Popular Science Monthly/Volume 12/December 1877/Dr Draper's Lecture on Evolution
ITS ORIGIN, PROGRESS, AND CONSEQUENCES.
WHEN, in the beginning of the present year, I received a request to deliver before this Institute a lecture on the subject of Evolution, I was at first disposed to excuse myself. Holding religious views which, perhaps, in many respects are not in accordance with those that have commended themselves to you, I was reluctant to present for your consideration a topic which, though it is in truth purely scientific, is yet connected with some of the most important and imposing theological dogmas. Whatever conclusion is eventually reached respecting it will have an influence on them. But there was that liberality of sentiment in your letter—that earnest desire for the ascertainment of truth—that I cast aside these hesitations, and am now here in obedience to your wishes.
Not that I can do justice in an hour to so great a subject, the literature of which ranges through many centuries. It is no new-fangled romance, as some would have us believe. It comes to us from a venerable antiquity. The theorems it expresses, and indeed on which it is based, have long ago been clearly known.
Considering the shortness of the time allotted me, the vast extent of the subject, the special character of this audience, and the nature of your request, I perceive that it is not an elaborate exposition of the evidence in favor of the theory of evolution that I must give, but a reference to those facts connected with it that are of chief interest to you. I must bear in mind that this is an institute of clergymen seeking information on a topic which they consider to have a bearing on their pursuits, and that it is from a corresponding point of view that I must present it.
Two explanations have been introduced to account for the origin of the assemblage of organic beings, plant and animal, that surround us. These are conveniently designated as the hypothesis of Creation and that of Evolution.
The hypothesis of Creation asserts that Almighty God called into sudden existence, according to his good pleasure, the different types of life that we see. This hypothesis has an ecclesiastical form, that the world, with all its various animals and plants, was created about six thousand years ago. The work was completed in six days, and was perfect, needing no improvement. At the close of each day the Almighty surveyed what he had done, and pronounced it very good. He brought all the animals thus made before Adam in the garden of Eden to receive their names. There was nothing more necessary, and on the seventh day he rested.
The hypothesis of Evolution asserts that from one or a few original organisms all those that we see have been derived, by a process of evolving or development. It will not admit that there has been any intervention of the divine power.
The former of these hypotheses considers each species as independent of all the others; the second considers them as inter-related. Creation reposes on the arbitrary act of God: Evolution on the universal reign of law.
The hypothesis of Evolution in its scientific form presents three factors: 1. Heredity; 2. Environment; 3. Adaptation. By heredity is meant the tendency manifested by an organism to develop in the likeness of its progenitor. By environment, the sum total of the physical conditions by which the developing organism is surrounded the ambient world. By adaptation, the disposition so to modify as to bring an organism and its environment into harmony. This may be accomplished either by progression or retrogression.
As to the origin of organisms, it withholds, for the present, any definite expression. There are, however, many naturalists who incline to believe in spontaneous generation. In its most improved form it occupies itself with two classes of problems, the direct and the inverse, considering in the former the effect of the environment on the organism, and in the latter deducing from the organism the nature of the environment. Thus Schleiden gathers from the structure of the stems of certain pine-trees the distribution of climates at the time of their growth; and the ancient geographical connections of Madagascar and of Australia may be thus ascertained from their fauna.
After a very long and exhaustive survey of the plants and animals of his own locality, and of all that the power and favor of Alexander the Great enabled him to inspect, this is the result to which Aristotle, the prince of ancient Greek naturalists, came. In the eighth book of his "History of Animals," when speaking of the chain of living things, he says: "Nature passes so gradually from inanimate to animate things, that from their continuity the boundary between them is indistinct. The race of plants succeeds immediately that of inanimate objects, and these differ from each other in the proportion of life in which they participate; for, compared with minerals, plants appear to possess life, though when compared with animals they appear inanimate. The change from plants to animals is gradual; a person might question to which of these classes some marine objects belong." Aristotle referred the primitive organisms to spontaneous generation.
In the Museum of Alexandria the views of Aristotle were greatly expanded. There it was discovered that animated Nature presents something more than a mere connection; that each link of Aristotle's chain, if such a phraseology must be continued, was the descendant of its predecessor, the progenitor of its successor. The idea now lost its mechanical aspect and assumed a physiological one.
