THE ELIMINATION OF THE UNFIT. 21 7 



Natural selection is most destructive of those birds which have 

 departed most from the ideal type, and its activity raises the 

 general standard of excellence by favoring those birds which 

 approach the structural ideal. 



Inasmuch as the variation in structure in the birds which 

 perished tends to centre about certain individuals, as, for 

 example, Nos. 45, 52, and 55, it might be claimed that the 

 accidental presence of a few of these extremely abnormal 

 individuals in this group is what really makes all the differ- 

 ence. Let us see. 



There are twenty-three birds among the seventy-two sur- 

 vivors whose measurements bear exponents of extreme vari- 

 ation, and there are twenty-four birds similarly distinguished 

 among the sixty-four which perished. But none of the birds 

 in the first group has more than three exceptional features, 

 whereas several of the birds which perished have a consider- 

 ably larger number of exceptional features : four, five, and in 

 one case, No. 52, even six. 



Of the twenty-three survivors which bear exponents, nine- 

 teen have only one exceptional character, and it is not surprising, 

 considering the high standard of excellence possessed by these 

 birds as a whole, that a single unfavorable feature does not 

 prove fatal. There are but ten of the eliminated birds which 

 have only one exceptional character, and the fact that some 

 are burdened with more than one is apparently the reason for 

 their mortality. 



In an earlier contribution to the Study of Variation I called 

 attention to a coincidence which may have considerable signifi- 

 cance. When specimens of Necturus varied in respect to any 

 one feature, there was a tendency for such specimens to' pre- 

 sent other and not necessarily correlated variations. Stated in 

 another way, instability in respect to any one feature is an 

 index of general organic instability. A similar coincidence of 

 variations occurs among the sparrows. 



Of the one hundred and thirty-six birds, five (Nos. 3, 47, 70, 

 21, 52) had albino feathers. Like other abnormalities endured 

 by the surviving birds, albinism in two out of the three cases 

 is the only affliction. But among those that were eliminated, 



