shells 



shells 





15 rays 16 rays 17 rays 18 rays 19 rays 



American Museum of Natural History 



Number per 1000 

 150 



150 



145 

 men 



110 



100 



90 

 men 



90 

 80 

 70 

 60 



57- 

 men 



50 

 40 



34 _ 



men 



30 



16 20 



men 



,10 



ill! 



ii 



■ 



R I 



■ 



E 



K 



"IIS 



ill 



ill 



I i » i « < 



: s I s 



IS IS 



7 " 



men 



il ill I 



:f1 1 In 



60 62 64 66 68 70 72 

 Height in inches 



74 



100 



65 



38 



men 



19 



men 



9 

 men 



6 



men 



THE NORMAL DISTRIBUTION OF VARIATIONS 



In any large sample of natural objects the variations fall into a regular pattern. 

 More than half the men in our army are within two inches of the "average height". 

 Only about a tenth are three inches taller than the average, and about the same 

 number are three inches shorter. The number in each stature-group declines as we 

 assemble groups of taller and taller or shorter and shorter men. If we arrange scal- 

 lops according to the number of ridges, or rays, or if we arrange earthworms accord- 

 ing to the number of rings, we find similar "curves of distribution" 



This fact of regularity furnishes a basis for a new kind of norm. It is 

 not enough to say that one is thicker or thinner than the "average". We 

 want to know how much thicker or thinner, or in what part of the range 

 of variation a particular individual stands, or how near to one or the other 

 extreme. 



Human beings probably differ from one another in more ways than the 

 individuals of any other species. At the same time, each of us is sensitive 

 about being "different". Many of us feel a constant struggle between the 

 desire to be distinctive, to stand out on our own, and the fear of being dif- 

 ferent. This is because our population is itself a mixture of many races and 

 groups that are but slowly learning to live with strangers. The most uni- 

 form objects of the same kind are the products of modern machinery — like 



69 



