6 



" kind of an animal ". Thus the horse is a different " kind " or species 

 from a donkey, a bluebird from a robin. Thteyare sharply marked off from 

 each other, regularly breeding together withia the species only and pro- 

 ducing like species as offspring. Distinct species do not commonly iaterbreed, 

 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 hke begets like so within certain limits Uke begets 

 unUke for no two creatures are ever exact duplicates. This is individual 

 variation, usually small 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 localities 

 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, to the finest shades 

 of dijEferentiation 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 a^ .lie 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." 



