l60 HUMAN BIOLOGY 



but their exact nature and degrees remain to be established. 

 There are, between the more distinct races at least, appar- 

 ently substantial differences in the higher psychical processes, 

 but they have not yet been precised; their study is much 

 comphcated by what are merely mental habits. 



The pathological racial differences are in the main those of 

 "predispositions" and immunities. They are mostly environ- 

 mental, and local rather than racial, in character. They 

 directly correlate but little with other racial features; but 

 in their indirect effects, survival or ehmination, range 

 among the basic factors in human evolution. Among patho- 

 logical conditions largely pecuhar to some races may be 

 mentioned the transient nutritional disorder in childhood 

 that leads to the frequent premature occlusion of the 

 sagittal suture, with consequent scaphocephaly, in the negro; 

 the pecuhar psychoses of the Malays; the neurasthenias, 

 various skin disorders, etc., among the whites; etc. 



The differences in all these Hues are in every human group 

 associated with astonishing similarities to identities, pointing 

 strongly to a common derivation of all the existing human 

 varieties. 



INSTABILITY 



All the racial characters, of whatever order, appear in 

 more or less wide ranges of individual and of group variation, 

 and the extremes of the group variation as a rule largely 

 overlap or interdigitate with those of other racial units. 



None of the characters in any group may be regarded as 

 wholly set and stable. A few examples will here suffice. 



Color 



Color oj Skin. In the "white" race the color of the skin 

 ranges from light bluish-white or pinkish, as in the Nordic 

 blond or red-haired, to all shades of tan (many Mediter- 

 raneans), or brown (some Arabs, Egyptians, Abyssinians, 

 etc.), to almost black (some Abyssinians, some Hindus). 



It varies from almost white to dark brown (solid chocolate) 

 in the Chinese and Japanese, from that of old leather to 

 dark brown in the American Indian. 