We remark an important extension of this view after the conquest of Alexandria by the Arabians. If we compare the order of affiliation in successive points, it obviously presents a new fact—progress; and not progress only, but progress from the imperfect to the more perfect. This view included lifeless as well as living Nature. A practical application of it arose, to which the designation Alchemy was given. There is an unceasing progression, in which all things take part, to a better and nobler state. In this slow development Nature has no need to hasten; she has eternity to work in. Thus, in the mineral world, base and unworthy metals, such as lead and tin, are slowly on their way to perfection. They reach their goal on turning into gold. It is, then, for us to ascertain the favoring conditions, and, by imitating or increasing them, to hasten on the work.
The literature of those ages is pervaded with the idea of the mutability of everything—a proneness of all living beings to suffer transmutation, with changes in the environment, or in the physical conditions to which they are exposed; and thus arises a slow but continuous procession, in the unceasing lapse of time, to the beautiful and good. We meet with this in both the serious philosophical works of the Mohammedans, and in their lighter compositions of romance. They wrote books on the production of animals both by generation and putrefaction. They thought that in the germ there exists a latent force tending to evolve it. Ibn Roschd says: "There are, as respects the origin of living beings, two opposite theories. Some explain their existence by development, others by creation. The latter is the opinion of the Christians, as well as of our Motacallemin." Abubacer accepts the reality of spontaneous generation by means of putrefaction and the action of the sun. These philosophers did not hesitate to say that the dogma of creation is an impossibility, an absurd opinion, only fit for the vulgar who will believe anything. According to these elevated views, living beings are merely a movement of matter under the influence of heat. Man himself is like the flame of a lamp, a form or shape through which material substance is passing, receiving supplies, dismissing wastes, and evolving force. As regards transmutation, Al Khazini says that an animal passes through successive stages of development, but we must not suppose that naturalists mean to say that "man was once a bull, and was changed into an ass, and afterward into a horse, and after that into an ape, and finally became a man."
Arabian philosophers had therefore speculated on spontaneous generation, and the conditions necessary for its occurrence; on the development of a germ by the latent force it contains; on the transmutation of species; and the production of the animal series. They had rejected the theory of creation, and adopted that of evolution. They had gained ideas respecting the unceasing dominion of law, but at these they had arrived through their doctrine of emanation and absorption, rather than from an investigation of visible Nature. In the religious revolt against philosophy that took place toward the twelfth century, these ideas were exterminated and never again appeared in Islam.
If the doctrine of the government of the world by law was thus held in detestation by Islam, it was still more bitterly refused by Christendom, in which the possibility of changing the divine purposes was carried to its extreme by the invocation of angels and saints, and great gains accrued to the Church through its supposed influence in procuring these miraculous interventions. The Papal Government was no more disposed to tolerate universal and irreversible law than its Paynim antagonist had been. The Inquisition had been invented and set at work. It speedily put an end, not only in the south of France, but all over Europe, to everything supposed to be not in harmony with the orthodox faith, by instituting a reign of terror.
The Reign of Terror in revolutionary France lasted but a few months; the atrocities of the Commune at the close of the Franco-German War only a few days; but the Reign of Terror in Christendom has continued from the thirteenth century with declining energy to our times. Its object has been the forcible subjugation of thought.
The Mohammedans had thus brought the theory of evolution up to that point at which, for any further advance, clear views of the operation of law in the government of the world were necessary. In their speculations in this particular they had been guided by theological considerations. These were now to be replaced by others of a more definite and solid kind, derived from physical science.
The starting-point of Christendom in the theory of evolution, for the Mohammedans had now ceased to philosophize, was the publication by Copernicus of the book "De Revolutionibus Orbium Celestium." In this the Pythagorean view of the emplacement of the solar system was revived. The way for this restoration had been prepared by such books as that of Cusa "On Learned Ignorance." He conceived of-the universe as a vast organism, the life of which is the breath of God, and which has neither centre nor circumference, but is infinite as its maker. Such views were largely prevalent in Italy, at that time the focus of infidelity, and there Copernicus had been. His work was followed by Kepler's great discovery of the three laws that bear his name.
After the invention of printing, the "Index Expurgatorius" of prohibited books had become essentially necessary to the religious Reign of Terror, and for the stifling of the intellectual development of man. The Papal Government, accordingly, established the Congregation of that Index.
It was very plain that the tendency of Kepler's discoveries was to confirm the dominating influence of law in the solar system, as well as to destroy geocentric and anthropocentric theories. It was, therefore, adverse to the Italian theological views, and to the current religious practices. Kepler had published an epitome of the Copernican theory. This, as also the book itself of Copernicus, was placed in the Index, and forbidden to be read.
