THE EVOLUTIONARY STGNTFICANCE OF SPECIES. 309 



(aac for the incniluM-s of the species to become more and more diverse, 

 not in order to snlxlivide into more mnnerons species, but because 

 diversity of descent increases the vij^or of the individual organisms 

 of which the species is composed. 



Sexual and other diversification inside the species has continued to 

 become more and more accentuated in Inmdreds of indei)endent 

 oroups of plants and animals, and is everywhere recognized as a 

 mark of greater organic perfection. Professor Weismann held that 

 under constant external influences variation would not occur;" but 

 ihe practical fact is that in the same species, and imder the same 

 <>eueral environments, variations not only occur, but are preserved, 

 acciunulated. and integrated into sexual differences, not by isolating 

 a part of the species from the rest, but under iconditions of free and 

 continuous interbreeding. The differences between the sexes are 

 i-onnnonly greater than those which separate the species and genera, 

 or even than those w'hich characterize the families and orders, show- 

 ing most conclusively that such differences can arise and become 

 established, even inside the species, and quite without segregation. 

 But instead of having been appreciated as the most important 

 agency and the most significant illustration of evolution, sex and 

 symbasic interbreeding have continued to be regarded as obstacles, 

 because they interfere with the fancied necessity of segregation. 



Evolutionists, too intent on a practical explanation of the diversity 

 of species, magnified the idea that organisms become adapted to 

 environment, and disregarded the more fundamental fact that spe- 

 cies are not by nature stationary, but have an independent motion of 

 their own. This oversight brought us the impossible task of explain- 

 ing how external conditions produce evolutionary changes, and 

 prevented the perception that adaptations are due to external causes 

 only as environment may influence the direction of the normal and 

 necessary movement of the species. 



That evolution is thus an active, universal, and truly physiological 

 process is not considered in current theories, largely because thought 

 and language have continued to follow^ the bias of the original Dar- 

 winian controversy in seeking in evolution an explanation of the 

 origin of species, and in expecting, conversely, that an explanation of 

 the origin of species would also explain evolution. Such a history 

 greatly increases the difficulty of presenting this alternative view, that 

 the multiplication of species is in no proper sense a result of evolution, 

 but is due to entirely distinct causes more often antagonistic than 

 favorable to evolutionary progress. 



a Weismaun, A., 189.3, The Germ riasni, 403. 



