Part 1

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DEGENERATION.

_NATURE SERIES._

DEGENERATION. A CHAPTER IN DARWINISM.

BY PROFESSOR E. RAY LANKESTER, F.R.S., FELLOW OF EXETER COLLEGE, OXFORD.

London: MACMILLAN AND CO. 1880.

_The Right of Translation and Reproduction is Reserved_

LONDON: R. CLAY, SONS, AND TAYLOR, BREAD STREET HILL, E. C.

TO MY FRIEND

ANTON DOHRN

THESE PAGES

Are Dedicated

IN MEMORY OF OUR COMPANIONSHIP

AT JENA AND NAPLES.

E. R. L.

_January, 1880._

DEGENERATION.

DEGENERATION.

It is the misfortune of those who study that branch of science which our President has done so much to advance—I mean the science of living things—that they are not able, in the midst of a vast assembly,[1] to render visible to all eyes the actual phenomena to which their inquiries are directed. Whilst the physicist and the chemist are able to make evident to the senses of a great meeting the very things of which they have to tell, the zoologist cannot hope ever to share with those who form his audience the keen pleasure of observing a new or beautiful organism; he cannot demonstrate by means of actual specimens the delicate arrangements of structure which it is his business to record, and upon which he bases his conclusions. It is for this reason that he who would bring to the notice of laymen some matter which at the moment is occupying the attention of biological students, must appear to be unduly devoted to speculation—hypothesis—to support which he cannot produce the facts themselves but merely the imperfect substitutes afforded by pictures. It is perhaps not altogether a matter for regret that there should be in one great branch of science, as there is in biology, so very marked a disproportion between the facilities for demonstrating facts and the general interest attaching to the theories connected with those facts. We may be thankful that at the present day we are not likely, in the domain of biology, to make the mistake (which has been made under other circumstances) of substituting the mere inspection and cataloguing of natural objects for that more truly scientific attitude which consists in assigning the facts which come under our observation to their causes, or, in other words, to their places in the order of nature. Though we may rightly object to the attempt which is sometimes made to decry the modern teachings of biology as not being “exact science,” yet we may boldly admit the truth of the assertion that we biologists are largely occupied with speculations, hypotheses, and other products of the imagination. All true science deals with speculation and hypothesis, and acknowledges as its most valued servant—its indispensable ally and help-meet—that which our German friends[2] call “Phantasie” and we “the Imagination.” Our science—biology—is not less exact; our conclusions are no less accurate because they are only _probably_ true. They are “probably true” with a degree of probability of which we are fully aware, and which is only _somewhat_ less than the probability attaching to the conclusions of other sciences which are commonly held to be “exact.”

These remarks are addressed to an Association for the advancement of science—of science which flourishes and progresses by the aid of suppositions and the working of the imagination. The Association has been holding its annual sitting in various parts of the British Islands for more than thirty years, and yet it is still a very common and widely spread notion that science, that is to say, _true_ science according to those who hold the notion, does not countenance hypotheses, and sternly occupies itself with the exact record of fact. On the other hand, there are many persons who run to an opposite extreme, and call by the name of science any fanciful attempt to deal with or account for a certain class of phenomena. The words “science” and “scientific” are used so vaguely and variously that one might almost come to the conclusion that it would be well for our Association to plainly state what is that thing for the advancement of which its meetings are held. I cannot venture to speak in the name of my colleagues; and no doubt a review of the work done by the Association would most fitly explain what that body understands by the word “science.” At the same time it is permissible to take this opportunity of briefly stating what science is and what it is not, so far as I am able to judge of the fitting use of the word.

Science is certainly _not_ any and every kind of knowledge. Knowledge of literature, of the beautiful things which have been written or otherwise produced by human ingenuity, is not science. Knowledge of the various manufacturing processes in use by civilised men is not science; nor knowledge of the names of the stars, or of the joints of a beetle’s leg. Science cannot be identified with knowledge of any particular _class_ of objects, however detailed that knowledge may be. It is a common mistake to consider all knowledge of raw products, of living objects or other natural objects, as necessarily “science.” The truth is, that a man may have great knowledge of these things as so many facts, and yet be devoid of “science.” And, on the other hand, that which is properly called science embraces not only such subject-matter as that just alluded to, but also may find its scope in the study of language, of human history, and of the workings of the human mind.

