194 FROM FISH TO PHILOSOPHER 



to the infraprimates, while among the subhuman pri- 

 mates the chimpanzee is the most adept at problem- 

 solving and the use of tools. Among the mammals gen- 

 erally, the carnivores belong above most rodents and 

 other herbivores. Conversely, many lower forms can 

 doubtless perceive relations of temperature and salinity 

 (fishes), smell and taste (other mammals), vibration 

 (bats), direction (birds), and other stimuli to which 

 man is wholly insensitive because he does not have the 

 appropriate receptor organs; but this is a matter of 

 qualitative equipment. The basic fact is that the capacity 

 to learn was perfected early in the course of evolution 

 of the brain; it is not the fact of learning but what is 

 learned that differentiates animals in the evolutionary 

 scale, the higher animals being able to perceive relations 

 that are beyond the comprehension of the lower forms. 

 In man, learning is importantly concerned with ab- 

 stractions such as numbers, qualities, symbols and rela- 

 tions, and specifically vdth language; and, as Emerson at 

 the age of twenty wrote in his journal (1824), 'Man is 

 an animal that looks before and after.' By turning his at- 

 tention from concrete objects to abstractions and to the 

 past and to the future, he has welded his thinking proc- 

 esses into a mighty tool. But when a writer manipulates 

 the twenty-six letters of the alphabet into a meaningful 

 sentence, or the mathematician manipulates numbers 

 from zero to infinity, he is using no specialized nerve cells 

 and no unique cellular operations. In respect to the basic 

 mechanism of operation, every nerve cell is hke every 

 other nerve cell, a generalization that applies not only 

 to the different types of nerves in man but to human 

 nerves, frog nerves and the nerves of the octopus. And 

 every impulse is, except for intensity and duration, es- 

 sentially identical with every other nerve impulse. More- 

 over, the structure of the nervous system is, on the whole, 

 determined genetically and it is therefore predetermined 

 at birth. No animal acquires or loses nerve cells, so far 

 as is known, as a consequence of learning or experience, 



