THE GENESIS OF PERSONAL TRAITS 151 



These differences among men are too plainly marked to be over- 

 looked. The usual judgment is, however, that they are due to heredity. 

 This claim I will not argue; I shall merely show that the differences 

 lend themselves to another interpretation. As the mind goes through 

 successive stages in its development after conception, may not each 

 stage have an environmental complement which reacts on it and helps 

 or hinders its growth? In any case, when we examine the two con- 

 trasted physical types from this point of view, some claims may be made 

 as to their genetic meaning. The first type has been retarded early in 

 pregnancy ; the other at a later period. The retardation in the one case 

 may be due to defective nutrition or excessive sex excitation; in the 

 other it is perhaps the result of irritants in the mother's system. Facts 

 that make satisfactory evidence in support of these suppositions are hard 

 to obtain, but a justifiable theoretical position is taken by assuming 

 that, in the one case, the child is carried an abnormally long time in the 

 womb, while in the other birth is premature. 



To render my classification clear it is important to contrast the 

 stages in a child's development that occur before and after birth. The 

 prenatal stages are physical, and physical defects are cases either of 

 prenatal retardation or acceleration before birth. Postnatal develop- 

 ment, on the other hand, is mainly mental, and mental defects have 

 their origin in the association of ideas, which comes necessarily after 

 birth. This simple distinction students of development fail to make; 

 consequently, they confuse relations which would otherwise be obvious. 



Let me carry my contrast one step further. The sensory develop- 

 ment of a child is prenatal; the motor development is postnatal. The 

 delay of motor development is due to the fact that bones are needed to 

 serve as fulcrums on which the muscles act. These bones can not 

 harden until after birth. The head is formed before birth; the bones 

 solidify after birth. It is, of course, the difficulty of child-bearing that 

 causes the delay of motor development. The sensory stage precedes the 

 motor stage of growth by several years, and from this fact important 

 consequences follow. At birth the sensory powers are fairly complete. 

 The stomach is ready for food, and the circulatory system is active. 

 The early impressions of the child come from these sources alone; it 

 lacks the motor coordinations which make adjustment to the environ- 

 ment effective. Immediately after birth, all impressions are sensory, 

 and are bound together by mental associations in which there are no 

 motor elements. Such associations may easily become disjustive. 



The mental life of a child should be pictured as arising from the 

 activity of a number of partially organized psychic centers. Each center 

 has stored up some latent energy which becomes active when adjacent 

 centers are aroused. A stimulus started by any external disturbance 

 excites these centers to activity with the result that a mental impression 

 is formed. A succession of these arousals fix definite grooves along 



