INTRODUCTION TO SOCIOLOGY 559
assisted. The general effect of human variations has been to realize the extension of the species best fit to colonize the whole planet through the formation of the great human society. This is not in consequence of a plan of Providence or of nature, but is a result of the very conditions of evolution.
If, as is probable, man has descended from the placental mam- mifers through the intermediation of the pithecoid man, himself issued from the anthropoid apes, it follows from the study of fos- sils and of the earth's strata, that this transformation may be traced back toward the end of the Tertiary age ; that is, to an epoch which dates back at least twenty thousand years, and per- haps even more than a hundred thousand years. It is equally probable, according to the general static laws, as we have indi- cated, that the appearance of this superior species, in consequence of insensible transformation favored by natural and sexual selec- tion, consolidated and developed by heredity, was brought about in environments whose climate and spontaneous alimentary resources corresponded closely to those of the present habitats of those families of apes which approximate nearest to man and of the habitats of some extinct intermediary pithecoid and anthropoid species.
This human variety, developing more and more into a distinct species, possesses qualities more favorable to expansion than any other known species. It is omnivorous, and knows how to locate and protect itself, and also how to preserve with more facility the internal heat of the body and how better to prevent its loss by radiation. These conditions are evidently favorable, not only to muscular activity, but also to the psychic life, both of which may be measured in calorics, in the same way that the latter may be reduced to mechanical terms, and through these, to the most gen- eral laws of movement. The muscular system and the nervous system of man, being organs of these movements and of his life- relations, are capable, through their complexity, of the most special and most extended adaptations. The Esquimos are met as far as the eightieth degree of latitude. Some populations live and prosper in the Andes and in the Cordilleras at an altitude of not less than 4,000 meters. Man, by his variability, adjusts
