22 Heredity. 



ultimate, the irresolvable character of all vital phenomena prove 

 sufficient to explain instinct. For if mechanism explains the lower 

 forms of spiritual life, it must also explain the higher the 

 difference is one only of degree and of complexity ; but then, also, 

 if mechanism does not explain the higher, neither can it explain 

 the lower. It has been said that thought is only translated 

 motion, and that it is but the highest form of the universal 

 mechanism. This theory is no doubt very alluring, inasmuch as 

 it enables us to bring under one law all the phenomena of the 

 universe, from simple impact up to the most complicated events of 

 social life and history. But it is only an hypothesis, which is 

 rendered doubtful by the fact that we can perceive no equivalence 

 between thought and motion. Each appears to us as an ultimate 

 fact, sui generis, and not reducible into the other. 



To these theoretic considerations we may add others drawn 

 from facts. If organization is the cause of instincts, then, as it 

 varies, so must they. But observation shows that this is not 

 the case. Observation teaches us that the correlation between 

 instincts and organs is not absolute ; that we may have the same 

 organization with different instincts, and the same instincts with 

 different organizations. Thus, the European beaver, which is 

 hardly to be distinguished from the American, burrows like the 

 mole, whereas the other builds houses. All spiders have the same 

 apparatus for weaving their webs, and yet one spider weaves a 

 circular web, another weaves a web of irregular form ; a third weaves 

 no web, but inhabits holes, simply making a door. Birds have their 

 beaks and feet as their only instruments for nest building, yet how 

 great are the differences of the form, architecture, and position of 

 nests. 



Let it be granted for the moment that the opinion we are 

 discussing is correct, although in the present state of our knowledge 

 it is a mere hypothesis. Science has accustomed us to revelations 

 so unexpected that it may be rash to say that the opinion is 

 untenable. Assuming, then, that instinct is not the result of the 

 organization, we shall still have to study its nature; for this 

 hypothesis only enlightens us as to its cause. It tells us whence it 

 comes, but not what it is. The reduction of all physical phenomena 

 to motion does not bar the separate study of electricity, of sound, 