The most frequent and objectionable misuse of the word ‘science’ is that which consists in confounding science with invention—in applying the term which should be reserved for a particular kind of knowledge to the practical applications of that knowledge. Such things as electric lighting and telegraphs, the steam-engine, gas, and the smoky chimneys of factories, are by a certain school of public teachers, foremost among whom is the late Oxford Professor of Fine Art, persistently ascribed to science, and gravely pointed out as the pestilential products of a scientific spirit. They are, in fact, nothing of the kind. American inventors and electric lamps, together with all the factories in Sheffield, might be obliterated without causing a moment’s concern to a single student of science. It is of the utmost importance for the progress and well-being of science that this should be understood; that the eager practical spirit of the inventor who gains large pecuniary rewards by the sale of his inventions should not be confounded with what is totally different and remote from it, namely, the devoted, searching spirit of science, which, heedless of pecuniary rewards, ever faces nature with a single purpose—_to ascertain the causes of things_. It seems to me impossible to emphasise too strongly in such a place and in such a meeting as this, that Invention is widely separate from, though dependent on, Science. Invention is worldly-wise, and despises the pursuit of knowledge for its own sake. She awaits the discoveries of Science, in order to sell them to civilisation, gathering the golden fruit which she has neither planted nor tended. Invention follows, it is true, the footsteps of Science, but at a distance: she is utterly devoid of that thriftless yearning after knowledge, that passionate desire to know the _truth_, which causes the unceasing advance of her guide and benefactress.

We may, it seems to me, say that of all kinds and varieties of knowledge that only is entitled to the name “science” which can be described as Knowledge of Causes, or Knowledge of the Order of Nature. It is this knowledge to which the great founder of European science—Aristotle the Greek—pointed as _true_ knowledge: τότε ἐπιστάμεθα ὅταν τὴν αἰτίαν εἴδωμεν. Science is that knowledge which enables us to demonstrate so far as our limited faculties permit, that the appearances which we recognise in the world around us are dependent in definite ways on certain properties of matter: science is that knowledge which enables, or tends to enable us, to assign its true place in the series of events constituting the universe, to any and every thing which we can perceive.

The method by which scientific knowledge is gained—knowledge of the causes of nature—is precisely the same as that by which knowledge of causes in every-day life is gained. Something—an appearance—has to be accounted for: the question in both cases is “Through what cause, in relation to what antecedent is this appearance brought about?” In scientific inquiry, as in every-day life, a hypothesis—a provisional answer or guess—is the reply; and the truth of that guess or hypothesis is then _tested_. This testing is an essential part of the process. “If my guess be true, then so-and-so as to which I can decide by inspection or experiment, must be true also,” is the form which the argument takes, and the inquiry is thus brought to a point where _observation_ can decide the truth of the hypothesis or first guess. In every-day life we have often to be content without fully testing the truth of our guesses, and hurry into action based on such unverified suppositions. Science, on the other hand, can always wait, and demands again and again the testing and verification of guesses before they are admitted as established truths fit to be used in the testing of new guesses and the building up of scientific doctrine.

The delicately-reared imaginations of great investigators of natural things have from time to time given birth to hypotheses—guesses at truth—which have suddenly transformed a whole department of knowledge, and made the causes of things quite clear which before seemed likely to remain always concealed. So great is the value of hypothesis, so essential to scientific discovery, that the most skilled and highly-trained observer may spend his life in examining and scrutinising natural objects and yet fail, if he is not guided by hypothesis, to observe particular facts which are of the uttermost importance for the explanation of the causes of the things which he is studying. Nature, it has been said, gives no reply to a general inquiry—she must be interrogated by questions which already contain the answer she is to give; in other words, the observer can only observe that which he is led by hypothesis to look for: the experimenter can only obtain the result which his experiment is designed to obtain.

For a long time the knowledge of living things, of plants and of animals could hardly be said to form part of the general body of science, for the causes of these things were quite unknown. They were kept apart as a separate region of nature, and were supposed to have been pitched, as it were, into the midst of an orderly and cause-abiding world without cause or order: they were strangers to the universal harmony prevailing around them. Fact upon fact was observed and recorded by students of plants and animals, but having no hypothesis as to the causes of what they were studying, the naturalists of twenty years ago, and before that day, though they collected facts, made slow progress and some strange blunders. Suddenly one of those great guesses which occasionally appear in the history of science, was given to the science of biology by the imaginative insight of that greatest of living naturalists—I would say that greatest of living men—Charles Darwin.

