198 THE STORY OF LIFE'S MECHANISM. 



environment an important agency in machine 

 building. This direct effect of the conditions 

 is apparently so manifest that one school of 

 biologists finds in it the chief cause of the varia- 

 tions which occur, telling us that the conditions 

 surrounding the organism produce changes in it, 

 and that these variations, being handed down to 

 subsequent generations, constitute the basis of 

 the development of the machine. If this factor 

 is entirely excluded, we are driven back upon the 

 natural selection of congenital variations as the 

 only kind of variations which can permanently 

 effect the modification of the machine. 



CONSCIOUSNESS. 



It may be well here to refer to one other 

 factor in the problem, because it has somewhat 

 recently been brought into prominence. This 

 factor is consciousness on the part of the animal. 

 Among plants and the lower animals this factor 

 can have no significance, but consciousness cer- 

 tainly occurs among the higher animals. Just 

 when or how it appeared are questions which 

 are not answered, and perhaps never will be. 

 But consciousness, after it had once made its 

 appearance, became a controlling factor in the 

 development of the machine. It must not be 

 understood by this that animals have had any 

 consciousness of the development of their body, 

 or that they have made any conscious endeavours 

 to modify its development." This has not always 

 been understood. It has been frequently sup- 

 posed that the claim that consciousness has an 



