THE GROWTH OF GROUPS 19 



by taxonomists as the identification marks of species. 

 The taxonomist holds that every individual animal is 

 of one species or of another. If this is true to-day it was 

 no less true in prehistoric times. If it is false it is time 

 some one exposed the fallacy. It is often ignored but 

 never called in question. Some persons who are un- 

 acquainted with the subject regard taxonomy as a vague 

 and unsatisfactory branch of biology. It is vague only 

 because the word species has been brought into it, and 

 various workers use the term differently. The cha- 

 racters are not vague, they are present or absent. If the 

 principles of taxonomy are true, namely, that every indi- 

 vidual belongs to a group and that each group has its 

 group marks, how can the groups undergo change except 

 by the addition and subtraction of the characters which 

 are their marks ? 



6. If we examine a large number of animals in respect 

 to a certain character which they have in common, we 

 shall see that the character is present in various degrees 

 in the different individuals. Those which possess it in 

 a particular degree, the mean amount, are more numerous 

 than others possessing it in greater or less degree. These 

 others are fewer and fewer in number, according as they 

 possess the character in a degree which is further and 

 further removed from the mean amount, both above and 

 below it. The name fluctuating variation was applied 

 to this phenomenon by De Vries. So far as I understand, 

 he regarded these departures from the mean as inheritable 

 but ineffectual in evolution. As it may be expressed, they 

 are ineffectual in the origin of species but effectual in 

 evolution. Other writers, following Johannsen, speak of 

 fluctuating variation as uninheritable, fortuitous occurrence 



