THE EVOLUTION OF LIVING BEINGS. 45 



nombre' ' . But this does not away with the fact that a spe- 

 cies, in as much as it consists mostly of a number of in- 

 dividuals, usually itself is a group. It is true that by 

 the identity of the constitution of the individuals 

 which compose it, it remains capable of being considered 

 as an entity, but this way of looking at a species, con- 

 sisting of more than one individual, is dangerous be- 

 cause it leads, almost unconsciously, to the unwarranted 

 conclusion that all the individuals of one species must 

 necessarily be the offspring of a single initial pair of 

 identical constitution, in one word, that species must 

 necessarily be monophyletic. Now this is unwarranted, 

 because the constitution of an individual depends ex- 

 clusively on the constitution of the gametes, from who- 

 se union the individual sprang, and is independent 

 of the source of these gametes. Therefore, if iden- 

 tical gametes can be obtained from different sour- 

 ces — and we will see in later chapters, that they 

 can — species need not necessarily have a monophyletic 

 origin. 



Such a polyphyletic species, though it, by the iden- 

 ty of the constitution of the individuals composing it, 

 remains capable of being considered as an entity, yet 

 is at the same time not only a group, but even a 

 group of individuals of different origin. 



Consequently the real difference between a species 

 on the one side and a Linneon or a genus on the other 

 side, is not so much that the one may be, and the other 

 must be a group, but is that a species is either a special- 

 ly constituted individual, always homozygotic, or a 

 group of such individuals of identical constitution, 



