Summary 187 



and took secondarily to exploring and exploiting the 

 fresh waters. 



10. Domestication and cultivation have been long- 

 continued experiments in evolution, showing how 

 much Man has been able to achieve in fixing and in- 

 creasing the raw materials or variations which Nature 

 supplies. Recent Mendelian breeding shows Man as 

 transformist with more precise methods than before. 

 There are a few interesting experiments indicating 

 that it is possible to induce heritable variations by 

 artificial stimuli; but in most cases man has simply 

 to take what comes. Striking blood-transfusing ex- 

 periments afford demonstration of literal blood- 

 relationship. 



11. The evidence from many fields points clearly 

 to the validity of the evolution formula. Organic evo- 

 lution may be defined as a continuous natural process 

 of racial change in a definite direction whereby dis- 

 tinctively new individualities arise, take root, and 

 flourish, alongside of or in place of the originative 

 stock. The difficulty is to develop this modal formula 

 into a causal theory. Little is certain in regard to the 

 origin of the great classes, such as Vertebrates ; little 

 is certain in regard to the causes that operated in the 

 great steps in evolution, such as the establishment of 

 the Vertebrate brain. We are not even clear how dis- 

 continuous species arise. The fact of evolution is 

 undeniable ; the factors in the process are still being 

 investigated. 



12. The first great idea in Darwinism is the corre- 

 lation of organisms in a web of life. No creature lives 



