(3) "Advantageous variations, not preserved in nature as they are by the breeder, are liable to be swamped by crossing or to disappear by atavism."
[We have already referred to various answers to this difficulty—in terms of Isolation, Prepotency, and other conceptions. But the answer which will occur to everyone at the present time is in terms of "Mendelism," into a discussion of which we cannot enter. Suffice it to say, that for the cases with which he dealt, Mendel has given evidence that variations which arise suddenly and are discontinuous—mutations, as De Vries calls them—are not likely to be swamped by in-breeding with the normal form, and that he has given a reason why this swamping does not occur.]
In regard to the second directive factor—Isolation, Spencer had no criticism to offer. It seemed to him that "in whatever way effected, the isolation of a group subject to new conditions and in course of being changed, is requisite as a means to permanent differentiation."
But after allowing full play to variation and modification, selection and isolation, Spencer felt that "though all phenomena of organic evolution must fall within the lines indicated, there remain many unsolved problems." "We can only suppose that as there are devised by human beings many puzzles apparently unanswerable till the answer is given, and many necromantic tricks which seem impossible till the mode of performance is shown; so there are apparently incomprehensible results which are really achieved by natural processes. Or, otherwise, we must conclude that since Life itself proves to be in its ultimate nature inconceivable, there is probably an inconceivable element in its ultimate workings."
[CHAPTER XIII]
EVOLUTION UNIVERSAL
The Starting-point—Inorganic Evolution—What Spencer tried to do—Summary of his Evolutionism—Notes and Queries—The Origin of Life—Evolution of Mind—Ascent of Man—The Scientific Position