CHAPTER XXI 



ADAPTATIONS 



253. Origin of adaptations. The strife for place in the 

 crowd of animals makes it necessary for each one to adjust 

 itself to the place it holds. As the individual becomes 

 fitted to its condition, so must the species as a whole. The 

 species is therefore made up of individuals that are fitted 

 or may become fitted for the conditions of life. As the 

 stress of existence becomes more severe, the individuals fit 

 to continue the species are chosen more closely. This 

 choice is the automatic work of the conditions of life, but 

 it is none the less effective in its operations, and in the 

 course of centuries it becomes 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 

 can not 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, leav- 

 ing no descendants. The warm fleece, so useful in Eng- 

 land, rendered them wholly unfit for survival in the tropics. 

 It is one advantage of man, as compared with other forms 

 of life, that so many of his adaptations are external to his 

 structure, and can be cast aside when necessity arises. 



254. Classification of adaptations. The various forms of 

 adaptations may be roughly divided into five classes, as fol- 

 lows : (a) food securing, (5) self-protection, (c)rivalry, (d) 

 defense of young, (e) surroundings. 



The few examples which are given under each class, 

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