118 EVOLUTION 



causally relate them in a direct way to pe- 

 culiarities in habits or surroundings; they 

 are often distinct at birth or even hinted at 

 before birth; they are rarely alike even among 

 forms whose conditions of life are uniform. 

 They are in many cases, if not always, trans- 

 missible. They form the raw material of 

 evolution. 



DARWIN'S POSITION IN REGARD TO VARIA- 

 TIONS. Darwin recognized two kinds of 

 hereditary variations, in addition to those 

 extrinsic changes which we now call modi- 

 fications. In the first place he recognized 

 large "single variations" or "sports," which 

 occur rarely and result in conspicuous diver- 

 gences from the type of the species. In the 

 second place he recognized slight "individ- 

 ual variations," which are practically ubi- 

 quitous, distinguishing child from parent, 

 brother from brother, cousin from cousin. 

 Both of these kinds of variations were called 

 "indefinite" and "spontaneous," to dis- 

 tinguish them from what he somewhat 

 unfortunately called "definite variations" 

 the direct result of environmental and 

 functional peculiarities. These correspond to 

 what we now call modifications, and it must 

 be noted that Darwin believed in then* oc- 

 casional transmissibility. 



Leaving aside the question of the possible 



