The sea forms the sharpest and broadest boundary; it makes in the island which it surrounds the conditions for differentiation.  Thus while an insular population is allied in race and civilization to that of the nearest continent, it nevertheless differs from the same more than the several sub-groups of its continental kindred differ from each other.  In other words, isolation makes ethnic and cultural divergence more marked on islands than on continents.  The English people, despite their close kinship and constant communication with the Teutonic peoples of the European mainland, deviate from them more than any of these Germanic nations deviate from each other.  The Celts of Great Britain and Ireland are sharply distinguished from the whole body of continental Celts in physical features, temperament, and cultural development.  In Ireland the primitive Catholic Church underwent a distinctive development.  It was closely bound up in the tribal organization of the Irish people, lacked the system, order and magnificence of the Latinized Church, had its peculiar tonsure for monks, and its own date for celebrating Easter for nearly three hundred years after the coming of St. Patrick.[840] The Japanese, in their physical and mental characteristics, as in their whole national spirit, are more strikingly differentiated from the Chinese than the agricultural Chinese from the nomadic Buriat shepherds living east of Lake Baikal, though Chinese and Japanese are located much nearer together and are in the same stage of civilization.  The Eskimo, who form one of the most homogeneous stocks, and display the greatest uniformity in language and cultural achievements of all the native American groups, have only one differentiated offshoot, the Aleutian Islanders.  These, under the protection and isolation of their insular habitat from a very remote period, have developed to a greater extent than their Eskimo brethren of the mainland.  The difference is evident in their language, religious ceremonies, and in details of their handiwork, such as embroidery and grass-fiber weaving.[841] The Haidas of the Queen Charlotte Archipelago show such a divergence in physique and culture from the related tribes of the mainland, that they have been accredited with a distinct origin from the other coast Indians.[842]

[Sidenote:  Differentiation of language in islands.]

The differentiating influence is conspicuous in the speech of island people, which tends to form a distinct language or dialect or, in an archipelago, a group of dialects.  The Channel Isles, along with their distinctive breeds of cattle, has each its own variant of the langue d’oil.[843] According to Boccaccio’s narrative of a Portuguese voyage to the Canaries in 1341, the natives of one island could not understand those from another, so different were their languages.  The statement was repeated by a later authority in 1455 in regard to the inhabitants of Lancerote, Fuerteventura, Gomera and Ferro, who