VARIATION AND HEREDITY 15 



color (rod) docs not ('omj)l('t('ly doiiiiiialc iln' oilier. In 

 this case the impure dominants show a color (pink) which 

 is a blend of the colors of the ])arental generation. 



This remarkable mode of inheritance has been dem- 

 onstrated to hohl for a great diversity of organisms: 

 in mice, rats, rabbits, guinea pigs, cattle, poultry, 

 canaries, snails, silk-moths ; in beans, maize, wheat, bar- 

 ley, and stocks. In cattle, for example, hornlessness is 

 llie dominant and presence of horns the recessive char- 

 acter. In wheat, rough and red chaff are the dominant 

 and smooth and white chaff the recessive characters.^^ 



It is difficult to draw definite conclusions from the study 

 of human inheritance on account of the great complexity 

 of the human organism. Man is the result of the inter- 

 luixture of so many different stocks that there are no 

 "pure lines." Since experiment is out of the question, 

 observation must be relied upon. But the rate of in- 

 crease of the human species is slow (about 60 generations 

 of men since the Christian era began), and the number of 

 offspring are few. In spite of these difficulties studies 

 have been made wit1i the result that certain human traits 

 appear to be inherited in accordance with Mendelian 

 proportions. ^2 For example, ^^ — 



Curly hair, dominant. Straight hair, recessive. 



Dark hair, Light to red hair, 



Brown eyes, Blue eyes, 



Normal pigmentation. Albinism, 



Polydactyly, Normal, 



Hereditary cataract. Normal, 



Normal nervous system, Hereditary feeble-raindedness, 



insanity, epilepsy, etc. 



11 Thomson &. Geddes, op. cit., p. 132. 



1:2 Boas, F.—The Mi)id of Primitive Man. l!tll, p. 78. 



13 Davenport, C. B. — Heredity in Rehition of Ku;ienies, ]^\^. .Tl, fifi. 77. 175. 



