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THE AMERICAN NATURALIST [Vol. XLIX 



widely, even in the same region. As long as organisms 

 live in the ocean or in the water generally, they are sub- 

 jected to certain relatively constant conditions dependent 

 upon the physico-chemical properties of the environment. 

 But it should be recognized that with organisms which 

 have migrated out upon the land the case is somewhat 

 different, as all conditions, except oxygen concentration 

 and pressure, vary more markedly on the land than in the 

 water. Temperature, in particular, varies greatly over 

 the land, and the poikilothermal animals have their activ- 

 ities greatly limited by the temperature conditions. 



From Henderson's premises, the conclusion follows 

 that life is what it is because the environment is what it 

 is. A different environment might, and in all probabil- 

 ity would, have resulted in, or been associated with, a dif- 

 ferent form of life on the earth. Certain characteristics 

 commonly called adaptations are, as Henderson shows, 

 the automatic and inevitable results of the physico-chem- 

 ical conditions obtaining in the environment. If such 

 a view assumes that an adaptation ceases to be an adap- 

 tation when the manner of its origin is discovered, it 

 would seem that we were in need of a more precise defini- 

 tion of adaptation. The question arises whether other 

 similar characteristics that have been called adaptations 

 are not also the inevitable and automatic result of the 

 physico-chemical conditions of the environment. We may 

 therefore consider the question of the reality of adapta- 

 tion, and also whether some of the characteristics of or- 

 ganisms are not really adaptations, 10 even if they arise 

 from the action of physico-chemical conditions in the en- 

 vironment. Again, since, in a given environment, with es- 

 sentially the same physico-chemical conditions for all its 

 inhabitants, there are many animal types, it would appear 

 that there were some influences operative within the or- 

 ganism itself to produce certain characteristic reactions, 

 known as adaptations, to the environment. As we will 

 show subsequently, these facts do not in any way pre- 

 clude an explanation of their origin on some hypothesis 



