CHAPTER II

CLASSES OF GEOGRAPHIC INFLUENCES

Into almost every anthropo-geographical problem the element of environment enters in different phases, with different modes of operation and varying degrees of importance.  Since the causal conception of geography demands a detailed analysis of all the relations between environment and human development, it is advisable to distinguish the various classes of geographic influences.

[Sidenote:  Physical effects.]

Four fundamental classes of effects can be distinguished.

1.  The first class includes direct physical effects of environment, similar to those exerted on plants and animals by their habitat.  Certain geographic conditions, more conspicuously those of climate, apply certain stimuli to which man, like the lower animals, responds by an adaption of his organism to his environment.  Many physiological peculiarities of man are due to physical effects of environment, which doubtless operated very strongly in the earliest stages of human development, and in those shadowy ages contributed to the differentiation of races.  The unity of the human species is as clearly established as the diversity of races and peoples, whose divergences must be interpreted chiefly as modifications in response to various habitats in long periods of time.

[Sidenote:  Variation and natural conditions.]

Such modifications have probably been numerous in the persistent and unending movements, shiftings, and migrations which have made up the long prehistoric history of man.  If the origin of species is found in variability and inheritance, variation is undoubtedly influenced by a change of natural conditions.  To quote Darwin, “In one sense the conditions of life may be said, not only to cause variability, either directly or indirectly, but likewise to include natural selection, for the conditions determine whether this or that variety shall survive."[34] The variability of man does not mean that every external influence leaves its mark upon him, but that man as an organism, by the preservation of beneficent variations and the elimination of deleterious ones, is gradually adapted to his environment, so that he can utilize most completely that which it contributes to his needs.  This self-maintenance under outward influences is an essential part of the conception of life which Herbert Spencer defines as the correspondence between internal conditions and external circumstances, or August Comte as the harmony between the living being and the surrounding medium or milieu.