PREFACE xiii 



single variations.' It is with great reluctance that 

 I have protested against the unduly important posi- 

 tion which, as I believe, is assigned to de Vries's 

 work and conclusions in the history of evolution. 



The Darwinian of the present day holds an inter- 

 mediate position between the followers of BuflPon 

 and Lamarck, and the Mutationists, with whom 

 the Mendelians are somewhat unnecessarily allied. 

 The disciple of the two first-named naturalists, 

 in these days calling himself an oecologist, main- 

 tains that organisms are the product of their 

 environment : the Mutationist holds that organ- 

 isms are subject to inborn transformation, and 

 that environment selects the fittest from among 

 a crowd of finished products. The Darwinian 

 believes that the finished product or species is 

 gradually built up by the environmental selection 

 of minute increments, holding that, among inborn 

 variations of all degrees of magnitude, the small 

 and not the large become the steps by which 

 evolution proceeds. He attempts to avoid, as 

 Darwin did, on the one hand the error of as- 

 cribing the species-forming forces wholly to 

 a creative environment, and, on the other, the 

 perhaps more dangerous error of ascribing them 

 wholly to creative internal tendencies. 



' Both professors of course admit that Darwin also believed in 

 an evolution founded on the selection of ' individual differences '- 



