186 WE AT IS LIFE 



result in maturity. And it is the cause of this retarda- 

 tion that mustfiyid its statement. 



Man is distinguished from the ape chiefly by his 

 superior psychic powers that wait on his long in- 

 fancy. That in a general way degree of psychic power 

 corresponds to size or weight of the brain, is, of 

 course, well known to everyone. At birth, man's 

 brain and the brain of the great anthropoids have 

 nearly the same weight. However, the ape's brain at 

 birth already has attained two-thirds of its full size; 

 whereas man's brain at birth weighs only about one- 

 fifth of its adult weight. (On the brain and psychic 

 properties see pp. 164, 165, 169-172.) 



The superior psychic powers of adult man (accord- 

 ing to the theory) indicate that the human brain 

 carries a far greater and more complex Z-system 

 than the ape's brain carries; and since the human 

 baby at birth is utterly helpless, and entirely wanting 

 in intellectual powers — its psychic powers developing 

 gradually — it would follow that even as four-fifths 

 of the brain-weight is added after birth, so most of 

 the Z-system of the brain, the mind, is accumulated 

 after birth. 



The units that build up the Z-system of the brain 

 are supplied primarily just as the "food" for all the 

 rest of the dual system is supplied. We find then 

 according to the theory not only that the common 