In the form in which Mr. Darwin presented his view to the world it was no longer a mere guess. He had already tried it and proved it in an immense series of observations; it had already been converted by twenty years’ labour on his part into an established doctrine, and the twenty years which have passed since he published the _Origin of Species_ have only served to confirm, by thousands of additional tests, the truth of his original guess.

Space will not allow me to go fully into the history of the Darwinian theory, but it is necessary for my present purpose that I should state precisely what that theory is. It involves a number of subordinate hypotheses which, together with the main hypothesis, furnish us with a complete “explanation,” as it is called, of the facts which have been ascertained as to living things; in other words, it assigns living things to their causes, gives them their place in the Order of Nature.

It is a very general popular belief at the present day that the Darwinian theory is simply no more than a capricious and anti-theological assertion that mankind are the modified descendants of ape-like ancestors.

Though most of my readers, I do not doubt, know how imperfect and erroneous a conception this is, yet I shall not, I think, be wasting time in stating what the Darwinian theory really is. In fact, it is so continuously misrepresented and misunderstood, that no opportunity should be lost of calling attention to its real character. Bit by bit, naturalists had succeeded in discovering the order of nature—so far that all the great facts of the universe, the constitution and movements of the heavenly bodies, the form of our earth, and all the peculiarities of its crust, had been successfully assigned to one set of causes—_the properties of matter_, which are set forth in what we know by the name of the “laws of physics and chemistry.” Whilst geologists, led by Lyell, had shown that the strata of the earth’s crust and its mountains, rivers, and seas were due to the long-continued operation of the very same general causes—the physico-chemical causes—which at this moment are in operation and are continuing their work of change, yet the living matter on the crust of the earth had to be excluded from the grand uniformity which was elsewhere complete.

The first hypothesis, then, which was present to Mr. Darwin’s mind, as it had been to that of other earlier naturalists, was this: “Have not all the varieties or species of living things (man, of course, included) been produced by the continuous operation of the _same_ set of physico-chemical causes which alone we can discover, and which alone have been proved sufficient to produce everything else?” “If this be so,” Mr. Darwin must have argued (and here it was that he boldly stepped beyond the speculations of Lamarck and adopted the method by which Lyell had triumphantly established Geology as a science), “these causes must still be able to produce new forms, and are doing so wherever they have opportunity.” He had accordingly to bring the matter to the test of observation by seeking for some case of the production of new forms of plants, or of animals, by natural causes at the present day. Such cases he found in the production of new forms or varieties of plants and animals, by breeders. Breeders (the persons who make it their business to produce new varieties of flowers, of pigeons, of sheep, or what not) make use of two fundamental properties of living things in order to accomplish their purpose. These two properties are, firstly, that no two animals or plants, even when born of the same parents, are _exactly_ alike; this is known as Variation: secondly, that an organism, as a rule, inherits, that is to say, is born with the peculiarities of its parents; this is known as Transmission, and is simply dependent on the fact that the offspring of any plant or animal is only a detached portion of the parent—a chip of the old block, as the saying is. The breeder selects from a number of specimens of a plant or animal a variety which comes nearest to the form he wishes to produce. Supposing he wished to produce a race of oxen with short horns, he would select from his herd bulls and cows with the shortest horns, and allow these only to breed; they would _transmit_ their relatively short horns to their offspring, and from these again the cattle with the shortest horns would be selected by the breeder for propagation, and so on through several generations. In the end a very short-horned generation would be obtained, differing greatly in appearance from the cattle with which the breeder started.

