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

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 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 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 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 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 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.

Climates in time and in place. As thus an examination was made from the most ancient to the later ages, indications were found of a climate arrangement more and more distinct – in the high latitudes, from the ultratropical through the tropical, the temperate, down to the present frigid state; in lower latitudes the declining process stopping short at an earlier point. It therefore appeared that there has been a production of climates both in an order of time and, in an order of locality, the greatest change having occurred in the frigid zone, which has passed through all mean temperatures, an intermediate change in the temperate, and a minimum in the torrid zone. The general effect has thus been to present a succession of surfaces on the same planet adapted to a varied organization, and offering a more magnificent spectacle than if we were permitted to inspect many different planets; for in them there might be no necessary connexion of their forms of life, but in this there is, so that, were our knowledge of Comparative Physiology more perfect, we might amuse ourselves with intercalating among the plant and animal organisms familiar to us hypothetical forms that would make the series complete, and verify our principles by their subsequent discovery in the deep strata of the earth.

Does not this progression of life in our planet suggest a like progression for the solar system, which in its aggregate is passing in myriads of years through all organic phases? May we not also, from our solar system, rise to a similar conception for the universe?

There are two very important considerations, on which we must dwell for the complete understanding of the consequences of these changes: 1st. The mechanism of the declining temperature; 2d. Its effect in the organic world.

The nature of terrestrial declining temperature. 1st. A uniformly high temperature could never be manifested all over the surface of our planet through any heating influence of the sun. A high and uniform temperature unerringly points to an internal cause; and the gradual appearance of climates, manifesting a relatively increasing power of the sun, indicates the slow diminution of that internal heat. But this is precisely the conclusion which was come to from a contemplation of the earth from a purely physical point of view. So long as its intrinsic heat overpowered that derived from the sun, it was not possible that any thing answering to climates could be established; and, until a certain degree of cooling by radiation had been accomplished, the heat must have been comparatively uniform in all latitudes; but, that point gained, there necessarily ensued an arrangement of zones of different temperatures, or, in other words, climates appeared, the process being essentially slow, and becoming slower as the loss of heat went on. Finally, when loss of heat from the earth ceased, an equilibrium was reached in the climate arrangement as we now find it. Thus purely physical as well as geological considerations brought philosophers on this point to the same conclusion – that conclusion which has been so often repeated – very long periods of time.

Consequent effect on the Flora and Fauna. 2nd. As to the effect on the organic world. Nothing can live at a temperature higher than the boiling-point of water, for the condition of life implies that there shall circulate from part to part of a living mechanism a watery liquid, sap, or blood. From this it necessarily follows that a planet, the temperature of which is above a certain limit, must necessarily have a lifeless surface; and this seemed to be the interpretation of that pre-organic time to which we have referred. Moreover, when the temperature suitably descends so as to come within the limit at which life is possible, its uniformity over the surface of a planet will produce a sameness in the organization. It would be an identity if heat were the only regulating condition of life. At this stage of things, the solar heat being overpowered, and a sensibly uniform temperature in all latitudes existing, still the only possible organic forms are those consistent with a high temperature, uniformity in the physical condition impressing a general uniformity in the aspect of life geographically. Production and distribution of new organisms. But the moment that climate arrangement has become possible, variety of organic form becomes possible. Now also ensues another all-important result – geographical distribution. Both of plants and animals, those whose vital conditions are inconsistent with the occurring change must retire from the affected locality. In plants this retrocession is brought to pass by the gradual sickening and death of individuals, or the impossibility of reproduction; in animals there is added thereto, because of their power of locomotion, voluntary retirement, at least in the case of individuals, and immobility in the species is corrected by locomotion in the individual. The affected region has become unsuitable, cheerless, uncomfortable; they abandon it; and as the boundary they thus, in the one case, can not, and in the other will not overpass, advances, so do they recede before it. If the change were abrupt, or took place by a sudden crisis, there would seem to be no other possible event than an overcrowding of the unaffected region and a desolation of the part that had varied. But, since a developing cell under a new condition produces a new form, and since the physical change is taking place with extreme slowness, the appearance of modified structures ensues. And thus, by decline of temperature, two distinct results are accomplished – first the production of organic forms in an order of succession, new ones replacing the old, as if they were transmutations of them, and, secondly, geographical distribution.