The Reformation came. It did not much change the matter. It insisted on the Mosaic views, and would tolerate no natural science that did not accord with them. Nevertheless, under the shadow of the political power it shortly gathered, Newton's "Principia" was safely published. The two great powers into which Christendom was divided held each other in check. The sectarian divisions fast springing up in Protestantism found occupation in their contentions with each other. The bearing which Newton's book had upon those already condemned consisted chiefly in this—it gave indisputable reasons that Kepler's laws are a mathematical necessity. For the finger of Providence it substituted mechanical force. And thus the Reign of Law, that great essential to the theory of evolution, was solidly established.
But not alone did the discoveries of physical astronomy lead to these views. If the heavens were observed, the earth, also, was examined. There could no longer be any doubt that fossil remains were the relics of beings that were once alive, as Xenophanes in the old times, and Da Vinci and Palissy more recently, had affirmed—not mere lusus naturæ; that the earth's strata were not all of the same age; that in the oldest no fossils could be found; that there had been a time when there was no life on the earth; that of the strata some are of marine, some of fresh-water formation; that they are often intercalated like leaves in a book, and therefore cannot be referred to any single cataclysm such as the deluge.
From considerations connected with the primary rocks, Leibnitz (1680) had inferred that the earth was once at a far higher temperature than now, and in fact must have been in an ignited state; that it had undergone a gradual cooling. Werner subsequently introduced the Neptunic theory, and Hutton the Plutonic. These cosmographical theories were, however, of less importance than what was clone in paleontology. It was discovered that while similar fossil remains extend over vast horizontal surfaces, different fossils are found to succeed each other very rapidly when a vertical examination is made. There is a geological as well as a geographical distribution of plants and animals—geological as to time, geographical as to surface.
In the works of Maillet (1748), and again in those of Buffon, the old doctrine of evolution reappears. A more formal presentment was, however, made by Lamarck in his "Philosophic zoologique," published in 1809. He advocated the doctrine of descent, and announced the propositions now known as Darwinism. According to him, organic forms originated by spontaneous generation, the simplest coming first, and the complex being evolved from them. Variations and transmutations occur through external influences, the environment modifying the organism, and as these in the lapse of time become essential differences, new species arise. Moreover, wants experienced cause the will to develop new organs by the modification of previously-existing ones, and these are transmitted by heredity or generation. Organisms are developed out of one another; so far from being permanent, they have only a temporary existence.
Though an organism tends to be like its progenitor, it will undergo changes by the use or disuse of its parts; by the former it is developed, by the latter deteriorated. The changes produced thus, or by the environment, always have been, and always will be, continuous, not catastrophic.
Lamarck recognized the struggle of each against all. He saw plainly the influence of heredity, and understood the relation of environment and adaptation. He defined in the clearest manner the doctrine of transmutation and theory of descent. According to him, if time enough be allowed, any modification may take place.
So far from meeting with acceptance, the ideas of Lamarck brought upon him ridicule and obloquy. He was as much misrepresented as in former times the Arabian Nature-philosophers had been. The great influence of Cuvier, who had made himself a champion of the doctrine of permanence of species, caused Lamarck's views to be silently ignored, or, if by chance they were referred to, denounced. They were condemned as morally reprehensible and theologically dangerous. In this, the authority of Cuvier in regard to evolution acted as the authority of Newton had done in regard to the undulatory theory of light.
In like manner the views of Oken met with resistance, especially his deduction that the highest animals are the result of development, not of creation. Man, he significantly says, has been developed, not created. He conceived all Nature to be in a process of evolution. His demonstration, that the bones of the skull are only vertebral modifications, however, reconciled many persons to a more favorable opinion of his hypothesis of development.
Geoffroy St.-Hilaire (1828) did not doubt that animals now living are descended by an unbroken succession from extinct ones, by transformation from form to form; that different species are degenerations of the same type, being due to the influence of the environment (monde ambiant). He thus became the opponent of Cuvier, and did very much to break down the influence of that zoölogist. In these variations he considered that the organism is passive, differing in this from Lamarck, who thought it active. His views of the influence of the environment were very precise: thus he thought that birds arose from reptiles, through the diminution of carbonic acid and increase of oxygen in the air, at the time of the formation of coal; the activity of the animal circulation becoming greater, and the reptile scales being transformed into the feathers of the bird. As is now known, this was substantially a correct interpretation.
Though the principles of the doctrine of evolution were thus thoroughly understood, the control of heredity, the influence of environment, the modeling by adaptation, public attention failed to be drawn to it until 1844, when there was published in England an anonymous book under the title of the "Vestiges of the Natural History of Creation." In this the author set forth Lamarck's views, and the work, being clearly and attractively composed, passed through a great many editions. Very fortunately, it may be said, it accepted some unsubstantiated facts and contained some physical mistakes. These tempted many skillful and bitter criticisms of hostile theologians. The reviews and journals were filled with their attacks and answers to them. Thus, happily, the whole subject was brought into such prominence that it could be withdrawn into obscurity no more.
