The first definite statement of his belief in “this something” other than material in the evolution of Man appeared in his essay on “The Development of Human Faces under the Law of Natural Selection” (1864).  In this he suggested that, Man having reached a state of physical perfection through the progressive law of Natural Selection, thenceforth Mind became the dominating factor, endowing Man with an ever-increasing power of intelligence which, whilst the physical had remained stationary, had continued to develop according to his needs.  This “in-breathing” of a divine Spirit, or the controlling force of a supreme directive Mind and Purpose, which was one of the points of divergence between his theory and that held by Darwin, is too well known to need repetition.

This disagreement has a twofold interest from the fact that Darwin, in his youth, studied theology with the full intention of taking holy orders, and for some years retained his faith in the more or less orthodox beliefs arising out of the Bible.  But as time went by, an ever-extending knowledge of the mystery of the natural laws governing the development of man and nature led him to make the characteristically frank avowal that he “found it more and more difficult ... to invent evidence which would suffice to convince”; adding, “This disbelief crept over me at a very slow rate, but was at last complete.  The rate was so slow that I felt no distress."[57] With Wallace, however, his early disbelief ended in a deep conviction that “as nothing in nature actually ‘dies,’ but renews its life in another and higher form, so Man, the highest product of natural laws here, must by the power of mind and intellect continue to develop hereafter.”

The varied reasons leading up to this final conviction, as related by himself in “Miracles and Modern Spiritualism” and “My Life,” are, however, too numerous and detailed to be retold in a brief summary in this place.

The correspondence that follows deals entirely with investigations on this side of the Atlantic, but a good deal of evidence which to him was conclusive was obtained during his stay in America, where Spiritualism has been more widely recognised, and for a much longer period than in England.

Some of the letters addressed to Miss Buckley (afterwards Mrs. Fisher) reveal the extreme caution which he both practised himself and advocated in others when following up any experimental phase of spiritual phenomena.  The same correspondence also gives a fairly clear outline of his faith in the ascending scale from the physical evidence of spirit-existence to the communication of some actual knowledge of life as it exists beyond the veil.

In spiritual matters, as in natural science, though at times his head may have appeared to be “in the clouds,” his feet were planted firmly on the earth.  This is seen, to note another curious instance, in his correspondence with Sir Wm. Barrett, where he maintains a delicate balance between natural science and “spirit impression” when discussing the much controverted reality of “dowsing” for water.