39.2 THE EVOLUTION THEORY 



we do not know under what external conditions the origin of living 

 matter, even in the smallest quantity, can take place ; I mean, 

 especially, that we do not understand how this one substance 

 should suddenly reveal qualities which have never been detected 

 in any other chemical combination whatever — the circulation of 

 matter, metabolism, growth, sensation, will, and movement. But 

 we may confidently say that we shall never be able fully to under- 

 stand these specific phenomena of life, as indeed how should we, 

 since nothing analogous to them is known to us, and since under- 

 standing always presupposes a comparison with something known. 

 Even although we assume that wo might succeed in understanding 

 the mere chemistry of life, as is not inconceivable, I mean the jjerpetuwm 

 mobile of dissimilation and assimilation, the so-called ' animal ' functions 

 of the living substance would remain un comprehended: Sensation, Will, 

 Thought. We understand in some measure how the kidneys secrete 

 urine, or the liver bile; we can also — given the sensitiveness to stimulus 

 of the living substance — understand how a sense-impression may be 

 conveyed by the nerves to the brain, carried along certain lefiux 

 paths to motor nerves and give rise to movement of the muscles, but 

 how the activity of certain brain-elements can give rise to a thought 

 tvhidi, emiaot he compared tvith anythiiii/ material, which is never- 

 theless able to react upon the material parts of our body, and, as 

 Will, to give rise to movement— that we attempt in vain to understand. 

 Of course the dependence of thinking and willing upon a material 

 substratum is clear enough, and it can be demonstrated with certainty 

 in many directions, and thus materialism is so far justified in drawing 

 parallels between the brain and thought on the one hand, and the 

 kidneys and urine on the other, but this is by no means to say that 

 we have understood how Thought and Will have come to be. In 

 recent times it has often been pointed out that the physical functions 

 of the body increase very gradually with the successive stages of the 

 organization, and from the lowest beginnings ascend slowly to the 

 intelligence of Man, in exact correspondence with the height of 

 organization that has been reached by the species ; that they begin 

 so imperceptibly among the lower animal forms that we cannot 

 tell exactly where the beginning is ; and it has been rightly concluded 

 from this that the elements of the Psyche do not originate in tlie 

 histological parts of the nervous system, but are peculiar to all living 

 matter, and it has further been inferred that even inorganic material 

 may contain them, although in an unrecognizable expression, and that 

 their emergence in living matter is, so to speak, only a phenomenon 

 of summation. If we are right in our assumption of a spontaneous 



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