THOUGHTS ON SPECIES. 163 



enemies, and its instruments and means of defence, and its 

 resources for the sustenance of life. For, if this be not true, 

 what significance can we assign to the harmony and intelli- 

 gent design, everywhere characterizing the relationships of 

 organic nature ? The natural history of the earth teaches us 

 to believe that physical influences were established antecedent 

 to the creation of organic bodies, and we know that vegetable 

 forms, being producers or creators from the simple elements 

 of the material for the sustenance of the animal, must likewise 

 have been its precursor, and we must look for adaptability in 

 the latter to the conditions under which it was to pass its life, 

 and not that it is capable of being indefinitely moulded, modi- 

 fied and controlled by the existence of agencies and condi- 

 tions, which had fully recognized and established existence 

 previously to its appearance upon the earth. I know, as 

 well as any one, that there is nothing like positive organic 

 immobility or fixity in the animal organism ; that it is a scene 

 of constant, perpetual fluctuation ; that the condition of life 

 is one of change, waste and renovation throughout its con- 

 tinuance, but under an immutable and predetermined plan, 

 comprehending a certain degree of adaptiveness, by which it 

 is accommodated to the unequal action of the conditions 

 under which it may exist. Within this limit the operation 

 of organic processes are evidently, one may say eminently, 

 influenced by physical agencies. Cold represses and retards 

 their action and development; heat stimulates and advances; 

 and the animal being incapable of generating or creating a 

 single element of the simplest of its constituents, but assimi- 

 lating those already prepared for its use by other organisms, 

 scarcity or abundance of food likewise affect it. And though 

 this, more than either the influences mentioned, may produce 

 physical degeneration, yet, even combined with the external 



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