6 
JOURNAL OP MAMMALOGY 
CRITERIA FOR THE RECOGNITION OF SPECIES AND 
GENERA 
By C. Hart Merriam 
In systematic work among animals and plants one is continually 
confronted by the theoretical question: what shall constitute the 
grounds for the segregation of forms into subspecies, species, sub- 
genera, genera, and higher groups; and by the practical question of 
drawing dividing lines between the groups recognized. And in exam- 
ining series of closely related species from different localities, one is 
often confronted by specimens that differ from the previously known 
forms, so that it becomes necessary to ascertain whether the observed 
peculiarities are genuine characters or merely individual variations. 
If they are exhibited by several specimens and it is known that these 
specimens came from the same area, the inference is that they represent 
a form worthy of recognition by name. And if the differences are com- 
paratively slight — not of sufficient importance to be accorded full spe- 
cific rank — it is customary to assume the existence of intergrades and 
call the form a geographic race or subspecies. 
Dividing lines are now drawn much finer than formerly, and in many 
cases it is difficult to make up one’s mind whether to treat a particular 
form as a species or a subspecies. When this has been decided, the 
result is usually published and the matter dismissed. But the next 
time the author has occasion to discuss the group, he is likely to find 
that his viewpoint has changed, or that additional specimens give the 
case a different aspect, so that the status of the form as previously 
published requires readjustment. The author himself may make the 
change, but if not, some other writer may be counted on to do it for 
him. In other words, irrespective of the stability or worth of the form, 
its RANK is subject to change. This may be due to information afforded 
by additional material, or to an altered point of view on the part of 
the author — for we must remember that after all we ourselves are the 
scales on which zoological characters are weighed, and that unhappily 
we have no ‘Bureau of Standards’ to adjust the balances of our 
judgment. 
For guidance in deciding whether a form shall be treated as a full 
species or a subspecies, two diametrically opposite methods have been 
advocated — one based on the presence or absence of intergrades, the 
other on the degree of differentiation of the form in question. While 
