



THE VARIATION OF ANIMALS 

 IN NATURE 



CHAPTER I 



INTRODUCTION 



The term variation is generally used in biology to connote 

 the differences between the offspring of a single mating or 

 between the individuals or groups of individuals placed in a 

 single species, subspecies, or race. It is sometimes used in a 

 more general way to connote, e.g., the differences between 

 genera and other groups above the rank of species (cf. Pel- 

 seneer, 1920 ; Gardner, 1925). The former usage, which is 

 more common and is regularly used in evolutionary, genetical 

 and taxonomic studies, is the one employed in this work. 



A division of the study of variation in animals according 

 to whether they are living under natural conditions or in 

 domestication is arbitrary from one point of view. We have 

 no reason to believe that either the origin of variation or its 

 mechanism of hereditary distribution is different in any essential 

 as between wild and domesticated animals. Nevertheless the 

 various procedures employed in the mating of domesticated 

 animals have, in the mixing or isolation of hereditary strains, 

 such different effects from the matings of animals in 

 nature that the distribution and evolutionary fate of variant 

 characters in domesticated and wild forms can rarely be 

 comparable. Whether the study of variation under domestica- 

 tion has the importance in evolutionary studies that Darwin 

 originally assumed is very doubtful : but if the study of 

 variation is to yield any results of value in assessing the causes 

 of evolution, it should primarily be conducted in natural 

 populations. 



