340 BIOLOGY 



nearest alike, there have been produced the different types which 

 we have in our world to-day. Recognizing, however, that all 

 of these types of dogs belong to the same species and must have 

 come from a single common type, the strains of dog illustrate 

 excellently well what is meant by race divergence. 



Both of these examples have been chosen from domestic 

 animals. There is no reason for doubting that the same facts 

 may occur in nature and that under proper conditions in nature 

 there may be a series of race variations similar to those found 

 in domestication. Perhaps divergence in nature is not quite 

 so rapid or so extreme as it is when controlled by the fancy 

 of the breeder, but the same general facts hold true. In nature 

 as well as under domestication, races are undergoing a constant 

 series of changes, sometimes slow, and sometimes rapid. 



Race variations must be variations of the germ plasm. 

 Individual variations, as we have seen, will affect the body of 

 the individual but will not affect the germ substance. From 

 this it follows that individual, acquired variations will not be 

 transmitted by heredity and will therefore have no lasting 

 effect on the race. On the other hand, if the race is to undergo 

 a change, as we have just seen that it does, this must be due 

 to modifications in the continuous germ substance. Hence it 

 follows that the only variations that can continue in the race 

 and can be carried on for successive generations, are those that 

 affect the germ material itself. Race variations are therefore 

 necessarily germ variations. 



The Divergence from Centers. A little thought will show 

 that the result of divergence of the descendants of any type 

 in different directions will, in the end, produce extremely wide 

 diversity among animals and plants. If the descendants of 

 any animals diverge in two directions, and then later their 

 descendants again diverge from each other, and if this process 

 goes on indefinitely, it becomes evident that in the course of time 

 the descendants of the original type will become widely unlike 

 each other, and will show great variation from primitive forms. 



