24 THE GROWTH OF GROUPS 



jcrdoni. Groups such as these will be dealt with in 

 this book, but no limitation will be placed upon the 

 number of the characters which are special to the various 

 groups, they may be one or many ; and no limit will 

 be placed upon the number of the individuals in the 

 groups. 



Before leaving the subject of place variation, we will 

 consider as a further example, the colour of the human 

 skin. The amount of pigment in the skin of man in- 

 creases steadily from northern latitudes towards the 

 equator. In India, races which are reputed to have 

 arrived after the aborigines are less dark than they. 

 Human pigment therefore appears to be different in 

 its mode of occurrence from that which is found in mela- 

 notic animals. The former appears in innumerable 

 degrees and is dependent somehow upon the sun's rays. 

 The latter does not occur in many degrees nor is it related 

 to any known physical condition. This difference cannot 

 be overlooked. The black sheep in every fold is pro- 

 verbial, but human beings with dark brown skins are 

 never born of white parents unless a coloured person 

 was admitted into the line. One of the first and most 

 convincing arguments in favour of the discontinuity of 

 evolution is that species are discontinuous while environ- 

 mental change, from place to place, is usually not so. 

 There are gaps in the living series, but not in the environ- 

 ment, as a rule. But latitude and human pigmentation 

 are an exception to this rule, as no doubt others have 

 pointed out. There is no gap in latitude from the poles 

 to the equator, nor is there a gap between the fairest 

 white man and the blackest negro. There is, however, 

 a sharp gap between the melanotic varieties and their 



