VARIATION AND HEREDITY 119 



birth or even hinted at before birth; they are 

 rarely alike even among forms whose con- 

 ditions of life are uniform. They are in many 

 cases, if not always, transmissible. 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 modifica- 

 tions. In the first place he recognized large 

 " single variations " or " sports," which occur 

 rarely and result in conspicuous divergences 

 from the type of the species. In the second 

 place he recognized slight " individual varia- 

 tions," which are practically ubiquitous, 

 distinguishing child from parent, brother from 

 brother, cousin from cousin. Both of these 

 kinds of variations were called " indefinite " 

 and *' spontaneous," to distinguish them from 

 what he somewhat unfortunately called 

 " definite variations " the direct result of 

 environmental and functional peculiarities. 

 These correspond to what we now call modi- 

 fications, and it must be noted that Darwin 

 believed in their occasional transmissibility. 



Leaving aside the question of the possible 

 racial importance of modifications, it is of 

 interest to notice Darwin's view of the 

 relative importance of " single variations " 