In the discussions of this book the author made use of a most important anatomical discovery, that even in the case of the highest species, man himself, the embryo does not simply grow or increase in size, but passes in succession through a series of forms, which, examined from epoch to epoch, are totally dissimilar. It had been the vulgar opinion that after the first moment of conception all the parts of the animal that is to be are present, and that they simply grow. The human embryo, according to this, reaches birth very much in the same way that the infant passes from birth to manhood. That was, I say, the vulgar opinion, but, in laying before our eyes the development of the individual, God has given us a revelation of the course of life by the world.
The evolutionary history of animals establishes that there is not this homogeneousness of development, but that the higher pass through the forms of the lower; that the mammal, for instance, passes through stages at which the lower vertebrates remain fixed. All are therefore pursuing a journey along the same road, though some may travel to a longer, some to a shorter, distance. There is thus a parallelism between individual and race development; a close connection between the phases of development in the individual and in the species.
The type of each animal is from the first as it were imbedded in the embryo and controls its evolvement. The embryo never makes any attempt to change from one type to another, but sometimes the tendency to a form and not the form itself is transmitted.
The parallelism that exists between the career of the individual and the career of the race reappears in the life of the world. There is a resemblance—indeed more than a resemblance—between the successive forms through which man himself in his prenatal life has passed, and those that have appeared in myriads of ages in the biography of the earth. Common-sense revolts against the idea that these transformations are in the individual due to divine intervention. In that, and in the case of the earth, they must be due to natural law.
In the year 1859 there was published by Mr. Darwin a work on "The Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life."
In this, and in other subsequent works, it is shown that the individuals of each species tend to increase in a very rapid ratio—an increase more rapid than that of their means of subsistence. Each has, therefore, to contend with his competitors; and hence all must exhibit "a struggle for existence."
But modifications are incessantly taking place in the form and characteristics of individuals, giving to some an advantage, to some a disadvantage, as compared with their competitors. Hence, the former will prevail, the latter will succumb in the struggle. This in the language of the hypothesis is formulated "the survival of the fittest."
And as the pigeon-fancier or other person who devotes himself to the breeding of animals can produce any form he wishes by selecting its progenitors and pairing them together, exercising thus artificial selection, so if any of the chance-forms that have arisen should be better adapted than others for perpetuation, they will be perpetuated, or Nature may be said to have made a selection. Hence the term "natural selection," which has been made to designate this hypothesis.
It is to be regretted that this phrase "natural selection" has been introduced. It is very unscientific, very inferior to the old expression adaptation. It implies a personification of Nature. It is anthropomorphic. But Nature never selects, never accepts or rejects, knows nothing about duties, nothing about fitness or unfitness. Nature simply obeys laws.
Natural selection is thus supposed to perpetuate an organism after adaptation to its environment has taken place. The change implied by adaptation must precede it. It should be regarded rather as a metaphorical expression than a scientific statement of an actual physical event.
Darwinism, therefore, does not touch the great question as to the manner in which variation of organisms arises. It only teaches how such variations are perpetuated.
The publication of Humboldt's "Essay on the Geography of Plants" (1805) first formally drew the attention of botanists to the connection between the distribution of plants and the distribution of heat on the surface of the earth. As an advance is made from the equator toward the pole in either hemisphere, the mean annual temperature declines, and in succession a series of vegetable zones is encountered, merging gradually into each other, though each, where best marked, is perfectly distinguished from its successor. In the tropics there are the palms which give so striking a characteristic to the landscape, the broad-leaved bananas, and great climbing plants throwing themselves from stem to stem like the rigging of a ship. Next follows a zone of evergreen woods, in which the orange and citron come to perfection. Beyond this, another of deciduous trees, the oak, the chestnut, and the fruit-trees of our orchards. Here the great climbers of the tropics are replaced by the hop and the ivy. Still farther is a belt of conifers, firs, larches, pines, and other needle-leaved trees; and these lead through a range of birches, becoming more and more stunted, to a region of mosses and saxifrages, but which at length has no tree nor shrub; and finally, as the perpetual polar ices are reached, the red-snow alga is the last trace of vegetable organization.
