January 10, 1913] 



SCIENCE 



49 



on the mind or soul; character is a tabula 

 rasa on which the self writes its own record 

 as it pleases and is responsible for the 

 result. This view, like the old epigenesis, 

 virtually postulates a new creation for each 

 individual. So far as the mind and soul 

 are concerned there is no hereditary con- 

 tinuity with past generations and none 

 with future ones. But while such a view 

 may be logically complete and theologically 

 satisfying, it is not scientific, for it contra- 

 dicts the evidence. 



The truth then seems to lie somewhere 

 between these two extremes. Our person- 

 alities were not absolutely predetermined 

 in the germ cells from which we came, and 

 yet they have arisen from those germ cells 

 and have been conditioned by them. When 

 it is said that any characteristic is prede- 

 termined in the germ cell, what does this 

 mean? What but that the development 

 of that characteristic is made possible? 

 Adult characteristics are potential and not 

 actual in the germ, and their actual ap- 

 pearance depends upon many complicated 

 reactions of the germinal units with one 

 another and with the environment. In 

 short, our actual personalities are not pre- 

 determined in the germ cells, but our pos- 

 sible personalities are. 



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 producing a whole 

 body, though this potency would never 

 have become an actuality except under the 

 stimulus of separation. In like manner a 

 part of an egg may, when separated from 

 the remainder, give rise to an entire ani- 

 mal. By modifying the conditions of de- 

 velopment animals may be produced which 

 have one eye, many eyes, or no eyes; ani- 

 mals in which the bodies are turned inside 

 out or side for side; animals in which all 



sorts of dislocation of organs have taken 

 place ; and the earlier the environmental 

 forces act the more profound are the modi- 

 fications produced. But leaving out of ac- 

 count 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 varia- 

 tions in the more or less perfect correlation 

 of these parts with one another, which 

 were determined by the conditions of de- 

 velopment 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 environment 

 can not be all things at once, many hered- 

 itary possibilities must remain latent or 

 undeveloped. Consequently the results of 

 development are not determined by hered- 

 ity alone, but also by extrinsic causes. 

 Things can not be predetermined in hered- 

 ity which are not also predetermined in 

 environment. 



Functional activity, or use, is one of the 

 most important factors of development. 

 Functional activity is response to stimuli, 

 which may be external or internal in 

 origin. The entire process of development 

 may be regarded as an almost endless series 

 of such responses on the part of the organ- 

 ism, whether germ cell, embryo, or adult, 

 to external and internal stimuli. It is a 

 truism that use strengthens a part and dis- 

 use weakens it; it is likewise a truism that 

 responses which are oft repeated become 

 more rapid and more perfect, and in this 

 way habits are formed. Practically all 

 education, whether of man or of lower ani- 



