History of the Intellectual Development of Europe, Volume II (of 2) / Revised Edition

by John William Draper

If the mean annual heat of the earth's surface were slowly to rise, and, in the course of some centuries, the temperature now obtaining in Florida should obtain in New York, the orange and lemon would certainly be found here. Boundary of organisms by heat. [309] With the increasing heat those plants would commence a northward march, steadily advancing as opportunity was given. Or, if the reverse took place, and for any reason the heat of the torrid zone declined until the winter's cold of New York should be at last reached under the equator, as the descent went on the orange and lemon would retreat within a narrow and narrower region, and end by becoming extinct, the conditions of their exposure being incompatible with the continuance of their life. From such considerations it is therefore obvious that not only does heat arrange the limits of the distribution of plants, erecting round them boundaries which, though invisible, are more insuperable than a wall of brass, it also regulates their march, if march there is to be—nay, even controls their very existence, and to genera, and species, and individuals appoints a period of duration.

Animals localized as well as plants.Such observations apply not alone to plants; the animal kingdom offers equally significant illustrations. Why does the white bear enjoy the leaden sky of the pole and his native iceberg? Why does the tiger restrict himself to the jungles of India? Can it be doubted that, if the mean annual temperature should decline, the polar bear would come with his iceberg to corresponding southern latitudes, or, if the heat should rise, the tiger would commence a northward journey? Does he not, indeed, every summer penetrate northward in Asia as far as the latitude of Berlin, and retire again as winter comes on? Why is it that, at a given signal, the birds of passage migrate, pressed forward in the spring by the heat, and pressed backward in the autumn by the cold? The annual migration of birds illustrates the causes of geological appearances and extinctions. Do we not herein recognize the agent that determines animal distribution? We must not deceive ourselves with any fancied terrestrial impediment or restraint. Let the heat rise but a few degrees, and the turkey-buzzard, to whose powerful wing distances are of no moment and the free air no impediment, would be seen hovering over New York; let it fall a few degrees, and he would vanish from the streets of Charleston; let it fall a little more, and he would vanish from [310] the earth. Shell-fish, once the inhabitants of the British seas, retired during the glacial period to the Mediterranean, and with the returning warmth have gone back northward again.

Control of animals by food.Animals are thus controlled by heat in an indirect as well as a direct way. Indirectly; for, if their food be diminished, they must seek a more ample supply; if it fails, they must perish. Doubtless it was insufficient food, as well as the setting in of a more rigorous climate, that occasioned the destruction of the mastodon giganteus, which abounded in the United States after the drift period. Such great elephantine forms could not possibly sustain themselves against the rigors of the present winters, nor could they find a sufficient supply of food for a considerable portion of the year. The disappearance of animals from the face of the earth was, as Palæontology advanced, ascertained to have been a determinate process, a condition of their existence, and either inherent in themselves or dependent on their environment. It was proved that the forms now existing are only an insignificant part of the countless tribes that have lived. Nature of creations and extinctions. The earth has been the theatre of a long succession of appearances and removals, of creations and extinctions, reaching to the latest times. In the Pleistocene of Sicily, ³⁵/¹²⁴ of the fossil shells are extinct; in the bone caverns of England, out of thirty-seven mammals eighteen are extinct. But judging, from what may be observed of the duration of races contemporary with us, that their life is prolonged for thousands of years, successive generations of the same species in a long order replacing their predecessors before final removal occurs, this again resistlessly brought forward the same conclusion to which all the foregoing facts had pointed, that there have transpired since the introduction of animal life upon this globe very long periods of time.

Through the operation of this law of extinction and of creation, animated nature, both on the continents and in the seas, has undergone a marvellous change. In the lias and oolitic seas, the Enaliosauria, Cetiosauria, and Crocodilia dominated as the Delphinidæ and Balænidæ do in ours; the former have been eliminated, the latter [311] produced. Along with the cetaceans came the soft-scaled Cycloid and Ctenoid fishes, orders which took the place of the Ganoids and Placoids of the Mesozoic times. One after another successive species of air-breathing reptiles have emerged, continued for their appointed time to exist, and then died out. The development has been, not in the descending, but in the ascending order; the Amphitheria, Spalacotheria, Triconodon of the Mesozoic times were substituted by higher tertiary forms. Nor have these mutations been abrupt. If mammals are the chief characteristic of the Tertiary ages, their first beginnings are seen far earlier; in the triassic and oolitic formations there are a few of the lower orders struggling, as it were, to emerge. The aspect of animated nature has altogether changed. No longer does the camelopard wander over Europe as he did in the Miocene and Pliocene times; no longer are great elephants seen in the American forests, the hippopotamus in England, the Rhinoceros in Siberia. The hand of man has introduced in the New the horse of the Old World; but the American horse, that ran on the great plains contemporary with the megatherium and megalonyx, has for tens of thousands of years been extinct. Even the ocean and the rivers are no exception to these changes.

