps, thought of either by him or by the author at first setting out." Some, who believe they at least are rigorously scientific, may here feel impelled to cry out that these inquiries are not scientific, but metaphysical, and that modern men of science have nothing to do with them. For my own part, I might be disposed to agree with them if the average human mind were, on these difficult 1 Huxley, VI., p. 200. INTRODUCTORY 2$ matters, a tabula rasa ; but ignorance and prejudice and education all conspire to predispose us to some form of a priori philosophy, and most men who have not given hard thought to the subject hold fast, consciously or unconsciously, to belief in the universal and necessary conservation of energy, to belief in a necessary law of universal progress or evolution, to belief in the arbitrary and absolute freedom of the will, or to belief in some other a priori notion which they hold necessary and ultimate, or arbitrary and absolute. " The maxim that metaphysical inquiries are barren of result," says Huxley, "and that the serious occupation of the mind with them is a mere waste of time and labor, finds much favor in the eyes of many persons who pride themselves on the possession of sound common sense; and we sometimes hear it enunciated by weighty authorities, as if its natural consequence, the suppression of such studies, had the force of a moral obligation." " In this case, however, as in so many others, those who lay down the law seem to forget that a wise legislator will consider, not merely whether his proposed enactment is desirable, but whether obedience to it is possible. For if the latter question be answered negatively, the former is surely hardly worth debate." " Here, in fact, lies the pith of the reply to those who would make metaphysics contraband of intellect Whether it is desirable to place a prohibitory duty upon philosophical speculations or not, it is utterly impossible to prevent the importation of them into the mind. And it is not a little curious to observe that those who most loudly profess to abstain from such commodities are, all the while, uncon- scious consumers, on a great scale, of one or another of their mul- titudinous disguises or adulterations. With mouths full of the particular kind of heavily buttered toast which they affect, they inveigh against the eating of plain bread. In truth, the attempt to nourish the human intellect upon a diet which contains no meta- physics is about as hopeful as that of certain Eastern sages to nourish their bodies without destroying life." " Everybody has heard the story of the pitiless micro&opist, who ruined the peace of mind of one of these mild enthusiasts by show- ing him the animals moving in a drop of the water with which, in the innocency of his heart, he slaked his thirst ; and the unsuspect- 26 THE FOUNDATIONS OF ZOOLOGY ing devotee of plain common sense may look for as unexpected a shock when the magnifier of severe logic reveals the germs, if not the full-grown shapes, of lively metaphysical postulates rampant amidst his most positive and matter of fact notions." 1 Kant has shown, as Berkeley showed before him, that, instead of discovering truth, philosophy has only the modest merit of preventing error, and if men never made mistakes, but always reasoned wisely and acted rightly, we should little need to study the nature of know- ledge ; but while few men think, all have opinions ; and there are certain perennial errors, idols, as Bacon calls them, which find in the mind of man a dwelling-place so congenial that the doctrine of idols bears the same relation to the interpretation of nature as that of sophisms does to common logic. As we are forced, by the imperfection of our nature, to study the principles of knowledge in order to guard ourselves from error, it makes little difference whether we call the principles of science metaphysical or not. We speak of physical science, but it would surely be more repug- nant to the usage of common speech to call the principles of science physical than to call them metaphysical; for, while the data of science are things known to sense, we must ask, with Berkeley, whether it is not certain that the principles of science are neither objects of sense nor of the imagination ; whether they do not arise in the mind itself; whether the sensible world is anything more than the stimulus which calls forth the innate or latent powers of the mind. We assuredly have no sense-organ by which a principle may be perceived, except so far as we have by nature an organ of com- mon sense. If the principles of science are perceived at all, rather than apprehended, they must be perceived by some inner sense, for which we know no sense-organ. " As understanding perceiveth not, that is, doth not hear, or see, or feel, so sense knoweth not ; and although the mind may use both sense and fancy, as means whereby to arrive at knowledge, yet sense or soul, so far forth as sensitive, knoweth nothing. For, as it is rightly observed in the ' Theaetetus ' of Plato, science con- sisteth not in the passive perceptions, but in the reasoning about them." 1 Huxley, " Collected Essays," VI., pp. 288, 289. INTRODUCTORY 2/ Some, who so far agree with Plato, may be led to remind Berke- ley that objects of sense are not only first considered by all men, but most considered by most men ; and that the possession of opinions may be no evidence of reason. Truth, he tells us, is the cry of all, but the game of few ; and while there may be wisdom in a multitude of counsellors, Huxley reminds us that it is in but one or two of them. Some may assert that, admitting that we have no sense-organ by which we perceive the relation between a pattering sound on the roof and a shower, the connection between the sound of rain and the falling drops is nevertheless physical and not mental ; and that response to the order of nature is no evidence of reason, since we do not attribute judgment to the mimosa, which, stimu- lated by the falling drops, folds its leaves that the rain may reach its roots. They may also assert that, if the structure and history of all parts of our own organic mechanism were fully known, we should be able to show that the principles of science are physical; that we apprehend them because our minds are the ones which have survived the struggle for existence ; and that these principles are no more than natural selection would lead one to expect ; although we must ask whether we find in nature any reason why what we expect must happen ; whether natural selection is an efficient cause, or only a generalization from experience ; and whether experience is not itself a state of mind. We may point out that hope is not science, and that no one has, as yet, deduced the principles of science from brain anatomy ; and we may ask whether, if this were accomplished, the anatomical structure of the brain, and of the other organs which we study by our senses, is not a thing perceived; whether perception is not mental; and whether a thing perceived by sense is not a phenomenon of mind. We may also ask whether proof that our organ of common sense has come about, like our eyes and ears, by the survival of the fittest, would tell us any more about the relation between mind and matter than our eyes and ears tell us now. I am not able to answer the question whether, in ultimate analysis, the principles of science are physical or metaphysical. I know nothing about things ultimate. I do not know what the 28 THE FOUNDATIONS OF ZOOLOGY relation between mind and matter is. I do not know whether the distinction between "things perceived by sense" and "rela- tions apprehended by the mind" is founded in nature or not; but I am sure that natural knowledge is useful to me, that it is pleasant, and profitable, and instructive; and I must ask whether all this does not show that nature is intended. This introductory summary of some of the topics I shall try to handle in the following lectures shows that these topics are neither few nor simple, nor am I so bold as to think that I can set any one of them on a firm foundation ; for, like William Harvey, I do not wish what I say "to be taken as if I thought it a voice from an oracle"; although I hope it may "stir up the intellects of the studious to search more deeply into so obscure a subject." I shall make no attempt at originality, but shall try to give you some of the results of my own study of the thoughts of others. Bacon tells us indeed that it is seldom in our power to both admire and surpass our author; since, like water, we rise not higher than the springhead whence we have descended; but I cannot agree with him that the attempt to put the thoughts of others in a new dress necessarily leads to the great injury of learning, for we often fail to master the wise thoughts of one who is not of our own times because his turn of words does not fit our point of view. All I have to say is anticipated in invention and is varied only by the method of treating it. " For," like Montaigne, " I make others to relate (not after my own fantastic, but as it best falleth out) what I cannot so well express, either through unskill of language or want of judgement. I number not my borrowings, but I weigh them. And if I would have made their number to prevail, I would have had twice as many." But I trust that, Bacon notwith- standing, I have neither corrupted the labors of my predecessors nor contributed to the slavery of the sciences. The lectures which follow have been prepared at different times, and for various reasons ; but I hope that, as I have arranged them, they will exhibit unity of purpose, and the logical develop- ment of that purpose, which, in a word, is this: To show to them who think with Berkeley, that " it is a hard thing to suppose INTRODUCTORY 29 that right deductions from true principles should ever end in consequences which cannot be maintained or made consistent," that, in my opinion, there is nothing in the prevalence of mechani- cal conceptions of life, and of mind, or in the unlimited exten- sion of these conceptions, to show that this hard thing to suppose is true. LECTURE II HUXLEY, AND THE PROBLEM OF THE NATURALIST LECTURE II1 HUXLEY, AND THE PROBLEM OF THE NATURALIST ALL thoughtful students will prize the essays and addresses on Education which make up the third volume of Huxley's " Collected Essays." When written, these were regarded by most readers as special pleas for scientific education ; but nothing could be farther from the truth, although the prominence of "science" in their titles gives some ground for this impression. They who read them now, after scientific education has become an assured fact, will find that Huxley shows, here as elsewhere, that he is no radical, seeking to sweep away the ancient landmarks, but an enthusiastic admirer of all that is good in the old, as well as a zealous advocate for the new in education. While he improves every opportunity to set forth the need for scientific education, he tells the student that he is a man and a citizen as well as a student ; and the delights and the discipline of literature and art and history are emphasized again and again, and each essay is a plea for liberal culture ; although he never fails to demand the removal of the accumulated ashes, and the rekindling of the pure^ flame, until the very air the student breathes shall become " charged with that enthusiasm for truth, that fanaticism of veracity, which is a greater possession than much learning ; a nobler gift than the power of increasing knowledge." No one — Huxley least of all — would dream of attributing the " New Reformation " to any one man, and he speaks of himself as " a full private who has seen a good deal of service in the ranks " of the army ranged around the banner of physical science ; but the object to which he tells us he has devoted his life — the diffusion among men of the scientific spirit of " organized common sense " — 1 This lecture is part of a Review of Huxley's Essays, which was printed in the Forum, November, 1895. D 33 34 THE FOUNDATIONS OF ZOOLOGY has made notable progress during his lifetime, and in this assurance he tells us at its end that he " shall be content to be remembered, or even not remembered," as one among the many who have brought it about. Of all Huxley's essays, those which deal with the development rather than the application of the method of using one's reason rightly in the search for truth are of most value to the student. Among them are the whole of Volume VI., " Hume ; with Helps to the Study of Berkeley" ; as well as the one "On Descartes' Dis- course Touching the Method of Using our Reason Rightly ; and of Seeking Scientific Truth " (I. iv.), and many others, such as "Possibilities and Impossibilities" (V. vi. 1891), and "Scientific and Pseudo-Scientific Realism " (V. ii. 1887). The opening paragraph of the book on Hume's Philosophy (VI. 57) may be taken as a statement of the purpose of all these essays : " Kant has said that the business of philosophy is to answer three questions : What can I know? — What ought I to do ? — and, For what may I hope ? But it is pretty plain that these three resolve themselves in the long run into the first. For rational expectation and moral action are alike based upon belief, and a belief is void of justification unless its