2i6 Changing Human Nature 



tions. It was assumed that the ratio of head width to head 

 length, of hmb length to stature, of chest girth to height, 

 and other proportions, are characteristic of races. With the 

 accumulation of more and more data, it became increasingly 

 difficult to maintain the fixity of race characteristics in such 

 terms. At the same time the accumulation of these records 

 made it perfectly clear that the size of the body, the propor- 

 tions of the limbs, the shape of the head, the form of the face 

 and other features of human beings, are constantly chang- 

 ing. These measurements applied to a large body of Ameri- 

 cans, descendants of immigrants, showed decided changes of 

 ** type," when compared to similar measurements for the 

 parental stocks. In the same way, the descendants of Span- 

 iards in Porto Rico showed decided changes in these pro- 

 portions and shapes. Similar studies had been made in 

 Germany, showing fairly constant differences between the 

 measurements of city dwellers and those of rural populations. 

 Some students attributed these differences to selection; that 

 is, it was supposed that certain types tend to move to 

 the cities, whereas other types tend to remain in the 

 country. But whether we consider the results due to selec- 

 tion or to the direct influences of environment, it is clear 

 enough that the constitution of a population does actually 

 change. 



These facts of physical anthropology are in every way 

 parallel to observations made upon domestic animals and 

 upon wild animals in captivity. The head-form and size of 

 skull, as well as size of the body and proportions of limbs, 

 have been found to change in cattle, in horses, in dogs and 

 cats, in lions and rats. 



Human Variability 



Within a given population every detail of structure in 

 human bodies shows a wide range of variations. We have 

 already seen that stature illustrates the so-called normal dis- 

 tribution (page 159), a characteristic of the chance opera- 



