26 UNIVERSITY OF COLORADO STUDIES 



mentally, and consequently that gained the ascendency, was man. 

 When he migrated he used fire, clothing, and shelter; he invented tools 

 and stratagems, and aided his fellows. He lived by his wits. As 

 man's intelligence increased and as he gained greater control over 

 nature, his body changed less, except such parts as are correlated with 

 intelligence (the cerebral hemispheres), which developed very rapidly. 



In addition to the correlation between the size of the cerebral hemi- 

 spheres and intelligence, there is another, viz.: between size of hemi- 

 spheres and period of helplessness after birth. The more intelligent 

 an animal, the larger its cerebral cortex, and also the longer the period of 

 infancy. 



Now, infancy has a double significance. It comes as the direct result 

 of increased cerebral capacity, and it affords a basis for learning by 

 experience. In the lower creatures with no cerebral development there 

 is but one course which the stimulus can take, and that is the course 

 phylogenetically open to it, the course through the lower centers. This 

 creature, devoid of such higher connections as the cerebrum affords, is 

 a reflex machine — an automaton. Development of the size of the 

 cerebrum means a multiplication of the number of cells in the brain 

 which may become connected with any stimulus. A creature with no 

 secondary brain has no infancy. It reacts the same as the parent to the 

 same stimulus. The infant possessed with a cortex does not make a 

 definite response, but the impulse is diffused throughout the various 

 possible channels afforded by the cortex. This is immediately a dis- 

 advantage, and the individual cannot survive unless cared for by the 

 adult parents. If the parents with large brains also possess the parental 

 instinct, their infants will survive, and the helplessness they manifest will 

 be the means of adapting them to their environment. 



If the impulse could go in but one direction, and thus give but one 

 element of response, the individual could never learn to discriminate 

 the difference between that and some other possible response. Where 

 the impulse is diffused, and produces consequently various elements of 

 response, the individual possessing them will have a basis for discrimi- 

 nating and, consequently, for valuing them. It is possible only at this 

 stage of development to become a hedonic creature. Pliability lies in 



