THEORY OF BROOKS. 28 1 



Evidently this would happen to all the offspring of 

 individuals in the same circumstances. Many indi- 

 viduals would thus vary simultaneously. Now, 

 natural selection, having simultaneous variations to 

 work upon, may preserve the favorable varieties 

 and destroy the unfavorable. Every organ placed 

 out of harmony with its environment will thus begin 

 to vary, and the variations will appear where they 

 are needed. Moreover, the inherited effects of use 

 and disuse receive explanation in the same way ; 

 for an organ, used either above or below its normal 

 amount, will be out of harmony with its conditions, 

 and will throw off gemmules. 



In a word, it is from the fact that a child and its 

 mother are both developed from part of the same 

 ovum, that is due the inheritance of the long-con- 

 tinued characteristics of the race. This is heredity. 

 But the origin of gemmules, and their introduction 

 into the ovum by fertilization, cause the ovum to 

 become different in its constitution, and the indi- 

 vidual arising from it is therefore in some respects 

 unlike its mother. This is variation. 



The important features of this theory are, first, 

 the claim that the male is an individual which has 

 become specialized for the production of variation, 

 while the female transmits race characteristics ; and, 

 second, the claim that the laws of the organism are 

 such that variations appear in abundance in those 

 organs where they are needed. The suggestion of 

 gemmules is simply an hypothesis to explain these 

 two laws. It is an important theory, because it is 

 the first attempt to explain the origin of simultane- 



