INTRODUCTION TO SOCIOLOGY 557
with time. Time and space are the essential conditions of varia- bility. However, in the present conditions, and whatever might have been the origin of the differences between races, the abrupt displacements from the different regions under the isothermal lines are prejudicial. They entail either immediate maladies or chronic anaemia, and therefore a less resistance to casual mala- dies and to premature old age. Either from the maladies of the first children among the offspring born in the country, or from a physical and intellectual degeneracy, there results a diminution of fecundity in the second and third generations. Mortality and the birth-rate are in harmony with degeneracy.
Regressive involution and progressive evolution are most surely movements which are slow and gradual, and it is thus in respect to acclimatization and adaptation in general. A family may remove from the north of France to Pau, at some genera- tions following to Cadiz, and several generations later to Morocco, and so forth. It is thus that immigrations have taken place and continue to take place, as Fustel de Coulanges shows, even among the invading barbarians at the commence- ment of our era and among certain slow immigrations setting out from central Asia, some advancing to the northwest toward the colder countries and others to the south toward India. We find the blond types where the English are not able to locate. The Esquimos, before becoming acclimated in the land of per- petual snow, lived in Asia under at least the fortieth degree of north latitude. It was thus that the Slavs penetrated by degrees from Russia into Siberia, and from the latter country into China, forming a peaceful advance guard, but conquering with their armies.
1 Acclimatization depends above all upon the nature of the par- ticular parts of the country to be penetrated. Morasses and deserts are unfavorable ; the altitude has its effect : the high plateaus of warm countries, as in the Congo, are more habitable. It is not alone for military, but also for climatic reasons that the conquering people generally instal themselves upon the heights. The climate favoring, they instal themselves from the very first in the valleys, chasing the natives toward the moun-