A similar series of facts had long previously been observed by Tournefort in an ascent of Mount Ararat. The distribution of vegetation from the base to the top of the mountain bears a general resemblance to the distribution from the base to the polar regions. These facts were generalized by subsequent observers. It was established that there exists an analogy between horizontal distribution on the surface of the globe, and vertical distribution at different altitudes above the level of the sea. Even in the tropics, if a mountain be sufficiently high, a short ascent suffices to carry us from the characteristic endogenous growths at its foot through a zone of evergreens into one of deciduous trees, and this again into one of conifers, the vegetation declining through mosses and lichens as we reach the region of perpetual snow.
In these cases of horizontal and vertical distribution which thus present such a striking botanical resemblance, there is likewise so clear a meteorological analogy that it is impossible to avoid the conclusion that the distribution of plants depends very largely on the distribution of heat. And, indeed, what better illustration of the influence of heat could we have than this, that by artificially adjusting the temperature of hot-houses we can cause any plant to grow in any latitude?
But temperature alone does not determine the distribution of plants. If it did, we should find the same species in the same isothermal zones. Throughout the old continent, with the exception of the torrid zone, heaths abound; but in America not a single heath occurs. In the New World, through forty degrees on each side of the equator, the cactus tribe flourishes; in the Old not a single cactus is to be seen—the spurges there replace them. So, again, in Australia, the forests present a melancholy, a shadeless character, from their casuarinas, acacias, eucalypti, whereas, if temperature alone were concerned, they should offer the same aspect as the forests of North America and Europe.
As regards animals the same remark may be made. In the temperate zone, eastward beyond the Caspian, there are men whose complexion is yellow; in Europe the complexion is white; the American Indian is red. Asia has its Tibet bear, Europe its brown bear, North America its black bear. The European stag finds in America its analogue in the wapiti, its Asiatic in the musk-deer. The wild-ox of Lithuania differs from the North American buffalo, and this, again, from the Mongolian yak. The llama in America replaces the camel of Asia, the puma replaces the lion. Brazil has had in times long past representatives of its existing sloths and armadillos. Australia, which has isothermal zones like those of other continents, has no apes or monkeys, no cats or tigers, no wolves or bears, hyenas, horses, squirrels, rabbits; no woodpeckers or pheasants. Instead of them it has the kangaroo, wombat, ornithorhynchus, cockatoos, and lories, nowhere else found.
Then, though heat is a dominating influence in the distribution of plants and animals, it is by no means the only one. There are also other conditions, such as the supply of water, the composition of the soil, the access of light, etc. It has been found convenient to group all these together, and to speak of them, as I have already stated, under a single designation, "The Environment."
Change in the environment, and change in its organisms, go hand in-hand. Should the warmth of the tropics be diffused into the polar circle, a tropical vegetation would replace the vanishing snows. Should the ices of the poles spread over the temperate region, the reindeer would accompany their invading edge.
While the environment thus influences the organism, the organism reacting influences the environment. The most striking instance of this, perhaps, will be found on comparing the constitution of the atmosphere before and since the Carboniferous epoch. Prior to that epoch, all the myriads of tons of coaly substance now inclosed in the strata of the earth existed as carbonic acid in the air. By the agency of the sunlight acting on the leaves of the luxuriant vegetation of those times, this noxious gas was gradually removed, and replaced by an equivalent volume of oxygen. A hot-blooded, quickly-respiring animal could not possibly exist in an atmosphere laden with carbonic acid. Anterior to the coal deposit, the fauna was cold-blooded and slow-respiring. The flora thus changed the aërial environment, and this, in its turn, reacting, changed the fauna.
It is on all sides admitted that plants tend by their removal of carbonic acid from the air, replacing it by oxygen, to compensate for the disturbance occasioned by animals. In this way, through very many centuries, the same percentage constitution of the atmosphere is maintained, the sum total of vegetable being automatically adjusted to the sum total of animal—life automatically, and not by any interference of Providence—a fact of great value in its connection with the theory of evolution. For, if we admit what has been conclusively established by direct experiment, that plants would grow more luxuriantly in an atmosphere somewhat richer in carbonic acid than the existing one, we may see how upon this condition depends a principle of conservation, which must forever retain the air at its present constitution, no matter how animal life may vary.
Cuvier speaks of the inferior organisms as furnishing us with a series of experiments made by the hand of Nature, an idea often quoted and often admired, but which, perhaps, is scarcely consistent with enlarged conceptions of the system of the world. An organism, no matter how high or low, is not in an attitude of isolation. It is connected by intimate bonds with those above and those beneath. It is no product of an experimental attempt, which, either on the part of Nature or otherwise, has ended in failure or only partial success.
