206 Mendelian Heredity in Man [CH. 



shire village and comparing them with their parents, the 

 type in which pigment is present on the front of the iris is 

 a dominant, the absence of such pigment being recessive. 

 When the pigment is present in some quantity the eye is 

 called brown or black, while when it is absent the eye is 

 called blue or grey. In general terms therefore it may be 

 said that brown eyes are dominant to blue eyes. Careful 

 examination however shows that many eyes which might 

 on a hasty glance be called blue really have some of the 

 characteristic pigment. Casual descriptions therefore made 

 by use of the popular names for the colours are quite 

 unreliable, and the propositions based on them can only be 

 received with great caution. Some further details and 

 pedigrees are given in the Chapter on Eye-Colour (see 

 p. 108). 



With respect to hair-colour in our own population 

 nothing can yet be said with much confidence. The segre- 

 gation of red hair from black hair may be seen in many 

 families and this red is presumably a recessive, but to work 

 out the interrelations of hair-colours in general would be 

 a very difficult undertaking*. Just as in the case of eye- 

 colours, so here, the attempt to force the various colours 

 into a continuous colour-scale and to classify the material 

 by reference to that scale is useless ; for though probably 

 intermediates could be found existing in such gradations as 

 to bridge the gaps between the more distinct types, there 

 cannot be the least doubt that so soon as a strict method of 

 analysis is instituted the various intermediates will be shown 

 to be caused by the interactions of a limited number of 

 definite factors. (See Intermediates, Chap, xin.) In the 

 analysis of such phenomena research must proceed by the 

 detection of the pairs of factors, beginning with the more 

 obvious, and when their behaviour and powers are thoroughly 

 understood, a search for the remainder may be attempted. 



The fact of continuous descent through many genera- 

 tions creates a probability that several notorious family 

 characteristics, such as the Hapsburg lip and many more 

 which could be cited, would prove on examination to be 

 dominants, but the evidence for a proper analysis has not 



* Cp. Hurst (162). 



