xii PEEFACE 



extraordinary and, — as many naturalists think, — 

 the unwarrantable exaggeration of the importance 

 of the Dutch botanist's contributions to evolution. 

 Omne ignotwm pro magnifico. If de Vries had 

 indeed proved, as his exponents assert, that the 

 * individual differences ' in which Darwin saw the 

 steps of evolutionary progress— the 'individual 

 differences ' whose behaviour in heredity is the life- 

 work of Francis Galton — that these are in fact non- 

 transmissible to offspring, then surely the great- 

 ness of him who demonstrated such a discovery to 

 the world might be justly measured by the depth 

 of the error into which his predecessors had fallen. 

 I need hardly say that de Vries makes no such 

 claim, but, on the contrary, shows us again and 

 again that hereditary transmission to offspring is 

 essential to his conception of 'fluctuating varia- 

 bility'. 



For de Vries's laborious and original investiga- 

 tions every one must feel the warmest admiration. 

 He and his friend Professor Hubrecht have 

 always been most anxious to emphasize their 

 conclusion that the Mutationstheorie is Darwinian, 

 and they are equally anxious to disown and dis- 

 credit any attempts to use it as a weapon against 

 Darwin. They have even fallen into the error of 

 maintaining that Darwin anticipated de Vries in 

 holding the main conclusion of the Mutationstheorie 

 — the origin of species by the selection of large 