subject-matter lies within the boundaries of possible knowledge, and unless its evidence satisfies the conditions of credibility. . . . Fundamentally, then, philosophy is the answer to the question, What can I know ? " Huxley is not drawn into this province by the fierce joy of con- troversy, nor by any desire to join those who flit forever over dusky meadows, green with asphodel, in vain search for some reality which is not within the reach of all. His motive is the most practical and serious one we know, — " to learn what is true in order to do what is right." This, he tells us, "is the summing up of the whole duty of man, for all who are not able to satisfy their mental hunger with the east wind of authority." The conclusion of the whole matter is that "there is but one kind of knowledge and but one method of acquiring it." This is the melody which runs through all the nine volumes ; now loud and clear, now hidden by the minor inter- est of a scientific topic, or by the heat of controversy or by the charm of literary genius; but always present, and easy — for one who listens — to detect. It is because scientific education helps us to acquire the method of using our reason rightly in the search HUXLEY, AND THE PROBLEM OF THE NATURALIST 35 for truth, and not because science is the one thing worth knowing, that he pleads for it so eloquently. It is because the improvement of natural knowledge is conclusive testimony to the value of this method that he devoted his life to the popularization of science. It is because his right to use this method — the right which is also the highest and first of duties — was disputed, that he entered the stormy waters of controversy. " If I may speak of the objects I have had more or less definitely in view, . . . they are briefly these : To promote the increase of natural knowledge, and to forward the application of scientific methods to all the problems of life, to the best of my ability, in the conviction, which has grown with my growth and strengthened with my strength, that there is no alleviation for the sufferings of mankind except veracity of thought and action, and the resolute facing of the world as it is when the garment of make-believe with which pious hands have hidden its uglier features is stripped off." To what nobler end could life be devoted than the attempt to show us how we may " learn to distinguish truth from falsehood, in order to be clear about our actions, and to walk surefootedly in this life " ? If he has succeeded, and every zoologist who is free to fol- low Nature wherever she may lead is a witness that he has suc- ceeded, — if, as the end of his lifelong labor, intellectual freedom is established on a firmer basis, — this is his best monument, even if the man should quickly be forgotten in the accomplishment of his end. No memorial could be more appropriate than the speedy establishment of that intellectual liberty which is not intellectual license on a basis so firm that the history of the struggle to obtain it shall become a forgotten antiquity. Huxley's lifelong devotion to the task of teaching the right method of using our reason in the search for truth has been so fruitful that the success or failure of his attempts to teach the application of this method to specific problems is a matter of very subordinate importance. As he was not only a man and a citizen, but, above all, a natu- ralist, peculiar interest attaches to his utterances on the problems of biology, although his various essays on this subject differ so much in perspective that their effect upon many thoughtful readers has proved to be practically equivalent to inconsistency. It is easy 36 THE FOUNDATIONS OF ZOOLOGY to show that, in this case, as in others, the responsibility rests with the reader and not with the author ; but, however this may be, the opinion that his utterances are inconsistent is real and therefore a proper subject for examination. Huxley's frame of mind in 1854 is embodied in the essay "On the Educational Value of the Natural History Sciences" (III. ii.), from which I copy the following passage (p. 43): — "What is the cause of this wonderful difference between the dead particles and the living particles of matter appearing in other respects identical? — that difference to which we give the name of life ? I, for one, cannot tell you. It may be that by and by philosophers will discover some higher laws of which the facts of life are particular cases, — very possibly they will find out some bond between physico-chemical phenomena on the one hand and vital phenomena on the other. At present, however, we assuredly know of none ; and I think we shall exercise a wise humility in confessing that for us, at least, . . . this spontaneity of action . . . which constitutes so vast and plain a distinction between living bodies and those which do not live is an ultimate fact : indicating, as such, the existence of a broad line of demarcation between the subject-matter of biological and that of all other sciences." Between 1854 and the publication of the essay "On the Physical Basis of Life" in 1868, natural science advanced with strides which have no parallel, and the "Origin of Species" brought about a revolution in our conceptions of the history of living nature. It is not surprising that Huxley's point of view undergoes significant change, and that a new aspect of nature now excites his interest and absorbs his attention. The establishment of the doctrine of the continuity of life on a firm basis, and the acceptance of the generalization that all living things are related by birth, had given new meaning to the familiar truth that they are all fundamentally identical in structure; and the essay of 1868 deals with this aspect of living organisms. The essay is regarded by many readers — both those who look upon it with horror and those who make it the basis of a biological creed — as contradictory to the essay of 1854; but I, for one, am unable to find in it any basis for this opinion. Its motive — the truth that "protoplasm is the basis of life"; that "it is the clay of the potter, which, bake it and paint HUXLEY, AND THE PROBLEM OF THE NATURALIST 37 it as he will, remains clay, separated by artifice and not by nature from the commonest brick or sundried clod," is no novelty. In fact, the essay is nothing more than a statement in modern terms of the new evidence which modern science furnishes in con- firmation of the familiar conviction that, so far as his physical basis is concerned, man hath no preeminence above the beasts ; that they all have one breath ; that is, the rain on the earth which causes the bud of the tender herb to spring forth ; that as for the earth, it giveth us bread ; that the vital spark is soon quenched unless it is kept alive by fuel from without ; that the living machine must soon break down and wear out ; and that then shall return the dust to the earth as it was. Huxley says : " Past experience leads me to be tolerably certain that when the propositions I have just placed before you are accessible to public comment and criti- cism they will be condemned by many zealous persons, and perhaps by some few of the wise and thoughtful." They who remember the reception of the essay are aware that this expectation was not disappointed, but it is hard to understand why ; for its substance, if not its modern language, has been the common property of some of the wise and thoughtful for ages. I do not see why any one should challenge Huxley's statement that "it seems to me that we are logically bound to apply to protoplasm or the physical basis of life the same conceptions which are held to be legitimate elsewhere. If the phenomena exhibited by water are its properties, so are those presented by protoplasm its properties." We may have practical objections, based on expediency and not on logic, to the further statement that "we live in the hope and in the faith that by the advance of molecular physics we shall, by and by, be able to see our way as clearly from the constituents of water to the properties of water as we are now able to deduce the operation of a watch from the form of its parts and the way they are put together." Faith and hope are good things no doubt, and "expectation is permissible when belief is not "(VIII. 1870); but experience teaches that the expectation or faith of the master is very apt to become belief in the mind of the student, and "science warns us that the assertion which outstrips evidence is not only a blunder, but a crime." (III., IV., 150, 1880). In order to avoid all danger of adding to the criminal classes it 38 THE FOUNDATIONS OF ZOOLOGY is perhaps as well for those who are teachers to keep their faith outside the laboratory as much as possible. With this qualification I have nothing but approval for the pas- sage quoted, as well as for the rest of the essay. Like Huxley, I hold that we are logically bound to apply to protoplasm the same conceptions as those which are held to be legitimate elsewhere. Without believing, I certainly see no reason for doubting that all the properties of organisms may possibly be some day deduced from the nature and disposition of their constituent molecules. If I should live to see this proved, I should believe it without remodel- ling any beliefs I now hold ; for most assuredly I do not believe that these activities are the result of anything else than physical structure. I simply do not know, and have no belief whatever on the subject, although I welcome every addition to our knowledge of the properties of the physical basis of life, in the conviction that this knowledge is a necessary condition for progress. I must also insist, however, that nothing seems more obvious to me than that we might study the form of the parts of a watch, and the way they are put together, till the crack of doom, without understanding it in any sense worthy the name. To understand it we must study not only its mechanism and the movements to be deduced from it, but the movements of the earth as well ; and then we must study a third thing, — that relation between the two which fits a watch for man's service. I hold that, in this sense of the word, we can "understand" watches, and that good common sense forces us to admit not only that the fitness of a watch is real, but that it is the only basis for rational interest in watches. Analogies are dangerous weapons, because of our fondness for pushing them farther than the facts warrant, and for assuming that resemblance in one feature involves resemblance in other features. The fact that living things are like watches in their fitness, in their adjustment to the phe- nomena of the external world, at once suggests many interesting questions with which I have no intention to deal at present. This particular resemblance is obvious, and I hold that whatever may be possible to the zoologist of future ages, the only method of study- ing this fitness which is available at the present day is like that which we apply to watches. Huxley says : " If the properties of water may be properly said HUXLEY, AND THE PROBLEM OF THE NATURALIST 39 to result from the nature and disposition of its component molecules, I can find no intelligible ground for refusing to say that the prop- erties of protoplasm result from the nature and disposition of its molecules." I know no reason why any one should "refuse to say" this, except that "the assertion which outstrips evidence is a crime." When it has been proved, I, for one, shall say it cheerfully ; but I cannot forget that we have been taught for two thousand years and more that life is not a property of the physical basis like the prop- erties of water, but a relation, an adjustment between the properties of the organism and of those of the environment, between the changes which take place in the body and those which go on in the world around it ; that this adjustment serves to promote the welfare of the species, and that we know nothing comparable to it in water or in anything else except living beings, and their products, such as watches, and spiders' webs, and birds' nests. ^ The author of our oldest book on zoology opens it with the following statement of its purpose : — " To say what are the ultimate substances out of which an animal is formed ... is no more sufficient than would be a similar account in the case of a couch. For we should not be content with saying that the couch was made of bronze or of wood, or whatever it might be, but should try to describe its design or mode of composition in preference to the material. ... It is plain that the teaching of the old physiologists is inadequate, and that the true method is to state what the definite characters are that distinguish the animal as a whole. ... In fact, to proceed in exactly the same way as we should do if we were giving a complete description of a couch." 