GENETIC TYPE AND THE ENDOCEINES 35 



influenced by the environmental conditions of climate and 

 food under which they exist. 



With our present knowledge of the influences of slight 

 dietary deficiencies and of light and other climatic condi- 

 tions on growth and development, and the modifications which 

 take place in habit and form as well as fecundity of wild 

 species when transplanted from one part of the world to 

 another, the degeneracy of breed types among imported dogs 

 is not surprising. No doubt much is to be learned from 

 careful study of such reactions. 



In discussing the origin of dog breeds, Darwin stated more 

 clearly than in any other connection his ideas of the possible 

 origin of species, through mutations, use-inheritance and se- 

 lection. He states: 



"Some of the peculiarities characteristic of the several 

 breeds of dog have probably arisen suddenly, and, though 

 strictly inherited, may be called monstrosities; for instance, 

 the shape of the legs and body in the turnspit of Europe and 

 India; the shape of the head and the under-hanging jaw in 

 the bull- and pug-dog, so alike in this one respect and so 

 unlike in all others. A peculiarity suddenly arising, and 

 therefore in one sense deserving to be called a monstrosity, 

 may, however, be increased and fixed by man's selection. We 

 can hardly doubt that long-continued training, as with the 

 greyhound in coursing hares, as with water-dogs in swimming 

 and the want of exercise, in the case of lapdogs must have 

 produced some direct effect on their structure and instincts. 

 But we shall immediately see that the most potent cause 2 of 

 change has probably been the selection, both methodical and 

 unconscious, of slight individual differences, the latter kind 

 of selection resulting from the occasional preservation, during 

 hundreds of generations, of those individual dogs which were 

 the most useful to man for certain purposes and under certain 

 conditions of life." (p. 40, v. 1.) 



In the absence of modern knowledge of mutations and the 

 mechanism of inheritance this statement of 60 years ago is 

 remarkable in parts and completely out-dated in others. The 

 origin and inheritance of the legs of the turnspit and the 



2 Italics supplied. 



