32 NATURAL SELECTION H 



increase the development of their own organs, and thus 

 modify their structure and habits has been repeatedly and 

 easily refuted by all writers on the subject of varieties and 

 species, and it seems to have been considered that when this 

 was done the whole question has been finally settled ; but 

 the view here developed renders such an hypothesis quite 

 unnecessary, by showing that similar results must be pro- 

 duced by the action of principles constantly at work in 

 nature. The powerful retractile talons of the falcon and 

 the cat tribes have not been produced or increased by the 

 volition of those animals ; but among the different varieties 

 which occurred in the earlier and less highly organised forms 

 of these groups, those always survived longest which had the 

 greatest facilities for seizing their prey. Neither did the 

 giraffe acquire its long neck by desiring to reach the foliage 

 of the more lofty shrubs, and constantly stretching its neck 

 for the purpose, but because any varieties which occurred 

 among its antitypes with a longer neck than usual at once 

 secured a fresh range of pasture over the same ground as their 

 shorter-necked companions, and on the first scarcity of food were 

 thereby enabled to outlive them. Even the peculiar colours of 

 many animals, more especially of insects, so closely resem- 

 bling the soil or leaves or bark on which they habitually 

 reside, are explained on the same principle ; for though in 

 the course of ages varieties of many tints may have occurred, 

 yet those races having colours best adapted to concealment from their 

 enemies would inevitably survive the longest. We have also 

 here an acting cause to account for that balance so often 

 observed in nature, a deficiency in one set of organs always 

 being compensated by an increased development of some 

 others powerful wings accompanying weak feet, or great 

 velocity making up for the absence of defensive weapons ; 

 for it has been shown that all varieties in which an un- 

 balanced deficiency occurred could not long continue their 

 existence. The action of this principle is exactly like that 

 of the centrifugal governor of the steam-engine, which checks 

 and corrects any irregularities almost before they become 

 evident ; and in like manner no unbalanced deficiency in the 

 animal kingdom can ever reach any conspicuous magnitude, 

 because it would make itself felt at the very first step, by 



