VARIATION 215 



stitution of the germ substance from which each has 

 been developed, but they may appear to be different. 

 Such differences may be due to a change in the environ- 

 ment which, acting upon the organism, may have modified 

 the apparent character of the individual. Such changes 

 are not variations in the true sense, but rather modifica- 

 tions. It is not always possible to distinguish readily 

 between changes which are merely modifications and 

 variations which are due to fundamental changes in the 

 germ. To the practical breeder, it is in the highest 

 degree important that this distinction between mere 

 modifications due to environment and germinal varia- 

 tions due to a change in the constitution of the germinal 

 substance be clearly recognized.. The latter variations 

 are strongly transmitted by heredity; the former are 

 not transmissible. Domestic animals kept under the 

 same conditions often exhibit wide variations, and these 

 are often germinal and consequently inherited. Those 

 variations or, more properly, modifications which appear 

 in individuals and are the result of environment are of 

 little significance to the breeder. If the breeder of speed 

 horses confined his selection solely to those horses that 

 had been trained, he might not secure the sum total of 

 those characters in the fundamental constitution of the 

 animal which represent the highest capacity for speed. 

 It is true that among horses of similar ancestry the train- 

 ing and development is the most accurate index of the 

 capacities which they have inherited. But a horse 

 that has not been trained and hence modified by environ- 

 ment may actually possess through inheritance a greater 

 capacity for speed. The latter horse may show less 

 speed than the horse that has been carefully developed, 

 but he will be a better breeder. Let us assume for example 



