THE ELIMINA TION OF THE UNFIT. 2 I I 



striking difference between the two classes of birds. Both 

 have an indicated average of 2.45 mm., although, to be more 

 exact, the birds which perished averaged 2.449, while those 

 that survived averaged 2.455, a difference too slight to be of 

 material significance. This similarity of the two groups is 

 not to be wondered at, since it is not to be expected that one 

 eliminative agent will express itself in all possible anatomical 

 features. Were the eliminative agent, for example, a severe 

 northerly wind of protracted duration, the alar extent might 

 then enter in as a factor of considerable selective value, and 

 survivors would then have an alar extent materially different 

 from that of the birds eliminated. 



The alar extent of the females, corresponding with their 

 smaller size, is less than that of the males. 



Test 4 : Weight. — Had I been called upon to express an 

 opinion as to whether heavy or light birds would be more suc- 

 cessful in resisting the severity of the February storm, I should 

 have declared unhesitatingly in favor of the heavy birds. An 

 examination of the third column of measurements, however, will 

 show that the birds which survived invariably average less in 

 weight than those which perished, and that among the males 

 this difference amounts to more than a gram ; that is, to about 

 one twenty-fifth of the weight. The surviving birds of both 

 sexes had an average weight of 25.2 grams, and those which 

 succumbed had an average weight of 25.8 grams. 



It may not be out of place to call attention here to certain 

 objections which may be raised to the method which I have 

 adopted, and to the conclusions thus far derived therefrom. 

 One may claim that the greater relative number of females in 

 the group of birds which perished vitiates the numerical result, 

 since the females are of less stature than the males. But it 

 will be noted that this objection answers itself, for the birds 

 which perished are not shorter, but longer, than those which 

 survived ; and again, that the birds which perished, though 

 having a disproportionate number of the lighter sex, never- 

 theless have an average weight considerably greater than that 

 of the birds which survived. Moreover, comparing, in the 

 two groups, adult males with adult males, young males with 



