GERMANY AND HER NEIGHBORS 243 



by fair treatment we should win her to a spirit of idealism, a spirit 

 which many of her sons showed most clearly in the generations 

 before the Great War. Bad training, indeed, led her astray, but 

 the power of Germany for good is as great today as ever. On 

 other nations quite as much as upon Germany lies the responsibil- 

 ity for seeing that every strong nation uses its strength for the 

 general good and not for its own selfish advancement. 



Finally, we come to the part of this book which is sure to be 

 most fiercely assailed. Today the swing of evolutionary thought 

 is all toward the side of heredity. Therefore scores of biologists 

 will feel that in placing so much emphasis upon the effect of en- 

 vironment I have committed a cardinal sin. They will say with 

 justice that there is far more proof of the importance of heredity 

 in causing stability from generation to generation than of the im- 

 portance of environment in causing mutations. Undoubtedly the 

 evidence as to the cause of mutations is still slight. That is inev- 

 itable when a subject first comes into the realm of scientific investi- 

 gation. On the basis of such scattered facts as are yet available 

 we have framed the hypothesis that the commonest cause of 

 mutations and thus of the origin of species is germinal changes due 

 to the action of extremes of heat and cold upon the organism in its 

 early stages of growth. If such an hypothesis is accepted, it will 

 doubtless demand a readjustment of many old ideas, but there is 

 nothing about it at all inconsistent with the strongest possible be- 

 lief in the importance of heredity. The scales have swung too far 

 in one direction because one side has been heavily weighted with 

 some of the most important and interesting facts that have ever 

 been discovered. Now we must find facts of other kinds and throw 

 them into the scales. It happens that the facts set forth in this 

 book fall into the side of the scale marked environment. By and 

 by we shall have more facts. As we dig them out we must care- 

 fully inspect them to see whether they belong in one scale or the 

 other. It is easy to mistake the scale in which a given fact should 

 fall, and sometimes we may have done so in this book. Yet even so 



