INTRODUCTION 3 



would constitute no exception to the rule that a man must real- 

 ize the fruit of his own labors and in his own generation, for 

 breeding is a business and must be made to pay. The breeder 

 must therefore work faster than nature, and thremmatology can- 

 not make use of a leisurely operating evolutionary principle unless 

 its action can be accelerated or its cumulative effects exaggerated. 

 Yet again, man cannot afford the immense numbers and the whole- 

 sale destruction that characterize nature's methods of working 

 changes. Animals and even plants cost money, and a relatively 

 large proportion must meet the conditions, or the enterprise must 

 be abandoned. 



Business considerations therefore set arduous limitations upon 

 thremmatology in respect to both time and numbers from which 

 evolution in general is entirely free. The breeding business has 

 its own particular problems, some of the most important of which 

 unfortunately the known facts of evolution are least able to 

 answer. The profitable study of this subject will, however, be 

 assisted by a clear statement of these problems. 



The problems of the breeder. Certain questions stand clearly 

 out in the minds of practical breeders, and though an attempt 

 to answer them seriatim would not be the best method of study, 

 and though some of them cannot be answered with certainty 

 in the present state of knowledge, yet nothing is of more con- 

 sequence at the outset than that the student get a clear idea of 

 the problems needing solution and towards whose solution the 

 study of thremmatology is directed. They are substantially as 

 follows : 



To what extent are the characteristics of an individual at matur- 

 ity due to its ancestry (heredity), and to what extent are they 

 due to the conditions of life (environment), such as food, climate, 

 exercise, and general care during development ? 



Are the influences of the conditions of life limited to the indi- 

 vidual or are they in certain instances and to some extent carried 

 over upon the offspring ? that is, are the effects of environment 

 inherited ? 



Can variations be directly controlled to any extent whatever, 

 or only indirectly through selection and by special care during 

 development ? 



