Wallace’s relations with Spencer, though somewhat controversial at times, were nevertheless cordial and sympathetic.  In “My Life” he tells of his first visit, and the impression left upon his mind by their conversation.  It occurred somewhere about 1862-3, shortly after he and Bates had read, and been greatly impressed by, Spencer’s “First Principles.”  “Our thoughts,” he says, “were full of the great unsolved problem of the origin of life—­a problem which Darwin’s ’Origin of Species’ left in as much obscurity as ever—­and we looked to Spencer as the one man living who could give us some clue to it.  His wonderful exposition of the fundamental laws and conditions, actions and interactions of the material universe seemed to penetrate so deeply into that ‘nature of things’ after which the early philosophers searched in vain ... that we hoped he would throw some light on that great problem of problems....  He was very pleasant, spoke appreciatively of what we had both done for the practical exposition of evolution, and hoped we would continue to work at the subject.  But when we touched upon the great problem, and whether he had arrived at even one of the first steps towards its solution, our hopes were dashed at once.  That, he said, was too fundamental a problem to even think of solving at present.  We did not yet know enough of matter in its essential constitution nor of the various forces of nature; and all he could say was that everything pointed to its having been a development out of matter—­a phase of that continuous process of evolution by which the whole universe had been brought to its present condition.  And so we had to wait and work contentedly at minor problems.  And now, after forty years, though Spencer and Darwin and Weismann have thrown floods of light on the phenomena of life, its essential nature and its origin remain as great a mystery as ever.  Whatever light we do possess is from a source which Spencer and Darwin neglected or ignored."[27]

In his presidential address to the Entomological Society in 1872 Wallace made some special allusion to Spencer’s theory of the origin of instincts, and on receiving a copy of the address Spencer wrote:  “It is gratifying to me to find that your extended knowledge does not lead you to scepticism respecting the speculation of mine which you quote, but rather enables you to cite further facts in justification of it.  Possibly your exposition will lead some of those, in whose lines of investigation the question lies, to give deliberate attention to it.”  A further proof of his confidence was shown by asking Wallace (in 1874) to look over the proofs of the first six chapters of his “Principles of Sociology” in order that he might have the benefit of his criticisms alike as naturalist, anthropologist, and traveller.

This brief reference to the illustrious group of men to whom we owe the foundations of this new epoch of evolutionary thought—­and not the foundations only, but also the patient building up of the structure upon which each one continued to perform his allotted task—­and the prefatory notes and the footnotes attached to the letters will serve to elucidate the historical correspondence between Darwin and Wallace which follows.