124 SOCIAL EVOLUTION 



those of skilled laborers, members of the mercantile class 

 and of the professional class. But these changes of 

 stature are not to be interpreted as changes in type. It 

 is better to regard them as due to the elimination of re- 

 tarding influences which prevent many individuals from 

 attaining their normal growth. 5 



The retarding and accelerating influences of physical 

 environment often bring about very considerable changes 

 in anthropometric traits during the period of growth. 

 Professor Boas says, "Setting aside the prenatal de- 

 velopment, we find that at the time of birth some parts 

 of the body are so fully developed that they are not far 

 removed from their final size, while others are quite un- 

 developed. Thus the skull is, comparatively speaking, 

 large at the time of birth, grows rapidly for a short time, 

 but very soon approaches its full size, and then continues 

 to grow very slowly. The limbs, on the other hand, grow 

 rapidly for many years. Other organs do not begin their 

 rapid development until much later in life. Thus it 

 happens that retarding or accelerating influences acting 

 upon the body at different periods of growth may have 

 quite different results. After the head has nearly com- 

 pleted its growth, retarding influences may still influence 

 the length of the limbs. The face, which grows rapidly 

 for a longer period than the cranium, can be influenced 

 later than the latter. In short, the influence of environ- 

 ment may be the more marked, the less developed the 

 organ that is subject to it." An important consequence 

 of this for the sociologist is that the retardation seems 

 to be lasting. "In other words, a retardation in develop- 

 ment is never completely made good by long-continued 

 development." 7 It has been demonstrated by the in- 



5 Boas, ibid. Hid., pp. 47-48. ^ Ibid. 



