thereby intends to imply that they form more numerous single variations and have thus a better opportunity to split up again into further species—so far de Vries (pp. 24-26).
I have purposely insisted on these points, because here and there a tendency seems to prevail to look upon Darwin's views on the origin of species as unsatisfactory and obsolete, and to proclaim the necessity of replacing them by a brand new hypothesis with which the name of de Vries should be coupled. These tendencies are in great favor with those that bear a grudge to the so-called Darwinism for other than scientific reasons, and who in their innermost heart would at the same time like to see a similar fate reserved for de Vries's demonstrations, and even for the whole theory of evolution.
We have, however, seen in de Vries's own words how little he considers himself an antagonist of Darwin. On the contrary, his great and imperishable merit consists in this, that his important and extensive experiments have provided us with a reliable basis concerning a subject about which Darwin had not fully made up his mind.
Darwin seems to have suspended his judgment; at all events, he has not drawn a hard and fast line between the results which artificial selection can attain when applied to fluctuating variations, on the one hand, and to mutations, on the other.
The experiments which de Vries has continued during many years on the two divergent processes, which Darwin has not sufficiently kept separate, have justified him in claiming that now, for the first time—forty years after the appearance of the 'Origin of Species'—the actual birth of a species has been observed by him. He has thus opened up a most extensive field for further investigations by other naturalists, and he has undoubtedly put an end to useless polemics which often threaten to become yet further burdened by subtleties.
Far from having undermined Darwin's Darwinism, de Vries has completed, purified and simplified it. To Wallace's Darwinism, however, de Vries has dealt a severe blow, Wallace having attached no significance to 'single variations' as possible sources of new species; whereas Darwin has always continued to acknowledge their importance as such, even though he did not thoroughly understand the laws to which fluctuating variability is subject. Even Weismann, who has only partially appreciated Darwin's philosophic indecision and who has, without wavering, followed a road which has now landed him in his 'germinal selection,' has undoubtedly taken notice of de Vries's experimental treatment of the subject with interest, though probably not with personal satisfaction.
Let us now try to picture to ourselves what conclusions de Vries has been able to reach experimentally with respect to the phenomena of mutation, and what he has taught us concerning the all-important question: How have species originated?
