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 their oc- 

 casional transmissibility. 



Leaving aside the question of the possible 