The organic series—an expression full of significance and full of truth implies the interconnection of all organic forms—the organic series is not the result of numberless creative blunders, abortive attempts or freaks of Nature. It presents a far nobler aspect. Every member of it, even the humblest plant, is perfect in itself. From a common origin, or simple cell, all have arisen; there is no perceptible microscopic difference between the primordial vesicle which is to produce the lowest plant, and that which is to produce the highest, but the one, under the favoring circumstances to which it has been exposed, has continued in the march of development, while the career of the other has been stopped at an earlier point. The organic aspect, at last assumed, is the representation of the physical agencies that have been at work—the environment. Had these for any reason varied, that variation would at once have been expressed in the resulting form, which is, therefore, actually a geometrical embodiment of the antecedent physical conditions. For what reason is an offspring like its parent, except that it has been exposed during development to the same conditions as was its parent. Comparative physiology is not a fortuitous collection of experiments. Our noblest conception of it is the conception we have of analytical geometry. Each member of the organic series is an embodied result of a discussion of the equation of life for one special case.
It was a felicitous thought of Descartes that we may represent a geometrical form in an algebraic equation, and, by the proper consideration and discussion of such an expression, determine and delineate all the peculiarities of such a form; that here it should become concave, there convex; here it should run out to infinity, there have a cusp. The equation determines all the peculiarities of the form, and enables us to construct it. In like manner, all living and lifeless forms are related; an increase in the value of one condition carries development forward in one direction; an increase in the value of another condition determines development in another way, and these variations give rise in their succession to the whole organic series.
Nature ever geometrizes and ever materializes. Every organism is the result of the development of a vesicle, under given conclusions, carried out into material execution. It is the incarnation, the embodiment, the lasting register of physical influences, the daughter of the environment.
Let us now rapidly survey the changes that have taken place in the earth's organisms:
In the earliest, or Primordial period, there existed of plants only water-organisms—tangled sea-weeds. Then in the following, the Primary, came the more perfect cryptogams, such as ferns. Then followed, in the Secondary, pine-forests. In the Coal period the phanerogamia developed out of the more perfect cryptogamia. Not until the Chalk did the higher corollifloræ appear. In the beginning of the Tertiary the earth had sufficiently cooled at the poles, climate-zones were produced, and the land was covered with leaved forests. Flowerless plants had been succeeded by flowering ones, the latter first without a distinct corolla, and then by those with one; and of these, first the lower and then the higher.
Turning to the order of succession of animal life—of the Primordial, the forms are skull-less; then in the following, the Primary, came fishes, first those with the heterocercal tail, as in the embryos of existing ones. In the Secondary, reptiles, and out of them birds, were developed; the decreasing amount of carbonic acid and the increasing amount of oxygen permitting that change. Of birds, the earliest had a long, lizard-like tail, composed of thin vertebrae, to every one of which were attached strong, rudder-like feathers in pairs. The same formation of the tail part of the vertebral column still occurs transiently in the embryos of later birds. The transition from the reptile to the bird is manifested by some of the latter having teeth set in one order in grooves, in another in distinct sockets. Among mammals as among fishes the imperfect appeared first. About the middle of the Mesolithic period, out of a branch of the cloacal animals the marsupials were evolved; and in the beginning of the Tertiary the placentals were developed out of the marsupials. The latter were at one time distributed over the whole earth; now they are fast approaching extinction. In Europe, Asia, Africa, not a single member of the group remains. The cloacal animals, the marsupials, the placentals, stand therefore in an order of succession.
Such has been the order of evolution in Europe. For its order in America I may refer you to the recent admirable address of Prof. Marsh before the American Association for the Advancement of Science. The general conclusions at which we arrive in one case are substantiated in the other.
In accordance with his descent, the cloacal structure exists in man in the earlier period of his embryonic life. The separation into two openings takes place about the twelfth week of his uterine development. Shall we not, therefore, infer from the evidence of his embryonic forms that he has been developed step by step out of the lower vertebrates?
In the early stages of their evolution, amphibia, reptiles, birds, cannot be distinguished. The first steps of development in all vertebrates are identical. Man passes now through the same series of transmutations which his animal predecessors passed through in immense spaces of time, long ago. The progress he makes in the lapse of a few days in the darkness of the womb is the same that has been followed by the procession of animated Nature in the lapse of myriads of centuries in the daylight of the world.