Creations and extinctions by law.What, then, is the manner of origin of this infinite succession of forms? It is often sufficient to see clearly a portion of a plan to be able to determine with some degree of certainty the general arrangement of the whole; it is often sufficient to know with precision a part of the life of an individual to guess with probable accuracy his action in some forthcoming event, of to determine the share he has borne in affairs that are past. It is enough to appreciate thoroughly the style of a master to ascertain without doubt the authenticity of an imputed picture. And so, in the affairs of the universe, it is enough to ascertain the manner of operation of a part in order to settle the manner of operation of the whole. When, therefore, it was perceived how the disappearance of vanishing forms from the surface of the globe is accomplished—that it is not by a sudden and grand providential intervention—that there is no visible putting [312] forth of the Omnipotent hand, but slowly and silently, yet surely, the ordinary laws of Nature are permitted to take their course—that heat, and cold, and want of food, and dryness, and moisture, in the end, as if by an irresistible destiny, accomplish the event, it seemed to indicate that, as regards the introduction of new-comers, a suitableness of external conditions had called them forth, as an unsuitableness could end them. Changes in the constitution of the air or its pressure, in the composition of the sea or its depth, in the brilliancy of light or the amount of heat, in the inorganic material of a medium, will modify old forms into new ones, or compel their extinction. Birth and death go hand in hand; creation and extinction are inseparable. The variation of organic form is continuous; it depends upon an orderly succession of material events; appearances and eliminations are managed upon a common principle; they stand connected with the irresistible course of great mundane changes. It was impossible that geologists could reach any other conclusion than that such phenomena are not the issue of direct providential interventions, but of physical influences. The procession of organic life is not a motley march; it follows the procession of physical events; and, since it is impossible to re-establish a sameness of physical conditions that have once come to an end, or reproduce the order in which they have occurred, it of necessity follows that no organic form can reappear after it has once died out—once dead, it is clean gone for ever.

Interstitial molecular creations.In the course of the life of individual man, the parts that constitute his system are undergoing momentary changes; those of to-day are not the same as those of yesterday, and they will be replaced by others to-morrow. There have been, and are every instant, interstitial deaths of all the constituent particles, and an unceasing removal of those that have performed their duty. In the stead of departing portions, new ones have been introduced, interstitial births and organizations perpetually taking place. In physiology it became no longer a question that all this proceeds in a determinate way under the operation of principles that are fixed, of laws that are invariable. The alchemists [313] introduced no poetical fiction when they spoke of the microcosm, asserting that the system of man is emblematical of the system of the world. The intercalation of a new organic molecule in a living being answers to the introduction of a new form in the universal organic series. It requires as much power to call into existence a living molecule as to produce a living being. Both are accomplished upon the same principle, and that principle is not an incessant intervention of a supernatural kind, but the operation of unvarying law. Physical agents, working through physical laws, remove in organisms such molecules as have accomplished their work and create new ones, and physical agents, working through physical laws, control the extinctions and creations of forms in the universe of life. The difference is only in the time. What is accomplished in the one case in the twinkling of an eye, in the other may demand the lapse of a thousand centuries.

The variation of organic forms, under the force of external circumstances, is thus necessary to be understood in connexion with that countless succession of living beings demonstrated by geology. It carries us, in common with so much other evidence, to the lapse of a long time. Nor are such views as those to which we are thus constrained inconsistent with the admission of a Providential guidance of the world. Man, however learned and pious he may be, is not always a trustworthy interpreter of the ways of God. In deciding whether any philosophical doctrine is consistent or inconsistent with the Divine attributes, we are too prone to judge of those attributes by our own finite and imperfect standard, forgetting that the only test to which we ought to resort is the ascertainment if the doctrine be true. If it be true, it is in unison with God. Perhaps some who have rejected the conception of the variation of organic forms, with its postulate—limitless duration, may have failed to remember the grandeur of the universe and its relations to space and to time; perhaps they do not recall the system on which it is administered. Like the anthropomorphite monks of the Nile, they conceive of God as if he were only a very large man; else how could it for a moment have been doubted that it is far more—I use the expression [314] reverently—in the style of the great Constructor to carry out his intentions by the summary operations of law? Defence of the process of all things by law. It might be consistent with the weakness and ignorance of man to be reduced to the necessity of personal intervention for the accomplishment of his plans, but would not that be the very result of such ignorance? Does not absolute knowledge actually imply procedure by preconceived and unvarying law? Is not momentary intervention altogether derogatory to the thorough and absolute sovereignty of God? The astronomical calculation of ancient events, as well as the prediction of those to come, is essentially founded on the principle that there has not in the times under consideration, and that there will never be in the future, any exercise of an arbitrary or overriding will. The cornerstone of astronomy is this, that the solar system—nay, even the universe, is ruled by necessity. To operate by expedients is for the creature, to operate by law for the Creator; and so far from the doctrine that creations and extinctions are carried on by a foreseen and predestined ordinance—a system which works of itself without need of any intermeddling—being an unworthy, an ignoble conception, it is completely in unison with the resistless movements of the mechanism of the universe, with whatever is orderly, symmetrical, and beautiful upon earth, and with all the dread magnificence of the heavens.