Delusive nature of organic equilibrium. In my "Physiology" I have endeavoured to explain in detail the principles here set forth. I have endeavoured to show that the aspect of sameness presented by an animal or plant is no proof of unchangeability. Those forms retain in our times their special aspect because the conditions of the theatre in which they live do not change; but let the mean temperature rise, let the sun-rays become brighter, change the composition of the air, and forthwith the world of organization would show how profoundly it was affected. Nor need such changes, in one sense, be more than insignificant to produce prodigious results. Thus the air contains only 1/2000 of its volume of carbonic acid gas. That apparently trifling quantity taken away, in an instant the whole surface of the earth would become a desolate waste, without the possibility of vegetable life.

The Coal period. As physical geology advanced, the Coal period was perceived to be the chief epoch in the history of our planet. Through a slow decline of temperature, a possibility had gradually been attained, so far as the condition of heat was concerned, for a luxuriant vegetable growth. All that prodigious mass of carbon now found in the earth in the various forms of coal existed as carbonic acid in the atmosphere. The proportion of free oxygen was less than at present by a volume equal to the excess of carbonic acid. Effects of light on the atmosphere, A change in the constitution of this primæval atmosphere was occasioned by the action of the light; for, under the influence of the sun-rays, plants decompose carbonic acid, appropriating its carbon, and, for the most part, setting the oxygen free. The quantity of carbon which can thus be condensed for the use of a plant, and, indeed, every such decomposing action by light, is directly proportionate to the quantity of light consumed, as experiments which I have personally made have proved. For the production of so great a weight of combustible matter a very long period of time was necessarily required, that the sun might supply the necessary luminous influence.

Age after age the sunbeams continued their work, changing the mechanical relations and composition of the atmosphere, the constitution of the sea, and the appearance of the surface of the earth. There was a prodigious growth of ferns, lepidodendra, equisetaceæ, coniferæ. The percentage of oxygen in the air continually increased, that of carbonic acid continually declined; the pressure of the air correspondingly diminished, partly because of the replacement of a heavy gas by a lighter one, and partly because of the general decline of temperature slowly taking place, which diminished the absolute volume of vapour. and also on the sea. The sea, in its deepest abysses, was likewise affected by the sunlight; not directly, but in an indirect way; for, as the removal of carbonic acid from the atmosphere went on, portions of that gas were perpetually surrendered by the ocean in order to maintain a diffusion-equilibrium between its dissolved gas and the free gas of the air. And now no longer could be held in transparent solution by the water those great quantities of carbonate of lime which had once been concealed in it, the deposit of a given weight of coal in the earth being inevitably followed by the deposit of an equivalent weight of carbonate of lime in the sea. This might have taken place as an amorphous precipitate; but the probabilities were that it would occur, as in fact it did, under forms of organization in the great limestone strata coeval with and posterior to the coal. The air and the ocean were thus suffering an invisible change through the disturbing agency of the sun, and the surface of the solid earth was likewise undergoing a more manifest, and, it may be said, more glorious alteration. Plants, in wild luxuriance, were developing themselves in the hot and dank climate, and the possibility was now approaching for the appearance of animal types very much higher than any that had yet existed. Cold-blooded animals succeeded by hot. In the old heavy atmosphere, full of a noxious gas, none but slowly-respiring cold-blooded animals could maintain themselves; but after the great change in the constitution of the air had been accomplished, the quickly-respiring and hot-blooded forms might exist. Hitherto the highest advancement that animal life could reach was in batrachian and lizard-like organisms; yet even these were destined to participate in the change, increasing in magnitude and vital capacity. The pterodactyl of the chalk, a flying lizard, measures nearly seventeen feet from tip to tip of its wings. The air had now become suitable for mammals, both placental and implacental, and for birds. One after another, in their due order, appeared the highest vertebrates: marine, as the cetacean; aerial, as the bat; and in the terrestrial, reaching, in the Eocene, quadrumanous animals, but not, until after the Pliocene, man.

