72 — 

 68 — 

 64 — 

 60 -t 



B 



10 



15 20 



23 

 1 



30 35 40 



45 



50 55 60 65 70 75 80 85 90 95 100 



VARIATION IN STATURE 



When 100 boys of the same age stood in a row in the order of height, the tops of 

 their heads formed a line like this row of dots. The middle part of the line was nearly 

 horizontal; that is, there were several boys of almost exactly the same height 



have fine, silky hair; the hair of others is coarse. The hair of some is 

 straight; that of others is wavy, curly or kinky. Rarely do we find two indi- 

 viduals with exactly "the same kind" of nose or mouth or ears or chin or 

 cheeks or lips. 



Chemical Differences Skin-colors distinguish the large groups we call 

 "races" — Caucasian, Mongolian, Negro, redskin, and so on. Color differ- 

 ences usually indicate chemical differences. There are, in fact, several dis- 

 tinct pigments in the human skin, hair and iris, and in corresponding parts 

 of other animals. And these pigments are present in varying proportions. 

 Even within any one "race" there are wide variations in the colorings, as 

 well as in the intensity of pigmentation. 



A person who has had the measles is usually unable to get that disease 

 again: he is said to be immune. This change does not show in one's appear- 

 ance, but is due apparently to some chemical alteration in the blood or in 

 other juices of the body. People differ also in their original immunity, or 

 resistance to disease. Thus, when two individuals are exposed to typhoid 

 fever, one may remain unaffected while the other gets sick. On the other 

 hand, one who is immune to typhoid may succumb to tuberculosis. Such 

 facts indicate chemical differences among people. 



Each of us knows some individual who suffers from asthma or hay 



VARIATION IN FACIAL FEATURES 



Whether we consider the form of any feature, such as the nose, mouth or chin, or 

 the color of hair or eyes, or any other trait, we find endless variations in countless 

 details 



63 



