930 



"WHAT IS A SPECIES?" 



BY 



R. S. Hole, f.l.s., f.e.s. 



1. The introduction of the word species into natural history as the unit of 

 classification is due to Linnaeus, but there appears to be considerable difference 

 of opinion as to the exact meaning which he attached to the word. 



In the Origin of Species Darwin notes: "Nor shall I here discuss the 

 various definitions which have been given of the term species. No one defini- 

 tion has satisfied all naturalists ; yet every naturalist knows vaguely what he 

 means when he speaks of a species."* Clearly, then, an accurate idea of the 

 conception of a species, as generally entertained by naturalists from the time 

 of Linnaeus to that of Darwin, is not to be found in the literal inter- 

 pretation of the famous Linnean or of any other definition. 



2. From what we know of the knowledge possessed by aboriginal and 

 savage races, may we not safely infer that the principal facts regarding 

 natural history on which the Linnean definitions of species and variety were 

 primarily based, and which must have been accepted as true from a very early 

 period, were as follows : — 



(1) Numerous distinct kinds (or species) of plants and animals exist, which 

 can be readily distinguished by appreciable differences or characters. 



(2) Cultivating plants and breeding animals shows that, throughout the 

 Natural Kingdom, "like begets like", that, with plants, as with animals, 

 although the immediate offspring of any individual usually differ slightly 

 from their parents and each other, they, on the whole, invariably 

 resemble their parents and each other very closely. As the distinguish- 

 ing marks of each species are thus transmitted unchanged from parents 

 to their immediate offspring, the species appears to be fixed and constant. 



(3) As organisms which are known to be closely related invariably resemble 

 each other closely, it is inferred that organisms which are very much 

 alike must be nearly related. 



3. Must we not look to these ideas for an explanation of the fact that, in 

 the early days of natural history classification, a distinction was made be- 

 tween the so-called Artificial and Natural Systems, and also of the fact that the 

 system was called natural which resulted in all those organisms being placed 

 in the same group which, on the whole, resembled each other more than they 

 resembled any other organism, and which were therefore considered to be very 

 closely related ? May we not account for the species being selected by the 

 early systematists as the most convenient unit for classification in natural 

 history by the fact that it was recognized as the smallest unit which could be 

 readily distinguished from all other units, and which appeared to be fixed and 

 constant, the individuals included in the species being able to propagate their 

 like from generation to generation ? 



* Origin of Species, 6th Ed., p. 30. 



