CHAPTER V 

 ADAPTATION OF LAND REPTILES TO LIFE IN THE WATER 



In the never-ceasing struggle for existence all forms of life 

 upon the earth, whether consciously or unconsciously, are con- 

 tinuously striving for improvement; striving to flee from adverse 

 environments, or to adapt themselves better to those which must 

 be endured; to escape their enemies, or to find means whereby 

 they may withstand them; to find more or better food, or to pre- 

 vent others from despoiling them of what they have. There is 

 always more or less of unrest, more or less of discontent, if such 

 terms may be used of the lower organisms. It sometimes happens 

 with groups of organisms that by reason of unusual or extraordinary 

 traits they become so perfectly adapted to their environments, to 

 their surroundings, or so easily adaptable to changes in their 

 environments, that they remain for long ages securely protected and 

 little changed. But, as with man himself, improvement is usually 

 the result of adversity — adversity which stimulates but does not 

 destroy. And the word improvement, translated into biological 

 language, means simply specialization, that specialization which 

 adapts the organism better to its mode of life, which fits it the 

 better to excel its less ambitious or less capable competitors. No 

 animals or plants are perfect; if they were, there would be no 

 advancement, no struggle. If all physical conditions stood still, 

 or remained uniform, perhaps life would stand still, but conditions 

 never have and never will stand still, and life must change to meet 

 changed conditions. 



Thus it is that that which makes life easier, which lessens the 

 dangers of destruction, which insures the continued prosperity of 

 the race, is seized upon and utilized by all plants and animals, so 

 far as possible. As said long ago by Tennyson, 1 the first law of life 



1 Are God and Nature then at strife, 

 That Nature lends such evil dreams? 

 So careful of the type she seems 

 So careless of the single life. — In Memoriam, lv. 



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