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And further, to one school variation seems without plan in all directions, simply plus or minus on either side of a mean; to the other, variation seems predetermined and in a definite direction—an “orthogenesis,” in fact, which is inherent in the organism, and which is indifferent to utility or disadvantage, or natural selection, or anything else, but simply follows its prescribed path in obedience to innate law.
In consequence of an interruption of orthogenesis a stoppage ensues in certain stages of the development, and this stoppage is the great cause of the arrangement of forms in different species. As a rule use and disuse are of great efficacy in this regard, and conjointly with these compensation and correlation." Occasionally also irregular development sets in, which proceeds by leaps.
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.
Indeed, we do not see how otherwise to explain the likeness of structure of the eye in species that have not the same history. Where we differ from Eimer is in his claim that combinations of physical and chemical causes are enough to secure the result. We have tried to prove, on the contrary, by the example of the eye, that if there is "orthogenesis" here, a psychological cause intervenes.
They are usually associated with a denial of the theory of natural selection, and with theories of “Orthogenesis,” “Heterogenesis,” and “Epigenesis.” We shall discuss them later when we are considering the factors in evolution. But we must first take notice of a work in which the theories opposed to Darwinian orthodoxy have been most decisively and aggressively set forth.
Or if Natural Selection did it, or orthogenesis or epigenesis, or any other genesis, have we not in any of these found a god equal to the occasion? Darwin goes wrong, if I may be allowed to say so, when he describes or characterizes the activities of Nature in terms of our own activities. Man's selection affords no clue to Nature's selection, and the best to man is not the best to Nature.
We should thus arrive at a demonstration of what Eimer called orthogenesis, or evolution in definite directions. The mutation lata cannot be said to breed true, as the pollen is almost entirely sterile. It has therefore been propagated by crossing with Lamarckiana pollen, with the result that both forms are obtained with lata varying in proportion from 4 per cent. to 45 per cent.
The importance of correlated growth and orthogenesis is explained on a similar basis, and the Darwinian conceptions of the independent variation of individual parts, of the exclusive dominance of utility, of the influence of the struggle for existence in regard to individual selection, and of the omnipotence of natural selection, are energetically denied.
There is the "Neo-Darwinian" view which attributes variation to the differences inherent in the germ borne by the individual, and not to the experience or behaviour of the individual in the course of his existence. Then there is the theory known as "Orthogenesis" which maintains that there is a continual changing in a definite direction from generation to generation.
This theory of Orthogenesis has not figured very strongly in the history of the movement, but it recurs at intervals. Both in America and France there is a constant tendency on the part of zoölogists to return to the Lamarckian idea that it is the use of an organ that develops it, its disuse that makes it fade away.
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