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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