ON VARIATIONS. 



343 



curve, which represents the eliminated individuals, is, 

 on the whole, much more flat-topped than the other 

 curve. The very long individuals seem especially 

 handicapped in the struggle for existence, as of the 18 

 birds obtained in which the length was 164 mm. and 

 upwards, no less than 14 perished. Also the two 

 shortest birds obtained perished. The conclusion 

 which Bumpus draws from these most interesting ob- 

 servations is as follows : " Natural Selection is most 

 destructive of those birds which have departed most 

 from the ideal type, and its activity raises the gen- 

 eral standard of excellence by favouring those birds 

 which approach the structural ideal." The observa- 

 tions really show more than this, however. It is 



15 



150 153 



1M 



154 - 1'56 J58 _ JC6Q _ 



Length of birds in millimeters. 



FIG. 27. Distribution of the lengths of surviving and of 



eliminated sparrows. 



true that, as a rule, the most extreme individuals in 

 either direction are eliminated, but if the distributions 

 of the various characters be plotted out as in the 

 above figure, it will be seen that in the case of some 

 of the other characters, as in that of length, the elimi- 

 nating process acts much more on the extreme in- 

 dividuals in one direction than on those in the other. 



