128 THE WORLD OF LIFE chap. 



while 64 perished. The happy thought occurred to 

 Professor H. C. Bumpus, that here was an opportunity 

 of discovering whether there were any visible characters 

 indicating why some of these birds, under exactly similar 

 conditions, were destroyed while others survived. He there- 

 fore made a very minute and careful examination of all the 

 birds, living and dead, with very interesting results, of which 

 the following is a summary : — 



( 1) Sex. — About two-thirds were males, one-third females. 

 Of the former, 51 lived, 36 died; of the latter, 21 lived, 

 28 died, showing a decided superiority of the males in 

 resisting cold and wet. 



(2) Sise. — Here the comparison was made of male adult 

 birds, male young, and females, separately ; in all three of 

 these groups those which died were larger than those which 

 survived. The difference was not very great, but it was 

 clearly marked, and as it occurred in all three groups it 

 could not possibly be imputed to chance. 



(3) Weight. — This gives the same result as in the last 

 case, the survivors being lighter than those which died, by 

 the considerable proportion of one-twenty-fifth. 



(4) Length of the Sternum (breast-bone). — This character 

 gives a rather unexpected result, those birds which survived 

 having" a decidedly longer sternum than those which perished. 

 The difference is about -013 (a little more than one-hundredth) 

 of the total length ; but as the smaller birds on the whole 

 survived, these evidently had their sterna proportionally very 

 long. Now the sternum is an indication of the size of the 

 pectoral muscles which move the wings in flight. The 

 surviving birds, therefore, were those that could fly quickest 

 and longest, and this probably led to the more rapid 

 production of animal heat. Another advantage would be, 

 that these muscles being larger proportionally there would 

 be less exposure of the internal organs to the extreme cold. 



The result of this interesting experiment is almost con- 

 clusive as to the reality of natural selection. In this case 

 those which actually survived one of nature's most common 

 tests — exposure to severe storms — and which must be pre- 

 sumed to have been the " fittest " at that particular time and 

 place, were found to differ in just such characters, and in 



