110 HEREDITY [OH. 



not absolutely perfect correlation between dark eye- 

 colour and dark hair suggests that similar factors 

 may perhaps be at work in both cases 1 . 



The inheritance of skin-colour in man is also one 

 of the cases which has hitherto defied Mendelian 

 analysis, and has been quoted more than once as 

 disproving the universality of Mendelian inheritance. 

 When a ' white ' European marries a negro, the off- 

 spring are 'mulattoes/ intermediate between the 

 parents. Mulattoes however are not all alike, some 

 have brown skins and some yellowish. When they 

 marry among themselves they are said never to 

 produce full blacks or full whites, but again mulat- 

 toes, who however vary in the depth of their colour. 

 When a mulatto marries a white, the ' quadroon' 

 offspring are lighter than mulattoes but usually 

 darker than Europeans ; there is evidence however 

 that they vary considerably, with possibly a certain 

 amount of discontinuity between the darkest and 

 lightest. Some evidence of segregation is also pro- 

 vided by the occasional instances of ' throw back' 

 to very dark skin and negroid features or hair among 

 children of apparently white people with some negro 

 ancestry. The whole problem however is very insuffi- 

 ciently known, and the difficulty of obtaining reliable 



1 In this connexion it may be mentioned that two recent writers 

 have maintained that the famous 'Habsburg lip' and the peculiar 

 Jewish physiognomy are Mendelian characters, the former dominant, 

 the latter recessive to the normal type. 



