CHARLES LYELL, 1797-1875, like Hutton, was a Scotchman, and was born in the year of Hutton's death. Lyell worked out in detail Hutton's suggestions, and collected with great care all that was known of the changes now going on in the world, and of the causes that produce them; the rate of denudation and the amount carried down by streams; the mode in which plants and animals are buried in mud, peat, and sand. The first volume of his "Principles of Geology" was published in January 1830, seven months before the Paris controversy. In it he dealt with the changes continually taking place on the earth's surface; the rising up and the subsidence of the earth's crust; the action of rivers and volcanoes ; and showed how the present configuration of the earth was due to these causes. He pointed out that causes now in action and influences now at work åre not merely competent to produce the present state of things, but must inevitably have done so. He showed the history of the earth to be continuous and uninterrupted, and that to explain its present condition and past history we have simply to look around us.

Lyell's facts were numerous and his reasoning cogent; his conclusions therefore steadily gained supporters. It is a curious fact that, as regards fossils, Lyell himself declined to apply to them the principles he so justly insisted on for the crust of the earth. Yet it was precisely by applying a similar train of reasoning to the further problem that the final solution was attained, and by the study of what is going on around us at the present day, that principles were determined competent to account for the changes in all past time, and the death-blow given to Cuvier's views.

Evidence as to the reality of Evolution was now rapidly accumulating, not only through the work and writings of those already mentioned, but from many other sides. Professor HUXLEY in 1859 refers to the hypothesis that species living at any time are the result of the gradual modification of pre-existing species, as the "only one to which physiology lends any countenance." Sir JOSEPH HOOKER in 1859, in his "Introduction to the Australian Flora," admits the truth of descent and modification of species, and supports the doctrine by many original observations.

HERBERT SPENCER's essay in the Leader, 1852, constitutes "the high-water mark" of Evolution prior to Darwin: "Even could the supporters of the development hypothesis merely show that the production of species by the process of modification is conceivable, they would be in a better position than their opponents. But they can do much more than this; they can show that the process of modification has effected and is effecting great changes in all organisms subject to modifying influences. They can show that any existing species-animal or vegetable-when placed under conditions different from its previous ones, immediately begins to undergo certain changes of structure fitting it for the new conditions. They can show that in successive generations these changes continue until ultimately the new conditions become the natural ones.

They

B

•

can show that in cultivated plants and domesticated animals, and in the several races of men, these changes have uniformly taken place. They can show that the degrees of difference so produced are often, as in dogs, greater than those on which distinctions of species are in other cases founded. They can show that it is a matter of dispute whether some of these modified forms are varieties or modified species. And thus they can show that throughout all organic Nature there is at work a modifying influence of the kind they assign as the cause of these specific differences; an influence which, though slow in its action, does in time, if the circumstances demand it, produce marked changes; an influence which, to all appearance, would produce in the millions of years, and under the great varieties of condition which geological records imply, any amount of change."

It is impossible to depict better than this the condition prior to Darwin. In this essay there is full recognition of the fact of transition, and of its being due to natural influences or causes, acting now and at all times. Yet it remained comparatively unnoticed, because Spencer, like his contemporaries and predecessors, while advocating Evolution, was unable to state explicitly what these causes were.

We have now traced the main steps in the history of the doctrine of evolution, and have mentioned the names of the chief men with whom this history is most closely associated. This doctrine was rendered possible by Linnæus by the introduction of definite and precise nomenclature in the language common to all civilised nations, which thereby enabled men to speak of animals and groups of animals with exactness and certainty. The difficulties of framing definitions based on facts, of which equally competent men took widely different views, led to the consideration of the question-Are species fixed or mutable? Buffon, Goethe, Lamarck, St. Hilaire, and Herbert Spencer are perhaps the most famous names among the supporters of Evolution. Lamarck and St. Hilaire are specially noteworthy, as they recognised the necessity of explaining the causes of the modification, and attempted, though with very partial success, to supply the explanation. Among the opponents of Evolution, Cuvier was by far the ablest.

The question first became a prominent one about the commencement of the present century. It was hinted at earlier by Buffon, but first obtained definite expression from Lamarck in 1801, and in more detail in the "Philosophie Zoologique," published in 1809.

It is very commonly assumed that the doctrine that animals are not immutable, or the doctrine of Evolution, is of very recent origin, and that for it we are indebted to Darwin. Nothing can be more erroneous, for, as we have seen above, not only was it very clearly and emphatically maintained by several writers at the commencement of the present century, or the conclusion of the last, but the idea is found stated more or less explicitly by Aristotle over 2000 years ago.

The "Doctrine of Evolution" teaches that there is a relationship between the animals of successive

periods or ages of exactly the same kind as that which exists between the men of successive generations or centuries-viz., a blood relationship. Just as men of each century are descendants of those of a preceding century, and progenitors of those of later ones, so it is with animals throughout all geologic history.

It is well to point out clearly the difficulty which has to be met. Animals of successive ages are unlike, and fossils do not give the intermediate series, nor satisfactory indications of them. The problem we have to consider is this: The men of successive generations are unlike in language, customs, dress, and appearance; now, are the differences between animals of successive ages of the same character as between men, though of wider nature ; or are they of such a kind as to forbid the idea of descent one from another? In other words, are species immutable or variable? The doctrine of Evolution requires that they should be variable. In order to establish this doctrine it must be shown that there are causes, actually existent causes, competent to give rise to modifications of animals such as we find in passing from one geologic age to another. This is what is effected by the “Darwinian Theory," or the "Theory of Natural Selection," propounded independently and simultaneously on July 1, 1858, by Darwin and Wallace.

CHARLES DARWIN was born in 1809, and studied at Cambridge from 1827 to 1831. The voyage of the Beagle occupied from 1831 to 1836, the greater part of the time being spent on the east and west