GEOGRAPHICAL RACES 
5 
The value of these divisions — that is, the amount of differentiation 
sufficient to raise a group of genera to a family, or a collection of families 
to an order — is a matter for experienced individual decision, as there is no 
authoritative ruling upon the subject. However, there has gradually 
grown up an approximate agreement on this subject, though the constant 
tendency among specialists has been to make finer and finer distinctions 
and to multiply the number of the various groups. 
The smallest division generally accepted is the Species. Though 
everyone has some conception of what a species is, whether it be called by 
that, name or another, no satisfactory definition has ever been constructed 
for it. It is what is commonly known as a “kind of an animal. ” Thus the 
horse is a different “kind” or species from a donkey, a bluebird from a 
robin. They are sharply marked off from each other, regularly breeding 
only within the species and producing offspring of like species. Distinct 
species do not commonly interbreed; when they do they form crosses or 
hybrids that are usually sterile. Up to comparatively recent years no 
smaller division was recognized, but from intensive study of material it 
has become evident to advanced students that within the species there is 
considerable individual and geographical variation. 
Individual variation is the normal difference that may occur at any 
time between members of common parentage such as full brothers and 
sisters. Though like begets like, within certain limits like begets unlike, 
for no two creatures are ever exact duplicates. This individual variation, 
usually small, occasionally larger and more distinct, the “mutations” of 
some authors, irregular in appearance and direction, but in some cases 
persisting progressively generation after generation in one direction, forms 
the successive steps by which present-day evolutionists explain the origin 
of new species . 1 Individual variation, however, is disregarded in classifica- 
tion unless it has proceeded far enough to produce marked and constant 
differentiation over a definable natural group of a species. 
GEOGRAPHICAL RACES OR SUBSPECIES 
Geographical variation may be regarded as a common variation of the 
individuals of a community trending towards a common goal, and is held 
to be directed by local climatic and other conditions. In many widespread 
species all individuals inhabiting certain localities have characteristics 
that separate them from those of surrounding areas. Individuals in a dry 
desert country are apt to be smaller and lighter in coloration than those 
in a warm, moist country. These differences are in some cases marked 
and obvious; in others they are so slight as to be noticeable only by 
comparing large numbers of specimens and can be detected only by aver- 
ages. Thus there is every degree of differentiation, due to geographical 
habitat, from pronounced departures from type, of almost specific value, 
to the finest shades of difference that the skilled specialist can distinguish 
and which are inappreciable to the ordinary eye. The outstanding fact, 
however, that prevents the most marked geographical variation from 
being given full specific standing, is that in intermediate localities every 
shade of difference between the extremes can be found. Between species 
this gradual merging of character is not supposed to occur, and however 
fine the distinctions may be, the divisions should be sharply defined. We 
1 It is this difference of opinion as to the relative importance of small and gradual or great and mutational steps 
of evolutionary progress that divides modern biologists into two schools of thought. 
