80 VARIATIONS, DUE TO REVERSION. 



characters which their ancient progenitors had; and, of 

 course, each does not tamely submit to the develop- 

 ment alone of that character to which the conditions 

 at first gave the ascendant, and which man afterwards 

 made very predominant, but strives ever to regain all of 

 the characters which it lacks, or (as Darwin once hap- 

 pily puts it, when he approaches very near to the true 

 law of development) " to bring all of the parts again 

 into harmony with each other." 



Darwin proceeds to arrange the " results " into 

 classes : 



" The cases of analogous variation, so far as their 

 origin is concerned, may be grouped, disregarding 

 minor sub-divisions, under "two main heads ; firstly, 

 those due to unknown (sic) causes having acted on 

 organic beings with nearly the same constitution, and 

 which consequently vary in an analogous manner ; and 

 secondly, those due to the reappearance of characters 

 which were possessed by a more or less remote pro- 

 genitor." 



When a scientist has a body of facts, and has, em- 

 pirically, or provisionally, arranged them under two 

 heads ; one head consisting of facts presumably due to 

 " unknown causes," and the other head comprehend- 

 ing facts acknowledging a known, scientific factor ; he, 

 when he is a fair, as well as able scientist, tests all of 

 those facts, and when he finds that the known cause 

 will cover all of the phenomena under either head, and 

 that no possible exception may be taken to the com- 

 petency of such factor, so to cover all, he relegates 

 them all to one head — to the one known cause ; and 



