PREFACE 



Two classes of people have been in mind in the preparation of 

 this text, viz. the student of agriculture in the college and experi- 

 ment station and the practical breeder upon the farm. Both need 

 to know all that evolution has to teach of methods that may be 

 employed in still further adapting to our needs such animals and 

 plants as have been domesticated because of their valuable natural 

 qualities. 



The general purpose has been first of all to define the problems 

 involved in animal and plant improvement ; to free the subject 

 from the prejudice and tradition that have always befogged it ; 

 to bring to the study whatever facts are fully known to biological 

 science ; to recognize and define somewhat clearly the present 

 limitations of knowledge, and to indicate as well as may be the 

 directions from which further and much-needed light is most 

 likely to come. Last of all and more than all, it has been the 

 purpose to encourage, and if possible induce, more exact methods 

 of study and of practice than have hitherto characterized this 

 branch of agricultural science. 



It is yet too early to prepare an ideal treatise upon this most 

 intricate subject, and no one is more conscious than the author 

 of the many deficiencies and shortcomings of this attempt. Some 

 effort, however, is surely needed at this time to clear the atmos- 

 phere, to give the student_pf agrjtffll| at least a rational point 

 of view, and to bring M^Bito wBHKship with those who are 

 earnestly studying biol^^Bl problems and through whose efforts 

 these vexed questions ^^^ure sooner or later to find a solution. 

 This, together with the^ressing need of a text in his own class 

 room, is the author's only warrant for the present volume. 



No new theories of evolution are proposed. The chief object 

 has been to distinguish what is known from what is merely tradi- 

 tional ; to give as much as possible, within the limits of available 

 space, of the best established facts bearing upon this subject ; to 