From a comparison of their studies embryologists and paleontologists unite in the conclusion that individual development is a rapid repetition of race-development, and that the paleontological movement is to be interpreted by the embryonic. The connecting links supposed to be missing in the former may be sought for in the latter. Individual development, paleontological development, and comparative anatomy, through their combined evidence guide us to a deduction of the genealogy of any organism. The dominion of law is everywhere manifest. The capricious intrusion of a supernatural agency has never yet occurred. Each of the geological periods has its dominating representative type of life. Perhaps it may he asked: "How can we be satisfied that the members of this long series are strictly the successive descendants by evolution from older forms, and in their turn the progenitors of the later? How do we know that they have not been introduced by sudden creations, and removed by sudden extinctions?" Simply for this reason: The new groups make their appearance while yet their predecessors are in full vigor. They come under an imperfect model which very gradually improves. Evolution implies such lapses of time. Creation is a sudden affair.
A striking illustration of this is offered by two of the most imposing types of life, the reptile and the mammal. The former is the characteristic of the Secondary, the latter of the Tertiary period. In the Secondary, when reptile life was at its culmination, there were reptiles flying in the air, swimming on or in the sea, crawling on the land, or climbing the trees. After this type of life had reached its culmination, and extinction began to set in, that process went forward in a gradual and orderly way. The flying lizards were the first to disappear, then those of the sea; they now have scarcely any representative left. The fluviatile and terrestrial ones, though greatly diminished both in numbers and size, still maintain a struggle for life; but the complete dying out of animated forms, though irresistible, requires for its completion countless centuries.
While reptile life was in full vigor, mammal life was introduced. It came under the lowest forms, the imperfect orders appearing first.
What does this coexistence of two different forms of life, through immense lapses of time—the one declining and on its way to disappearance, the other marching forward to increase—what does this overlapping mean? Not sudden creation, but slow development. The environment is slowly becoming unsuitable to the one, and slowly becoming suitable to the other.
If time permitted, I would ask your close attention to rudimentary organs, for they illustrate strikingly the theory of evolution. They are organs existing in an apparently undeveloped and useless condition, such, for instance, as the incisor teeth in the mid-bone of the upper jaw in embryos of common cattle, the rudimentary wings of the penguin and dodo, the mammæ of the male mammalian, the subcutaneous feet of certain snakes. In the embryos of whales teeth are found in the jaw, precisely as we find them at birth in the human infant. In the latter instance, we think we see a wise provision and foresight of Nature, which does not give to man these masticatory organs before the time they are wanted. But what are we to make of the parallel case of the whale? Shut up as these rudimentary teeth are in the interior of the jaw, never to be developed and never to be used, does not that look something like a useless work? And why has Nature, in the case of certain snakes, placed under the skin bony representatives of the extremities, the movements of those animals being by the use of the ribs, and feet never being wanted?
We may also turn to the vegetable world, and there we find rudimentary organs, excesses and deficiences of development. As Treviranus says, adaptation to the surrounding world may be shaped either by gradual development or by degeneration, which is equally effective. The same organ may be expanded into a compound leaf, or degenerated into a scale. Development can turn a reptile into a bird; degeneration can turn it into a serpent. Any flower may be regarded as a transformed branch—that which might have evolved into a leaf turns indifferently, as circumstances may direct, into a sepal, a petal, or a stamen.
Rudimentary organs come into existence as part of a general plan. They are the manifestation of heredity in the type of life of the animals or plants in which they occur. They prove that the form has been developing, not teleologically, or for a purpose, but in obedience to law.
Now I have answered, and I know how imperfectly, your question, "How does the hypothesis of evolution force itself upon the student of modern science?" by relating how it has forced itself upon me, for my life has been spent in such studies, and it is by meditating on facts like those I have here exposed that this hypothesis now stands before me as one of the verities of Nature.
In doing this I have opened before you a page of the book of Nature—that book which dates from eternity and embraces infinitude. It reveals millions of suns and worlds of surpassing glory. Among its most insignificant pages are the vast rock-strata of the earth. We have been looking at some of them. No Council of Laodicea, no Tridentine Council, is wanted to indorse its authenticity, nothing to assure us that it has never been tampered with by any guild of men, to perpetuate their influence, secure their profits, or otherwise promote their ends.
Then it is for us to study it as best we may, and to obey its guidance, no matter whither it may lead us.
And this brings me face to face with the third division of my subject. I have spoken of the origin and the progress of the hypothesis of evolution, and should now consider the consequences of accepting it. Here it is only a word or two that time permits, and very few words must suffice. I must bear in mind that it is the consequences from your point of view to which I must allude. Should I speak of the manner in which scientific thought is affected, should I dwell on the influence this theory is exerting on general knowledge, I should be carried altogether beyond the limits of the present hour.
