In the massive volumes of the later editions of the Principles of Geology all these points are discussed and illustrated with such a wealth of facts and such cogent yet cautious reasoning as have carried conviction to all modern students. It affords us perhaps the very best proof yet given of evolution in one department of the universe—that of the surface and the crust of the earth we inhabit. Not only have all the chief modifications during an almost unimaginable period of time been clearly depicted, but they have in almost every case been shown to be the inevitable results of real and comparatively well-known causes, such as we now see at work around us.
The grand generalizations of Lyell have been strengthened since his death by more complete investigations of certain phenomena and their causes than were possible in his day; while the only objections to them seem to be founded, to some extent, upon a misconception. He has been termed a “Uniformitarian,” and it is alleged that it is unphilosophical to take the limited range of causes we now see in action, as a measure of those which have acted during all past geological time. But neither Lyell nor his followers make any such assumption. They merely say, we do not find any proof of greater or more violent causes in action in past times, and we do find many indications that the great natural forces then in action—seas and rivers, sun and cloud, rain and hail, frost and snow, as well as the very texture and constituents of the older rocks, and the mode in which the organisms of each age are preserved in them, must have been in their general nature and magnitude very much as they are now. Other objections, such as that the internal forces were greater when the earth was hotter, and that tidal effects must have been more powerful when the moon was nearer the earth, are altogether beside the question until we can obtain more definite measures of past time than we now possess in reference to both geological and cosmical phenomena. It may well be that the physical changes above referred to have been so slow that they would have produced no perceptibly increased effect at the epoch of the early stratified rocks. Lyell’s doctrine is simply that of real against imaginary causes, and he only denies catastrophes and more violent agencies in early times, because there is no clear evidence of their actual existence, and also because known causes are quite competent to explain all geological phenomena. It must be remembered, too, that uniformitarians have never limited the natural forces of past geological periods to the precise limits of which we have had experience during the historical period. What they maintain is, that forces of the same nature and of the same order of magnitude are adequate to have brought about the evolution of the crust of the earth as we now find it.
ORGANIC EVOLUTION, ITS LAWS AND CAUSES
We now come to that branch of the subject which is the most important and distinctive of our age, and which, in popular estimation, alone constitutes evolution—the mode of origin of the innumerable species of animal and plant life which now exist or have ever existed upon the earth.
The origin of the different forms of life has till quite recent times been looked upon as an almost insoluble problem, although a few advanced thinkers, even in the eighteenth century, perceived that it was probably the result of some natural process of modification or evolution; but no force or law had been set forth and established in any way adequate to produce it until the publication of Darwin’s Origin of Species, in 1859. In the later editions of that work, Darwin has given a historical sketch of the progress of opinion on the subject. I shall, therefore, now only notice a few great writers which he has not referred to.
We have seen what an impossible and even ludicrous explanation had to be given by Lucretius; and from his day down to the middle of the eighteenth century no advance had been made. Either the problem was not referred to at all, or the theological doctrine of a special creation was held to be the only possible one. But in the middle of the eighteenth century the great French naturalist, Buffon, published his very important work, Histoire Naturelle, in fifteen volumes (1749–1767), in which, besides describing the characters and habits of all the animals then known, he introduced much philosophical and speculative thought, which would probably have been carried much further had he not felt obliged to conform to the religious prejudices of the age. We are indebted to Mr. Samuel Butler for having brought together all the important passages of Buffon’s voluminous and now little-read works bearing upon the question of evolution, and it is from his volume that I quote.
Buffon lays stress on the great resemblance of all mammalia in internal structure, showing that the most unlike creatures may be really alike structurally. He says: “The horse, for example—what can at first sight seem more unlike mankind? Yet when we compare man and horse, point by point and detail by detail, our wonder is excited rather by the resemblances than by the differences between them.” He then shows that all the parts of the skeleton agree, and that it is only in proportions, the increase of some bones and the suppression of others, that they differ, adding: “If we regard the matter thus, not only the ass and the horse, but even man himself, the apes, etc., might be regarded as forming members of one and the same family.” Then, after a few more illustrations, he remarks: “If we once admit that there are families of plants and animals, so that the ass may be of the family of the horse, and that the one may only differ from the other by degeneration from a common ancestor, we might be driven to admit that the ape is of the family of man, that he is but a degenerate man, and that he and man have had a common ancestor.... If it were once shown that we had right grounds for establishing these families, if the point were once gained that among plants and animals there have been even a single species which had been produced in the course of direct descent from another species, then there is no further limit to be set to the power of nature, and we should not be wrong in supposing that with sufficient time she could have evolved all other organized forms from one primordial type.”
This indicates clearly enough his own opinion, but to save himself from the ecclesiastical authorities he at once adds this saving clause: “But no! It is certain, from revelation, that all animals have alike been favored with the grace of an act of direct creation, and that the first pair of every species issued full formed from the hands of the Creator.”
Such examples of disarming religious prejudice are frequent, but he continually recurs to statements as to mutability which neutralize them. Here, for example, is a broad claim for nature as opposed to creation. He has been showing how variable are many animals, and how changes of food, climate, and general surroundings influence both their forms and their habits; and then he exclaims:
“What cannot nature effect with such means at her disposal? She can do all except either create matter or destroy it. These two extremes of power the Deity has reserved for Himself only; creation and destruction are the action of His omnipotence. To alter and undo, to develop and renew—these are powers which He has handed over to the charge of nature.”