WHAT EVOLUTION IS 137 



white in the guinea pig's coat. These 

 opposing traits were called unit or 

 elementary characters by de Vries 

 and, in describing them as elementary, 

 he meant that they partook in their 

 separateness of the nature of the 

 chemical elements. Every organism 

 is marked by a great array of these 

 unit characters. In the guinea pig, 

 for instance, there are coat colors, 

 white, black, piebald and the like, dif- 

 ferences in hair, long, short, rosetted, 

 or smooth, and a host of other features 

 all of which are inherited in accord- 

 ance with Mendelian principles. 

 Thus the pairs of traits in Mendelian 

 inheritance are the unit characters of 

 the mutation theory. 



According to de Vries a real species, 

 or as he called it an elementary species, 

 is to be described from its unit char- 

 acters and any new combination of 

 unit characters is a new species. A 



