Chapter 1
Produced by Frank van Drogen, Jeannie Howse and the Online Distributed Proofreading Team at http://www.pgdp.net (This book was produced from scanned images of public domain material from the Google Print project.)
BIOLOGY
BY
EDMUND BEECHER WILSON PROFESSOR OF ZOOLOGY COLUMBIA UNIVERSITY
New York THE COLUMBIA UNIVERSITY PRESS 1908
BIOLOGY
A LECTURE DELIVERED AT COLUMBIA UNIVERSITY IN THE SERIES ON SCIENCE, PHILOSOPHY AND ART NOVEMBER 20, 1907
BIOLOGY
BY
EDMUND BEECHER WILSON PROFESSOR OF ZOOLOGY COLUMBIA UNIVERSITY
New York THE COLUMBIA UNIVERSITY PRESS 1908
COPYRIGHT, 1908, by THE COLUMBIA UNIVERSITY PRESS.
Set up, and published March, 1908.
BIOLOGY
I must at the outset remark that among the many sciences that are occupied with the study of the living world there is no one that may properly lay exclusive claim to the name of Biology. The word does not, in fact, denote any particular science but is a generic term applied to a large group of biological sciences all of which alike are concerned with the phenomena of life. To present in a single address, even in rudimentary outline, the specific results of these sciences is obviously an impossible task, and one that I have no intention of attempting. I shall offer no more than a kind of preface or introduction to those who will speak after me on the biological sciences of physiology, botany and zoology; and I shall confine it to what seem to me the most essential and characteristic of the general problems towards which all lines of biological inquiry must sooner or later converge.
It is the general aim of the biological sciences to learn something of the order of nature in the living world. Perhaps it is not amiss to remark that the biologist may not hope to solve the ultimate problems of life any more than the chemist and physicist may hope to penetrate the final mysteries of existence in the non-living world. What he can do is to observe, compare and experiment with phenomena, to resolve more complex phenomena into simpler components, and to this extent, as he says, to "explain" them; but he knows in advance that his explanations will never be in the full sense of the word final or complete. Investigation can do no more than push forward the limits of knowledge.
The task of the biologist is a double one. His more immediate effort is to inquire into the nature of the existing organism, to ascertain in what measure the complex phenomena of life as they now appear are capable of resolution into simpler factors or components, and to determine as far as he can what is the relation of these factors to other natural phenomena. It is often practically convenient to consider the organism as presenting two different aspects--a structural or morphological one, and a functional or physiological--and biologists often call themselves accordingly morphologists or physiologists. Morphological investigation has in the past largely followed the method of observation and comparison, physiological investigation that of experiment; but it is one of the best signs of progress that in recent years the fact has come clearly into view that morphology and physiology are really inseparable, and in consequence the distinctions between them, in respect both to subject matter and to method, have largely disappeared in a greater community of aim. Morphology and physiology alike were profoundly transformed by the introduction into biological studies of the genetic or historical point of view by Darwin, who did more than any other to establish the fact, suspected by many earlier naturalists, that existing vital phenomena are the outcome of a definite process of evolution; and it was he who first fully brought home to us how defective and one-sided is our view of the organism so long as we do not consider it as a product of the past. It is the second and perhaps greater task of the biologist to study the organism from the historical point of view, considering it as the product of a continuous process of evolution that has been in operation since life began. In its widest scope this genetic inquiry involves not only the evolution of higher forms from lower ones, but also the still larger question of the primordial relation of living things to the non-living world. Here is involved the possibility so strikingly expressed many years ago by Tyndall in that eloquent passage in the Belfast address, where he declared himself driven by an intellectual necessity to cross the boundary line of the experimental evidence and to discern in non-living matter, as he said, the promise and potency of every form and quality of terrestrial life. This intellectual necessity was created by a conviction of the continuity and consistency of natural phenomena, which is almost inseparable from the scientific attitude towards nature. But Tyndall's words stood after all for a confession of faith, not for a statement of fact; and they soared far above the _terra firma_ of the actual evidence. At the present day we too may find ourselves logically driven to the view that living things first arose as a product of non-living matter. We must fully recognize the extraordinary progress that has been made by the chemist in the artificial synthesis of compounds formerly known only as the direct products of living protoplasm. But it must also be admitted that we are still wholly without evidence of the origin of any living thing, at any period of the earth's history, save from some other living thing; and after more than two centuries Redi's aphorism _omne vivum e vivo_ retains to-day its full force. It is my impression therefore that the time has not yet come when hypotheses regarding a different origin of life can be considered as practically useful.
