CHAPTER III. 



OF SPECIES AMONG LIVING BODIES AND THE IDEA THAT WE 

 SHOULD ATTACH TO THAT WORD. 



It is not a futile purpose to decide definitely what we mean by the 

 so-called species among living bodies, and to enquire if it is true that 

 species are of absolute constancy, as old as nature, and have all existed 

 from the beginning just as we see them to-day ; or if, as a result of 

 changes in their environment, albeit extremely slow, they have not 

 in course of time changed their characters and shape. 



The solution of this question is of importance not only for our 

 knowledge of zoology and botany, but also for the history of the 

 world. 



I shall show in one of the following chapters that every species has 

 derived from the action of the environment in which it has long been 

 placed the habits which we find in it. These habits have themselves 

 influenced the parts of every individual in the species, to the extent 

 of modifying those parts and bringing them into relation with the 

 acquired habits. Let us first see what is meant by the name of species. 



Any collection of like individuals which were produced by others 

 similar to themselves is called a species. 



This definition is exact ; for every individual possessing life always 

 resembles very closely those from which it sprang ; but to this definition 

 is added the allegation that the individuals composing a species never 

 vary in their specific characters, and consequently that species have 

 an absolute constancy in nature. 



It is just this allegation that I propose to attack, since clear proofs 

 drawn from observation show that it is ill-founded. 



The almost universally received belief is that living bodies con- 

 stitute species distinguished from one another by unchangeable 

 characteristics, and that the existence of these species is as old as 

 nature herself. This belief became established at a time when no 

 sufficient observations had been taken, and when natural science 