1 If this is true, if life is not a property like those of water, but an adjustment between properties, it must be clear that no amount of knowledge of any properties of the physical basis except the property of fitness can ever give us a science of life, although it must be equally clear that knowledge of all its properties is a necessary condition for progress. My comment on the essay " On the Physical Basis of Life " is that, while I fully agree with it, I hold with Aristotle that it is "inadequate," although I am quite prepared to admit the possibility that this inadequacy may be due 1 Aristotle, " Parts of Animals," I. i. 40 THE FOUNDATIONS OF ZOOLOGY to my own limitations, and not to the nature of the subject. While I find nothing in the essay which need give any one a moment's " nightmare," I am equally unable to find in it any warrant except "faith "for the dogma that biology — the science of life — now is, or is at all likely soon to be, the study of the physical and chemi- cal properties, or any other property except fitness, of the physical basis. The partial failure of training in biological laboratories to make naturalists of the students, or to excite in them that interest in the homes of living things which has so often proved a greater delight than art or literature ; its failure to stimulate the investigation of those relations between animals and plants and the world around them which constitute life, — has begun to attract attention and to excite comment. Among the many reasons assigned for this failure " microtomes " have occupied a prominent place and have been held to be the seat of the mischief, although no one can treat seriously the assertion that we can have too many or too refined means for research into structure. From long acquaintance with many students and from much discussion with them I have satisfied myself that the belief that our biology (the biology of the present day, and not that of the unknown future) ends with the study of the structure and functions of the physical basis — the belief that biology is "nothing but" the discovery of its physical and chemical properties — has much to do with it. My experience also tells me that the essay " On the Physical Basis of Life " is appealed to as a scientific warrant for this belief, although we have seen that it affirms nothing more than a " hope " for this consummation. This ground was all worked over before Aristotle's day, and perhaps it may not be too much of a flight of the imagination to inquire what he might have thought of this essay. Do not his reflections in the " Parts of Animals " warrant the assertion that his comment would be something like this ? — " Your natural science interests me more than anything else in your modern world ; and your century is distinguished beyond all others for progress in the history of life. I am delighted with this essay, and no other pleasure could compare with that which I should find in a course of study in the properties of living things with the aid of your appliances for research ; but are you quite sure HUXLEY, AND THE PROBLEM OF THE NATURALIST 41 that the whole case is stated in the essay ? While clay is the physical basis of the potter's art, its essence is fitness for the use of man : and what concerns us is not that he uses clay, but that he makes from it now a foundation-brick and now an ornamental coping ; now a homely kitchen pot, and now a graceful urn. I have studied your wonderful chronometers until I am 'able to deduce the operations of a watch from the form of its parts and the way they are put together'; but I failed to understand them until I perceived that relation between their movements and those of the earth which constitutes their fitness for man's service. I tried, long ago, to show that something very similar is true of living things. We may sometime be able to foresee or deduce all their actions from their structure, but at present, as in my own day, the only available way to understand them is to study their relations to the world around them. " My teaching that the essence of a living being is not what it is made of, nor what it does, but why it does it, has been rendered by one of your contemporaries into the statement that life is the continuous adjustment between internal and external relations. If this is true, is not the biology which restricts itself to the physical basis, and forgets the external world, like your play of ' Hamlet ' without the Hamlet ? Is not the biological laboratory which leaves out the ocean and the mountains and meadows a monstrous ab- surdity ? Was not the greatest scientific generalization of your times reached independently by two men who were eminent in their familiarity with living things in their homes ? " You ask, ' What better philosophical status has vitality than aquosity ? ' — and I ask you in turn what better status has voli- tion than vitality? — yet you find the employment of this word 'both useful and justifiable.' You can separate water into its elements and then, by recombining them, you can get water again ; and this you may repeat as often as you choose ; but can you, as yet, do anything of the sort with living things ? When by the methods of the laboratory you have made a living being ; when you have made not merely protoplasm, — nor even protoplasm capa- ble of nutrition, growth, reproduction, and contraction, — but proto- plasm able to maintain persistent adjustment to the shifting world around it, — then, and not till then, will I admit that my word 42 THE FOUNDATIONS OF ZOOLOGY ' vitality ' (^y%e) has reached the end of its long career of useful- ness. "I admitted long ago that it is as truly a property of a bird to build a nest as it is a property of water to freeze ; but our interest in the nest lies in its fitness for maintaining the species. I hear it said among you that science has nothing to do with the Why, but only with the How ; but we can surely give answers to the questions 'Why do men make and buy watches ?'-—' Why do birds pursue their prey ? ' — ' Why do they flee their enemies ? ' — and ' Why do they make nests ? ' — answers which are good and sensible, although they are incomplete. "The naturalists of your day are adding continually to the overwhelming evidence for a truth which was unsuspected in mine — the mutability of species and the continuity of life. If I could now publish a new edition of the ' Parts of Animals,' I should treat with more consideration than they seemed to merit two thousand years ago the views of my contemporaries who held that extermination and survival have a good deal to do with fitness, but I should still contend that the study of fitness is the true aim of biology." This comment on the current interpretation of the essay on "The Physical Basis of Life" seems to me to be good common sense and therefore good science ; and it also seems to me to be a legitimate application of the teachings of the "Parts of Animals." Huxley makes many references to the problems of biology in later essays, but space will permit us to examine none except the last. In 1894 I find certain Prolegomena (IX. I, 1894) in which it is easy to read between the lines clear indications that, notwith- standing the period represented by the essay on "The Physical Basis of Life," Huxley ended as he began, — almost, if not alto- gether, in the old-fashioned conviction that living things do, in some way and in some degree, control or condition inorganic nature ; that they hold their own by setting the mechanical properties of matter in opposition to each other, and that this is their most notable and distinctive characteristic. He says the flora of the region where he writes was in a " state of nature " until three or four years before, when the " state of nature was brought to an end, so far as a small patch of soil is concerned, by the interven- HUXLEY, AND THE PROBLEM OF THE NATURALIST 43 tion of man. The patch was cut off from the rest by a wall. . . . In short, it was made into a garden. ... It will be admitted that the garden is as much a work of art or artifice as anything that can be mentioned. The energy localized in certain human bodies, directed by similarly localized intellects, has produced a collocation of other material bodies which could not be brought about in a state of nature. The same proposition is true of all the works of man's hands, from a flint implement to a cathedral or a chronom- eter : and it is because it is true that we call these things arti- ficial, term them works of art or artifice, by way of distinguishing them from the products of the cosmic process, working outside man, which we call nature, or works of nature. The distinction thus drawn between the works of nature and those of man is universally recognized, and it is, as I conceive, both useful and justifiable." I trust that the thoughtful reader will perceive that the legiti- mate pursuit of this line of reflection leads straight back to the Aristotelian statement, in the essay of 1854 (III. ii. 40), that "to the student of life [as contrasted with the student of physics] the aspect of nature is reversed. Here incessant and, so far as we know, spontaneous change is the rule ; rest the exception — the anomaly to be accounted for. Living things have no inertia and tend to no equilibrium." Many biologists find their greatest triumph in the doctrine that the living body is a "mere machine"; but a machine is a colloca- tion of matter and energy working for an end, not a spinning toy ; and when the living machine is compared to the products of human art, the legitimate deduction is that it is not merely a spinning eddy in a stream of dead matter and mechanical energy, but a little garden in the physical wilderness ; that the energy localized in living bodies, directed by similarly localized vitality, has pro- duced a collocation of other material bodies which could not be brought about in a state of physical nature, and that the distinc- tion thus drawn between the works of non-vital nature and those of life is both useful and justifiable. What this distinction may mean in ultimate analysis I know no more than Aristotle or Huxley ; nor do I believe that any one ever will know until we find out. One thing we may be sure it 44 THE FOUNDATIONS OF ZOOLOGY does not mean — that the living world is anything but natural ; for all men of science must agree with Aristotle (" Parts of Animals," III. ii. 16) that "in all our speculations, therefore, concerning nature, what we have to consider is the general rule " (not forces, or causes, or necessary laws). " For that is natural which holds good either universally or generally." If we are to understand this fitness which is so distinctive of living things, this must be brought about, not by keeping it locked out of sight as a chamber of horrors, but by bringing it into the bright light of day; by " intending the mind " upon it ; by attacking it with Descartes' method of using one's reason rightly for the discovery of truth. Whether this method is or is not adequate, we shall know when we find out ; but we have no other, and the discoveries of Wallace and Darwin give a basis, not for a belief, but for a hope that it may some day prove adequate. Times are changed since Huxley warned his hearer in 1868 that, in accepting protoplasm as the physical basis of life, he was "placing his foot on the first rung of a ladder which, in most people's estimation, is the reverse of Jacob's and leads to the an- tipodes of heaven." Nowadays "Scientific Rip Van Winkle" and " Aristotelian " arc the mildest phrases applied to him who holds that life is i.iore than a basis, — to him who doubts whether the essay states the whole or even the most essential part of the case ; and he is lucky if he is not told that he is a " Spiritualist," "false to the spirit of Science"; or at the very least that he is "illogical." In this case he can only say with Huxley (IX. 10, 1894) that "if it is urged that the . . . cosmic process cannot be in antagonism with that . . . which is part of itself, I can only reply that if the conclusion that the two are antagonistic is logi- cally absurd, I am sorry for the logic, because, as we have seen, the fact is so " ; or, as Aristotle expresses it, it holds good. My own interest in this distinction is entirely practical and not philosophical. Whatever philosophical basis it may have or may not have, it seems to me that no one can question its practical bearing on the study of biology at the present day and for many ages to come. If it is urged that our knowledge of the external world is destined to be resolved, in the long run, into our con- sciousness of changes in the physical basis of our minds, and HUXLEY, AND THE PROBLEM OF THE NATURALIST 45 that the "external world" to which plants and animals respond is also to be resolved into changes in their physical basis, I am quite willing to admit this possibility ; as I am ready to admit that, for anything I know to the contrary, the reality of both the external world and the physical basis itself may consist in being perceived or known, but I hold it unwise to forget that the same daily experience which justifies our confidence in the orderly se- quence of external nature also warrants the assumption that their external world is the same as ours. The question whether its reality is ideal or material or both has no more to do with this purely practical confidence than has the presence or absence in a dog or an oak tree of conscious belief in it. They who hold the faith that science will some day be able to demonstrate, in the structure of the brain, the origin of such actions as writing a review of Huxley's Essays, are quite welcome to their faith ; but I hold, as a purely practical matter, that they may find out in a much shorter way