334 ^^^ Theory of Natural Selection 



were large departures from the parental type, such as sports, 

 as well as the minute fluctuating variations. He did not 

 make any serious attempt to differentiate the one class of 

 variations from the other as a possible source of new varieties 

 or species. Nor did he make any attempt to discover how 

 far any kinds of variations were inherited. 



We have already seen (page 185) that it is necessary to 

 discriminate between continuous variations and discontinu- 

 ous variations. This is not primarily a question of degree 

 but a question of genetic relationship. The continuous va- 

 riations are those that seem to be due to fluctuations in the 

 conditions of growth and development. They are ordinarily 

 very small, but occasionally rather large. The discontinuous 

 variations, on the other hand, are departures from the pa- 

 rental type that are inherited in subsequent generations. 

 These too may be trivial or rather extensive. We see among 

 human beings, for example, variations in color of hair which 

 may represent distinct hereditary manifestations; but we 

 may see also variations in skin pigment which are due at the 

 moment to the fact that some have had a longer vacation 

 than others. Seeds from the same pod will yield plants of 

 which the largest may be twice as large as the smallest, show- 

 ing a wide variation in a non-heritable character. Among 

 the fruit flies are found many variations of the wings. Cer- 

 tain of these, quantitatively no more striking than others, 

 are definitely inherited, whereas other variations come within 

 our notion of fluctuations. 



Darwin, failing to make this discrimination, assumed 

 that succeeding generations would inherit the favorable 

 variations, in larger proportions. According to the La- 

 marckian doctrine, this ought to be true regardless of 

 whether the variations were innate or the results of environ- 

 mental stimulus. Darwin himself accepted readily enough 

 the Lamarckian assumption of the transmission of acquired 

 modifications, although he was rather disdainful of La- 

 marck's theory that such modifications could come about 

 through *' the inner strivings " of an animal. 



