Variation and Natural Selection. 81 



and Micrococcus prodigiosus, remain in the field during 

 cold weather when other less hardy microbes have perished. 

 The insects of Madeira may fairly be regarded as affording 

 another instance. The ground-loving forms allied to 

 insects of normally slow and heavy flight have in Madeira 

 become wingless or lost all power of flight. Those which 

 attempted to fly have been swept out to sea by the winds, 

 and have thus perished ; those which varied in the direction 

 of diminished powers of flight have survived this eliminating 

 process. On the other hand, among flower-frequenting 

 forms and those whose habits of life necessitate flight, the 

 Madeira insects have stronger wings than their mainland 

 allies. Here, since flight could not be abandoned without 

 a complete change of life-habit, since all must fly, those 

 with weaker powers on the wing have been eliminated, 

 leaving those with stronger flight to survive and procreate 

 their kind.* In Kerguelen Island Mr. Eaton has found 

 that all the insects are incapable of flight, and most of them 

 in a more or less wingless condition. f Mr. Wallace regards 

 the reduction in the size of the wing in the Isle of Man 

 variety of the small tortoiseshell butterfly as due to the 

 gradual elimination of larger-winged individuals.^ These 

 are cases of elimination through the direct action of sur- 

 rounding physical conditions. Even among civilized 

 human folk, this form of elimination is still occasionally 

 operative — in military campaigns, for example (where the 

 mortality from hardships is often as great as the mortality 

 from shot or steel), in Arctic expeditions, and in arduous 

 travels. But in early times and among savages it must be 

 a more important factor. 



Elimination by enemies needs somewhat fuller exempli- 

 fication. Battle within battle must, throughout nature, 

 as Darwin says, be continually recurring with varying 

 success. The stronger devour the weaker, and wage war 

 with each other over the prey. In the battle among co- 

 ordinates the weaker are eliminated, the stronger prevail. 



* " Origin of Species," p. 109. f " Darwinism," p. 106. 



t Ibid. p. 106. 



G 