If I have the temerity to ask your attention to the fundamental problem towards which all lines of biological inquiry sooner or later lead us it is not with the delusion that I can contribute anything new to the prolonged discussions and controversies to which it has given rise. I desire only to indicate in what way it affects the practical efforts of biologists to gain a better understanding of the living organism, whether regarded as a group of existing phenomena or as a product of the evolutionary process; and I shall speak of it, not in any abstract or speculative way, but from the standpoint of the working naturalist. The problem of which I speak is that of organic mechanism and its relation to that of organic adaptation. How in general are the phenomena of life related to those of the non-living world? How far can we profitably employ the hypothesis that the living body is essentially an automaton or machine, a configuration of material particles, which, like an engine or a piece of clockwork, owes its mode of operation to its physical and chemical construction? It is not open to doubt that the living body _is_ a machine. It is a complex chemical engine that applies the energy of the food-stuffs to the performance of the work of life. But is it something more than a machine? If we may imagine the physico-chemical analysis of the body to be carried through to the very end, may we expect to find at last an unknown something that transcends such analysis and is neither a form of physical energy nor anything given in the physical or chemical configuration of the body? Shall we find anything corresponding to the usual popular conception--which was also along the view of physiologists--that the body is "animated" by a specific "vital principle," or "vital force," a dominating "archæus" that exists only in the realm of organic nature? If such a principle exists, then the mechanistic hypothesis fails and the fundamental problem of biology becomes a problem _sui generis_.
In its bearing on man's place in nature this question is one of the most momentous with which natural science has to deal, and it has occupied the attention of thinking men in every age. I cannot trace its history, but it will be worth our while to place side by side the words of three of the great leaders of modern scientific and philosophic thought. The saying has been attributed to Descartes, "Give me matter and I will construct the world"--meaning by this the living world as well as the non-living; but Descartes specifically excepted the human mind. I do not know whether the great French philosopher actually used these particular words, but they express the essence of the mechanistic hypothesis that he adopted. Kant utterly repudiated such a conception in the following well known passage: "It is quite certain that we cannot become adequately acquainted with organized creatures and their hidden potentialities by means of the merely mechanical principles of nature, much less can we explain them; and this is so certain that we may boldly assert that it is absurd for man even to make such an attempt or to hope that a Newton may one day arise who will make the production of a blade of grass comprehensible to us according to natural laws that have not been ordered by design. Such an insight we must absolutely deny to man." Still, in another place Kant admitted that the facts of comparative anatomy give us "a ray of hope, however faint, that something may be accomplished by the aid of the principle of the mechanism of nature, without which there can be no science in general." It is interesting to turn from this to the bold and aggressive assertion of Huxley: "Living matter differs from other matter in degree and not in kind, the microcosm repeats the macrocosm; and one chain of causation connects the nebulous origin of suns and planetary systems with the protoplasmic foundations of life and organization."
Do not expect me to decide where such learned doctors disagree; but I will at this point venture on one comment which may sound the key-note of this address. Perhaps we shall find that in the long run and in the large sense Kant was right; but it is certain that to-day we know very much more about the formation of the living body, whether a blade of grass or a man, than did the naturalists of Kant's time; and for better or for worse the human mind seems to be so constituted that it will continue its efforts to explain such matters, however difficult they may seem to be. But I return to our more specific inquiry with the remark that the history of physiology in the past two hundred years has been the history of a progressive restriction of the notion of a "vital force" or "vital principle" within narrower and narrower limits, until at present it may seem to many physiologists that no room for it remains within the limits of our biological philosophy. One after another the vital activities have been shown to be in greater or less degree explicable or comprehensible considered as physico-chemical operations of various degrees of complexity. Every physiologist will maintain that we cannot name one of these activities, not even thought, that is not carried on by a physical mechanism. He will maintain further that in most cases the vital actions are not merely accompanied by physico-chemical operations but actually consist of them; and he may go so far as definitely to maintain that we have no evidence that life itself can be regarded as anything more than their sum total. He is able to bring forward cogent evidence that all modes of vital activity are carried on by means of energy that is set free in protoplasm or its products by means of definite chemical processes collectively known as metabolism. When the matter is reduced to its lowest terms, life, as thus viewed, seems to have its root in chemical change; and we can understand how an eminent German physiologist offers us a definition or characterization of life that runs: "The life-process consists in the metabolism of proteids." I ask your particular attention to this definition since I now wish to contrast with it another and very different one.
