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We shall, for instance, presently follow the evolution of the horse, and see four of its toes shrink and disappear, while the fifth toe is enormously strengthened. In the facts themselves there is nothing whatever to decide whether this evolution took place on the lines suggested by Weismann, or on the lines suggested by Lamarck and accepted by Darwin.
The more philosophical thinkers, like Spencer, Darwin, Haeckel, Michael Foster, August Weismann, and many others, believe that such "intermediate units must exist, whether or not the microscope reveals them to view."
The explanation of natural evolution given by Darwinism and the principles of Weismann, Mendel, and De Vries, still fails to solve the mystery completely, and appeal has been made to other agencies, even to teleology and to "unknown" and "unknowable" causes as well as to circumstantial factors.
In a very distinct and severe manner he gives expression to his opposition to his former friend Weismann. He attacks with telling effect the fantastic Darwinian "Mimicry." In his "General Introduction" Eimer first treats of Orthogenesis in opposition to the Darwinian theory of selection.
One of the most peculiar incidents in this scientific tragi-comedy is the fact that Weismann, the mainstay of contemporary decadent Darwinism, attacks with might and main its fundamental assumption, the transmission of acquired characters, whereas Eimer, who is thoroughly convinced that he has proved that doctrine, in his turn attacks Darwinism and proves with telling effect the impotence of its principles.
For it needs little reflection to perceive that the most familiar facts of our experience and observation never fail to confirm the doctrine based by Weismann upon the revelations of the microscope when applied to the developmental processes of certain simple animal and vegetable forms.
But Professor Weismann does not like such cases, and admits that he cannot explain the facts in connection with the climatic varieties of certain butterflies, except "by supposing the passive acquisition of characters produced by the direct influence of climate." Nevertheless, in his next paragraph but one he calls such cases "doubtful," and proposes that for the moment they should be left aside.
When we see a person "ostrichising" the evidence which he has to meet, as clearly as I believe Professor Weismann to be doing, we shall in nine cases out of ten be right in supposing that he knows the evidence to be too strong for him.
English biologists are little likely to find Weismann satisfactory for long, and if he breaks down there is nothing left for them but Lamarck, supplemented by the important and elucidatory corollary on his theory proposed by Professor Hering.
The belief that whatever is acquired by sires is inherited by sons, and the ignoring of purely inner variations, are weak points; but to have brought in the environment as vital was a master stroke. I may say that Spencer's controversy over use-inheritance with Weismann, entered into after he was sixty, seems to me in point of quality better than any other part of his work.