The consequences! What are they, then, to you? Nobler views of this grand universe of which we form a part, nobler views of the manner in which it has been developed in past times to its present state, nobler views of the laws by which it is now maintained, nobler expectations as to its future. We stand in presence of the unshackled, as to Force; of the immeasurable, as to Space; of the unlimited, as to Time. Above all, our conceptions of the unchangeable purposes, the awful majesty of the Supreme Being, become more vivid. We realize what is meant when it is said, "With Him there is no variableness, no shadow of turning." Need I say anything more in commending the doctrine of evolution to you?
Let us bear in mind the warning of history. The heaviest blow the Holy Scriptures have ever received was inflicted by no infidel, but by ecclesiastical authority itself. When the works of Copernicus and of Kepler were put in the Index of prohibited books, the system of the former was declared, by what called itself the Christian Church, to be "that false Pythagorean system, utterly contrary to the Holy Scriptures." But the truth of the Copernican system is now established.
There are persons who declare of the hypothesis of evolution, as was formerly declared of the hypothesis of Copernicus, "It is utterly contrary to the Holy Scriptures." It is for you to examine whether this be so, and, if so, to find a means of reconciliation. Let us not be led astray by the clamors of those who, not seeking the truth and not caring about it, are only championing their sect r or attempting the perpetuation of their own profits.
My friends, let me plead with you. Don't reject the theory of evolution. There is no thought of modern times that more magnifies the unutterable glory of Almighty God! Remember, I beseech you, what was said by one of old times: "Ye men of Israel, take heed to yourselves what ye intend to do. And now I say unto you, if this counsel be of men it will come to naught; but if it be of God, ye cannot overthrow it, lest haply ye be found to be fighting against God"—shall I continue the quotation?—"and to him they all agreed!"
We often hear it affirmed that our are is becoming more and more irreligious, and that men wantonly reject sacred things of which their ancestors approved. But I think we may profitably inquire whether very much of this is not due to the profound changes that are taking place in our conceptions of the Supreme Being? Things and acts which at one time men attributed to him without hesitation, they can attribute to him no more. They have learned to demand of every dogma, "Is it derogatory to the awful majesty of God?"
These modifications of opinion have had no little to do with the progress of the subject we have been considering. Let us ever bear in mind that the doctrine of evolution has for its foundation not the original, the immutable fiat of God. In whatever direction we commune with Nature, the dominion of universal, of everlasting law confronts us.of incessant divine interventions, but a recognition of the
The establishment of the theory of evolution has not been due to any one science, but is attributable to the conjoint movement of all. It is due to the irresistible advance of human knowledge. To refer it to geology alone, as is often done, is altogether a mistake. It was not possible that Astronomy should fail to maintain her grand position. She took the lead in the intellectual revolution which marks the close of the middle ages. Single-handed and alone, she fought and won the great battles of the globular form of the earth, the central sun, the plurality of worlds. It cost her the blood of some of her leaders. For some there wag the fagot, the rack, the prison-cell, the scourge. But they departed from their tormentors, rejoicing that they were accounted worthy to suffer even death in this cause. And now she found stepping-stones for herself in the trackless infinitude of space, and beckoned her comrade sciences to come and share with her the glorious view she had gained of the majesty of the universe. Anatomy, both human and comparative, paleontology, chemistry, physiology, microscopy, even philosophical history, have given their aid. Wherever any one science has made a marked advance, its movement has been covered by some of the others, and the ground thus occupied secured. As matters now stand, all are well to the front—the entire line is dressed.
It often takes many victories to establish one conquest. Knowledge, fresh from so many triumphs, unfalteringly continues her movement on the works of Superstition and Ignorance.
Now, in parting, let us bear this in mind: So great is the intellectual advance men have made, that questions which at one time divided Christendom into sects are now far in the rear. Those which once separated good men socially, are passing out of sight. They are replaced by others of a very different order. Among such, one of surpassing importance confronts us—the eternal reign of law. Let us bear in mind what the theory of evolution so loudly proclaims: "We are what we are, because the universe is what it is." If it acts upon us, we react upon it. Our conception of the sphere of being we occupy is enlarging, and we are thus brought into close relationship with all that is beautiful on earth, all that is magnificent in the heavens.
Then let us reverently commune with Nature. Let us try to raise our eyes from the varying phenomena of the world, to the solemn grandeur of that silent, that imperishable reign of law that governs all those changes; let each of us earnestly address to himself the remonstrance of "The Minstrel:"
"Oh! how canst thou renounce the boundless store
The warbling woodland, the resounding shore,