Historical sketch of early Palæontology.It was in Italy that particular attention was first given to organic remains. Leonardo da Vinci asserts that they are real shells, or the remains thereof, and hence that the land and sea must have changed their relative position. At this time fossils were looked upon as rare curiosities, no one supposing that they were at all numerous, and many were the fantastic hypotheses proposed to account for their occurrence. Some referred them to the general deluge mentioned in Scripture; some to a certain plastic power obscurely attributed to the earth; some thought that they were engendered by the sunlight, heat, and rain. To Da Vinci is due the first clear assertion of their true nature, that they are actually the remains of organic beings. Soon the subject was taken up by other eminent Italians. Fracaster wrote on the petrifactions [315] of Verona; Scilla, a Sicilian, on marine bodies turned into stone, illustrating his work by engravings. Still later, Vallisneri, 1721, published letters on marine bodies found in rocks, attempting by their aid to determine the extent of the marine deposits of Italy. These early cultivators of geology soon perceived the advantage to be gained by the establishment of museums and the publication of catalogues. The first seems to have been that of John Kentman, an example that was followed by Calceolarius and Vallisneri. Subsequently Fontanelle proposed the construction of charts in accordance with fossil remains; but the principle involved was not applied on the great scale as a true geological test until introduced by Smith in connexion with the English strata.

The pre-organic time. To Steno, a Dane, is due the recognition of pre-organic in contradistinction to organic rocks, a distinction the terms of which necessarily involve the idea of time. Soon it became generally recognized that the strata in which organic remains occur are of a later date than those devoid of them, the pre-organic rocks demonstrating a pre-organic time. Moreover, as facts were developed, it was plain that there are essential differences in the relations of fossils, and that, though in Italy the same species of shells may occur in the mountains that occur in the adjacent seas, this was very far from being the case uniformly elsewhere. At length the truth began to emerge, that in proportion as the strata under examination are of an older date, so are the differences between their organic remains and existing species more marked. It was also discovered that the same species often extends superficially over immense districts, but that in a vertical examination one species after another rapidly appears in a descending order—an order which could be verified in spite of the contortions, fractures, and displacements of the strata. A very important theoretical conclusion was here presented: for the rapid succession of essentially different organic forms, as the rocks were older, was clearly altogether inconsistent with one catastrophe, as the universal deluge, to which it had been generally referred. It was plain that the thickness of the strata in which they were enveloped, and the prodigious numbers in which [316] they occurred, answered in some degree to the period of life of those fossils, since every one of them, large or small, must have had its time of birth, of maturity, and of death. Insufficiency of a single catastrophe. When, therefore, it could be no longer doubted that strata many hundreds of feet in thickness were crowded with such remains, it became altogether out of the question to refer their entombment to the confusion of a single catastrophe, for every thing indicated an orderly and deliberate proceeding. Still more cogent did this evidence become when, in a more critical manner, the fossils were studied, and some strata were demonstrated to be of a fresh-water and others of a marine origin, the one intercalated with the other like leaves in a book. To this fact may be imputed the final overthrow of the doctrine of a single catastrophe, and its replacement by a doctrine of periodical changes.

The orderly progression of organization.From these statements it will therefore be understood that, commencing with the first appearance of organization, an orderly process was demonstrated from forms altogether unlike those with which we are familiar, up to those at present existing, a procedure conducted so slowly that it was impossible to assign for it a shorter duration than thousands of centuries. Moreover, it seemed that the guiding condition which had controlled this secular march of organization was the same which still determines the possibility of existence and the distribution of life. The succession of organic forms indicates a clear relation to a descending temperature. The plants of the earliest times are plants of an ultratropical climate, and that primitive vegetation seemed to demonstrate that there had been a uniform climate—a climate of high temperature—all over the globe. The coal-beds of Nova Scotia exhibited the same genera and species as those of Europe, and so well marked was the botanical connexion with the declining temperature in successive ages that attempts were made to express eras by their prevailing organisms; thus Brongniart's division is, for the Primary strata, the Age of Acrogens; the Secondary, exclusive of the Cretaceous, the Age of Gymnogens; the third, including the Cretaceous and Tertiary, the Age of Angiosperms. It is to be particularly remarked that[317] the Cretaceous flora, in the aggregate, combines the antecedent and succeeding periods, proving that the change was not by crisis or sudden catastrophe, but that the new forms rose gently among the old ones. After the Eocene period, dicotyledonous angiosperms became the prevalent form, and from that date to the Pleistocene the evidences of a continued refrigeration are absolute.