"A quarter of a century ago, you and I must have been in something like the same state of mind on the main question. But you were able to see and work out the quo modo of the succession, the all-important thing, while I failed to grasp it."
In his earlier attitude towards evolution, my father was on a par with his contemporaries. He wrote in the Autobiography:—
"I occasionally sounded not a few naturalists, and never happened to come across a single one who seemed to doubt about the permanence of species:" and it will be made abundantly clear by his letters that in supporting the opposite view he felt himself a terrible heretic.
Mr. Huxley[131] writes in the same sense:—
"Within the ranks of biologists, at that time [1851-58], I met with nobody, except Dr. Grant, of University College, who had a word to say for Evolution—and his advocacy was not calculated to advance the cause. Outside these ranks, the only person known to me whose knowledge and capacity compelled respect, and who was, at the same time, a thorough-going evolutionist, was Mr. Herbert Spencer, whose acquaintance I made, I think, in 1852, and then entered into the bonds of a friendship which, I am happy to think, has known no interruption. Many and prolonged were the battles we fought on this topic. But even my friend's rare dialectic skill and copiousness of apt illustration could not drive me from my agnostic position. I took my stand upon two grounds: firstly, that up to that time, the evidence in favour of transmutation was wholly insufficient; and, secondly, that no suggestion respecting the causes of the transmutation assumed, which had been made, was in any way adequate to explain the phenomena. Looking back at the state of knowledge at that time, I really do not see that any other conclusion was justifiable."
These two last citations refer of course to a period much later than the time, 1836-37, at which the Darwinian theory was growing in my father's mind. The same thing is however true of earlier days.
So much for the general problem: the further question as to the growth of Darwin's theory of natural selection is a less complex one, and I need add but little to the history given in the Autobiography of how he came by that great conception by the help of which he was able to revivify "the oldest of all philosophies—that of evolution."
The first point in the slow journey towards the Origin of Species was the opening of that note-book of 1837 of which mention has been already made. The reader who is curious on the subject will find a series of citations from this most interesting note-book, in the Life and Letters, vol. ii. p. 5, et seq.
The two following extracts show that he applied the theory of evolution to the "whole organic kingdom" from plants to man.