328 



EVOLUTION AND ANIMAL LIFE 



it ma}^ be considered unerring. When conditions change, the 

 perfection of adaptation in a species may be the cause of its 

 extinction. If the need of a special fitness cannot be met, 

 immediately the species will disappear. For example, the 

 native sheep of England have developed a long wool fitted to 

 protect them in a cool, damp climate. Such sheep, transferred 

 to Cuba, died in a short time, leaving no descendants. The 

 warm fleece, so useful in England, rendered them wholly unfit 



Fig. 188. — Nest of T'espa, a social wasp. (Photograph by A. L. ilelander and 



C. T. Brues.) 



for survival in the tropics. It is one advantage of man, as 

 compared with other forms of life, that so many of his adapta- 

 tions are external to his structure, and can be cast aside when 

 necessity arises. 



The great fact of nature is adaptation. But while general 

 adaptation to widespread conditions is universal, there exist 

 also a multitude and variety of special adaptations fitting 

 organisms to special conditions. These special adaptations 

 arrest our attention to a greater degree than general adaptations 

 because they furnish the element of contrast. 



The various types of special adaptations may be roughly 

 divided into five classes as follows: (a) Food-securing; (b) self- 



