Mammalia: Nervous System 721 



gencies. Mammals took the other road and elaborated the "super- 

 brain" to a degree which has given them the advantage over all other 

 animals. 



Statements to the effect that large brains, or brains containing 

 large quantities of "gray matter," or brains having a "richly con- 

 voluted" cortex are indicative of a high degree of intelligence may 

 carry unwarranted implications. Protoplasm can secrete substance 

 and it can throw off energy in doing mechanical work or as heat, 

 electricity, or light. Intelligence is not a substance, nor is it a physical 

 force or form of energy. The relation of intelligence to protoplasm is 

 the centuries-old and unsolved problem of the "relation of mind to 

 matter." It is certain, however, that the existence of intelligence is 

 not dependent on mere size of a mass of cells or mere quantity of any 

 particular kind of nervous material. As a matter of fact, so far as 

 quantity of substance is concerned, "white" is just as important as 

 "gray" nervous substance because every "white" fiber is the product 

 of a "gray" cell with which it is permanently connected. Nor can 

 intelligence result from mere increase in number of neurons. No reason 

 appears why 1000 cells should be more intelligent than 10 cells. They 

 might all be somehow connected together but, even so, and supposing 

 that they are connected in some systematic way, there still appears to 

 be no reason why the group should be any more intelligent than a group 

 of electric batteries and wires connected in some systematic way. 

 Emphasis has been laid on the extraordinary complexity of the rela- 

 tions of neurons in the brain. There may, however, be great complexity 

 with little intelligence. Birds have relatively large brains, and the 

 much-enlarged corpora striata are occupied by nervous mechanisms 

 of the extreme complexity necessary for execution of the bird's highly 

 elaborate instinctive behavior. In this case a high degree of complexity 

 is accompanied by very inferior intelligence. It is conceivable that a 

 brain of this instinctive type might be relatively larger than that of an 

 animal whose behavior, although of a simpler sort, shows some degree 

 of intelligence. Granting the extreme of complexity, it does not appear 

 how intelligence must result from mere complexity. On the other hand, 

 it does appear that complexity of nervous mechanism is essential if 

 intelligence is to control the complex activities of the animal. Com- 

 plexity cannot create intelligence, but the operation of intelligence requires 

 complexity. 



Among mammals in all of which the neencephalon is more or less 

 dominant, in contrast to birds in which the palaeencephalon domi- 

 nates, relative size of brain, bulk of "gray matter," convolutions, num- 

 ber of neurons and complexity of their relations, and — especially 



