THE INDIVIDUAL AND THE SPECIES 203 



The species, then, whether it is the systematic 

 group of the biological systems, or the elementary 

 species based on the study of variability and inherit- 

 ance, is an intellectual construction : an artifice 

 designed to facilitate our description of nature. This 

 is clearly the case with the higher orders of groups 

 in classifications : genera, families, orders, classes, and 

 phyla express logical relationships, or describe in a 

 hypothetical form our notions of an evolutionary 

 process. But species, it may be said, have an actual 

 reality : there are no genera in nature, only species. 

 These categories of organisms really exist ; they have 

 individuality, a certain kind of organic unity, inas- 

 much as the individuals composing them have de- 

 scended from a common ancestor. Yet just as much 

 may be said of genera, families, and the other groupings. 

 One species originates from another by a process of 

 transmutation : a genus is a group of species which 

 have all had a common origin ; a family is a similarly 

 related group of genera, and so on. The higher 

 categories of biological science are intended to intro- 

 duce order and simplification into the confusion and 

 richness of nature as we observe it, but obviously 

 the concept of the species has the same practical 

 object. Must we then say that there are no species 

 in nature, only individuals ? If so, we are at once 

 embarrassed by the difficulty of forming a clear notion 

 of what is meant by organic individuality. Does it 

 not indicate that life on the earth is really integral, 

 and that our analysis of its forms — species, genera, 

 families, and so on — are only convenient ways of 

 dealing actively with all its richness ? 



Systematic biology is a very matter-of-fact occupa- 

 tion, and one is surprised to find upon reflection how 

 he, in his handling of the concepts of the science, 



