200 SCIENCE PROGRESS 



brain. The decrease in prognathism is obviously associated 

 with the degree and duration of civilisation, so that this char- 

 acter in negroes and Australians is adaptive. Perhaps the same 

 may be said of the extreme dolichocephaly associated with a 

 sloping forehead in the same races ; but we cannot say that the 

 men with the shortest skulls are the most civilised, for some of 

 the least civilised Mongolians are more brachycephalic than the 

 English. In my opinion there is good evidence that dark or 

 black skin-colour is correlated with the light and heat of the 

 tropical sun. It may be objected to this that the American 

 Indians of the tropics are not black like the negroes ; but I 

 believe they are considerably darker than those of the north. 

 At any rate, we have the following facts : that no very dark 

 race occurs in temperate climes either north or south, that the 

 negroes of equatorial Africa are distinctly darker than the 

 Bantus and Hottentots of South Africa, and that the negroes 

 of North America have become lighter since their importation. 



I have sometimes thought that perhaps modifications due to 

 stimuli might differ from mutations in not exhibiting Mendelian 

 segregation ; but the evidence, so far as we have any, is con- 

 tradictory, for, while crossing of negroes with whites always 

 gives intermediates in all degrees of mixture, we have a con- 

 stantly repeated segregation when dark whites and fair whites 

 interbreed. Eimer mentions this as especially conspicuous in 

 South German villages, where the inhabitants continually inter- 

 marry, and yet pure blondes and dark children occur constantly 

 in the same family. This may not be typical Mendelism, for 

 we do not find dominance in the heterozygote ; it may be a 

 case of alternate dominance, and we do not know whether 

 segregation takes place. 1 There are, however, many race 

 characters which seem to be evidently mutations, since there 

 is no evidence that they are useful or due to external conditions. 

 As examples of these, we may mention the character of the 

 hair with regard to curling, the direction of the eye-aperture, 

 the prominence of the nose. We have little precise evidence 

 concerning Mendelian inheritance in these. Mr. Mudge pub- 

 lished lately some data concerning the inheritance of such 

 features in crosses between Canadian Indians and Europeans ; 



1 Mr. C. C. Hurst has recently shown that dark eyes of any shade are dominant 

 to blue eyes, and that the two characters segregate in Mendelian fashion {Proc. 

 Roy. Soc. 1908). 