why I have written this article ; and I also hold that this is likely to be the case for some considerable time. I also believe with Aristotle that the most practical way within our reach of studying that adjustment between the organism and the external world — that fitness — which constitutes life, is to learn all we can about the physical basis and all we can about its fitness ; and I hold fast to this purely practical confidence without any faith in the unknown biology of the distant future, and most assuredly without any desire to discount it. I must ask, however, what reason there is for thinking that belief that my volition is both real and part of the cosmic process is logically absurd. The greatest of all my many great debts to Huxley is the clear perception that there is no antagonism between belief that all the phenomena of nature, including those of life and mind, are mechanical, and my confidence in the value of my reason. If Huxley is right in the assertion that mechanical principles are nothing more than generalized statements of our experience, — as I am convinced that he is, — and if the widest of all generaliza- tions from my experience is that my volition counts ; how can belief in the value of my reason be logically absurd ? May not the logical absurdity lie with them who hold that proof that my 46 THE FOUNDATIONS OF ZOOLOGY rational actions are no more than might have been expected from the working of the mechanism of my body, would also prove that my reason is "as completely without any power to modify that working, as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery"? LECTURE III NATURE AND NURTURE LECTURE III NATURE AND NURTURE THIS chapter, which all who have attended my lectures during the last ten years will find familiar, does not deal with the inter- minable question whether "acquired characters" are inherited, but, granting that this may be the case, it is an attempt to weigh the value of this "factor" in natural history. Herbert Spencer tells us that the segmentation of the backbone is the inherited effect of fractures, caused by bending, but Aristotle has shown ("Parts of Animals," I. i.)that Empedocles and the ancient writers err in teaching that the bendings to which the backbone has been subjected are the cause of its joints, since the thing to be accounted for is not the presence of joints, but the fitness of the joints for the needs of their possessor. It is an odd freak of history that we of the end of the nine- teenth century are called upon to reconsider a dogma which was not only repudiated two thousand years ago, but was even then called antiquated. " Is there anything whereof it may be said : See ! this is new ? It hath been already of the old time which was before us." In this day of laboratories, are we not in danger of forgetting the first principle, so clearly put by Aristotle, that the thing to be explained is not the structure of organisms, but the fitness of this structure for the needs of living things in the world in which they pass their lives ? We must be on our guard lest the great discovery that protoplasm is the physical basis of life obscure the truth that what Huxley has called the physical basis is one thing, while what Aristotle has called the essence of life is quite another thing. The physical basis of a locomotive engine is the expan- sion of steam, but its essence is fitness for the service of man. E 49 50 THE FOUNDATIONS OF ZOOLOGY Since we accept the utility of steam-engines as a fact that does not call for explanation, we say we understand them when we have discovered that they do neither less nor more than their mechanical structure would lead us to expect. It is also clear that we might understand them, in this sense of the word, even if they grew, like animals, ready made ; although it is equally clear that we should ask, in this case, how they became fitted for human needs ; and that we should not admit that we understand them so long as this question is unanswered. So it is, not only with the works of man and other living things, but with the liv- ing things themselves. All they do may sometime prove no more than might be expected from their physical basis ; but this proof would not show why the things they do are useful to the beings that do them, or to their species. While there is nothing novel in Herbert Spencer's well-known dictum, that life is adjustment, it should help the modern reader to grasp the significance of Aristotle's teaching, to the effect that the essence of a living being is not protoplasm, but purpose. A living being is a being with properties which are useful to the possessor or to his species. If, like Paley, I kick a stane, I may change its position, raise its temperature, and bring about other changes that might all be computed from a few simple data. What happens if, instead of a stone, I kick a dog ? In addition to certain changes which are obviously mechanical, like those in the stone, I start a new set of changes which could never be computed from the study of the kick alone. But note this remarkable fact : Show me the dog, and I may be able to tell you what he will do. If he have short hair, a pink skin, a big occipital crest, great cheek muscles, a long mandibular bone, a short nose with little pigment, small red eyes and crooked legs, he will not act like a dog with silky ears, curly hair, large dark eyes, a long, black pointed nose, a bushy tail, and long legs with big feet. What has the color of a dog's nose or the size of his feet to do with the effect of the kick ? Obviously, nothing at all ; but the changes in the dog which follow the kick are not its effect, for they might follow an unsuccessful attempt to kick precisely as NATURE AND NURTURE 51 they follow an actual blow. The color of his eyes and the other marks are racial characteristics which show what his ancestry has been ; how his parents and more remote progenitors have behaved under similar assaults. With this scientific knowledge of dogs we may conjecture, with some confidence, how this one will behave ; but in order to compute his conduct with anything like accuracy, we must have still more information. If his master habitually beat or bully him, he will not act like a dog brought up with more discretion. If he be young, and have not learned in- dependence and self-reliance and distrust of strangers, he will not act like an older and wiser dog; and if eyes and teeth and limbs be failing from old age, his conduct will be still different. If the kick wake him from sleep, he will not act like a dog disturbed while eating ; nor will a lost dog, oppressed by a sense of his own friendlessness, act like one whose master is near; nor one assaulted at home like one on strange ground, where he has no rights ; nor one attacked in the discharge of his duty like one detected in forbidden pleasure or in theft. The attitude of the assailant, or even such little things as the size of the pupil of his eye, or the contraction of one or another facial muscle, will tell the dog what emotions accompany the kick; and, if I myself be accompanied by a dog, this third party may modify the result without any share in the assault. What a difference between a kick against a dog and one against a stone ! In one case the simple conditions may be stated in few words, and the result may be computed; while in the other, a book would not suffice for the statement of all the facts, and the best science of our day is powerless to compute the result. I am fully prepared to believe, whenever it is proved, that all the conditions which modify the result are embodied, in one way or another, in the structure of the dog; for I know no reason why we should seek them anywhere else. While there will be plenty of time for a positive opinion when it is proved, I see no reason to doubt that, if the dog's body could be preserved without change, it might, some day in the ages to come, be studied by a naturalist who would be able to tell what conduct would have followed the kick, just as we foresee the effect of an opened valve 52 THE FOUNDATIONS OF ZOOLOGY in a steam-engine. If absence of disproof were proof, they who assert that, so far as complexity is in question, the difference be- tween the actions of a stone and those of a dog is merely a differ- ence of degree, not of kind, may have some ground for their belief, inasmuch as no one can say it may not some day be demonstrated. I, for one, see no other reason, than that no one knows, for doubt whether sufficient knowledge might not enable us to foresee or deduce the actions of the dog from the structure of his body ; but we have not yet noted the most essen- tial characteristic of his actions. They are significant. They have a meaning. They stand in judicious adjustment to the canine world ; and their meaning can never, so far as I can see, be learned by studying his body; for if the meaning which our minds apprehend is embodied in any structure, it must be in our own, rather than in that of the dog. It may be that all that makes up the dog's external world is imprinted in his organiza- tion, and that the naturalist of some distant age may be able to there exhibit it, just as the photographer brings out the picture on his negative ; but even if this were done, the picture would still remain only an image of an external world which, while more limited, is otherwise practically the same as our own. However this may be, the only way to study the meaning of the dog's actions, at the present day, is to seek it in his environment; in the conditions under which he and his ancestors have lived ; nor, in order to study this meaning, need one know whether the dog is aware of it. While there seems to be good ground for reasonable confi- dence that the dog is conscious and rational, we know nothing whatever concerning the presence or absence of consciousness in most living things, although we do know that their actions are beneficial to them and such as our reason approves; and that this is the real difference between them and a stone; for while the actions of the stone may, for all I know to the contrary, be useful to the stone, my reason does not approve the statement that this is the case, for it is a matter about which I know nothing. Science may some day enable us to predict the actions of the dog from the study of his body; but I do not see how we are to understand them without studying the conditions under which he NATURE AND NURTURE 53 and his ancestors have passed their lives. Whether he shut his eyes, throw back his ears, and, straightening his tail, plant his teeth in my leg, or crouch at my feet, with his muscles relaxed, his ears pendent, and his tail trailing on the ground, or, putting his tail between his legs, run away howling, the reason for his conduct is not the pain of the blow, but the importance of escape from the further injury which may follow. The means he adopts are those which have been favorable to this result in the past history of dogs. The dog, no doubt, knows, just as we do, that, in the ordinary course of events, the attack is a sign of a disposition to do him farther harm ; and he also knows he may arrest or avert this by doing something, on his own part, to meet it ; but, in case of most organisms, we know only the response and not the consciousness of it. The kick is a sign of something which may follow, and the actions which do follow are not the effect of the kick, for they are directed or adjusted, either consciously or unconsciously, to an event of which it is only the forerunner. This is what we mean, or, at least, an essential part of our meaning, when we say the dog is alive, while the stone is not. It is possible that the properties of the stone may be useful to the stone, but these words are mean- ingless to us ; although we do know that the properties of the dog are useful to the dog or to his species. The changes in the stone are the effect of the blow ; while those in the dog are, in some way, the result of the past history of the dog and of his an- cestors ; for, all through this history, violent assaults have been asso- ciated with danger of further violence. This difference is as wide as the difference between life and its absence ; and the inde- pendence of biology as a science is due to its existence. It is what Herbert Spencer means by the statement that life is adjustment, and it is what Aristotle means by teaching that the essence of a living being is not what it is made of nor what it does, but why it does it. A living thing is a being which responds to the changes which go on in the world around it ; for life consists in the maintenance of adjustment between the changes which occur in the external order of nature and those which go on in the living body. Life is response to the established order of external nature; and, so 54 THE FOUNDATIONS OF ZOOLOGY far as it is joined to consciousness and volition and reason, it is identical with the practical application of scientific knowledge. If we were sure that all living things are conscious and endowed with memory and volition, as they may be for all I know to the contrary, we might define life as knowledge in use ; for the re- sponsive actions of living things are such that our reason approves them as judicious and beneficial. This truth has often found ex- pression in the