316 Correspondence . 



Auk 

 April 



CORRESPONDENCE 



IDENTIFICATIONS. 



(Characters vs. Geography). 



Editor of 'The Auk'; 



We are between two horns of a dilemna. On the one hand, vide Dr. 

 Dwight, how can we verify a specimen as subspecies "x" unless it carries 

 the distinguishing marks by which "x" is characterized? Subspecific 

 and other similar distributions must be founded upon observed differences 

 in specimens; to reverse the process and identify specimens geographically 

 without regard to characters neither adds to nor verifies existing knowledge 

 and is reasoning in a vicious circle. It can confirm error but never correct 

 it. 



On the other hand, as Dr. Grinnell points out, taxonomic relationship 

 descends genetically. An individual is form "y" because it comes of "y" 

 parentage, not because it happens to show certain peculiarities of form or 

 color. Just as distribution maps must be based upon exhibited characters, 

 so genesis is more fundamental than appearance or form which manifes- 

 tations may at any time be obscured by atavism, mutation or migration. 

 The very fact that a certain subspecies exists in some part of a specific 

 range is indicative that it is a possible variation in that species and sug- 

 gests a certain tendency in that direction latent in every individual of 

 that specific form. We can therefore expect, every now and then, to 

 find individuals of pure "x" blood resembling, in varying degree, "y" of 

 the same species. To name such a specimen "y" is as logical as calling 

 a Viceroy butterfly a Monarch because it superficially resembles one. 

 On these points, Dr. Grinnell is as sound as Dr. Dwight is on his. 



The flaw in Dr. Grinnell's reasoning is however in his advising the geo- 

 graphical identification of aberrant specimens on the assumption that 

 genetic and geographical relationship are synonymous. Dealing with 

 stationary forms of life, such as plants, proximity of station is only strong 

 presumptive evidence of genetic affinity. With mobile birds such proba- 

 bility is tremendously reduced. With Scissor-tailed Flycatchers from 

 Hudson Bay and Black-capped Petrels from the Mississippi Valley it is 

 evident that community of association is only presumptive of community 

 of descent and that geography is an uncertain guide to identification. 



Dr. Grinnell pleads for the exercise of "the judgment based upon experi- 

 ence ■ — just as is needed in any other advanced field of knowledge." No 

 one will quarrel with him over the value of this necessary qualification of 

 decision. The only question is where shall it be used? Is not the first 

 duty of the scientific investigator the elimination of the human equation 

 in the statement of fact? In the deductions drawn therefrom full scope 



