

CHAPTER XIV 

 WHAT IS A SPECIES? 



BEFORE proceeding further we must consider the 

 basic unit in terms of which the animal world 

 is measured. This basic unit is the so-called 

 species. In everyday language a species is a distinct 

 kind or sort of animal. 



The accepted definition of a species is an assemblage 

 of individuals which agree with each other in form, 

 size, color and in other characters, in one or more of 

 which they constantly differ from related assem- 

 blages of individuals; which normally and freely 

 interbreed; and which transmit to their offspring their 

 proper characters unchanged, or with that little modi- 

 fication which is due to conditions of environment. 



While technically correct, this definition is decep- 

 tive. It is simply a broadening of the definition of an 

 individual. It contemplates primarily material in 

 museum collections and is based almost entirely upon 

 the vertebrates, especially birds and mammals. It 

 scarcely applies to other forms of life even as repre- 

 sented in museums. 



What, then, is a species? That is difficult to say, 

 for the different kinds of animals vary very greatly in 

 the interrelationships of the included individuals, and 

 in their relations to allied types. 



Each species is always separate and distinct from 

 every other species. But a species is not a static 



