Page:Popular Science Monthly Volume 70.djvu/372

368 or less definite categories—kingdoms, sub-kingdoms, classes, orders, families, genera, species and varieties, with many intermediate divisions—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 physiological principle of variability, or mutability, by which biologists mean the susceptibility to modification inherent in organic life, that plasticity 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 generation. 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 evolution, 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 accordingly as the regulative factor of organic evolution—so in last analysis variations become "the accomplishment of that which variability 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 progressive, 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: Vertebrata, 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 constitute 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