NOTE V 



(To page 44) 

 ON THE RELATION OF BRAIN WEIGHT TO INTELLIGENCE 



Observations and comparisons, beginning with 

 animals possessing barely rudimentary brains, con- 

 tinued through a gradually ascending series until 

 the brain of primitive man is reached, have fre- 

 quently been made, and leave no doubt that, c&teris 

 paribus, intelligence increases with brain weight. 



Exceptions to this rule are traceable to three 

 causes, viz: Firstly, to differences in the sizes of 

 the organisms from which the brains compared were 

 taken. Secondly, to differences in the complexity 

 of these organisms. Thirdly, to differences in the 

 energy and activity of the forms of life from which 

 the brains were taken. 



With reference to the first kind of exceptions, it 

 must necessarily require greater amounts of nerve 

 energy to move the larger members of larger bodies ; 

 therefore are larger masses of nerve and brain re- 

 quired for the movements of larger brutes. There- 

 fore do larger brutes, cceteris paribus, require larger 

 brains for survival. 



With reference to the second kind of exceptions: 

 more complex organisms, performing wider ranges 



235 



