THE TREND OF EVOLUTION 157 



mitted to the germ cells so as to reappear in the next genera- 

 tion. In short, there is no inheritance of specific characters 

 acquired by the soma. Evolutionary changes do not first 

 occur in developed organisms and then by some mysterious 

 process get into the germ-plasm, but evolution consists in an 

 evolution of germ-plasm which then manifests itself in the 

 developed organism. 



It is known as a matter of fact that acquired somatic char- 

 acters are not usually, if ever, inherited. Environment, train- 

 ing, education, may greatly modify glands, muscles, nerves, and 

 brains, but they do not change the germ-plasm so as to produce 

 these identical modifications in the next generation. In a few 

 instances it seems probable that chemical substances in the 

 bodies of parents, such as hormones, or anti-bodies, may in- 

 fluence the germ cells or developing embryos so as to produce 

 bodily changes in offspring similar to those in the parents, but 

 in general it may be said that there is no satisfactory evidence 

 that the specific modifications of development, due to particular 

 conditions of life, enter into the germ-plasm and appear again 

 in the next generation, in the absence of the environment which 

 first called them forth. In short, the effects on development 

 of environment, training, and education are not inherited 

 through the germ cells and the hope of permanently improving 

 the human race, or any other species, in this manner can only 

 lead to disappointment and failure. 



Social Inheritance. At the same time it must be remem- 

 bered that man transmits to his descendants not only a par- 

 ticular germ-plasm which determines bodily qualities and men- 

 tal capacities, but he also hands down through language, edu- 

 cation, and customs, his own acquirements, experiences, and 

 possessions as well as those of former generations. This has 

 been called "social inheritance" to distinguish it from "ger- 

 minal inheritance"; it is inheritance in the legal rather than in 

 the biological sense. In this sense we have inherited from our 



