THE EVOLUTION OF THE BRAIN 93 



less than what might have been expected. In both sets of 

 changes, decrease and increase, the brain seems to lag 

 behind the rest of the animal, and gives evidence in this 

 way of a degree of independence not commonly associated 

 with animal growth. The brain in its evolution, as compared 

 with other parts, exhibits what may be described as an 

 organic conservatism for it tends to maintain its size irrespec- 

 tive of the surrounding flux. 



The amount of brain substance in different animals 

 is often taken as an indication of their intelhgence, and in a 

 measure this is justified. Thus the brain weights of three 

 animals of about the same bodily size, a very large dog, 

 a gorilla, and a man, are respectively 135 grams, 430 grams, 

 and 1360 grams, a rough measure of their comparative 

 mental powers. Even among the races of men such differ- 

 ences are not unknown. Thus the brain of the Austrahan 

 native weighs only about 1185 grams, an amount quite 

 compatible with his low mentahty. 



But such measures are necessarily of only very general 

 appHcabihty. When the weights of various human brains of 

 European stock are compared great individual differences 

 are to be observed from the extreme of microcephaly to 

 that of macrocephaly. MicrocephaHc brains are those of 

 1000 grams or less. Such brains are known to range as func- 

 tional organs down to a httle under 300 grams. But individ- 

 uals possessing brains of this size are always abnormal and 

 often idiotic. MacrocephaHc brains range from 1500 to 

 somewhat over 1900 grams. Individuals thus equipped are 

 by no means always geniuses, but in many cases are abnor- 

 mal or even idiotic. It is, however, interesting to observe 

 that many highly intellectual men have, if not macrocephahc, 

 at least unusually heavy brains. If the weight of the average 

 male brain of European stock is taken as 1360 grams, and if 

 the weights of the brains of male European intellectuals are 

 compared with this as a standard, it is found that the brains 

 of the majority of such individuals are heavier than this 

 standard. Thus of 46 brains of intellectuals, 33 were heavier 

 and only 13 were lighter than the standard brain. The 

 average weight of these 46 brains was a little over 1440 

 grams or 80 grams heavier than the standard. The heaviest 