I shall introduce it to your attention by asking a very simple question. We may admit that digestion, for example, is a purely chemical operation, and one that may be exactly imitated outside the living body in a glass flask. My question is, how does it come to pass that an animal has a stomach?--and, pursuing the inquiry, how does it happen that the human stomach is practically incapable of digesting cellulose, while the stomachs of some lower animals, such as the goat, readily digest this substance? The earlier naturalists, such as Linnaeus, Cuvier or Agassiz, were ready with a reply which seemed so simple, adequate and final that the plodding modern naturalist cannot repress a feeling of envy. In their view plants and animals are made as they were originally created, each according to its kind. The biologist of to-day views the matter differently; and I shall give his answer in the form in which I now and then make it to a student who may chance to ask why an insect has six legs and a spider eight, or why a yellowbird is yellow and a bluebird blue. The answer is: "For the same reason that the elephant has a trunk." I trust that a certain rugged pedagogical virtue in this reply may atone for its lack of elegance. The elephant has a trunk, as the insect has six legs, for the reason that such is the specific nature of the animal; and we may assert with a degree of probability that amounts to practical certainty that this specific nature is the outcome of a definite evolutionary process, the nature and causes of which it is our tremendous task to determine to such extent as we may be able. But this does not yet touch the most essential side of the problem. What is most significant is that the clumsy, short-necked elephant has been endowed--"by nature," as we say--with precisely such an organ, the trunk, as he needs to compensate for his lack of flexibility and agility in other respects. If we are asked _why_ the elephant has a trunk, we must answer because the animal needs it. But does such a reply in itself explain the fact? Evidently not. The question which science must seek to answer, is _how_ came the elephant to have a trunk; and we do not properly answer it by saying that it has developed in the course of evolution. It has been well said that even the most complete knowledge of the genealogy of plants and animals would give us no more than an ancestral portrait-gallery. We must determine the causes and conditions that have cooperated to produce this particular result if our answer is to constitute a true scientific explanation. And evidently he who adopts the machine-theory as a general interpretation of vital phenomena must make clear to us how the machine was built before we can admit the validity of his theory, even in a single case. Our apparently simple question as to why the animal has a stomach has thus revealed to us the full magnitude of the task with which the mechanist is confronted; and it has brought us to that part of our problem that is concerned with the nature and origin of organic adaptations. Without tarrying to attempt a definition of adaptation I will only emphasize the fact that many of the great naturalists, from Aristotle onward, have recognized the purposeful or design-like quality of vital phenomena as their most essential and fundamental characteristic. Herbert Spencer defined life as the continuous _adjustment_ of internal relations to external relations. It is one of the best that has been given, though I am not sure that Professor Brooks has not improved upon it when he says that life is "response to the order of nature." This seems a long way from the definition of Verworn, heretofore cited, as the "metabolism of proteids." To this Brooks opposes the telling epigram: "The essence of life is not protoplasm but purpose."
Without attempting adequately to illustrate the nature of organic adaptations, I will direct your attention to what seems to me one of their most striking features regarded from the mechanistic position. This is the fact that adaptations so often run counter to direct or obvious mechanical conditions. Nature is crammed with devices to protect and maintain the organism against the stress of the environment. Some of these are given in the obvious structure of the organism, such as the tendrils by means of which the climbing plant sustains itself against the action of gravity or the winds, the protective shell of the snail, the protective colors and shapes of animals, and the like. Any structural feature that is useful because of its construction is a structural adaptation; and when such adaptations are given the mechanist has for the most part a relatively easy task in his interpretation. He has a far more difficult knot to disentangle in the case of the so-called functional adaptations, where the organism modifies its activities (and often also its structure) in response to changed conditions. The nature of these phenomena may be illustrated by a few examples so chosen as to form a progressive series. If a spot on the skin be rubbed for some time the first result is a direct and obviously mechanical one; the skin is worn away. But if the rubbing be continued long enough, and is not too severe, an indirect effect is produced that is precisely the opposite of the initial direct one; the skin is replaced, becomes thicker than before, and a callus is produced that protects the spot from further injury. The healing of a wound involves a similar action. Again, remove one kidney or one lung and the remaining one will in time enlarge to assume, as far as it is able, the functions of both. If the leg of a salamander or a lobster be amputated, the wound not only heals but a new leg is regenerated in place of that which has been lost. If a flatworm be cut in two, the front piece grows out a new tail, the hind piece a new head, and two perfect worms result. Finally, it has been found in certain cases, including animals as highly organized as salamanders, that if the egg be separated into two parts at an early period of development each part develops into a perfect embryo animal of half the usual size, and a pair of twins results. In each of these cases the astonishing fact is that a mechanical injury sets up in the organism a complicated adaptive response in the form of operations which in the end counteract the initial mechanical effect. It is no doubt true that somewhat similar self-adjustments or responses may be said to take place in certain non-living mechanical systems, such as the spinning top or the gyroscope; but those that occur in the living body are of such general occurrence, of such complexity and variety, and of so design-like a quality, that they may fairly be regarded as among the most characteristic of the vital activities. It is precisely this characteristic of many vital phenomena that renders their accurate analysis so difficult and complex a task; and it is largely for this reason that the biological sciences, as a whole, still stand far behind the physical sciences, both in precision and in completeness of analysis.
What is the actual working attitude of naturalists towards the general problem that I have endeavored to outline? It would be a piece of presumption for me to speak for the body of working biologists, and I will therefore speak for only one of them. It is my own conviction that whatever be the difficulties that the mechanistic hypothesis has to face, it has established itself as the most useful working hypothesis that we can at present employ. I do not mean to assert that it is adequate, or even true. I believe only that we should make use of it as a working program, because the history of biological research proves it to have been a more effective and fruitful means of advancing knowledge than the vitalistic hypothesis. We should therefore continue to employ it for this purpose until it is clearly shown to be untenable. Whether we must in the end adopt it will depend on whether it proves the simplest hypothesis in the large sense, the one most in harmony with our knowledge of nature in general. If such is the outcome, we shall be bound by a deeply lying instinct that is almost a law of our intellectual being to accept it, as we have accepted the Copernican system rather than the Ptolemaic. I believe I am right in saying that the attitude I have indicated as a more or less personal one is also that of the body of working biologists, though there are some conspicuous exceptions.