No. 579] PROGRESSIVE EVOLUTION 



177 



We are told, of course, that such adjustments will only 

 be preserved so long as the environmental stimuli by 

 which they were originally called for continue to exer- 

 cise their influence. Those who raise this objection are 

 apt to forget that this is exactly what happens in evolu- 

 tion, and that the sine qua non of development is the 

 proper maintenance of the appropriate environment, 

 both internal and external. Natural selection sees to it 

 that the proper conditions are maintained within very 

 narrow limits. 



A great deal of the confusion that has arisen with re- 

 gard to the question of the inheritance of acquired char- 

 acters is undoubtedly due to the quite unjustifiable limi- 

 tation of the idea of " inheritance ' ' to which we have ac- 

 customed ourselves. The inheritance of the environ- 

 ment is, as I have already said, just as important as the 

 inheritance of the material foundation of the body, and 

 whether or not a newly acquired character will be in- 

 herited must depend, usually at any rate, upon whether 

 or not the conditions under which it arose are inherited. 

 It is the fashion nowadays to attach very little impor- 

 ance to somatogenic characters in discussing the problem 

 of evolution. The whole fundamental structure of the 

 body must, however, according to the epigenetic view, 

 be due to the gradual accumulation of characters that 

 arise as the result of the reactions of the organism to its 

 environment, and are therefore somatogenic, at any rate 

 in the first instance, though there is reason to believe 

 that some of them may find expression in the germ-cells 

 in the formation of organ- forming substances, and pos- 

 sibly in other ways. Blastogenic characters which ac- 

 tually originate in the germ-cells appear to be of quite 

 secondary importance. 



We still have to consider the question, How is it that 

 organic evolution has led to the formation of those more 

 or less well-marked groups of organisms which we call 

 species? We have to note in the first place that there 



