RECENT PROGRESS 



IN THE STUDY OF VARIATION, 



HEREDITY, AND EVOLUTION 



CHAPTER I 



INTRODUCTION 



THE present volume deals with variation and inheri- 

 tance in plants and animals, especially in so far as 

 those subjects bear upon the problem of the origin of 

 species. By inheritance we mean those methods and 

 processes by which the constitution and characteristics 

 of an animal or plant are handed on to its offspring, 

 this transmission of characters being, of course, asso- 

 ciated with the fact that the offspring is developed by 

 the processes of growth out of a small fragment de- 

 tached from the parent organism. The term ' varia- 

 tion,' on the other hand, includes a number of different 

 phenomena which will be described at greater length 

 as the work proceeds ; but, broadly speaking, we may 

 say that the study of variation is concerned with the 

 circumstance that members of the same species are 

 not all alike, and more particularly with the fact that 



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