434 HEREDITY AND SELECTION IN SOCIOLOGY 



the right direction, is not sufSciently rapid to keep pace with a 

 rapidly changing environment. In a former chapter on the 

 origin and extinction of species we remarked that in a great 

 many cases the extinction of species may undoubtedly be traced 

 to the fact that the necessary variations called forth by the 

 readaptation of the species are not forthcoming quickly enough. 

 We saw that the extinction of the Trilobites at the end of the 

 Silurian epoch was very probably due to the fact that this type 

 of animal, long adapted to constant conditions, was unable to 

 readapt itself with sufficient rapidity to the suddenly modified 

 environment. In the same way nations which are more adapt- 

 able are more likely to survive than those which are less adapt- 

 able. If the environment change more rapidly than the nation 

 is able to change, that nation will be superseded by others whose 

 power of readaptation is greater. Nations which have long 

 been adapted to similar conditions are, as a rule, less readily 

 readaptable than young nations ; but the theory that nations, 

 long habituated to a similar environment, are necessarily afiected 

 by senile decay, is entirely contradicted by the astonishing ease 

 with which Japan, adapted for 2,500 years to a given system of 

 government, changed that system radically in an extraordinarily 

 short space of time. With nations, as with species, survival is 

 dependent on plasticity. 



Traditional progress is necessarily much faster than organic 

 progress. Those who have followed our exposition of the theory 

 of descent in the first part of this book will imderstand how diffi- 

 cult it is for the germ -plasm of an aggregate, be it a species, a 

 race, or a nation, to be altered ; for acquired characters which 

 afEect only the body of the individuals are not transmitted by 

 heredity. The alterations of the germ-plasm are all produced 

 by variations which arise within itself by movements among 

 the determinants, by shiftings of the balance caused by differ- 

 ences in intragerminal nutrition. And the vast majority of 

 variations are called forth by the need for adaptation. As soon 



