AMERICAN 
JOURNAL OF BOTANY 
Vol. X May, 1923 No. 5 
THE SPECIES CONCEPT FROM THE POINT OF VIEW 
OF A GENETICIST 1 
George H. Shull 
Classification is a fundamental characteristic of scientific work in every 
field, and recognition of the fact that plants and animals may be described 
and discussed in group terms was doubtless the earliest manifestation of 
biological science. The advantages to every branch of biology of having 
group descriptions designated by brief names, which pass current in the 
language of all civilized peoples, is so manifest as to make the statement of 
the fact little more than a platitude. Indeed, the grouping of individuals 
into definitely limited categories whose names are common to all languages 
may be likened in its importance to the discovery of language itself. It 
provides the means of intercommunication, not only among biologists, but 
between biologists and humanity in general. 
In order that this primary function of biological classification, as a 
basis of effective intercommunication, may be fulfilled, it is important that 
the limitations of the categories be such as may be capable of observation 
and comprehension by those among whom intercommunication is to be 
established or maintained. It seems, therefore, that the proper basis for 
classification is intimately related to the question of convenience. A 
consideration of all the different grades of classification: kingdoms, phyla, 
orders, families, genera, species, subspecies, forms, etc., etc., shows that the 
species represents the simplest concept, and it is therefore the one best 
adapted to serve as a vehicle of general communication. 
Species may be defined as the easily recognized kinds of organisms, and 
in the case of macroscopic plants and animals their recognition should rest 
on simple gross observation such as any intelligent person can make with 
the aid only, let us say, of a good hand-lens. Genera, families, and higher 
orders of classification belong rather to biological philosophy, while the 
subspecific categories represent refinements which are of interest only or 
chiefly to specialists. In other words, species belong to biological “Main 
Street,” and their chief usefulness lies in the very fact of the ease and 
definiteness with which they may be recognized. 
1 Read in the symposium on “The Utility of the Species Concept,” at the joint meeting 
of Section G of the American Association for the Advancement of Science, the American 
Phytopathological Society, and the Botanical Society of America, at Toronto, December 
28, 1921. 
[The Journal for April (io : 167-220) was issued April 18 , 1923]. 
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