THE WHITE HLACKRERRY 



Nevertlieless tbciv is a degree of vagueness 

 about the use ot the \vord "tendencies" that robs 

 the exphmation of complete satisfactorincss. 



Meantime the human mind is always grt)j)ing 

 after tangible explanations of observed pJienom- 

 ena. It is always more satisfactory to be able to 

 visualize processes of nature. It was for this rea- 

 son that Darwin's theory that natural selection is 

 the most powerful moving factor in the evolution 

 of races gained such general recognition and still 

 remains as the most satisfactory of all hypotheses 

 of evolution. 



And it is for the same reason that a tangible 

 explanation of the phenomena of atavism or the 

 reversion to ancestral types has gained a tremen- 

 dous vogue in recent years. 



The explanation in question is associated with 

 the name of the Austrian monk Mendel, who made 

 some remarkable experiments in plant breeding 

 about half a century ago, and who died in 1884, 

 but whose work remained quite unknown until his 

 obscure publications were rediscovered by Pro- 

 fessor Hugo De Vries and two other contemporary 

 workers, and made known to the world about the 

 year 1900. Since then a very large part of the 

 attention of the biological world has been devoted 

 to the further examination of what has come to be 

 spoken of as Mendelian principles. 



[55] 



