368 POPULAR SCIENCE MONTHLY 



or less definite categories — kingdoms, sub-kingdoms, classes, orders, 

 families, genera, species and varieties, with many intermediate divi- 

 sions — and arranged in an ascending series culminating, as we view it, 

 in man. The extrinsic cause, or perhaps I should say the condition, of 

 these variations is environment. The intrinsic cause is the physio- 

 logical principle of variability, or mutability, by which biologists mean 

 the susceptibility to modification inherent in organic life, 'that plas- 

 ticity or modifiability of any organism in virtue of which an animal or 

 a plant may change in form, structure, function, size, color, or other 

 character, lose some character or acquire another, and thus deviate from 

 its parent form.' This tendency of all organisms to become unlike 

 their parents is, as I say, in first instance an intrinsic quality, and, 

 like other natural attributes, transmissible from generation to genera- 

 tion. But though originally instrinsic, variability is only called into 

 play by extrinsic conditions. As a result, organic variations are the 

 outcome of an interaction between intrinsic and extrinsic factors, 

 variability and environment. Looking along the line of organic evolu- 

 tion, the general tendency appears to be toward the preservation of the 

 more useful and the extinction of the less useful or useless characters. 

 This is due, in first instance, to adaptation, and then to the fact that 

 selection in one form or another has been operative all along the line, 

 eliminating the unfit or ill-adapted from the struggle for existence and 

 allowing only the fittest or best adapted to survive. Selection acts ac- 

 cordingly as the regulative factor of organic evolution — so in last 

 analysis variations become " the accomplishment of that which vari- 

 ability permits, environment requires, and selection directs." To be 

 noted also is the fact that variability, or the tendency to vary under 

 environmental conditions, is counteracted to a considerable extent by 

 heredity, or the tendency to breed true, the former being the pro- 

 gressive, the latter the conservative, principle of organic evolution. 



Man himself is an animal, the final product, apparently, of organic 

 evolution. Classified biologically he belongs to the sub-kingdom : Ver- 

 tcbrata, class: Mammalia, order: Primates, sub-order: Anthropoidea, 

 family: Hominidae, which family constitutes one genus and a single 

 species. In the course of its evolution this single species has, however, 

 become further differentiated into at least four sub-species, which con- 

 stitute the great races of man — and these in turn into a great number 

 of ethnic varieties. Arranged in an ascending series, we rank the 

 Negro, or Black race, lowest ; next the American, or Eed race ; then the 

 Mongolic, or Yellow race, and finally the Caucasic, or White race. 

 Within this last we take the Anglo-Saxons to represent the highest 

 ethnic type — though this is more or less arbitrary, depending upon the 

 point of view. But whatever the order of arrangement, there can be 

 no doubt of this: these several races and numerous varieties of man- 



