VARIATION 211 



New characters may arise or old ones be lost through 

 accidents to the germ substance during the processes of 

 cell division incident to reproduction and growth. It is 

 conceivable that a chromosome bearing within its ma- 

 terial substance a character or set of characters may be 

 lost or destroyed at some stage of the complicated pro- 

 cesses which eventually result in the formation of a new 

 germ-cell. If such a thing occurs, it must influence 

 greatly the ultimate characters of the individual. It is 

 also apparent that a fundamental change in the germinal 

 material may influence not alone the resulting individual 

 but the race or breed. Sudden marked variations may 

 and do often occur, and these may become the beginnings 

 of new races. These sudden variations are called muta- 

 tions by De Vries, and the mutation theory of evolution 

 is regarded as one of the most important advances since 

 Darwin. A fuller discussion of mutations will be found 

 on another page. 



It is difficult to differentiate between those variations 

 which are merely the result of the action of environment 

 on the soma- or body-cells and those variations which 

 are the result of a fundamental change in the constitu- 

 tion of the germ substance. The former are generally 

 temporary and affect only the individual, but do not 

 influence the germ sufficiently to cause the same varia- 

 tion to appear in the offspring. The highly improved 

 types of domestic swine if permitted to run wild in the 

 woods lose their rounded full-fleshed form and assume 

 much the appearance of the unimproved " razor-back." 

 Their appearance is so changed by this treatment that 

 the most skillful judge of swine would be greatly deceived. 

 The " razor-back," on the other hand, has subsisted for 

 generations upon the mast of the forest. This has in- 