Now we know of no facts which forbid us to suppose that could a breeder continue his operations indefinitely for any length of time—say for a few million years—he could convert the short-horned breed into a hornless breed; that he could go on and thicken the tail, could shorten the legs, get rid of the hind limbs altogether by a series of insensible gradations, and convert the race into forms like the Sirenia, or sea-cows. But if he could do this, you have only to give him a longer time still and there is no obstacle remaining to the conversion, by the same kind of process, of a polyp into a worm, or of a worm into a fish, or even of a monkey into a man.[3]

So far we have supposed the interference of a breeder who selects and determines the varieties which shall propagate themselves; so far we have not got a complete explanation, for we must find a substitute in nature for the _human selection_ exercised by the breeder. The question arises, then, “Is there any necessary selective process in nature which could have operated through untold ages, and so have represented the selective action of the breeder, during an immense period of time?” Strangely enough, Mr. Darwin was led to the discovery of such a cause existing necessarily in the mechanical arrangements of nature, by reading the celebrated book of an English clergyman, the Rev. Mr. Malthus, _On Population_. On happening to read this book, Mr. Darwin himself tells us that the idea of “natural selection” flashed upon him. That idea is as follows. Not only among mankind, but far more largely among other kinds of animals and of plants, the number of offspring produced by every pair is immensely in excess of the available amount of the food appropriate to the particular species in question. Accordingly, there is necessarily a struggle for existence—a struggle among all those born for the possession of the small quantum of food. The result of this struggle is to pick out, or select, a few who survive and propagate the species, whilst the majority perish before reaching maturity. The fact that no two members of a species are alike has already been shown to be the starting-point which enables the breeder to make _his_ selection. So, too, with _natural_ selection in the struggle for existence; the fact that all the young born of one species are not exactly alike—but some larger, some smaller, some lighter, some darker, some short-legged, some big-eyed, some long-tongued, some sharp-toothed, and so on—furnishes the opportunity for a selection. Those varieties which are best fitted to obtain food and to baffle their competitors, gain the food and survive, the rest perish.

We have, then, to note that the hypothesis that there _must be a selection_—which was framed or deduced as a “test hypothesis” from the earlier hypothesis that species have arisen by the action of causes still competent to produce new forms—led Mr. Darwin to the discovery of this great cause—the “_natural selection_,” or “survival of the fittest,” in the struggle for existence. Just as the breeder can slowly change the proportions of the animals or plants on which he operates, so in inconceivably long periods of time has this struggling of varieties, and the consequent natural selection of the fittest, led to the production, from shapeless primitive living matter, of all the endless varieties of complicated plants and animals which now people the world. Countless varieties have died out, leaving only their modified descendants to puzzle the ingenuity of the biologist.

Of the tens and hundreds of thousands of intermediate forms we know nothing by direct observation. They have perished as better fitted forms ousted them in the never-ending conflict. But we feel sure that they once were in existence, and can infer what was their structure, and what were their peculiarities, by the study of the structure and attributes of their now living descendants.

If all the forms of life at present living are the modified offspring of a smaller number of ancestral forms which have died out, and if these again were the modified descendants produced by ordinary parentage of a single original living thing—then the whole series of forms that have _ever_ lived could, if we had them before us, be arranged in the form of a great family-tree—the various branches presenting a perfect gradation of forms arranged one after another, leading down from the terminal twigs (which would represent the latest forms produced) to larger and larger branches, until the common trunk representing the original ancestor would be reached. Our actual means of observing the genealogical affinities of different kinds of animals and plants may be understood by a further use of the metaphor of a genealogical tree in shape like an elm or an oak. Suppose the genealogical tree completely written out—a perfect record—to be sunk in muddy water so that only its topmost branches and twigs are here and there visible—then you have a fair notion of the present condition of the great family of organisms. Only the topmost twigs remain visible, the rest of the great family-tree of living beings is hidden from view, submerged beneath the muddy waters of time. Naturalists have, however, undertaken to reconstruct this great genealogical tree. It is a main object now in the study both of zoology and of botany to find out what are the cousinships, what the exact genetic relationships of all the various species of plants and animals, and so to show, even to the minutest detail, in what particular ways physico-chemical causes have brought about and modified the forms of living things.

The task is not quite so difficult as the comparison to a submerged forest-tree would lead one to expect; at the same time it is more difficult than those who have boldly attempted it appear to believe. We have one great help in the carefully worked out systematic classification of animals and plants according to their structure. We are justified in assuming as a general law that animals or plants of like structure have descended from common ancestors—that is to say, that the same kind of organisation (especially where a number of elaborate details of structure are involved) has _not been twice_ produced by natural selection. Thus we are entitled to conclude that _all_ the animals which have a backbone and pharyngeal gill-slits combined—the Vertebrates, as we call them—have descended from a common parent; that all the animals with a muscular foot-like belly and lateral gill filaments, the Molluscs, have also had a common parent, and so on.