286 Prof. Guthrie^ LL,B. — On the Subjective Causes of [April 25. • 



have been discussing are not so easily ascertained as might be sup- 

 posed, owing probably to the fact that Darwin's views underwent a 

 change, which he himself admits, between the times of the publication 

 of the first and last edition of the Origin of Species. 



I. Thus with respect to the descent of all individuals of the same 

 species from a single ancestor or pair of ancestors, we have the 

 following passages (sixth edition) : 



(p. 320). ..." Individuals of the same species 



must have proceeded from one spot where their parents were 

 first produced." 

 (p. 259) "If we bear in mind. . . . how often a species may 

 have ranged continuously over a wide area and then become 

 extinct in the intermediate tracts, the difficulty is not 

 insuperable in believing that all the individuals of the same 

 species are derived from common parents." 

 (p. 406) " All individuals of the same species. . . . are- 

 descended from common parents." 

 On the other hand we have the following passage : 



(p. 322). ..." Individuals of the same species inhabiting 



the same area will be kept nearly uniform by intercrossing f 



so that many individuals will go on simultaneously changing, 



and the whole amount of modification at each stage will not be 



dvie to descent from a single parent." 



This last passage, though somewhat ambiguous, leaves us in some 



doubt whether Darwin held that species are to be traced back to a 



single ancestor or ancestral couple, but they leave no doubt but that he 



was of opinion that each species originated in a single locality from 



which it spread by migration. 



II. On the closely allied point as to the existence in the individuals of 

 species of a tendency to parallel variations there is a somewhat 



similar though less uncertainty as to Darwin's final opinion. 

 Thus, on page 125, he heads a paragraph with the words : 



Distinct species present analogous variations, so that a variety^ 



of one species often assumes a character proper to an 



allied species. 



This he illustrates by the frequent occurrence in one breed of 



domestic pigeons of a characteristic of another breed, but not found 



among the aboriginal rock pigeons from which both have descended, 



as for example the occurrence of fourteen or sixteen tail feathers in^ 



