THE SUMMIT OF THE YEARS 



As a scientist one cannot admit anything mystical 

 or transcendental in nature, while, on the other 

 hand, the final explanation of the least fact is beyond 

 us. We know certain things about chemical affinity, 

 for instance; but what makes chemical affinity? 

 Why are certain substances so crazy to be locked in 

 each other's embrace? Why, that is chemical affinity. 

 But what is chemical affinity? The instinct of migra- 

 tion in birds doubtless has a psychological basis; 

 but whence this basis? How did it come about? The 

 instinct of the male for the female doubtless has a 

 physiological basis, but whence the basis? All in- 

 stincts have their physics, but are they on that ac- 

 count less instinctive? After we have explained 

 them, are they any the less untaught, any the less 

 independent of experience? Some kinds of chemical 

 and physiological stimuli make the heart beat, but 

 does that clear up the mystery? Why is this muscle 

 and no other so susceptible to these stimuli? Why is 

 the heart the heart? 



It takes time to develop and establish the in- 

 stincts of the lower orders, as it takes time to de- 

 velop the reason in man. Not until an animal's 

 organization approaches maturity do all its reflexes 

 act promptly and surely. It is not a question of ex- 

 perience or of acquired habits, but of physiological 

 development. It takes nine days for the kitten's 

 eyes to open, and it takes longer than that for the 

 preying instincts to develop. The baby does not 

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