BIOMETRIC IDEAS AND METHODS 57 



is distinguished from other similar groups. In 

 making this statement there is, of course, no im- 

 plication that the facts set forth by the systematist 

 are not desirable and useful. But something more 

 is needed to gain a well-rounded, adequate idea of 

 the group, whether species, variety, or any other. 



It is a particular and fundamental point of 

 significance of biometry for biology that it offers 

 an adequate solution of just this problem of the 

 description of the group as a whole or a unit in 

 terms, not of its component individuals, but of 

 its own attributes and qualities. The biometrical 

 constants (mean, standard deviation, coefficient 

 of variation, etc.) are, within the limits of error of 

 random sampling, constants characteristic of the 

 group as such, and not of any particular individual 

 or individuals in it. So, further, the shape of the 

 variation curve for a particular group of organisms 

 is something definitely characteristic for the group. 



The fact that in statistical methods we have the 

 means of accurately describing the attributes of 

 groups or organisms as groups affords an oppor- 

 tunity of investigating why groups {i.e., species, 

 varieties, etc.) come to have the characteristics 

 which they do. It is the highest aim of the bio- 

 metrical study of variation to determine the bio- 

 logical causes which underlie the formation of 

 the particular sort of frequency curves which 

 actually are found, rather than some one of the 

 innumerable other sorts which might conceivably 



