STAGES OF VITAL MOTION. 17 



tion and other aspects, is a negative and not a positive factor in evolu- 

 tion. Instead of causing biological motion, environment is able only 

 to influence its direction by presenting obstacles to some tendencies of 

 variation while permitting others to go forward* 



Potential Characters. 



This separation of evolution from environment is not lessened by 

 the fact that environment frequently determines the existence or degree 

 of expression of characters. The absence of a substance necessary to 

 the formation of a certain color or pigment prevents its formation, as 

 may also the absence of the heat or sunlight necessary for its elabora- 

 tion. To expect that external conditions should not influence organ- 

 isms would be to ignore the fact that they grow by what they take in 

 from the outside, and can not build without materials. By being 

 placed under different conditions two individuals can be rendered far 

 more different than they otherwise would have been, but to call these 

 differences ' variations ' and then to generalize that variations are caused 

 by environment is simply the old-fashioned fallacy of the undistributed 

 middle.f There is not the slightest probability that the causes which 

 make related organisms different under different conditions are those 

 which make organisms of common origin different under the same 

 conditions. In his paper on 'Nutrition and Selection' Professor 

 De Yries shows that one of the variations of the poppy depends for 

 the degree of its manifestation upon the abundance of food, or is 

 correlated with vegetative vigor. This does not justify, however. Pro- 

 fessor De Vries' inference that all characters are so correlated; and 

 that the dependence was not absolute, even in the instance described, 

 was shown when a reversal of cultural methods did not eradicate the 

 character. The same reasoning applied to the human species would 

 discover that some characters appear only among well-fed people, and 

 that such characters are hereditary and persistent, but we are not 

 compelled on this account to infer that all the differences now existing 

 among us have arisen through over-eating. 



Unsuspected differences or powers of variation sometimes appear 

 under new environments, but it has not been shown that such poten- 

 tial or latent characters are less congenital, or otherwise less normal 



* As explained later on, a result of extreme segregation or narrow inbreed- 

 ing is to accentuate variation or produce abrupt changes or mutations. It is 

 as though the closing of all except one of the avenues of change compelled ab- 

 normal speed in that direction. 



t Even under static theories it has been found advisable to distinguish 

 between ' physiological ' or ' direct,' non-hereditary variations due to environ- 

 ment, and ' congenital,' 'direct ' or ' fortuitous ' variations notably hereditary, 

 though doubtfully connected with environment. 



VOL. LXIII. — 2. 



