6 
‘‘kind of an animal ’’. Thus the horse is a different ‘“‘ kind ”’ or species 
from a donkey, a bluebird from a robin. Theyare sharply marked off from 
each other, regularly breeding together within the species only and pro- 
ducing like species as offspring. Distinct species do not commonly interbreed, 
but, when they do so, they form crosses or hybrids that are usually sterile. 
Up to comparatively recent years no smaller division was recognized, but 
with intensive study of material it has become evident to advanced students 
that within the species there is considerable individual and geographic 
variation. 
Individual variation is the natural difference that may occur at any 
time between members of common parentage such as amongst full brothers 
and sisters. Just as like begets like so within certain limits like begets 
unlike for no two creatures are ever exact duplicates. This is individual 
variation, usually smail and irregular in appearance and direction, but 
sometimes persisting progressively generation after generation in one direc- 
tion and forming the basis upon which present day evolutionists explain 
the origin of new species. Individual variation, however, is disregarded in 
classification, unless it has proceeded far enough to produce marked 
and constant differentiation over a definable natural group of a species. 
Geographical variation can be regarded as the result of a common 
tendency of individual variation acting over a whole community of indi- 
viduals tending towards a common goal and is held to be induced and 
directed by local climatic and other conditions. Thus we often find that 
within a widespread species all individuals inhabiting certain iocalities 
have characteristics that separate them from those of the surrounding areas. 
Individuals in a dry desert country are apt to be smaller and lighter in 
coloration, whereas those in a warm, moist country are usually larger and 
darker. These differences are sometimes marked and obvious; at other 
times they are so slight as to be noticeable only by comparison of large 
numbers of specimens and can be detected only by averages. Thus there 
is every degree of differentiation, due to geographical habitat, from pro- 
nounced departures from type, of almost specific value, te the finest shades 
of differentiation that skilled specialists can distinguish and which are 
inappreciable to the ordinary eye. The outstanding fact, however, that 
prevents the most marked geographical variation from full specific standing 
is that these minor forms intergrade and in intermediate localities 
every shade of differentiation 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 sharp and 
defined. We, therefore, recognize these intergrading variations due to or 
based upon geographical distribution as Geographical Races, Varieties, or 
Subspecies, the latter term being now in best current use, and we regard 
them as species in the making before the connecting stages binding them 
to the original stock have disappeared, owing to the growing sterility 
between the extreme variants. Except in such rare cases of physical 
isolation, as where an oceanic island habitat precludes continuous distri- 
bution, we take, in practice, the existence of intergrades as the evidence 
of subspecific status. Besides these divisions of taxonomic value there 
are a few other variants that, owing to their erratic occurrence, cannot 
be recognized in our classification. These are ‘“Albinos,” ‘‘ Melanos,” and 
‘“* Dichromatic Forms.” 
