THE MECHANICAL SYSTEM AND ITS LIMITS 373 



the mechanical, as we are accustomed to looking for 

 ends and purposes. But as we have given only 

 mechanical processes in the character of facts, we need 

 now merely rectify our form of expression. 



In the first place we must give up the term 

 "purposive." There can be no question of "purposes" 

 in a scientific investigation. We can only speak of a 

 structure in an organism as purposive in the sense that 

 the animal has the faculty of self-preservation in its 

 momentary circumstances. 



We must also be careful in using the word " evolu- 

 tion." When we speak of the evolution of the animal 

 world, the thought involuntarily forces itself on us that 

 they have advanced from lower to higher forms. But 

 we have no right to speak of "lower" or "higher" 

 forms. We should in that case have to suppose that 

 there was from the first a principle in the living 

 substance that gradually creates the higher forms, and 

 we have rejected that view. By higher and lower 

 animals we can only mean more complex and simpler. 



Natural selection is not a principle of progress, always 

 creating higher animals. Selection merely seeks to 

 adapt organisms better to their environment. But 

 greater complexity of organisation has no relation to 

 good adaptation. We pointed out previously that man 

 is not better adapted than the bacillus. From the 

 point of view of the birds man must be a very 

 imperfect being. 



If greater intricacy of structure were the same thing 

 as better adaptation, natural selection would gradually 



