Genetics and Ethics 307 



In all organisms the potentialities of development are much 

 greater than the actualities. In many animals a small part of 

 the body is capable, when separated from the remainder, of pro- 

 ducing a whole body, though this potency would never have be- 

 come an actuality except under the stimulus of separation. In 

 like manner a part of an egg may, when separated from the re- 

 mainder, give rise to an entire animal. By modifying the con- 

 ditions of development animals may be produced which have one 

 eye, many eyes or no eyes ; animals in which the body is turned 

 inside out, or side for side; animals in which all sorts of dislo- 

 cation of organs have taken place; and the earlier the environ- 

 mental forces act the more profound are the modifications. 



But leaving out of account all forms which are so monstrous 

 that they are incapable of reaching maturity we find that there are 

 left many variations in the size and vigor of the body as a whole, 

 as well as of its parts; many variations in the more or less per- 

 fect correlation of these parts with one another, which were 

 determined by the conditions of development rather than by 

 heredity. In a given germ cell there is the potency of any kind 

 of organism that could develop from that cell under any kind of 

 conditions. The potencies of development are much greater than 

 the actualities. Anything which could possibly appear in the 

 course of development is potential in heredity and under given 

 conditions of environment is predetermined. Since the environ- 

 ment cannot be all things at once many hereditary possibilities 

 must remain latent or undeveloped. Consequently the results of 

 development are not determined by heredity alone but also by 

 extrinsic causes. Things cannot be predetermined in heredity 

 which are not also predetermined in environment. 



Of all animals I suppose that man enjoys the most extensive 

 and the most varied environment, and its effect upon his person- 

 ality is correspondingly great. Of all animals man has the long- 

 est period of immaturity and it is during this period that the play 

 of environmental stimuli on the organism is effective in modify- 

 ing development. In addition to the material environment he 



