'Now touching my opinion,' concerning the creation of new species at the present day, 'I have no right to object, as I really entertain it, to your controverting it; at the same time you will see, on reading my chapter on the subject, that I have studiously avoided laying down the doctrine dogmatically as capable of proof. I have admitted that we have only data for extinction, and I have left it to be inferred, instead of enunciating it even as my opinion, that the place of lost species is filled up (as it was of old) from time to time by new species. I have only ventured to say that had new mammalia come in, we could hardly have hoped to verify the fact[81].'
That Lyell was convinced of the truth of the doctrine of the evolution of species is shown by his correspondence with friends and sympathisers like Scrope and John Herschel. But he wrote:
'If I had stated ... the possibility of the introduction or origination of fresh species being a natural, in contradistinction to a miraculous process, I should have raised a host of prejudices against me, which are unfortunately opposed at every step to any philosopher who attempts to address the public on these mysterious subjects[82].'
That Lyell was justified in not increasing the difficulties which would retard the reception of his views, by introducing matter, which he still regarded as of a more or less speculative character, I think everyone will be prepared to admit. Darwin had to contend with the same difficulty in writing the Origin of Species. To have included the question of the origin of mankind prominently in that work would have raised an almost insurmountable barrier to its reception. He says in his autobiography, 'I thought it best, in order that no honourable man should accuse me of concealing my views, to add that by the work "light would be thrown on the origin of man and his history." It would have been useless and injurious to the success of the book to have paraded, without giving evidence, my conviction with respect to his origin[83].'
Huxley and Haeckel have both borne testimony to the fact that Lyell, at the time he wrote the Principles, was firmly convinced that new species had originated by evolution from old ones. Indeed in a letter to John Herschel in 1836 he goes very far in the direction of anticipating the lines in which enquiries on the method of evolution must proceed, having even a prevision of the doctrine of mimicry, long afterwards established by Bates and others. Lyell wrote:—
'In regard to the origination of new species, I am very glad to find that you think it probable that it may be carried on through the intervention of intermediate causes. I left this rather to be inferred, not thinking it worth while to offend a certain class of persons by embodying in words what would only be a speculation.... One can in imagination summon before us a small part at least of the circumstances that must be contemplated and foreknown, before it can be decided what powers and qualities a new species must have in order to enable it to endure for a given time, and to play its part in due relation to all other beings destined to coexist with it, before it dies out.... It may be seen that unless some slight additional precaution be taken, the species about to be born would at a certain era be reduced to too low a number. There may be a thousand modes of ensuring its duration beyond that time; one, for example, may be the rendering it more prolific, but this would perhaps make it press too hard upon other species at other times. Now if it be an insect it may be made in one of its transformations to resemble a dead stick, or a leaf, or a lichen, or a stone, so as to be somewhat less easily found by its enemies; or if this would make it too strong, an occasional variety of the species may have this advantage conferred on it; or if this would be still too much, one sex of a certain variety. Probably there is scarcely a dash of colour on the wing or body of which the choice would be quite arbitrary, or which might not affect its duration for thousands of years. I have been told that the leaf-like expansions of the abdomen and thighs of a certain Brazilian Mantis turn from green to yellow as autumn advances, together with the leaves of plants among which it seeks its prey. Now if species come in succession, such contrivances must sometimes be made, and such relations predetermined between species, as the Mantis, for example, and plants not then existing, but which it was foreseen would exist together with some particular climate at a given time. But I cannot do justice to this train of speculation in a letter, and will only say that it seems to me to offer a more beautiful subject for reasoning and reflecting on, than the notion of great batches of new species all coming in and afterwards going out at once[84].'
We have cited this very remarkable passage, as it affords striking evidence of how deeply Lyell had thought on this great question at a very early period. Nevertheless it is certain that when he wrote the second volume of the Principles, he had not been able to satisfy himself that any hypothesis of the mode of evolution, that had up to that time been suggested, could be regarded as satisfactory.
The only serious attempt to explain the derivation of new species from old ones that came before Lyell was that of the illustrious Lamarck.
Very noteworthy was the work of that old wounded French soldier, afflicted in his later years as he was by blindness. By his early labours, Lamarck had attained a considerable reputation as a botanist, and later in life he turned his attention to zoology, and then to palaeontology and geology. In zoology, he did for the study of invertebrate animals what his great contemporary Cuvier was accomplishing for the vertebrates; but, with regard to the origin of species, he arrived at conclusions directly at variance with those of his distinguished rival.
We are indebted to Professor Osborn[85] for calling attention to that remarkable, but little known work of Lamarck's—Hydrogéologie—published in 1802, seven years before his Philosophie Zoologique appeared. This work is especially interesting as showing to how great an extent—as in the case of Darwin, Wallace and others—it was geological phenomena which played an important part in leading Lamarck to evolutionary convictions. "In Geology," Professor Osborn writes,