132 EVOLUTION: THE AGES AND TOMORROW 



dents of the human brain find "blank areas" where there does 

 not seem to be a specific motor function. Similar areas are 

 found in apes but are less well developed, particularly in the 

 frontal region. Injury to these areas, although not producing 

 any change in sense reception or movement, seems to alter 

 the behavior and mentality of the individual. It is in these 

 "blank regions" that most authorities assume a function asso- 

 ciated with the highest human mental faculties. Over-all, 

 man has the largest and most highly differentiated cerebrum; 

 apes are next, and other mammals fall away from the top form 

 gradually. The chief, and perhaps the only, difference be- 

 tween man and apes is in the development of the cerebral 

 hemispheres and in the use of the "blank areas" or associa- 

 tion areas. 



As a carry-over from the distant evolutionary past, man 

 also has in his total nervous make-up a rather diffuse set of 

 nerves and nerve cells, the autonomic nervous system. It is 

 this system that controls unconscious functions such as the 

 secretions of glands, the activities and movements of the in- 

 testinal tract, and the internal situation in general. This sys- 

 tem consists of ganglia distributed mostly through the body 

 cavity; here and there it is connected with the spinal nerves, 

 but not intimately. An ancient, autonomous control of the 

 vegetative functions, it is outside consciousness but not 

 completely removed from the influence of higher brain cen- 

 ters which may under the stress of environmental pressures 

 (anxiety, fear, frustration, and so on) alter and even dan- 

 gerously upset the proper activity of the system. 



The learning capacities of the vertebrates rise sharply as 

 we approach the level of man, but they begin at levels some- 

 what below the recorded behavior of some higher inverte- 

 brates. Fish learn, but rather slowly. In a typical experiment 

 with these animals a glass partition in an aquarium separated 

 perch from their natural food, small minnows. After a great 

 many experiences of bumping into the glass, the perch 

 learned to suppress their attacks on the minnows, and the 