statement that living things use the properties of the world around them for their own good or the good of their species. The same thought may be expressed by the statement that life is the use of the natural language of signs; for each stimulus to a vital act is a sign with a significance; and the act is itself a response to the significance of which, in course of nature, the stimulus is a sign. To study life we must consider three things : first, the orderly sequence of external nature ; second, the living organism and the changes which take place in it ; and, third, that continuous adjust- ment between the two sets of phenomena which constitutes life. The physical sciences deal with the external world, and in the laboratory we study the structure and activities of organisms by very similar methods ; but if we stop here, neglecting the rela- tion of the living being to its environment, our study is not biology or the science of life. Now, whatever its equivalent in the struct- ure of organisms may be, the reality in our own minds behind such words as use, fitness, and response, is not a phenomenon, which can, in this century at least, be weighed or measured or made manifest to sense, but a relation, apprehended by our think- ing minds ; for beneficial response is one thing, and conscious apprehension of the benefit of response quite another thing. Men who know nothing of the sciences of optics and acoustics profit, like philosophers, by seeing and. hearing; as do also the snail and the jelly-fish, whether they know they have eyes and ears or not. While biology presents endless opportunities for the profita- ble application of the methods of research which are employed in physical science, it also brings before us a new problem, the problem of fitness, which demands new methods of inquiry, and is different from the physics and chemistry of the living body. NATURE AND NURTURE 55 The origin of those useful properties in the employment of which life consists is one of the most fascinating and instructive subjects in the whole range of human inquiry, for to it knowledge itself owes its significance. While there is so much that we do not know, we do know that the qualities which fit the dog for his place in nature, and enable him to respond to the changes which go on in the world around him, are, in part, transmitted from his ancestors, while they are, in part, the result of his individual training and experience and education and contact with the world. The opinion that the effects of his individual history may be transmitted to his descendants, the belief that he may inherit the effects of the experience and education and training of his an- cestors, has come to be formulated as " the inheritance of ac- quired characters"; although I, for my own part, never use this form of words without protest. If any assert that the dog in- herits anything which his ancestors did not acquire, their words seem meaningless ; for, as we use words, everything which has not existed from the beginning must have been acquired ; although one may admit this without admitting that the nature of a dog is, wholly or to any practical degree, the inherited effect of the environment of his ancestors. Francis Galton, borrowing, I suppose, from "The Tempest," many years ago contrasted the nature and the nurture of living things ; and I propose to examine the question whether the nature of a dog or of any other living being is inherited nurture. This is very different from the question whether the effects of nurture are ever inherited, and I have no desire or intention to discuss this interminable subject; for I find as little value in the a priori arguments of those who hold that " acquired characters " cannot be inherited as I find in Haeckel's assertion that "belief in the inheritance of acquired characters is a necessary axiom of the Monistic creed." So far as the question is whether the nature of organisms is wholly or to any practical degree inherited nurture, I think it no more than right to say that my own view of the matter was formed many years ago, before the recent revival of discussion, and that, while I have followed this, I have found no reason for 56 THE FOUNDATIONS OF ZOOLOGY making any essential change. One morning, some time ago, I found in my mail two papers by naturalists whose well-earned reputation in their own fields would seem to entitle them to speak with authority. In one I read that American indifference to the destruction of our valuable timber is the inherited effect of the long war with the primeval forest which our ancestors were forced to carry on in order to make a home in the new world. The author of the second paper accounts for the great size of the eyes of certain deep-sea fishes by attributing their enlarge- ment to the efforts of many generations to see in " total " darkness. Conrad Gesner tells us, in his " Book of Animals," that no book is so bad the thoughtful reader may not learn something from it; and if these speculations can be made to point a moral, they are not quite in vain, as they may help us to fix attention on certain first principles which seem so obvious that one would think all must admit them. Familiar experience teaches that living things are often greatly modified by the conditions to which they are exposed during their individual life, and that the modifications which are thus produced are often useful ; for if this were not the case, no bene- ficial effect could come from training or education. We all know that the congenital or natural powers and faculties of children and of those who grow up in ignorance are very limited, and that it is practice which makes perfect. That judicious use often devel- ops and strengthens the parts which are used is unquestionable and the efficiency of neglected organs often becomes impaired. We are born with a nature that makes the normal use of our powers a pleasure, and while aceticism may despise mere bodily delights, more generous wisdom sees, in the keen enjoyment of normal or- ganic life, and in the discomfort or pain which attends repression, especially in the young, some of those wonderful adjustments which are the very essence of natural science. While hard work is exhausting, and while the organic machine is easily damaged by abuse, and is, at last, worn out by use, normal use is a condition of its perfect development, and the amount of normal work it may do without deterioration is astonishing. In the highly civilized and self-indulgent, it is much less likely to wear out than to rust out; and nothing could be more short- NATURE AND NURTURE 57 sighted than impatience with the restlessness of children, although no effeminacy can wholly repress the joyous exuberancy of child- hood ; nor can any thoughtful person fail to see that the impulse which leads young animals to train and develop their bodies by sports and gambols is adaptive. All this, and more, is implied by the admission that there is such a thing as nurture; and one of the first questions to present itself, when we consider the matter, is why living things are not like the imaginary Caliban ; how they come by a nature on which nurture will stick ; for it is plain that, far from being an explana- tion of nature, nurture is a fact which itself calls for explanation. The most stable organs may be modified by novel or excep- tional use, and the most profound structural changes may be brought about by nurture. After Hunter had fed a sea-gull on grain for a year, he found that the inner coat of its stomach had grown hard, and its muscles had thickened, thus forming a true gizzard, although the sea-gull normally has a soft stomach, as it lives upon the soft flesh of fishes. It is well known that living things are often changed by mechanical influences. The skull of a hornless ram has been found to weigh only one-fourth as much as the skull of a ram with horns ; and the whole configu- ration of the skull of lop-eared rabbits is altered by the mechanical pressure of the drooping ears. Hemp seed causes bulfinches and some other birds to become black ; and we know, from the obser- vations of many naturalists, that change of food sometimes changes the colors of caterpillars, or even those of the moths which they produce. Many curious cases of this sort have been recorded, in birds and insects, and it seems reasonable to believe that, if un- natural food may change the normal colors of a species, the normal colors may themselves, in some cases, be due to the direct action of the natural food. Sometimes the effect of the conditions of life is injurious, some- times neutral, but often it is useful to a notable degree; and it is this usefulness — the power to respond to changed conditions by adaptive modification — which is most worthy of consideration. Cold weather promotes the growth of hair on mammals, and thus protects them from the cold. The muscle which is used grows stronger, and the hand becomes skilful by training. 58 THE FOUNDATIONS OF ZOOLOGY Look at a young pine tree and examine its mode of growth. No one can doubt that the long, straight, tapering trunk, and the successive circles of branches, uniformly decreasing in length from the spreading base to the pointed crown, serve a useful end ; that the arrangement offers great resistance to storms, exposes a great area of foliage to sun and air, and has other advantages. Now examine the arrangement of the buds. At the tip of the central axis is a terminal bud, pushing straight upwards and building the crown of the tree, and giving off lateral buds which build the branches, and, becoming their terminal buds, leave behind them their own series of lateral buds to repeat the same process. The shape of the tree, so characteristic that it may be identified miles away, is the result of this simple law of growth ; and this itself is, in a certain sense, a result of the mechanical conditions of life. The bud at the top of the crown is the only one which is sym- metrically placed with reference to the sources of light and air and food, and its symmetry is the result; while the unequal distribu- tion of these conditions of growth results in the one-sided develop- ment of the other buds. If the crown of the young pine tree be destroyed by lightning or storm, or by an enemy, a bud that would otherwise have played a subordinate part, may fall heir to its advantages and build up a new crown. If the tree be prostrated by an accident, a new trunk, with its tapering crown, may spring, in time, from a bud far down the trunk. From one point of view the shape of the pine tree seems to be the effect of the mechanical conditions under which it grows, for unnatural or exceptional changes in these conditions may be followed by abnormal deviations from the type ; but from another point of view the type of the pine tree is fixed by the constitution or inherent tendency of the tree itself, and is independent of external conditions ; for when a pine, a spruce, and a larch grow side by side under the same conditions, each conforms to its own type. The so-called conditions of individual life are stimuli, without which normal growth does not take place, but they are not deter- mining factors, for the change that follows is due to something prior to and independent of the stimulus. While it is a matter of familiar experience, in every moment of our lives, that the stimulus under which a vital action takes place NATURE AND NURTURE 59 is one thing, while the character of the action itself is quite another thing, this fact tends from its very familiarity, to slip out of the minds of students ; and two views of the nature of the process of development of the living thing out of the germ, which have been argued for centuries, illustrate this tendency. One school of embry- ologists has long held that the egg or germ produces the living thing in virtue of its inherent potency, or specific constitution, which is, in some way, an embodiment of all that is to be unfolded out of it ; while the other school finds, in the stimulus which is given by nurture, in the influence of the external world, and in that which the parts of the segmenting egg and those of the growing organism exert on each other, the explanation of each successive step in the process of development. Advocates of these two views have regarded themselves as opponents, but except that latent potency is hard to lay hold of, while mechanical conditions readily lend themselves to experiment, I cannot see why there should be any real antagonism; for the evi- dence that each may be true seems ample. Every change that takes place in the living being, from the beginning to the end of individual life, may be called forth by some mechanical stimulus, either within the body or without; and yet the outcome of the whole process may be no more than exhaustive knowledge of the nature of the germ would lead one to expect. The gun does not go off until the cap is exploded, but it hits the mark because it is aimed. While the distinction between the stim- ulus to a vital change and the nature of the change itself is obvious enough in simple cases, we may easily become confused and lose sight of it in handling complicated problems. A hen's egg will not develop without heat and fresh air, and when these are properly supplied it becomes a chick, although belief that the heat