THE ELEMENTS OF ORGANIC EVOLUTION. 79 



would be no sensorium. If there were no environment 

 there would be no concessions to it. Without conces- 

 sion there would be no specialization of functions or 

 organs. Without variation in environment there could 

 be no choice in action. The concessions to the environ- 

 ment constitute, therefore, practically the whole structure 

 of any animal and the whole of the functions of its life. 

 It is in the response to environment, the concession, the 

 adaptation, the specialization, that the progress of life 

 consists. It is in characters thus produced that man and 

 the higher animals differ from the protozoa. Even the 

 protozoan has its concessions. The phenomenon of 

 growth causes the substance of the one-celled animal to 

 increase faster than its absorptive power. The waste of 

 the body varies as the substance — that is, as the cube 

 of the diameter of the creature. The absorptive power 

 of its surface must increase as the square of the diameter 

 — that is, as the surface. Hence, a one-celled animal 

 passing a given small size must either starve to death 

 or else make some concession to its surroundings. 

 This concession is reproduction — the one-celled crea- 

 ture must split into two animals. This increases the 

 digestive power, with no increase of substance. Even 

 the presence of skin on a protozoan is a concession to 

 its surroundings. That a given protozoan is developed 

 with an outside covering shows that natural selection 

 has been long at work on its ancestry in preparing such 

 a concession to external demands. 



A creature which had known no environment and 

 which had inherited no concession would be formless and 

 structureless. It could be little if anything more than 

 an organic molecule, or at the most a nebulous mist of 

 organic molecules without parts or form or function. 

 We know no such nebulous life as this. All the ani- 

 mals and plants on the records of science show traces of 

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