VARIATION 293 



process of measurement it would be found " that a very large 

 proportion of the total number of individuals constituting a 

 species would diverge considerably from its average condition 

 as regards each part or organ ; and as we know . . . that 

 each part varies to a considerable extent, independently, the 

 materials constantly ready for natural selection to act upon 

 are abundant in quantity and very varied in kind. Almost 

 any combination of variations of distinct parts will be avail- 

 able where required, and this . . . obviates one of the most 

 weighty objections which have been urged against the efficiency 

 of natural selection in producing new species, genera and higher 

 groups ". 



An actual illustration of the relation of variation to natural 

 selection has been given by an American naturalist — Mr. 

 Bumpus. This was furnished by the Common English Sparrow 

 {Passer douiesticns) which some years since was introduced into 

 the United States. One hundred and thirty-six of these 

 Sparrows were collected after a very severe storm of snow, 

 sleet and rain. Of these seventy-two revived, while sixty-four 

 perished. On comparing the survivors with the eliminated 

 individuals, very appreciable differences were found. The 

 average characters differed but little. But the eliminated in- 

 dividuals were i'2'j per cent, greater in length, and 2'38 per 

 cent, greater in weight, while they were about i per cent, 

 smaller than the survivors in respect of most of the other char- 

 acters measured. The variability, or range of variation of the 

 eliminated birds about their mean was, however, very much 

 greater than in the case of the survivors. Of the nine char- 

 acters measured, the variability is greater in eight, the average 

 excess being no less than i8"8 per cent. The variability was 

 less in respect of the sternum alone, and then only by 3'i per 

 cent. The struggle for existence appeared to fall heaviest on 

 the very long individuals, as of the eighteen birds obtained in 

 which the length was 164 mm. and upwards, no less than four- 

 teen perished. Also the two shortest birds perished. The 

 conclusion drawn by Bumpus from these observations was that 

 " 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 favouring those birds 

 which approach the structural ideal". But Mr. H. M. Vernon, 