causes the chick is too grotesque for the sane mind ; for the production of a duckling from a duck's egg in the same nest proves, if any proof be needed, that while the egg will not develop without incubation, the outcome of the process of incubation is the result of the inherent capacity of the egg itself. The most notable peculiarity of this inherent tendency or specific constitution of living things is its fitness. The egg not only gives rise to a specific organism, but to one that is beautifully and 60 THE FOUNDATIONS OF ZOOLOGY wonderfully fitted for the normal life of its species. What interests us is not that the hen's egg becomes a chick while the duck's egg becomes a duckling ; but that one grows into exquisite adjustment to the life of fowls, while the other becomes as admirably fitted for the life of ducks. In truth, the assertion that the future chick is latent in the egg seems to be no more than a generalized statement of observed facts, and of our confidence that they may be repeated ; although it by no means follows that the words, inherent potency, are useless ; for they serve a useful purpose if they fix attention on the fact that, while that which was an egg may under certain conditions become a chick adapted for the life of fowls, knowledge of these conditions fails to show us why it should. Here the stimulus comes from the external world, but the case is just the same when it is internal. The well-known results of castration prove that the normal development of many male mam- mals and birds depends upon some constitutional stimulus which comes from the reproductive organs to the parts of the growing body; but who can believe this an adequate explanation of the short, sharp horns, the thick neck, and the ferocity of the bull, or of the bright colors, the sharp spurs, and the high courage of the cock ? Have we any reason for a different opinion when the result varies with the stimulus ? Under one internal stimulus a bud becomes a jelly-fish, while, under others, it may become a hydranth or a machopolyp or a blastostyle, but the real problem, in this case as in the others, is the production of a beautifully coordinated organism, with the distinctive characteristics of its species, and with exquisite fitness for a life like that of its ancestors. I showed, some years ago, that a small crustacean, Alpheus heterochelis, develops according to one plan at Beaufort in North Carolina, according to a second at Key West in Florida, while it has still a third life history at Nassau in the Bahama Islands; but no one can believe that the influences which cause this diver- sity in the metamorphosis of Alpheus have anything to do with the final outcome, which is the same in all three places. The case is exactly the same when a cell which would normally give rise to a half or a quarter of the body gives rise to the whole under a different stimulus. NATURE AND NURTURE 6 1 All the machinery in a great industrial exposition may be started by a single electrical contact, but, however much the dis- covery of the button may interest us, it helps us but little to understand the result. So it is with living organisms. External conditions press the button, but it takes all the inherent potency of living matter to do the rest. It is an error to suppose great knowledge is needful for a clear grasp of first principles. " The largest views are not always the clearest, for he who is short-sighted will be obliged to draw the object nearer, and may, perhaps, by a closer and nearer sur- vey, discover that which had escaped far better eyes." The riches of a great store of information "cannot be spared or left behind, but it hindereth the march ; yea, and the care of it sometimes loseth or disturbeth the victory." Students who are drifting on the sea of facts, with which the modern laboratory has flooded us, sometimes declare that the doctrine of adaptation is antiquated and unscientific and perni- cious. They tell us that organisms have many properties which are not adaptive, and that we are often unable to tell whether a property is adaptive or not. Of course this is true. No one supposes that susceptibility to poisons, for example, is adaptive as such, and our knowledge of nature is incomplete beyond measure. They tell us, too, that many attempts to explain the uses of parts are fanciful and worthless. Unfortunately this is true also, but the logic which makes it a reason for denying the reality of fitness is enough to raise Paley from his grave. While protoplasm is, no doubt, the physical basis of life, the intellectual basis of biology is adjustment. I should like to see hung on the walls of every laboratory Herbert Spencer's defini- tion, to the effect that life is not protoplasm, but adjustment; or the older teaching of the father of zoology, that the essence of a living thing is not what it is made of nor what it does, but why it does it. It may seem to some that, since capacity for nurture is part of the nature of living things, the difference between nature and nurture is, after all, apparent rather than real. Since what is transmitted from parent to child is not actual or manifest nature, but only its latent potency, or, in other words, a capacity for 62 THE FOUNDATIONS OF ZOOLOGY nurture, the question whether nature is inherited nurture or not may seem a matter of words and definitions, rather than a real problem of things ; although no one can lose sight of the truth that aptitude for nurture is not, unfortunately, the same as apti- tude for beneficial nurture. It is, at most, no harder to acquire pernicious habits than to acquire good ones ; no harder to culti- vate bodily infirmity, or logical inconsequence, or mental imbe- cility, or moral obliquity, than to develop and make the best of our faculties and opportunities. He who has passed the plastic age without adding to his nature much nurture he would gladly be quit of, is either more fortunate or less particular than the bulk of mankind. While it may be true that we acquire no nurture but that which our nature permits, it is no less true that this nature permits a wide range of good and bad ; and that it by no means binds us to make of our nature all that it permits. All this seems true of other living things as well, and the view that nature is inherited nurture throws no light on the problem of fitness. •Belief that something is added to our nature by experience, and training, and education, rests on deliberate or unconscious acceptance of some such definition of nature as that which Alci- phron gives ; and, as the modern zoologist, who regards nature as the inherited effect of past nurture, seems to lose sight of Euphra- nor's analysis of this definition, I beg leave to refresh his memory by a short quotation from the old dialogue. v Euphranor. You seem very much taken with the beauty of nature. Be pleased to tell me, Alciphron, what those things are which you esteem natural, or by what mark I may know them. Alciphron. For a thing to be natural, for instance, to the mind of man, it must appear originally therein : it must be universal in all men : it must be invariably the same in all nations and ages. These limitations of origi- nal, universal, and invariable exclude all those notions of the human mind which are the effect of custom and education. The case is the same with respect to all other species of beings. A cat, for example, hath a natural inclination to pursue a mouse, because it agrees with the forementioned marks. But if a cat be taught to play tricks, you will not say these tricks are natural. For the same reason, if upon a plum tree peaches and apricots are engrafted, nobody will say they are the natural growth of the plum tree. Euph. But to return to man : it seems you allow those things alone NATURE AND NURTURE 63 to be natural to him which show themselves upon his first entrance into the world ; to wit, the senses, and such passions and appetites as are dis- covered upon the first application of their respective objects. Ale. That is my opinion. Euph. Tell me, Alciphron, if from a young apple tree, after a certain period of time, there should shoot forth leaves, blossoms, and apples, would you deny these things to be natural, because they did not discover and display themselves in the tender bud? Ale. I would not. Euph. And suppose that in a man, after a certain season, the appe- tite of lust, or the faculty of reason, shall shoot forth, open, and display themselves, as leaves and blossoms do in a tree ; would you, therefore, deny them to be natural to him, because they did not appear in his original infancy ? Ale. I acknowledge I would not. Euph. It seems, therefore, that the first mark of a thing's being natural to the mind was not warily laid down by you ; to wit, that it should ap- pear originally in it. Ale. It seems so. Euph. Again, inform me, Alciphron, whether you do not think it natural for an orange-plant tree to produce oranges? Ale. I do. Euph. But plant it in the north end of Great Britain, and it shall with great care produce, perhaps, a good salad ; in the southern parts of the same island, it may, with much pains and culture, thrive and produce indifferent fruit ; but in Portugal or Naples it will produce much better fruit with little or no pains. Is this true or not? Ale. It is true. Euph. The plant being the same in all places, doth not produce the same fruit — sun, soil, and cultivation making a difference. Ale. I grant it. Euph. And since the case is, you say, the same with respect to all species, why may we not conclude, by a parity of a reason, that things may be natural to humankind, and yet neither found in all men, nor invariably the same when they are found? And, as those fruits which grow from the most generous and mature stock, in the choicest soil, and with the best culture, are most esteemed ; even so ought we not to think those sublime truths, which are the fruits of mature thought, and have been rationally deduced by men of the best and most improved understandings, to be the choicest productions of the rational nature of man? And, if so, being in fact reasonable, natural, and true, they ought not to be esteemed unnatural whims, errors of education, and groundless prejudices, because they are raised and forwarded by manuring and cultivating our tender minds, because they take early root, and sprout forth betimes by the care and diligence of our instructors. 64 THE FOUNDATIONS OF ZOOLOGY The belief that nature is inherited nurture so obviously fails to throw light on the problem of fitness that most of the modern advo- cates of this opinion claim no more than that nurture supplies the raw material from which natural selection picks out and preserves the good, the useful, the fit; while the bad, the injurious, the unfit, is neglected ; but I hope my readers may find reason to ask whether we can be sure that nurture has even this amount of influence. Living things are preeminently distinguished by what is best expressed by the word fitness; they are adjusted to the world around them in such a way as to force us to believe that the use to which their organization is put has, in some way, been the con- trolling factor in the production of the organization itself. There is no escape from the belief that the adjustment of the eye to the principles of optics, its fitness for vision, has, in some way, guided and controlled its history; that it has come into existence for seeing, or by seeing, or because it sees. Darwin and Wallace have shown how the use of a part determines its structure through the extermi- nation of the relatively unfit, and the survival of the relatively fit; and I shall try, in another place, to show that this explanation is adequate and satisfactory; but at present we are concerned only with the opinion that the eye has been made, wholly or in part, by seeing. Since the conditions of life often tend, as we have seen, to modify organisms in such a way as to fit them for these very con- ditions; since, for example, the trained eye sees more than the untrained eye; since, within certain limits, extra demands upon a muscle make it more able to do the extra work, — may not the spe- cific constitution of each organism have been produced in somewhat the same way? May it not be the inherited result of the influence of the conditions under which its ancestors lived; preserved, it may be, by natural selection? Since the pine tree does not grow up without the mechanical influence of its environment, may not the inherited tendency to which its shape is due have been caused by the direct mechanical action of the environment of past generations ? This is a fair question, and if it were asked by a boy, or by one unfamiliar with the subject, I should welcome it as a sign of intelli- gent interest; but when it is asked by a naturalist, I can look at it NATURE AND NURTURE 65 only as an indication of culpable ignorance of history; for the hypothesis has been tried and found wanting, and it was rejected as inadequate more than two thousand years ago. To come down to modern times, Wallace, Darwin, Huxley, and Gray, men who were, assuredly, unprejudiced by opposition to the doctrine of the mutability of species, have all told us that they studied Lamarck with all diligence, and found, in his works on this subject, nothing of value. The views of the