The date of organisms may change, but the order not. Although the advance of geology may hereafter lead to a correction of some of the conclusions thus attained to respecting the first dates of different organic forms, and carry them back to more ancient times, it is scarcely likely that any material modification of their order of occurrence will ever be made. Birds, mammals, reptiles, fishes, and invertebrates may each be detected in earlier strata; even in some of those formations now regarded as non-fossiliferous, organisms may be found; but it is not at all probable that the preponderance of reptiles will ever cease to be the essential characteristic of the Secondary rocks, or that of mammals of the Tertiary, or that a preceding period of vast duration, in which the type of life had been the invertebrate, will ever be doubted. Nothing, probably, will ever be discovered to invalidate the physical conclusion that, while there was an excess of carbonic acid in the air, the Flora would tend to be Cryptogamic and Gymnospermic, and that there would be a scarcity of monocotyledons and dicotyledonous angiosperms in the coal; nothing to disprove the fact that the animals were slow-breathing and cold-blooded; and that it was not until after the oxygen of the air had increased and the mean temperature had declined that birds made their appearance. Though both placental and marsupial animals may hereafter be found earlier than in the Stonesfield slate; though wood and herb-eating beetles, grasshoppers, dragon-flies, and May-flies may be found beneath the lias, and scorpions and cockroaches beneath the coal, though, also beneath the coal, salamanders and Sauroid batrachians, of which the archegosaurus is an example, may occur; though reptiles, as the telerpeton, may be found deeper than the old red sandstone; yet the connexion between aerial constitution and form of life will never be shaken. Still will remain the facts that the geographical distribution of types was anterior to the appearance of existing species, that organisms first appeared in a liquid medium, primitively marine, then fluviatile, and at last terrestrial; that Radiates, Molluscs, Articulates, Vertebrates, were all at first aquatic, and that the Radiates have ever remained so; that the plane of greatest vital activity has ever been the sea-level, where the earth and air touch each other; that the order of individual development is the order of mundane development. Still will remain the important conclusions that the mammalian Fauna has diverged more rapidly than the testaceous; that hot-blooded animals have not had that longevity of species which has been displayed by the cold, just as we observe in the individual the possibility of muscular contraction by a given galvanic force lasts much longer in the latter than in the former; that if the hot-blooded tribes have thus a briefer duration, they enjoy a compensation in the greater energy of their life – perhaps this being the cause and that the effect; that, notwithstanding the countless forms exhibited by species, their duration is so great that they outlive vast changes in the topographical configuration of countries – the Fauna of some countries having been in existence before those countries themselves; that the plan of individual development has ever been as it is now, and that sameness of external influence produces similarity of organization.

The doctrine of catastrophes and uniformity. In its early history theoretical geology presented two schools – one insisting on a doctrine of catastrophes, one on a doctrine of uniformity. The former regarded those changes which have manifestly taken place in the history of our planet as having occurred at epochs abruptly. To this doctrine the prevailing impression that there had been providential interventions lent much force. The other school, reposing on the great principle of the invariability of the laws of Nature, insisted that affairs had always gone on at the same rate and in the same way as they do now. Hence it maintained an opposition to the catastrophists, and in this, it may be said, was actually not true to its own principles. Any doctrine of uniformity, rightly considered from its most general point of view, includes an admission of catastrophes. Numerous illustrations of this truth spontaneously suggest themselves. A tower, the foundations of which are slowly yielding, may incline more and more for many centuries, but the day must come in which it will fall at last. In the uniformity of the disturbance a catastrophe was eventually involved. And thus, in what has been said respecting geological events, though they are spoken of as proceeding quietly and with uniformity, it may be understood that sudden crises are also contemplated. Moreover, those who adopt the doctrine of uniformity in an absolute sense must pay a due regard to the variations in intensity of physical acts which their own principles imply. The uniform cooling of a hot body actually means a cooling at first fast, and then slower and slower; and invariability of chemical change actually implies more violent and summary modifications at a high temperature than at one which is low.