FEATURES AND HABITAT 219 



most harmoniously in a temperate climate. In 

 the soil, surface features and climate of a locality 

 there may exist stimulating or directing elements 

 which are too subtle to be detected in the present 

 state of our knowledge. This supposition is 

 strengthened by the closeness with which some 

 species of plants and animals are localized 

 within their habitats, and, even more, by the 

 replacement of one species by a closely related 

 species on the further side of a geographical 

 boundary line. In India, for instance, the black 

 francolin of the northern alluvial districts gives 

 place on the peninsular plateau to the painted 

 francolin : there are three varieties of hares, 

 each confined to its particular region : the Indian 

 peacock is in Burma replaced by a species in 

 which the green colour is more predominant. 

 These species differ from one another by pecu- 

 liarities of marking or colour which cannot be 

 directly associated with any feature of the 

 environment. Yet it is difficult to believe that 

 environal influences did not contribute to the 

 spread of these distinctions until they became 

 universal throughout the species. 



It follows that the features and characters of 

 the different races of mankind may, in great 

 measure, be the outcome of the environment in 

 which these races have lived during a long course 

 of generations : racial peculiarities that are now 

 innate and heritable may have been in the first 

 instance derived from soil, geographical features, 

 or climate. This theory will be strengthened if 

 we find that similar conditions, in widely separated 

 regions of the earth, are accompanied by similar 

 innate peculiarities of feature and disposition. 

 Around the globe a dark complexion is almost 

 invariably associated with a tropical sun. As a 

 rule it grows darker with approach to the equator, 



