The ethnic unity of the American races, as urged by Morton and others, hardly meets the requirements of the problem in the opinion of most later students, like Sir Daniel Wilson, for instance; and yet, if A. H. Keane represents, as he claims, the latest ethnological beliefs, the connection with Asia, of the kind that forms ethnic traces, must have been before the history of the present Asiatic races, since the correspondence of customs, etc. is not sufficient for more recent affiliation.[546] It should be remembered also, that if this is true, and if there is the strong physical resemblance between Asiatics and the indigenous tribes of the northwest coast which early travellers and physiologists have dwelt on, we have in such a correspondence strong evidence of the persistency of types.[547] The Asiatic theory was long a favorite one. So popular a book as Lafitau’s _Mœurs des Sauvages_ (Paris, 1724) advocated it. J. B. Scherer’s _Recherches historiques et géographiques sur le nouveau monde_ (Paris, 1777) was on the same side. One of the earliest in this country, Benj. Smith Barton, to give expression to American scholarship in this field held like opinions in his _New Views of the Origin of the Tribes of America_ (Philad., 1797).[548] Twenty years later (1816) one of the most active of the American men of letters advocated the same views,—Samuel L. Mitchell in the _Archæologia Americana_ (i. 325, 338, 346). The weightiest authority of his time, Alex. von Humboldt, formulated his belief in several of his books: _Vues des Cordillères; Ansichten der Natur; Cosmos_.[549] [Illustration: BEHRING SEA AND ADJACENT WATERS NOTE.—Sketch map from the _U. S. Geodetic Survey_, 1880, App. xvi; also in _Journal Amer. Geog. Soc._, xv. p. 114. Cf. Bancroft’s _Nat. Races_, i. 35.] Of the northern routes, that by Behring’s Straits is the most apparent, and Lyell says that when half-way over Dover Straits, which have not far from the same dimensions, he saw both the English and French shores at the same time, he was easily convinced that the passage by Behring’s Straits solved many of the difficulties of the American problem.[550]