H. F. Osborn 341 



agree in believing that the power of plastic modification to new 

 circumstances, or what the Rev. Dr. Henslow has termed ' self- 

 adaptation,' is in itself a result of natural selection. In other 

 words, they hold that natural selection has established in organ- 

 isms this power of invariable 1 response to new conditions, which, 

 in the vast majority of cases, is essentially adaptive. I disagree 

 with this assumption in toto, maintaining that this plastic modi- 

 fication is, so far as we know, an inherent power or function of 

 protoplasm. This view, I understand, is also held by Driesch, 

 E. B. Wilson, T. H. Morgan, and probably by many others. 

 The only cases in which self-adaptation may be demonstrated 

 as produced by natural selection are where organisms are 

 restored to an environment which some of their ancestors expe- 

 rienced. We can then imagine that the adaptive response to 

 the old environment is something which has never been lost, as 

 in the well-known reappearance of the pigment in flounders. 



" It may be urged against the Morgan, Baldwin, Poulton 

 view that the remarkable powers of self-adaptation, which in 

 many cases are favorable to the survival of the individual, are 

 in many cases decidedly detrimental to the race, as where a 

 maimed or mutilated embryo by regeneration reaches an adult 

 or reproductive stage. It is obvious that reproduction from 

 imperfect individuals would be decidedly detrimental, yet, from 

 the view taken by the above authors, such reproduction would 

 be necessary to secure the power of plastic modification for the 

 race. 



"It is certain that, at the present time, one of the surest and 

 most attractive fields of inductive research, leading towards the 

 discovery of the additional factors of evolution, or what I have 

 elsewhere called 'the unknown factor,' is in experimental em- 

 bryology and experimental zoology. If we could formulate the 

 laws of self-adaptation or plastic modification, we would be de- 

 cidedly nearer the truth. It appears that Organic Selection is 

 a real process, but it has not yet been demonstrated that the 

 powers of self-adaptation which become hereditary are only 

 accumulated by selection." 



1 Variable (?). J. M. B. 



