This movement is and has been universal and varied.  When most unobtrusive in its operation, it has produced its greatest effects.  To seize upon a few conspicuous migrations, like the Voelkerwanderung and the irruption of the Turks into Europe, made dramatic by their relation to the declining empires of Rome and Constantinople, and to ignore the vast sum of lesser but more normal movements which by slow increments produce greater and more lasting results, leads to wrong conclusions both in ethnology and history.  Here, as in geology, great effects do not necessarily presuppose vast forces, but rather the steady operation of small ones.  It is often assumed that the world was peopled by a series of migrations; whereas everything indicates that humanity spread over the earth little by little, much as the imported gypsy moth is gradually occupying New England or the water hyacinth the rivers of Florida.  Louis Agassiz observed in 1853 that “the boundaries within which the different natural combinations of animals are known to be circumscribed upon the surface of the earth, coincide with the natural range of distinct types of man."[128] The close parallelism between Australian race and flora, Eskimo race and Arctic fauna, points to a similar manner of dispersion.  Wallace, in describing how the Russian frontier of settlement slowly creeps forward along the Volga, encroaching upon the Finnish and Tartar areas, and permeating them with Slav blood and civilization, adds that this is probably the normal method of expansion.[129] Thucydides describes the same process of encroachment, displacement, and migration in ancient Hellas.[130] Strabo quotes Posidonius as saying that the emigration of the Cimbrians and other kindred tribes from their native seats was gradual and by no means sudden.[131] The traditions of the Delaware Indians show their advance from their early home in central Canada southward to the Delaware River and Chesapeake Bay to have been a slow zigzag movement, interrupted by frequent long halts, leaving behind one laggard group here and sending out an offshoot there, who formed new tribes and thereby diversified the stock.[132] It was an aimless wandering, without destination and purpose other than to find a pleasanter habitat.  The Vandals appear first as “a loose aggregation of restless tribes who must not be too definitely assigned to any precise district on the map,” somewhere in central or eastern Prussia.[133] Far-reaching migrations aiming at a distant goal, like the Gothic and Hunnish conquests of Italy, demand both a geographical knowledge and an organization too high for primitive peoples, and therefore belong to a later period of development.[134]

[Sidenote:  Number and range.]