But the question now arises, whether both Darwinism and Lamarckism must not be replaced, or at least reduced to the level of accessory theories and factors, by another theory of evolution which was in the field before Darwin, and which since his time has been advanced anew, especially by Nägeli, and has now many adherents who support it in whole or in part. This view affects the very foundations of the Darwinian doctrine. The theory of “indefinite” variation, bringing about easy transitions and affecting every part of [pg 171] the organism separately, which is the necessary correlate of the “struggle for existence,” is rejected altogether. Evolution takes place only along a few definite lines, predetermined through the internal organisation and the laws of growth. It is wholly indifferent to “utility,” and brings forth only what it must according to its own inner laws, not seldom even the monstrous. According to this view, new species arise, not in easy transition, but with a visible leap, by a considerable and far-reaching displacement of the organic equilibrium. What Darwin calls the correlation of parts, and in no way denies, is here maintained in strong opposition to his doctrine of the isolated variation of individual parts; every member or character of the organism depends upon others, and variation of one affects many, and in some way all of the rest.
This theory is for the most part intended by its champions to be purely naturalistic. But every one of its points yields support to teleological considerations, most obviously so the concrete instances of correlation. If any one were to attempt to make a theory of evolution from a decidedly teleological standpoint, he would probably construct one very similar to the one we are now considering.
It is noteworthy that it has generally been the botanists who have especially supported these views of saltatory evolution in a definite direction and according to internal law, who have therefore tended to react most strongly from Darwinism. We find examples in Nägeli's [pg 172] large and comprehensive work, “Mechanisch-physikalische Theorie der Abstammungslehre”; and, before him, in Wigand's “Darwinismus und die Naturforschung Newton's und Cuvier's”; in von Kölliker's “Heterogenesis”; in von Baer's “Endeavour after an End”; in the chapter added by the translator, Bronn, to the first German edition of the “Origin of Species,” where he urges weighty objections against the theory of selection, and refers to the “innate impulse to development, persistently varying in a definite direction”; in Askenasy's oft-quoted “Beiträge zur Kritik der Darwinschen Lehre,” also referring to “variation in a definite direction,” for instance, in flowers; in Delpino's views, and in the works of many other older writers. But we must leave all these out of account here, since we are concerned only with the present state of the question.
De Vries's Mutation-theory.
The work that has probably excited most interest in this connection is De Vries' “Die Mutationstheorie: Versuche und Beobachtungen über die Entstehung von Arten im Pflanzenleben.”[46] In a short preliminary paper he had previously given some account of his leading experiments on a species of evening primrose (Œnothera lamarckiana), and the outlines of his theory. In the work itself he extends this, adding much concrete material, and comparing his views in detail with other [pg 173] theories. Darwin, he says, had already distinguished between variability and mutability; the former manifesting itself in gradual and isolated changes, the latter in saltatory changes on a larger scale. The mistake made by Wallace and by the later Darwinians has been that they regarded this latter form (“single variation”) as unimportant and not affecting evolution, and the former as the real method of evolutionary process. That fluctuating individual variations do occur De Vries admits, but only within narrow limits, never overstepping the type of the species. Here De Vries utilises the recent statistical investigations into the phenomena of individual variation and their laws, as formulated chiefly by Quetelet and Bateson, which were unknown to Darwin and the earlier Darwinians. The actual transition from “species to species” is made suddenly, by mutation, not through variation. And the state of equilibrium thus reached is such a relatively stable one that individual variations can only take place within its limits, but can in no way disturb it.
De Vries marshals a series of facts which present insurmountable difficulties to the Darwinian theory, but afford corroboration of the Mutation theory. In particular, he brings forward, from his years of experiment and horticultural observation, comprehensive evidence of the mutational origin of new species from old ones by leaps, and this not in long-past geological times, but in the course of a human life and before our very eyes. The main importance of the book lies in the record of these [pg 174] experiments and observations, rather than in the theory as such, for the way had been paved for it by other workers.
In contrast to Darwinism, De Vries states the case for “Halmatogenesis” (saltatory evolution) and “Heterogenesis” (the production of forms unlike the parents), taking his examples from the plant world, but his attitude to Darwinism is conciliatory throughout. Eimer, on the other hand, is sharply antagonistic, especially to Weismann; he takes his proofs from the animal kingdom, and in the second volume of his large work already mentioned, which deals with the “orthogenesis of butterflies,” he attempts to set against the Darwinism “chance theory,” a proof of “definitely directed evolution,” and therefore of the “insufficiency of natural selection in the formation of species.”