248 THE DESCENT OF MAN. Part I. 



jecting supra-orbital ridges. It is not improbable that 

 the texture of the hair, which differs much iu the dif- 

 ferent races, may stand in some kind of correlation with 

 the structure of the skin ; for the colour of the hair 

 and skin are certainly correlated, as is its colour and 

 texture with the Mandans. 53 The colour of the skin 

 and the odour emitted by it are likewise in some man- 

 ner connected. With the breeds of sheep the number 

 of hairs within a given space and the number of the 

 excretory pores stand in some relation to each other. 54 

 If we may judge from the analogy of our domesticated 

 animals, many modifications of structure in man pro- 

 bably come under this principle of correlated growth. 



We have now seen that the characteristic differences 

 between the races of man cannot be accounted for in a 

 satisfactory manner by the direct action of the condi- 

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

 parts, nor through the principle of correlation. We 

 are therefore led to inquire whether slight individual 

 differences, to which man is eminently liable, may 

 not have been preserved and augmented during a long 

 series of generations through natural selection. But 

 here we are at once met by the objection that beneficial 

 variations alone can be thus preserved ; and as far as 

 we are enabled to judge (although always liable to 

 error on this head) not one of the external differ- 

 ences between the races of man are of any direct or 



53 Mr. Catlin states (' N. American Indians,' 3rd edit. 1842, to] . 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 silvery grey hair, 

 which is hereditary. Now this hair is as coarse and harsh as that of 

 a horse's mane, whilst the hair of other colours is fine and soft. 



54 On the odour of the skin, Godron, ' Sur 1'Espece,' torn. ii. p. 217. 

 On the pores in the skin, Dr. Wilckens, ' Die Aufgaben der landwirth. 

 Zootechnik,' 1869, s. 7. 



