Islanders are always coast dwellers with a limited hinterland.  Hence their stock may be differentiated from the mainland race in part for the same reason that all coastal folk in regions of maritime development are differentiated from the people of the back country, namely, because contact with the sea allows an intermittent influx of various foreign strains, which are gradually assimilated.  This occasional ethnic intercrossing can be proved in greater or less degree of all island people.  Here is accessibility operating against the underlying isolation of an island habitat.  The English to-day represent a mixture of Celts with various distinct Teutonic elements, which had already diverged from one another in their separate habitats—­Jutes, Angles, Saxons, Danes, Norse and Norman French.  The subsequent detachment of these immigrant stocks by the English Channel and North Sea from their home people, and their arrival in necessarily small bands enabled them to be readily assimilated, a process which was stimulated further by the rapid increase of population, the intimate interactive life and unification of culture which characterizes all restricted areas.  Hence islands, like peninsulas, despite ethnic admixtures, tend to show a surprising unification of race; they hold their people aloof from others and hold them in a close embrace, shut them off and shut them in, tend to force the amalgamation of race, culture and speech.  Moreover, their relatively small area precludes effective segregation within their own borders, except where a mountainous or jungle district affords a temporary refuge for a displaced and antagonized tribe.  Hence there arises a preponderance of the geographic over the ethnic and linguistic factors in the historical equation.

The uniformity in cranial type prevailing all over the British Isles is amazing; it is greater than in either Spain or Scandinavia.  The cephalic indices range chiefly between 77 and 79, a restricted variation as compared with the ten points which represents the usual range for Central Europe, and the thirteen between the extremes of 75 and 88 found in France and Italy.[850] Japan stands in much the same ethnic relation to Asia as Britain to Europe.  She has absorbed Aino, Mongolian, Malay and perhaps Polynesian elements, but by reason of her isolation has been left free to digest these at her leisure, so that her population is fairly well assimilated, though evidences of the old mixture can be discerned.[851] In Corsica and Sardinia a particularly low cephalic index, dropping in some communes to 73, and a particularly short stature point to a rare purity of the Mediterranean race,[852] and indicate the maintenance here of one ethnic type, despite the intermittent intrusion of various less pure stocks from the Italian mainland, Africa, Phoenicia, Arabia, and Spain.  The location of the islands off the main routes of the basin, their remoteness from shore, and the strong spirit of exclusiveness native to the people,[853] bred doubtless from their isolation, have combined to reduce the amount of foreign intermixture.