Neo-Lamarckians, as I understand them, are somewhat broader than those of Lamarck, but fundamentally the same, and, briefly stated, are as follows: The useful changes which are produced in the structure, habits, instincts, and other faculties of living things, through contact with the world around them, are inherited by their children; and this inheritance, aided, it may be, by natural selection, is an efficient factor in the origin of species, and has gradually adjusted, or given material aid in adjust- ing, the characteristics of each organism to its needs. Stated still more briefly, it is the doctrine that organic evolution has been brought about, or at least greatly aided, by the inheritance of nurture. We must now dwell upon a point which seems worthy of atten- tion. Lamarck believed that the useful effects of the conditions of life are the ones which are inherited, and this is the only point worth notice; for if these effects may be indifferently useful, use- less, or injurious, they can have no bearing upon the origin of adjustment. In inorganic nature it may be an even chance whether an external change be destructive or preservative, but, when we remember how narrow the range of adjustment of each living being is, the probability that haphazard effects will be injurious or neutral rather than beneficial is prodigious. Even if they are inherited, the effects of nurture cannot cumulate in adaptation except as an acci- dent so improbable that only the most conclusive evidence can prove such an event; unless indeed it can be shown that nurture is beneficial independently of selection. While the chances seem all against adaptive modification by the direct action of the conditions of life, I think we may challenge the Lamarckian to show a single species which has been modified to its own disadvantage. There are species which 66 THE FOUNDATIONS OF ZOOLOGY have been thrown out of harmony with their environment by some external change to which they failed to respond, and individuals are often put at the greatest disadvantage, or even destroyed, for the good of the species as a whole, but there is not a single example of the disadvantageous modification of a species in a state of nature ; although man is able to produce, for his own purposes, such monsters as double flowers, oranges and grapes without seeds, and laying hens which never sit, and thus to demonstrate that species present no inherent obstacle to injurious modification. The Lamarckians have brought together a long list of examples of the useful modification of individuals by external influences, but no one has tabulated the neutral or hurtful modifications. Still we find reason to believe that organisms do tend to respond, in a favorable way, to certain external changes, and we may fairly call upon the Lamarckian to explain how this useful property was acquired. How, for example, did our muscles acquire the ten- dency to become strengthened by exercise ? Certain zealous Lamarckians tell us, as if it were a sufficient explanation, that the benefit which comes with the normal use of our muscles is due to the properties of living matter ; although I am not aware that any modern naturalist attributes it to anything else. I shall try to show, Lectures VIII. and IX., that the only path in which we can have any well-grounded hope for progress in the explanation of adaptive types takes its departure from that con- ception of nature which leads us to seek for the origin of the properties which exhibit adaptation in the physical basis of living beings. If any interpret the opinion that the origin of these properties must there be sought as an assertion that it has there been found, I do not see that their impetuosity has any bearing on the point at issue, which here, as in other cases, is the question how the living being comes to exhibit these properties under normal stimuli in such a way as to be adaptive. The increased power to use our muscles, which comes with practice, is, no doubt, due, in the main, to improvement in the nervous system, although normal use is essential to the healthful development of the muscle itself, for its nutrition is promoted by normal exercise, and this result may be imitated by massage or by electrical stimulation. NATURE AND NURTURE 67 It has seemed to some that the pathological hypertrophy of certain muscles under abnormal conditions is evidence of an inherent or innate capacity for adaptive response. For example, pathological conditions which throw extra work upon the heart are often followed by the hypertrophy of the heart itself; and, as these conditions are abnormal or exceptional, it is said that the capacity of the heart for responding to them cannot be due to the survival, in past generations, of those ancestors whose hearts thus responded ; but a moment's thought will show that the survival of every mammal does depend upon the power of its heart to re- spond to increasing demands by increasing efficiency. If the work- ing capacity of the heart did not keep pace with the growth of the body, no mammal could grow up, but growth is a normal process, common to all. No mammal could survive the great changes which take place in the circulation before and at the time of birth, if the capacity of its heart for doing work did not keep pace with the normal changes in the amount of work which is required. As we have already seen, page n, that the responsive activities of liv- ing things may be called out by either the normal stimulus or any other which acts in the same way, the pathological hypertrophy of the heart is no more than the past history of mammals would lead us to expect. Improvement of our muscles under exercise is the outcome of structural adjustments for bringing this useful end about — it is an adaptation ; and the heart is as obviously fitted for improve- ment by use as it is for propelling blood. Exercise fits a muscle for its normal work only so far as structural adjustments for bringing this about already exist, in the brain, and in the nervous system, and in the muscle itself ; and the real problem, the origin of the adaptation, is in no way different from that presented by any other structural adjustment. This is still further illustrated by the fact that while many organs are improved by normal or natural use, abnormal or un- natural use is well called abuse. When our bodies are used in what is popularly called the way they were intended to be used, use is beneficial ; but injudicious or excessive training may be as pernicious as neglect. If we acquire no nurture except that which our nature pro- 68 THE FOUNDATIONS OF ZOOLOGY vides for, what are we to say of the acquisition of knowledge ? Does this come by nature and not by nurture ? The use of language is an acquired art, and not an innate faculty. Whitney reminds us (" Life and Growth of Language," p. 279) that "though possessing the endowments of a Homer or a Demosthenes, no man can speak any language until he has learned it, as truly learned it as he learns the multiplication table, or the demonstrations of Euclid." I have tried to show, page 53, that since each vital act is a response to a sign with a significance, life is the use of the language of nature ; and it follows, if this phrase is to be taken literally, that life is an acquired art, and not a natural inheritance. I have tried to show, page 9, that this may be the case, since it may be the adaptive mechanism, and not its responsive activity, which is inherited from parent by child. While no one can come into possession of a language without learning it, and while each acquires the tongue which the acci- dent of birth places within his reach, Whitney reminds us that man learns language because " he possesses, as one of his most marked and distinctive characteristics, a faculty or capacity of speech, — or, more accurately, various faculties and capacities which lead inevitably to the production of speech ; but the faculties are on.e thing, and their elaborated products are another and very different one." " It needs not only the inward power, but also the outward occasion, to make man what he is capable of becoming." This is no place for a treatise on human knowledge, but I think that the mind to know truth seems, to most, as essential as truth to be known ; for it does not seem good common sense to attribute our minds to either the direct or the indirect effects of knowledge. The general opinion seems to be that our minds come by nature, rather than by nurture, although some, who admit that our minds are ours by nature, strangely suppose that these same minds may be efficient causes of changes in our nature. It is legitimate and relevant to ask the difficult question whether natural knowledge is the discovery of truth, or only the avoidance of error; and there is much to be said in favor of NATURE AND NURTURE 69 Berkeley's assertion, that "the work of science is to unravel our prejudices and mistakes, untwisting the closest connections, distin- guishing things that are different; instead of confused and per- plexed, giving us distinct views ; gradually correcting our judgment and reducing it to a philosophical exactness." Physical exercise corrects our bodily movements, and reduces them to exactness, by giving us distinct movements, instead of confused and perplexed ones; but we are unable to believe that training gives us any new muscles, and their fitness for improve- ment by exercise is itself an adaptation which calls for explana- tion. If Berkeley is right, as he seems to me to be, and if what we call natural knowledge is no more than the correction of our judgment and its reduction to exactness, it seems clear that knowledge no more accounts for our judgment than training ac- counts for our muscles, and that physical culture and mental cult- ure are, in this respect, exactly alike. The modern zoologist, who reflects upon the phenomena of nature, is forced, like all who have gone before him, to consider anew the ancient and difficult question whether there are "innate ideas " ; and, even if his success be slight, and his conclusions indefinite, he may, perhaps, make use of his acquaintance with living things to focus the point at issue, and to show that this may be, in part at least, a matter of words and definitions. "It is Plato's remark, in his ' Thesetetus,' that while we sit still we are never the wiser, but going into the river, and moving up and down, is the way to discover its depths and shallows. If we exercise and bestir ourselves, we may even here discover something."1 So far as it concerns the zoologist, the question seems to be this : Is it something we find in our nature, or something we discover in the outer world, which justifies our confidence in our mental states and in our responsive actions ; or may there not be a sense in which each point of view is the true one ? I have tried to show, page 59, that, while the responsive activities of living things do not take place until they are called forth by a proper stimulus, the things they do under stimulus are no more than their organic mechanism would lead us to expect ; and that there 1 Berkeley, " Siris," p. 367. 70 THE FOUNDATIONS OF ZOOLOGY need be no necessary antagonism between those who attribute the development of the germ to mechanical conditions and those who attribute it to the inherent potency of the germ itself. We must now ask whether there is any more necessary antag- onism between those who attribute knowledge to experience and those who attribute it to our innate reason. If this question could be considered in itself, it might not be formidable ; but it is hedged about with complications, for some of which the modern zoologist is responsible, although only a few of the perplexities by which his efforts are beset can be laid to his own charge. Some zoologists tell us that the value of our responses is equiva- lent to confidence in their value, although it is clear that our hearts had value before men studied anatomy, and that digestion was useful to them before they knew that it occurs. We are also told, in effect, that confidence in the value of our mental states is -the same as judicious confidence in their value, although we all know that while one who has led an uneventful life may dread all accidents, a life of adventure may teach that, while some accidents are to be avoided at any cost, the danger from others is trifling. The confidence of the man with little experience is no less strong than that of the adventurer, but it is less judicious; and, as we use words, we do not call it knowledge, but " ignorant " prejudice, or "unreasoning" cowardice, although there is no reason why those who wish should not use words in some other sense. The question whether experience is or is not the only source of knowledge clearly turns, in part at least, on our definition of know- ledge. An infant who has never known a tumble may act as they act who know the danger of a fall, and, if response to the order of nature were evidence of knowledge, it would be obvious that some knowledge is innate, or independent of experience ; but it is not our custom to call the blind prejudice of ignorance and the prudent conservatism of the wise by the same name. Some zoologists hold that beneficial response to a stimulus is evidence that the stimulus is perceived, and that the response