THE RAGES OF MAN. 225 



reduced size of the jaws from lessened use the habitual 

 play of different muscles serving to express different emo- 

 tions and the increased size of the brain from greater 

 intellectual activity have together produced a considerable 

 effect on their general appearance when compared with 

 savages. * Increased bodily stature, without any corre- 

 sponding increase in the size of the brain, may (judging 

 from the previously adduced case of rabbits), have given 

 to some races an elongated skull of the dolichocephalic 



Lastly, the little understood principle of correlated de- 

 velopment has sometimes come into action, as in the case 

 of great muscular development and strongly projecting 

 supra-orbital ridges. The color of the skin and hair are 

 plainly correlated, as is the texture of the hair with its 

 color in the Mandans of North America. \ The color also 

 of the skin and the odor emitted by it are likewise in some 

 manner connected. With the breeds of sheep the number 

 of hairs within a given space and the number of the ex- 

 cretory pores are related.^ If we may judge from the 

 analogy of our domesticated animals, many modifications 

 of structure in man probably come under this principle 

 of correlated development. 



We have now seen that the external characteristic differ- 

 ences between the races of man cannot be accounted for in 

 a satisfactory manner by the direct action of the conditions 

 of life, nor by the effects of the continued use of parts, 

 nor through the principle of correlation. We are there- 

 fore led to inquire whether slight individual differences, to 

 which man is eminently liable, may not have been pre- 

 served and augmented during a long series of generations 

 through natural selection. But here we are at once met 



*See Prof. Schaaffhausen, translat., in "Anthropological Review," 

 Oct., 1868, p. 429. 



fMr. Catlin states (" North American Indians," 3d edit., 1842, vol. 

 i, p. 49) that in the whole tribe of the Mandans, about one in ten or 

 twelve of the members, of all ages and both sexes, have bright sil- 

 very gray hair, which is hereditary. Now this hair is as coarse and 

 harsh as that of a horse's mane, while the hair of other colors is fine 

 and soft. 



JOn the odor of the skin, Godron, " Sur 1'Espece," torn ii, p. 217. 

 On the pores in the skin, Dr. Wilckens, " Die Aufgaben der Land- 

 wirth. Zootechnik," 1869, s. 7. 



