34 ETHICAL ASPECTS OF EVOLUTION 



would be quite a legitimate analogy to speak of those as 

 selective. 



What is meant by nature in biological theory is the whole 

 environment, or everything that affects the organism from 

 without. It may be doubted in what class the houses of 

 men, or the nests of birds, or the webs of spiders, or other 

 specific products of the organism itself, should be included ; 

 but this, though really a difficult question (the waste 

 products of men, for instance, have a very important 

 bearing on their life-history), must be passed by. The 

 opposition between the organism and its environment may 

 be taken for granted, without any exact delimitation of 

 frontiers. 



Nature, then, or the environment, is never exactly the 

 same for two consecutive moments. Besides the constant 

 changes, such as the alternations of night and day, summer 

 and winter, to which all existing species must already have 

 become adapted, there are always other processes which, 

 by effecting permanent alterations in the conditions of life, 

 demand permanent alterations in the structure of the 

 individual organism, in order that its necessary adjustment 

 to its surroundings may be restored. Theoretically, it 

 makes no difference whether the changes are slow and 

 secular, as when a glacial period supervenes, or sudden, 

 like the irruption of a horde of barbarians. No doubt 

 the second of these differs from the other in that it may be 

 repelled, but then there will have been no permanent change 

 it will have been averted. If the barbarians succeed in 

 establishing themselves, the former inhabitants must either 

 adjust themselves to the new conditions, or depart, or cease 

 to exist. The competition between two species for the means 

 of subsistence is only a special case of change in the environ 

 ment, and does not call for separate notice in a general dis 

 cussion of the concept of natural selection. It will be 

 remembered that it is not always the most highly organized 

 which wins. 



There are three different modes in which nature, or the 

 environment, acts on the organism. Of these, two resemble 