is made with knowledge, and, if this were admitted, it would be clear that some knowledge is innate in living things ; for all admit that they may respond to the order of nature without experience, NATURE AND NURTURE 71 although few assert that every response is evidence of knowledge. The impulse to eat when we are hungry is useful, but we do not call it knowledge, although we do give this name to the physiology which tells us when and how far food is beneficial ; and we distin- guish our innate "moral sense" from knowledge of good and evil. We are sometimes told by those who are not zoologists, that, admitting that all the responsive actions of living things may be useful, rational responses may nevertheless be distinguished, by perfectibility, from fixed instincts and blind mechanical reflex acts. It is said that while mechanical responses are persistent, those which are due to knowledge are improvable; but no zoologist can admit that any property of living things is immutable, or that perfecti- bility is evidence of knowledge. If the correction of our natural responses and their gradual reduction to exactness by the suppres- sion of those which are confused and perplexed, and the survival of those which are distinct and useful were evidence of knowledge, might not the zoologist ask, in this case, whether the whole history of the origin of species by means of natural selection may not be a history or the acquisition of knowledge ? For it is a history of the acquisition of something which our reason approves, even if we are quite unable -to tell, in most cases, whether it is accompanied by mind or not. Whether perfectibility be held to be evidence of knowledge or not, may not the zoologist ask if the question whether knowledge is or is not innate may not depend upon the answer we give to the farther question whether it is the activity of the organic mechanism, or only the mechanism itself, that is transmitted from parent to child ; for if no act is inherited, is it not hard to see how there can be any innate or hereditary knowledge ? No one who has propagated plants from cuttings or seen a sea- anemone divide into two, can ask whether a material organism may be multiplied ; but they who hold that actions may be transmitted and multiplied by inheritance seem to hold that the law of the con- servation of energy does not here hold good. While all who hold that this law is empirical and experimental must stand ready to admit exceptions to it when proved, he must be of bold mind who holds that inheritance is an exception ; and we have already, page 59, examined evidence which seems to show that, while the things which living beings do under stimuli are no more than their nature would /2 THE FOUNDATIONS OF ZOOLOGY lead one to expect, we have no reason to expect these things to take place in the absence of these stimuli or some equivalent. If the believer in innate ideas tells us all this is quite con- sistent with his principles; if, while admitting that he knows no mental act or state without physical concomitants, he assert that the subjective or mental aspects of our responsive actions arise in us because of our inherent nature; if he tell us that the physi- cal concomitants are only the " occasion " of the mental states, or the stimulus under which they arise in our minds, — I do not see why the zoologist should not agree, and admit that he is, to this extent, an intuitionist after the ancient school of Plato ; for, so far as science tells us, what we call the " causes " of physical events are no more than "occasions." In physical science all we mean, when we say we understand a thing, is that, certain conditions or occasions being given, it may be counted on with confidence, while we cannot judiciously expect it in their absence. The question at issue between the Lamarckian and the Dar- winian is not whether knowledge arises in the mind in the absence of experience, but whether experience is anything more than the "physical cause," or occasion, or stimulus, in the pres- ence of which knowledge may be expected to arise in the mind, and in the absence of which it cannot reasonably be looked for. If this latter is the case, is it not hard to see how experience can be either the efficient or the physical cause of the mind in which it arises ? It is hard to calmly ask whether training and education and experience add anything to our nature, for we know that a man educated is different from the same man uneducated. If, at first thought, the question seems repugnant to common sense, we must remember that it is also hard, when looking through a bit of colored glass at a neutral wall, to believe that no color is added, and that the effect is due to negative and passive ex- clusion by selection or sifting. The assertion that there is no more redness on the wall, or on the retina, than there was before the red glass was interposed, seems, at first, to be contradicted by our sensations, and repug- nant to common sense. Who can imagine more color outside the limits of a rainbow NATURE AND NURTURE 73 than within the borders of the arch ? When the rich colors of evening spread over the glowing clouds, after a dull, gray day, we feel that new wealth of beauty has been added at the end, and that the dying day has taken on new splendors, which were absent in our working hours. The emotional value of nature, and its moral influence, gain so much strength as the day dies, that the impression of a cor- responding gain in sensible value is irresistible, and effort to imagine all this glorious color in the common light of day is vain; yet there are more rays of crimson and red and purple at noonday than in the declining light of evening. One modern zoologist has defined life as "memory"; and while Plato's belief that learning may, in effect, be reminiscence seems repugnant to common sense, the zoologist must hold it an approximation to the truth ; although he cannot forget that, so far as natural selection is a physical explanation of the " archetype," or species, of which the germ becomes reminiscent in develop- ment, just so far is it a physical explanation of those "forms," or "necessities of intellect," of which the "soul" becomes remi- niscent in knowledge ; for improvement under experience is, as much as embryonic development, a part of the life history of a normal human being. We are told that "it is a maxim of the Platonic philosophy that the soul of man was originally furnished with native inborn notions, and stands in need of sensible occasions, not absolutely for producing them, but only for awakening, rousing, or exciting into act what was already preexistent, dormant, and latent in the soul; as things are said to be laid up in the memory, though not actually perceived until they happen to be called forth and brought into view by other objects." The zoologist of our day may ask whether all that the living organism does may not be latent in its physical organization, ready to be called forth by that " sensible occasion " which we now call a stimulus ; although, when pressed for an exhaustive definition of latent potency, he may find no better answer than an admission that these words are no more than a generalized statement of his observations on the actions of living things in general, and on the operations of his own mind in particular, 74 THE FOUNDATIONS OF ZOOLOGY joined to an expression of his confidence that these observations may be repeated, and are no more than might have been expected. When the believer in innate ideas goes farther than this, and asserts that the "forms" or "archetypal ideas" which thus arise in the mind are universal or necessary, the zoologist must ask him how this is known. Things that are innate, or natural, are not always universal or necessary, for while parental affection is natural, some parents are unnatural. If the believer in innate ideas asserts that, while our latent or potential sensational knowledge does not become active or mani- fest until it is called forth by some change in the physical world, we are the ultimate and efficient causes of our own thoughts, the zoologist must ask, once more, how this is known. If any assert that we know that our thoughts are ours because we can control them, the physiologist, while admitting the control, asks how we know that the way we control them is different from the way we control our visual sensations by going into a dark room, or by shutting our eyes. All admit that all normal human beings who are not helpless infants, or aged dotards, are able to control their thoughts, and the actions which follow them, in some practical sense of the words. " If I take things as they are and ask any plain, untutored man whether he acts or is free in any particular action, he readily assents, and I as readily believe him from what I find within. And if man be free, he is plainly accountable. But if you shall define, abstract, suppose, and it shall follow that according to your definitions, abstractions, and suppositions, there can be no free- dom in man, and you shall therefore infer that he is not account- able, I shall make bold to depart from your metaphysical abstract sense and appeal to the common sense of mankind." May not the modest zoologist, who humbly admits that, while he does not know what the relation between mind and matter is, he would like to find out, also ask, in all sincerity, whether it is he who has perplexed our common sense by defining and ab- stracting and supposing? May he not also ask, not in a critical spirit, but in order that he may approach this difficult subject without prejudice, whether some of the responsibility for this NATURE AND NURTURE 75 perplexity may not be laid to the charge of those metaphysicians and theologians and philosophers who have told him that actions which are mechanical cannot be free, because they are necessary ? When we control our visual sensations by shutting our eyes, we employ physical means, and while one who is thus enabled to control some of his mental states by physical means may also be able to use these means or not as he chooses, how can this be evidence that his ability is independent of physical means? Is it necessary to know what the relation between mind and matter is, in order to study mind ? As we know what we mean by a plant, and may study botany, without knowing when or how plants become differentiated from animals, and without knowing any absolute diagnosis of a plant, so, too, may we not study know- ledge, without knowing when or how it becomes differentiated from instinct and impulse and emotion and unperceived cerebration ? As we use the words, is knowledge equivalent to response, or to beneficial response, or to the improvement of response, or to response which is immediately controlled ? Is it not rather the correction of our judgment and its reduction to exactness ? Whether knowledge is innate or not, does any one believe that our judgment is ever corrected without a "sensible occasion"? May not the amount of this correction be measured by experi- ence ? If what we mean by knowledge is the correction of our judgment under the stimulus of experience, is it not idle to ask whether we may have knowledge without experience, for is not this a contradiction in terms ?. If any choose to define knowledge as response, and to thus use the word consistently, no one need object, for words are conventional symbols, which change their meaning continually, although no one who uses common words in an uncommon way, without defining them, can hope to be understood. We are told that if the- " Lamarckian factors " are in any degree operative at all, their great function " must be that of supplying to natural selection the incipient stages of adaptive modification, in all cases where, but for this agency, there would be nothing of the kind to select"; but unless these "factors" can be proved to have this function, they are unworthy of con- sideration as a contribution to the history of adaptive modification. 76 THE FOUNDATIONS OF ZOOLOGY I, for one, have found little to interest me in the interminable dispute as to the inheritance or non-inheritance of the effects of the conditions of individual life, because the gist of the whole matter has seemed to me to lie in the deeper question whether these effects are inherently adaptive ; and I am forced to ask for evidence that the " Lamarckian factors " can give rise to even the incipient stages of adaptive modification, before I care to inquire whether they are or are not inherited. We are told that, " Inas- much as we know to what a wonderful extent adaptive modifica- tions are secured during individual lifetime, by the direct action of the environment on the one hand, and by increased or dimin- ished use of special organs and mental faculties on the other, it becomes obvious of what importance even a small measure of transmissibility on their part would be, in furnishing to natural selection ready made variations in required directions, as distin- guished from promiscuous variations in all directions." This a priori argument to prove that the effect of these "factors" must be inherited, because if so, it would be so useful, has seemed plausible to many; but its fallacy is clear, unless the inheritance of nurture can be proved to be beneficial prior to selec- tion ; for, while the ways t